Process for catalytic co2 desorption and catalyst for said process

Abstract

The present invention generally relates to the field of carbon dioxide (CO2) capture and storage. More particularly, the present invention pertains to a solid catalyst composition for CO2 desorption in an overall CO2 absorption / desorption procedure. The present invention further relates to a method for preparing the solid catalyst composition and to the use of the 5 catalyst composition in a process and system for catalytic CO2 desorption.

Description

[0001] PROCESS FOR CATALYTIC CO2DESORPTION AND CATALYST FOR SAID PROCESS

[0002] FIELD OF THE INVENTION

[0003] The present invention generally relates to the field of carbon dioxide (CO2) capture and storage. More particularly, the present invention pertains to a solid catalyst composition for CO2 desorption in an overall CO2 absorption / desorption procedure. The present invention further relates to a method for preparing the solid catalyst composition and to the use of the catalyst composition in a process and system for catalytic CO2 desorption.

[0004] BACKGROUND

[0005] The increasing concentration of carbon dioxide (CO2) in the Earth's atmosphere is a major contributor to global climate change. As a greenhouse gas, CO2 traps heat, leading to the warming of the planet, which has significant environmental, economic, and societal impacts. To mitigate these effects, there has been a growing focus on reducing CO2 emissions from industrial sources and developing technologies for capturing and storing CO2. Under that premise, CO2 capture and storage (CCS) and CO2 capture and utilization (CCU) have become promising routes to limit increasing CO2 emission. Importantly, for both routes, CO2 capture is always the first step. In order to meet mid-to-long-term CO2 reduction targets, it is necessary to develop a cost-effective CO2 capture technology.

[0006] Existing CO2 capture technologies can be broadly classified into three categories: precombustion capture, post-combustion capture, and oxy-fuel combustion. Each of these technologies aims to isolate CO2 from other gases in flue gas streams or process gases before it is released into the atmosphere. However, post-combustion capture, using amine solvent as a CO2 absorber, is one of the most widely used methods due to its applicability to existing power plants.

[0007] Extensive studies have been carried out to reduce the energy cost during regeneration of the amine solvent and release of CO2. For instance, new amine solvents and bi-phasic amine solvents can significantly reduce the energy cost during desorption while maintaining a relatively high CO2 absorption rate. However, said approaches are still economically inefficient due to the high price of the solvent and complex reactor.

[0008] From a catalytic perspective, using a proper catalyst can decrease the activation energy of CO2 desorption and boost the reaction rate, thereby decreasing the stripping time and increasing the solvent regeneration efficiency. Moreover, some catalysts allow CO2 desorption at a temperature lower than 100°C, which could significantly reduce equipment size, energy consumption and solvent loss.

[0009] Nevertheless, while showing some improvement, various solid catalysts are unable to meet application requirements due to limitations such as poor catalytic performance or catalyst dissolution problems. Finding proper catalysts for CO2 desorption therefore requires balancing multiple performance metrics, including efficiency, stability, selectivity, and cost.

[0010] Therefore, there remains a need for improved catalysts and improved processes for CO2 desorption.

[0011] SUMMARY OF THE INVENTION

[0012] It has now been found that the above objectives can be attained either individually or in any combination by using the specific and well-defined solid catalyst composition and processes as disclosed herein.

[0013] More specifically, the present inventors have developed a solid catalyst composition comprising (at least two) different metal oxide-based catalysts that exhibit both acidic and basic properties. It has been found that this catalyst composition shows advantageous and unexpected properties when applied in a CO2 desorption process. For example, the catalytic activity of the solid catalyst composition according to the invention, and embodiments thereof, is far greater than any previously reported catalysts or its constituents. Moreover, overall CO2 desorption performance increases with increase in catalytic loading. Catalyst durability is further confirmed as catalytic activity is retained after multiple use cycles.

[0014] The solid catalyst composition according to the present invention is particularly characterized in that it has a specific ratio of acidic to basic groups. Extensive experimentation has revealed that such a designed solid catalyst composition allows to increase CO2 desorption rates even at low temperatures. Hence, providing efficient absorbent regeneration during CO2 postcombustion.

[0015] In a first aspect, the present invention provides a solid catalyst composition for CO2 desorption. The solid catalyst composition preferably comprises: at least one first metal oxide-based catalyst having a ratio of acidic hydroxyl groups to basic hydroxyl groups of at most 0.7; and, at least one second metal oxide-based catalyst having a ratio of acidic hydroxyl groups to basic hydroxyl groups of at least 1 .3. The catalyst composition preferably has a ratio of acidic hydroxyl groups to basic hydroxyl groups of from at least 0.7 to at most 2.0, preferably of from at least 0.8 to at most 1.3.

[0016] It has been found herein that the solid acid catalyst composition according to the present invention, or embodiments thereof, provides for a more efficient CO2 desorption with improved reaction rates, high selectivity, and minimal byproducts when compared to existing catalysts, or the first metal oxide-based catalyst and / or second metal oxide-based catalyst as such. As a result, the current catalyst composition can outperform the metal oxide-based catalysts comprised therein when applied separately.

[0017] The first metal oxide-based catalyst typically comprises an excess of basic sites. In some preferred embodiments, the at least one first metal oxide-based catalyst may have a ratio of acidic hydroxyl groups to basic hydroxyl groups of at most 0.6, preferably at most 0.5.

[0018] The second metal oxide-based catalyst typically comprises an excess of acidic sites. In some preferred embodiments, the at least one second metal oxide-based catalyst may have a ratio of acidic hydroxyl groups to basic hydroxyl groups of at least 1 .4, preferably at least 1 .5.

[0019] In some preferred embodiments, the metal oxide-based catalysts comprises zirconium, titanium, scandium, hafnium, aluminium, silicon, vanadium, chromium, manganese, iron, zinc, gallium, copper, nickel, cobalt, calcium, cadmium, lanthanum, lead, thallium, ytterbium, molybdenum, tungsten, indium, or a combination thereof; and preferably comprises zirconium and / or titanium, a combination thereof, or a mixture thereof.

[0020] In some preferred embodiments, the at least one first metal oxide-based catalyst and the at least one second metal oxide-based catalyst may comprise a different centre atom or ion. Preferably the different centre atoms or ions are zirconium and titanium.

[0021] In some preferred embodiments, at least one of the metal oxide-based catalysts may comprise ZrxOy(OH)zand / or TixOy(OH)z.

[0022] In some preferred embodiments, the solid catalyst composition may comprise from at least 5.0 to at most 95.0 wt.% of the first metal oxide-based catalyst; and from at least 5.0 to at most 95.0 wt.% of the second metal oxide-based catalyst; with wt.% relative to the total weight of the solid catalyst composition.

[0023] In some preferred embodiments, the metal oxide-based catalysts comprise metal oxyhydroxides, metal oxides, and / or metal hydroxides.

[0024] In some preferred embodiments, the metal oxide-based catalysts may be supported metal oxide-based catalysts or unsupported metal oxide-based catalysts. In a second aspect, the present invention provides a method for preparing the solid catalyst composition according to a first aspect of the present invention, or embodiments thereof. Preferably, the method comprises the steps of: preparing at least one first metal oxide-based catalyst and at least one second metal oxide-based catalyst, wherein each preparation procedure comprises forming a synthesis mixture by mixing a metal source, a solvent, and optionally a basic precipitating agent, thereby precipitating each metal oxide-based catalyst; and mixing the at least one first metal oxide-based catalyst and at least one second metal oxide-based catalyst, thereby obtaining the solid catalyst composition.

[0025] The solid catalyst compositions prepared according to the invention, or embodiments thereof, can be used in MEA solvent and other amines in a CO2 capture plant. The boosting of CO2 desorption rate with the catalysts makes it possible for the solvent regeneration process to run under a lower temperature which can significantly decrease the energy cost of postcombustion capture and prevent the amine solution from degradation and evaporation. The catalyst is stable and insolubilized in amine solvent, which makes it easy to be separated and regenerated. Furthermore, the catalyst can be deposited on a structured support (inert packing) to replace traditional packing, or can be shaped in solid structure to replace traditional packing.

[0026] The present invention, and embodiments thereof, also allows for a reduction in size of the desorption column leading to lower capital expenditure (CAPEX). The present invention, and embodiments thereof, also allows for a reduction in temperature of CO2 desorption, which in turn leads to lower energy requirements and operating expense (OPEX). The present invention, and embodiments thereof, also allows to reduce the cost of regeneration of solvents in the desorption process.

[0027] It should be noted that (preferred) embodiments of the first aspect of the present invention and any associated advantages thereof are also (preferred) embodiments of the second aspect of the present invention and vice versa.

[0028] The method is preferably characterized in that the pH of the synthesis mixture is at least 2 and at most 11 .

[0029] In some preferred embodiments, the metal source may be a metal complex comprising zirconium, titanium, scandium, hafnium, aluminium, silicon, vanadium, chromium, manganese, iron, zinc, gallium, copper, nickel, cobalt, calcium, cadmium, lanthanum, lead, thallium, ytterbium, molybdenum, tungsten, indium, or a combination thereof; and preferably further comprising nitrate, oxynitrate, halide, oxyhalide, sulphate, alkoxide, carboxylate or a combination thereof.

[0030] In some preferred embodiments, the synthesis mixture comprises a basic precipitating agent, wherein the basic precipitating agent preferably is a hydroxide, alkylamine, ammonia, dialkylamine, trialkylamine, alkanolamine, urea, hydrazine, carbonate, bicarbonate, or carboxylate; preferably a hydroxide selected from the group comprising sodium hydroxide, potassium hydroxide, ammonium hydroxide, calcium hydroxide, magnesium hydroxide, lithium hydroxide, and mixtures thereof.

[0031] In some preferred embodiments, the metal oxide-based catalysts may be supported metal oxide-based catalysts. Preferably, in that event, the method comprises the steps of: preparing at least one first metal oxide-based catalyst and at least one second metal oxide-based catalyst, wherein each synthesis procedure comprises forming a synthesis slurry by mixing a metal source, a solid catalyst support, a solvent, and optionally a basic precipitating agent, thereby precipitating each metal oxide-based catalyst on the solid catalyst support; and, mixing the at least one first metal oxide-based supported metal catalyst and at least one second metal oxide-based supported metal catalyst, thereby obtaining the solid catalyst composition.

[0032] In some preferred embodiments, the solid catalyst support is a porous solid catalyst support, preferably a mesoporous solid catalyst support.

[0033] In some preferred embodiments, the at least one first metal oxide-based catalyst may be a supported metal oxide-based catalyst and the at least one second metal oxide-based catalyst may be an unsupported metal oxide-based catalyst. Preferably, in that event, the method comprises the steps of: preparing at least one first metal oxide-based catalyst, wherein the synthesis procedure comprises forming a synthesis slurry by mixing a metal source, a solid catalyst support, a solvent, and optionally a basic precipitating agent, thereby precipitating the first metal oxide-based catalyst on the solid catalyst support; preparing at least one second metal oxide-based catalyst; wherein the synthesis procedure comprises forming a synthesis mixture by mixing a metal source, a solvent, and optionally a basic precipitating agent, thereby precipitating the second metal oxide-based catalyst; and, mixing the at least one first supported metal oxide-based catalyst and at least one second unsupported metal oxide-based catalyst, thereby obtaining the solid catalyst composition.

[0034] In some preferred embodiments, the at least one first metal oxide-based catalysts may be an unsupported metal oxide-based catalyst and the at least one second metal oxide-based catalyst may be a supported metal oxide-based catalyst. Preferably, in that event, the method comprises the steps of: preparing at least one first metal oxide-based catalyst; wherein the synthesis procedure comprises forming a synthesis mixture by mixing a metal source, a solvent, and optionally a basic precipitating agent, thereby precipitating the first metal oxidebased catalyst; preparing at least one second metal oxide-based catalyst, wherein the synthesis procedure comprises forming a synthesis slurry by mixing a metal source, a solid catalyst support, a solvent, and optionally a basic precipitating agent, thereby precipitating the second metal oxide-based catalyst on the solid catalyst support; and, mixing the at least one first unsupported metal oxide-based catalyst and at least one second supported metal oxide-based catalyst, thereby obtaining the solid catalyst composition.

[0035] In a third aspect, the present invention relates to the use of the solid catalyst composition according to a first aspect of the present invention, or embodiments thereof, or obtained or obtainable by means of the method according to a second aspect of the present invention, or embodiments thereof, in a process for CO2 desorption from a CC>2-containing absorbent, preferably wherein the CC>2-containing absorbent comprises one or more nitrogen compounds such as amines.

[0036] It should be noted that (preferred) embodiments of the first aspect and second aspect of the present invention and any associated advantages thereof are also (preferred) embodiments of the third aspect of the present invention and vice versa.

[0037] In some preferred embodiments, the solid catalyst composition is contacted with the CO2- containing absorbent at a temperature of from 50°C to 150°C and a pressure of from 0.5 bar to 7.0 bar, preferably of from 1.0 to 4.0 bar, preferably wherein the contacting of the solid catalyst composition and the CC>2-containing absorbent is performed in a CO2 stripper.

[0038] In some preferred embodiments, the solid catalyst composition may act as a non-solubilized heterogeneous catalyst composition. The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, which illustrate, by way of example, the principles of the invention.

[0039] BRIEF DESCRIPTION OF THE FIGURES

[0040] The teaching of the application is illustrated by the following Figures which are to be considered as illustrative only and do not in any way limit the scope of the claims.

[0041] FIG. 1 shows the reaction route for CO2 desorption from a primary and secondary amine solvent.

[0042] FIG. 2 illustrates a carbon capture process schematic.

[0043] FIG. 3 illustrates a schematic lab-scale CO2 desorption apparatus.

[0044] FIG. 4 illustrates the CO2 desorption kinetics of individual Zr-based oxides compared with a physical mixture.

[0045] FIG. 5 illustrates the CO2 desorption kinetics of individual metal-based oxides compared with a physical mixture.

[0046] DETAILED DESCRIPTION OF THE INVENTION

[0047] Unless otherwise defined, all terms used in disclosing the invention, including technical and scientific terms, have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. By means of further guidance, term definitions are included to better appreciate the teaching of the present invention.

[0048] The discussion of the background to the invention herein is included to explain the context of the invention. This is not to be taken as an admission that any of the material referred to was published, known, or part of the common general knowledge in any country as of the priority date of any of the claims.

[0049] As used herein, the singular forms “a”, “an”, and “the” include both singular and plural referents unless the context clearly dictates otherwise. By way of example, "a step" means one step or more than one step.

[0050] The terms “comprising”, “comprises” and “comprised of’ as used herein are synonymous with “including”, “includes” or “containing”, “contains”, and are inclusive or open-ended and do not exclude additional, non-recited members, elements, or method steps. The terms also encompass “consisting of” and “consisting essentially of”, which enjoy well-established meanings in patent terminology.

[0051] Whereas the terms “one or more” or “at least one”, such as one or more members or at least one member of a group of members, is clear per se, by means of further exemplification, the term encompasses inter alia a reference to any one of said members, or to any two or more of said members, such as, e.g., any >3, >4, >5, >6 or >7 etc. of said members, and up to all said members. In another example, “one or more” or “at least one” may refer to 1 , 2, 3, 4, 5, 6, 7 or more.

[0052] The terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order, unless specified. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the disclosure described herein are capable of operation in other sequences than described or illustrated herein.

[0053] As used herein, the term “and / or” when used in a list of two or more items, means that any one of the listed items can be employed by itself or any combination of two or more of the listed items can be employed. For example, if a list is described as comprising group A, B, and / or C, the list can comprise A alone, B alone, C alone, A and B in combination, A and C in combination, B and C in combination, or A, B, and C in combination.

[0054] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” or “in a particular embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments. Furthermore, while certain embodiments described herein include some, but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art.

[0055] The recitation of numerical ranges by endpoints includes all integer numbers and, where appropriate, fractions subsumed within that range (e.g. 1 to 5 can include 1 , 2, 3, 4 when referring to, for example, a number of elements, and can also include 1 .5, 2, 2.75 and 3.80, when referring to, for example, measurements). The recitation of endpoints also includes the end point values themselves (e.g. from 1.0 to 5.0 includes both 1.0 and 5.0). Any numerical range recited herein is intended to include all sub-ranges subsumed therein. This applies to numerical ranges irrespective of whether they are introduced by the expression “from... to...” or the expression “between... and...” or another expression.

[0056] As used herein, the terms “about” or “approximately” are used to provide flexibility to a numerical value or range endpoint by providing that a given value may be “a little above” or “a little below” said value or endpoint, depending on the specific context. Hence, the terms “about” or “approximately” as used herein when referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, are meant to encompass variations of and from the specified value or endpoint, such as variations of + / -10% or less, preferably + / -5% or less, more preferably + / -1 % or less, and still more preferably + / -0.1 % or less of and from the specified value, insofar such variations are appropriate to perform in the disclosed invention.

[0057] Unless otherwise stated, use of the terms “about” or “approximately” in accordance with a specific number or numerical range should also be understood to provide support for such numerical terms or range without the term “about”. For example, the recitation of “about 30” should be construed as not only providing support for values a little above and a little below 30, but also for the actual numerical value of 30 as well.

[0058] As used herein, the term “substantially” refers to the complete or nearly complete extent or degree of an action, characteristic, property, state, structure, item, or result. For example, an object that is “substantially” enclosed would mean that the object is either completely enclosed or nearly completely enclosed. The exact allowable degree of deviation from absolute completeness may in some cases depend on the specific context. However, generally speaking the nearness of completion will be so as to have the same overall result as if absolute and total completion were obtained. The use of “substantially” is equally applicable when used in a negative connotation to refer to the complete or near complete lack of an action, characteristic, property, state, structure, item, or result.

[0059] The terms “wt.%,” “vol%”, or “mol%” refers to a weight percentage of a component, a volume percentage of a component, or molar percentage of a component, respectively, based on the total weight, the total volume of material, or total moles, which includes the component.

[0060] It should be understood that any reference to “metal oxide-based catalysts” in the present application refers to the at least one first metal oxide-based catalyst and at least one second metal oxide-based catalyst of the present invention.

[0061] Preferred features, embodiments, and uses of this invention are set herein below. Each embodiment of the invention so defined may be combined with any other embodiment unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous. Hereto, the present invention is in particular captured by any one or any combination of one or more of the below embodiments, with any other aspect and / or embodiment.

[0062] In a first aspect, the present invention provides a solid catalyst composition for CO2 desorption. The solid catalyst composition preferably comprises: at least one first metal oxide-based catalyst having a ratio of acidic hydroxyl groups to basic hydroxyl groups of at most 0.7; and, at least one second metal oxide-based catalyst having a ratio of acidic hydroxyl groups to basic hydroxyl groups of at least 1 .3.

[0063] The catalyst composition preferably has a ratio of acidic hydroxyl groups to basic hydroxyl groups of from at least 0.7 to at most 2.0.

[0064] The present catalyst composition, being a combination of at least one first metal oxide-based catalyst and at least one second metal oxide-based catalyst, was found to provide a significant improvement on CO2 desorption properties without significant dissolution, as illustrated in the example section. More specifically, a catalyst composition with a ratio of acidic hydroxyl groups to basic hydroxyl groups in the range indicated herein may result in a catalytic activity that significantly exceeds the sum of the individual activities of each constituting metal oxidebased catalyst. This synergistic effect provides the advantage that various metal oxide-based catalysts, which typically do not meet stringent performance requirements, may be combined to provide a catalyst composition that exhibits improved reaction rates and selectivity in CO2 release from a CC>2-containing absorbent.

[0065] The terms “solid catalyst composition” and “catalyst composition” as used herein interchangeably refer to a mixture or combination of two or more metal oxide-based catalysts. Preferably, the combined catalytic activity or performance of the catalyst composition is greater than the sum of the individual activities of the separate metal-oxide based catalysts when used independently.

[0066] In the following, (preferred) embodiments, particularities, and features of the present solid catalyst composition and its constituents are explained in further detail.

[0067] It has been found herein that the strength and presence of both acidic and basic sites of the catalyst composition can greatly influence catalytic performance for CO2 desorption. In particular, catalyst compositions as described herein typically have a number of acidic hydroxyl groups and basic hydroxyl groups in a specified proportion. In some embodiments, the catalyst composition may have a ratio of acidic hydroxyl groups to basic hydroxyl groups of from at least 0.1 to at most 10.0, or from at least 0.2 to at most 10.0, or from at least 0.3 to at most 10.0, or from at least 0.4 to at most 10.0, or from at least 0.4 to at most 9.0, or from at least 0.4 to at most 8.0, or from at least 0.4 to at most 7.0, or from at least 0.4 to at most 6.0, or from at least 0.4 to at most 5.0, or from at least 0.4 to at most 4.0, or from at least 0.5 to at most 4.0, or from at least 0.6 to at most 4.0, or from at least 0.7 to at most 4.0, or from at least 0.7 to at most 3.5, or from at least 0.7 to at most 3.0, or from at least 0.7 to at most 2.5, preferably from at least 0.7 to at most 2.0.

[0068] In some preferred embodiments, the catalyst composition may have a ratio of acidic hydroxyl groups to basic hydroxyl groups of from at least 0.7 to at most 1 .9, or from at least 0.7 to at most 1 .8, or from at least 0.7 to at most 1 .7, or from at least 0.7 to at most 1 .6, or from at least 0.7 to at most 1 .5, or from at least 0.7 to at most 1 .4, preferably from at least 0.8 to at most 1 .3, or from at least 0.8 to at most 1 .2, more preferably from at least 0.9 to at most 1 .2, most preferably from at least 0.9 to at most 1.1. As illustrated in the example section, further optimizing the ratio of acidic hydroxyl groups to basic hydroxyl groups was found to advantageously improve CO2 desorption properties.

[0069] The term “acidic hydroxyl groups” has a well-established meaning within the art and is used herein as such. Acidic hydroxyl groups refer to hydroxyl functional groups (-OH) that possess the ability to donate a proton (H+), thereby exhibiting acidic behaviour.

[0070] The term “basic hydroxyl groups” has a well-established meaning within the art and is used herein as such. Basic hydroxyl groups refer to hydroxyl functional groups (-OH) that possess the ability to accept a proton (H+), or participate in nucleophilic reactions, thereby exhibiting basic behaviour.

[0071] Hence, the term “ratio of acidic hydroxyl groups to basic hydroxyl groups” of a compound or substance is a quantitative measure that compares the number of hydroxyl groups within the molecule that can act as acids (capable of donating protons) to the number of hydroxyl groups that are associated with basic sites (capable of accepting protons). By experimentally determining the number of acidic hydroxyl groups and basic hydroxyl groups present in a compound, a ratio can be calculated. Preferably, the ratio of acidic hydroxyl groups to basic hydroxyl groups is measured by Thermogravimetric Analysis (TGA), for example as conducted on a TGA Q500 from TA Instruments. The TGA measurement may be performed under a 10 mL / min N2 atmosphere, with a temperature ramping from 50°C to 150°C for 30 min to make sure all free water is released, and then to 800°C. The temperature ramping rate may be 10°C / min. In accordance with the present invention, the catalyst composition comprises at least two different metal oxide-based catalysts. As used herein the term “metal oxide-based catalyst” refers to a substance composed of one or more metal oxides, and optionally derivatives thereof including hydrates, which causes a change in the rate of a reaction. The present metal oxide-based catalysts may be supported or unsupported.

[0072] In preferred embodiments, the first metal oxide-based catalyst and / or second metal oxidebased catalyst is an amphoteric compound. The term “amphoteric” has a well-established meaning in the art and generally refers to compounds or substances that exhibit both acidic and basic properties. In the context of the present invention, the first metal oxide-based catalyst is more basic compared to the second metal oxide-based catalyst. This combination of metal catalysts has been found to be particularly beneficial for the CO2 desorption process, wherein several proton transfers may be assisted or catalysed.

[0073] In some preferred embodiments, the at least one first metal oxide-based catalyst may have a ratio of acidic hydroxyl groups to basic hydroxyl groups of at most 0.6, preferably at most 0.5. In other words, the first metal oxide-based catalyst comprises a larger amount of basic hydroxyl groups compared to acidic hydroxyl groups.

[0074] In some preferred embodiments, the at least one first metal oxide-based catalyst may have a ratio of acidic hydroxyl groups to basic hydroxyl groups of from at least 0.1 to at most 0.7, or at least 0.1 to at most 0.6, or at least 0.1 to at most 0.5, or at least 0.2 to at most 0.5.

[0075] In some preferred embodiments, the at least one second metal oxide-based catalyst may have a ratio of acidic hydroxyl groups to basic hydroxyl groups of at least 1.4, preferably at least 1.5, more preferably at least 1.6. In other words, the second metal oxide-based catalyst comprises a larger amount of acidic hydroxyl groups compared to basic hydroxyl groups.

[0076] In some preferred embodiments, the at least one second metal oxide-based catalyst may have a ratio of acidic hydroxyl groups to basic hydroxyl groups of from at least 1.3 to at most 20.0, or at least 1 .4 to at most 20.0, or at least 1 .5 to at most 20.0, or at least 1 .6 to at most 20.0, or at least 1 .6 to at most 15.0, or at least 1 .6 to at most 10.0.

[0077] In an exemplary embodiment, the present catalyst composition comprises: at least one first metal oxide-based catalyst having a ratio of acidic hydroxyl groups to basic hydroxyl groups of from at least 0.1 to at most 0.7; and, at least one second metal oxide-based catalyst having a ratio of acidic hydroxyl groups to basic hydroxyl groups of from at least 1 .3 to at most 20.0; wherein the catalyst composition has a ratio of acidic hydroxyl groups to basic hydroxyl groups of from at least 0.7 to at most 2.0.

[0078] In another exemplary embodiment, the present catalyst composition comprises: at least one first metal oxide-based catalyst having a ratio of acidic hydroxyl groups to basic hydroxyl groups of from at least 0.1 to at most 0.5; and, at least one second metal oxide-based catalyst having a ratio of acidic hydroxyl groups to basic hydroxyl groups of from at least 1 .5 to at most 10.0; wherein the catalyst composition has a ratio of acidic hydroxyl groups to basic hydroxyl groups of from at least 0.8 to at most 1 .3.

[0079] In preferred embodiments, the metal oxide-based catalysts as described herein (i.e., the at least one first metal oxide-based catalyst and at least one second metal oxide-based catalyst) comprise one or more metals (M), oxygen atoms (O), and hydrogen atoms (H).

[0080] For the purposes of the present invention, suitable metals include transition metals and posttransition metals capable of forming an oxygen-containing compound. Non-limiting examples of such metals include zirconium (Zr), titanium (Ti), scandium (Sc), hafnium (Hf), aluminium (Al), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), zinc (Zn), gallium (Ga), copper (Cu), nickel (Ni), cobalt (Co), calcium (Ca), cadmium (Cd), lanthanum (La), lead (Pb), thallium (TI), ytterbium (Yb), molybdenum (Mo), tungsten (W), indium (In), cations thereof, or a combination thereof. In addition, the metal oxide-based catalysts may further comprise metalloids such as silicon (Si). Preferably, the metal oxide-based catalysts comprises zirconium (Zr) and / or Titanium (Ti). The listed metals were found to provide solid catalyst compositions with a desired catalytic activity.

[0081] It should be clear that the metal oxide-based catalysts as disclosed herein may further comprise chemical mixtures or combinations of transition metals, post-transition metals, or metalloids such as silica-alumina, silica-iron, or silica-zinc.

[0082] In some preferred embodiments, the purity of each metal oxide-based catalyst comprised in the present solid catalyst composition is at least 80%, preferably at least 85%, preferably at least 90%, preferably at least 95%.

[0083] Experimentation has revealed that metals or metal cations bound to oxygen species, such as oxides and hydroxides, may advantageously provide metal oxide-based catalysts with unique chemical and physical properties, such as high surface area, variable oxidation states, and catalytic activity. In some embodiments, the at least one first metal oxide-based catalyst and the at least one second metal oxide-based catalyst are of a different chemical nature and may comprise a different centre atom or ion. Preferably the different centre atoms or ions are zirconium and titanium. For instance, the first metal oxide-based catalyst may comprise zirconium and the second metal oxide based catalyst may comprise titanium. Alternatively, the first metal oxidebased catalyst may comprise titanium and the second metal oxide based catalyst may comprise zirconium.

[0084] In some embodiments, the metal oxide-based catalysts as described herein may comprise metal oxyhydroxides. Metal oxyhydroxides are compounds that can be represented by the following chemical formula Mx(O)y(OH)z, wherein x, y, and z are positive numbers which are greater than zero and M is a suitable metal. The value of x, y, and z depends on the oxidation number of the respective metal M. Preferably, the metal oxide-based catalysts as described herein may comprise at least 60 wt.% of metal oxyhydroxides, or at least 70 wt.%, preferably at least 80 wt.%, preferably at least 90 wt.%, for example at least 95 wt.%, for example at least 98 wt.%, for example at least 99 wt.%; with wt.% relative to the total weight of the metal oxidebased catalyst.

[0085] In some embodiments, the metal oxide-based catalysts as described herein may comprise metal oxides. Metal oxides are compounds that can be represented by the following chemical formula Mx(O)y, wherein x, and y are positive numbers which are greater than zero and M is a suitable metal. The value of x, and y depends on the oxidation number of the respective metal M.

[0086] In some embodiments, the metal oxide-based catalysts as described herein may comprise metal hydroxides. Metal hydroxides are compounds that can be represented by the following chemical formula MX(OH)Z, wherein x, and z are positive numbers which are greater than zero and M is a suitable metal. The value of x, and z depends on the oxidation number of the respective metal M.

[0087] In some preferred embodiments, at least one of the metal oxide-based catalysts as described herein (i.e. , the at least one first metal oxide-based catalyst and / or at least one second metal oxide-based catalyst) may comprise Zrx(O)y(OH)z, preferably ZrO(OH)2.

[0088] In some preferred embodiments, at least one of the metal oxide-based catalysts as described herein (i.e., the at least one first metal oxide-based catalyst and / or at least one second metal oxide-based catalyst) may comprise Tix(O)y(OH)z, preferably TiO(OH)2.

[0089] It has been found herein that metal oxide-based catalysts with variable metal-to-oxygen atomic ratios may be used to provide catalyst compositions with optimized crystal structures that can maximize exposure of active sites. A particular metal-to-oxygen ratio may advantageously provide oxygen vacancies, which may improve the catalyst’s ability to participate in chemical reactions.

[0090] The atomic ratio of oxygen to metal is herein defined as the bulk ratio and can be measured by the weight loss of the respective metal oxide-based catalyst between 170°C to 800°C assuming the weight loss is from the loss of hydroxyl groups forming H2O, and the rest of the solids are metal oxides. The weight loss can be measured by Thermalgravimetric analysis (TGA) tested under N2 flow and a temperature rate of between 5 to 20°C / min, preferably 10°C / min, assuming all the weight decrement after a temperature of 180°C forms water and the final solid species above 600-800°C is considered metal oxide.

[0091] The present solid catalyst composition is not particularly limited to a specific proportion of each metal oxide-based catalyst. For instance, and in some embodiments, the solid catalyst composition may comprise an excess of the first metal oxide-based catalyst or an excess of the second metal oxide-based catalyst.

[0092] In some preferred embodiments, the solid catalyst composition comprises a weight ratio of the first metal oxide-based catalyst to the second metal oxide-based catalyst of between 0.2 and 5.0, or between 0.3 and 5.0, or between 0.4 and 5.0, or between 0.5 and 5.0, or between 0.5 and 4.0, or between 0.5 and 3.5, or between 0.5 and 3.0, or between 0.5 and 2.9, or between 0.5 and 2.8, or between 0.5 and 2.7, or between 0.5 and 2.6, or between 0.5 and 2.5.

[0093] In some preferred embodiments, the solid catalyst composition comprises at least 5.0 wt.% of the first metal oxide-based catalyst, or at least 7.5 wt.%; or at least 10.0 wt.%; with wt.% relative to the total weight of the solid catalyst composition.

[0094] In some preferred embodiments, the solid catalyst composition comprises at most 95.0 wt.% of the first metal oxide-based catalyst, or at most 92.5 wt.%, or at most 90.0 wt.%; with wt.% relative to the total weight of the solid catalyst composition.

[0095] In some preferred embodiments, the solid catalyst composition comprises from at least 5.0 to at most 95.0 wt.% of the first metal oxide-based catalyst, or at least 7.5 to at most 95.0 wt.%, or at least 7.5 to at most 92.5 wt.%, or at least 10.0 to at most 92.5 wt.%; or at least 10.0 to at most 90.0 wt.%; with wt.% relative to the total weight of the solid catalyst composition.

[0096] In some preferred embodiments, the solid catalyst composition comprises at least 5.0 wt.% of the first metal oxide-based catalyst, or at least 7.5 wt.%; or at least 10.0 wt.%; with wt.% relative to the total weight of the solid catalyst composition. In some preferred embodiments, the solid catalyst composition comprises at most 95.0 wt.% of the first metal oxide-based catalyst, or at most 92.5 wt.%, or at most 90.0 wt.%; with wt.% relative to the total weight of the solid catalyst composition.

[0097] In some preferred embodiments, the solid catalyst composition comprises from at least 5.0 to at most 95.0 wt.% of the first metal oxide-based catalyst, or at least 7.5 to at most 95.0 wt.%, or at least 7.5 to at most 92.5 wt.%, or at least 10.0 to at most 92.5 wt.%; or at least 10.0 to at most 90.0 wt.%; with wt.% relative to the total weight of the solid catalyst composition.

[0098] In an exemplary embodiment, the solid catalyst composition comprises from at least 5.0 to at most 95.0 wt.% of the first metal oxide-based catalyst; and from at least 5.0 to at most 95.0 wt.% of the second metal oxide-based catalyst; with wt.% relative to the total weight of the solid catalyst composition.

[0099] In some embodiments, preferably wherein the metal is zirconium, at least one of the metal oxide-based catalysts comprised in the present catalyst composition has a surface charge Zeta potential of at least -25 mV, or at least -20 mV, or at least -15 mV, or at least -10 mV, preferably at least -5 mV.

[0100] Catalysts with such a high surface charge were found to provide improved CO2 desorption properties.

[0101] The Zeta potential is preferably measured on a NanoPlus HD with an Auto-Titrator from Particulate Systems. Typically, 40 mg well-grinded sample powder may be mixed with 40 g ultrapure water, followed by a 20 min ultrasonic treatment. The finely dispersed sample solution may be used for the testing. The Zeta potential may be tested under a pH of from 3 to 12. For example, 0.1 M HCI and 0.1 M NaOH may be used for pH adjustment.

[0102] In a second aspect, the present invention provides a method for preparing the solid catalyst composition according to a first aspect of the present invention, or embodiments thereof. Preferably, the method comprises the steps of: preparing at least one first metal oxide-based catalyst; wherein the preparation procedure comprises forming a synthesis mixture by mixing a metal source, a solvent, and optionally a basic precipitating agent, thereby precipitating the first metal oxidebased catalyst; preparing at least one second metal oxide-based catalyst, wherein the preparation procedure comprises forming a synthesis mixture by mixing a metal source, a solvent, and optionally a basic precipitating agent, thereby precipitating the second metal oxidebased catalyst; and, mixing the first metal oxide-based catalyst and second metal oxide-based catalyst, thereby obtaining the solid catalyst composition.

[0103] It should be noted that (preferred) embodiments of the first aspect of the present invention and any associated advantages thereof are also (preferred) embodiments of the second aspect of the present invention and vice versa.

[0104] The present method for preparing solid catalyst compositions thus preferably pertains to precipitation step(s) for preparing metal oxide-based catalysts followed by mixing the precipitated catalysts to obtain a solid catalyst composition as defined herein. The precipitation step(s) are preferably characterized in that the pH of the synthesis mixture is at least 2 and at most 11 .

[0105] A solid catalyst composition prepared this way was found to provide a significant improvement on CO2 desorption properties without significant dissolution, as illustrated in the example section. More specifically, the present precipitation step(s) can influence the ratio of acidic and basic hydroxyl groups and surface charge properties of the precipitated metal oxide-based catalysts, which is demonstrated herein to cause an additional improvement in catalytic performance.

[0106] In some embodiments, the pH of the synthesis mixture for preparing the at least one first metal oxide-based catalyst may be different from the at least one second metal oxide-based catalyst. For instance, the synthesis mixture for preparing the at least one first metal oxide-based catalyst may be more basic compared to the synthesis mixture for preparing the at least one second metal oxide-based catalyst.

[0107] The pH of the synthesis mixture may depend on the nature and amount of the metal source and optional basic precipitating agent as is apparent to the person skilled in the art. The pH may be preferably determined by placing a calibrated pH meter equipped with a suitable electrode in the synthesis mixture. The pH may be monitored and adjusted during the precipitation step(s) by adding small aliquots of the basic precipitating agent or by adding parts of the metal source to the mixture.

[0108] In some preferred embodiments, the metal source is a metal complex, preferably a metal salt, comprising zirconium, titanium, scandium, hafnium, aluminium, silicon, vanadium, chromium, manganese, iron, zinc, gallium, copper, nickel, cobalt, calcium, cadmium, lanthanum, lead, thallium, ytterbium, molybdenum, tungsten, indium, or a combination thereof. In some preferred embodiments, the metal source is a metal complex, preferably a metal salt, further comprising nitrate, oxynitrate, halide, oxyhalide, sulphate, alkoxide, carboxylate or a combination thereof. For instance, the metal source may be ZrO(NOs)2, Cu(NC>3)2, or TiO(SC>4). Alternatively, the metal source may be a metal alkoxide such as Ti(O- / C3H7)4.

[0109] In some preferred embodiments, the metal source is selected from zirconyl-nitrate, zirconylhalides, zirconyl-sulphate, zirconium-alkoxide or zirconium halide.

[0110] In some preferred embodiments, the metal source is a titanium alkoxide, such as titanium tetra-isopropoxide.

[0111] In accordance with the present invention, the metal source may be dissolved in a suitable solvent, thereby forming a synthesis mixture as described herein. Suitable solvents include water or an organic solvent comprising one or more hydroxyl groups, such as methanol. Preferably, the solvent is water. In some embodiments, the synthesis mixture comprises at least 2.00 M and at most 4.00 M, for example about 3.00 M of the metal source.

[0112] The optional basic precipitating agent may be contacted with the synthesis mixture as such or as a separate basic solution, such as an aqueous solution of a suitable hydroxide. For instance, the basic solution may comprise at least 1.00 M and at most 1.50 M, for example about 1.25 M of the basic precipitating agent.

[0113] In some preferred embodiments, the basic precipitating agent comprises hydroxide, carbonate, bicarbonate, or carboxylate, and an alkali metal cation, alkaline earth metal cation, or ammonium cation.

[0114] Suitable hydroxides include sodium hydroxide, potassium hydroxide, ammonium hydroxide, calcium hydroxide, magnesium hydroxide, lithium hydroxide, and mixtures thereof.

[0115] Suitable carbonates include sodium carbonate, potassium carbonate, ammonium carbonate, calcium carbonate, magnesium carbonate, lithium carbonate, and mixtures thereof.

[0116] Suitable bicarbonates include sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate, calcium bicarbonate, magnesium bicarbonate, lithium bicarbonate, and mixtures thereof.

[0117] Suitable carboxylates include sodium formate, potassium formate, ammonium formate, calcium formate, magnesium formate, lithium formate, sodium acetate, potassium acetate, ammonium acetate, calcium acetate, magnesium acetate, lithium acetate, sodium propionate, potassium propionate, ammonium propionate, calcium propionate, magnesium propionate, lithium propionate, sodium butyrate, potassium butyrate, ammonium butyrate, calcium butyrate, magnesium butyrate, lithium butyrate and mixtures thereof. Alternatively, the basic precipitating agent comprises an alkyl-amine (e.g., methyl and ethyl amine), dialkyl-amine (e.g., dimethyl and diethyl amines), trialkyl-amine (e.g., trimethylamine and triethylamine), alkanolamine (e.g., mono-ethanol-amine), urea, hydrazine, or mixtures thereof.

[0118] Contacting of the synthesis mixture and the basic precipitating agent may be performed under constant stirring, and optionally maintaining the temperature of the mixture between 20°C and 80°C, preferably around 20°C, to facilitate the formation of the precipitate (i.e. metal oxidebased catalyst).

[0119] To ensure complete precipitation, the reaction may be performed over a time period of between 10 minutes and 24 hours, or between 30 minutes and 24 hours, or between 1 hour and 24 hours, or between 1 hour and 12 hours, or between 1 hour and 6 hours, or between 2 hours and 6 hours. In addition, the synthesis mixture and the basic precipitating agent may be contacted at a controlled rate to ensure uniform precipitation. For instance, contacting may comprise dripping the synthesis mixture to the basic precipitating agent.

[0120] The precipitate may be further aged in the synthesis mixture for at least 10 minutes, or at least 30 minutes, or at least 1 hour, or at least 2 hours, or at least 3 hours, preferably at a temperature of around 20°C. This has the advantage that the crystallinity and stability of the precipitate may be improved. After ageing, the precipitate can be filtered and washed with a suitable solvent (e.g., deionized water) to remove any residual material. Washing can be continued until the pH of the mixture is neutral.

[0121] Each precipitated metal oxide-based catalyst may be dried at a temperature of between 60°C and 160°C, or between 80°C and 120°C, preferably at a temperature of around 100°C, for 12 hours to 5 days, preferably 48 hours.

[0122] Each precipitated metal oxide-based catalyst may be calcined at calcination temperature Tc is at most 400°C, preferably at most 350°C, preferably at most 300°C, preferably at most 250°C, preferably at most 200°C, preferably at most 150°C, preferably at most 100°C, for 2 to 6 hours, preferably 4 hours. Calcination can convert the precipitate into a stable metal oxidebased catalyst with high surface area and desired catalytic properties.

[0123] It was found that a calcination step at too high temperatures removed the OH groups and reduced the catalyst (completely) to metal oxides, thereby severely reducing the catalytic activity.

[0124] In some preferred embodiments, at least one of the precipitated metal oxide-based catalysts is a zirconium oxide-based catalyst, wherein the zirconium oxide-based catalyst remains in an amorphous phase upon heating / calcining in ambient / inert until 200-300°C. The inventors have surprisingly found that the best-performing catalysts do not show the tetragonal crystalline t- ZrC>2 phase upon heating / calcining in ambient / inert until 200-300°C, but remain in an amorphous phase, whereas inferior catalysts do give clear formation of the t-ZrC>2 phase (as measured using classic state of the art powder X-ray diffraction analysis, for example as illustrated in the example section) upon the same thermal treatment.

[0125] In some preferred embodiments, the zirconium oxide-based catalyst may comprise at most 20.0 wt% of the tetragonal crystalline t-ZrC>2 phase, preferably at most 10.0 wt%, preferably at most 5.0 wt%, preferably at most 2.0 wt%, preferably at most 1 .0 wt%, preferably essentially no tetragonal crystalline t-ZrC>2 phase, after heating / calcining in ambient / inert until 200-300°C.

[0126] In some embodiments, a co-precipitation method is used, preferably to simultaneously prepare two or more metal oxide-based catalysts.

[0127] Suitable mixing methods to obtain the solid catalyst composition as described herein may comprise mechanical mixing of the at least one first metal oxide-based catalyst and the at least one second metal oxide-based catalyst. For instance, mechanical mixing may be performed using a ball mill or mortar and pestle to ensure uniform distribution.

[0128] The solid catalyst composition comprising the at least one first metal oxide-based catalyst and the at least one second metal oxide-based catalyst, may be mixed and the mixture formulated in a particulate shape by methods known in the art, like extrusion, pelletizing, pilling, oildropping, spray-drying, or atomizing.

[0129] Each formulated solid catalyst composition may be calcined at calcination temperature Tc, preferably wherein Tc is at most 400°C, preferably at most 350°C, preferably at most 300°C, preferably at most 250°C, preferably at most 200°C, preferably at most 150°C, preferably at most 100°C, for example for 2 to 6 hours, preferably 4 hours. Calcination can strengthen the mechanical properties of the particulate solid catalyst composition.

[0130] The solid catalyst composition of the present invention has the advantage that it can be used easily in a continuous mode where the CC>2-containing absorbent (a liquid) is sent continuously over the solid catalyst composition that itself remains confined in a given space of the desorption equipment, particularly since it can act as a non-solubilized heterogeneous catalyst as demonstrated herein in the example section. The solid catalyst composition in such continuous mode embodiment is used in particulate shapes, like balls, pellets, extrudates or powder. The particulate shapes of the solid catalyst composition can be confined as a fixed bed, fluidized bed, entrained bed or can be fixed on the trays or packing of a desorption equipment. The particulate shapes of the solid catalyst composition can be confined as a fixed bed, fluidized bed, entrained bed in a reactor vessel upstream or parallel to the desorption equipment.

[0131] In exemplary embodiments, the method for preparing the solid catalyst composition according to a first aspect of the present invention, or embodiments thereof, may comprise the steps of: preparing at least one first metal oxide-based catalyst; wherein the preparation procedure comprises forming a synthesis mixture by mixing a metal source, a solvent, and optionally a basic precipitating agent, thereby precipitating the first metal oxidebased catalyst; preparing at least one second metal oxide-based catalyst, wherein the preparation procedure comprises forming a synthesis mixture by mixing a metal source, a solvent, and optionally a basic precipitating agent, thereby precipitating the second metal oxidebased catalyst; drying the at least one first metal oxide-based catalyst and at least one second metal oxide-based catalyst; optionally calcining the at least one first metal oxide-based catalyst and at least one second metal oxide-based catalyst; and, mixing the first metal oxide-based catalyst and second metal oxide-based catalyst, thereby obtaining the solid catalyst composition.

[0132] In some preferred embodiments, the metal oxide-based catalysts as described herein or at least one metal oxide-based catalyst is a supported metal oxide-based catalyst. In the event that the metal oxide-based catalyst is a supported metal oxide-based catalyst, the method for preparing a solid catalyst composition as described herein may comprise the steps of: preparing at least one first metal oxide-based supported catalyst, wherein the synthesis procedure comprises forming a synthesis slurry by mixing a metal source, a solid catalyst support, a solvent, and optionally a basic precipitating agent, thereby precipitating the first metal oxide-based catalyst on the solid catalyst support; preparing at least one second metal oxide-based supported catalyst, wherein the synthesis procedure comprises forming a synthesis slurry by mixing a metal source, a solid catalyst support, a solvent, and optionally a basic precipitating agent, thereby precipitating the second metal oxide-based catalyst on the solid catalyst support; and, mixing the at least one first metal oxide-based supported catalyst and at least one second metal oxide-based supported catalyst, thereby obtaining the solid catalyst composition.

[0133] In some preferred embodiments, at least one metal oxide-based catalyst is a supported metal oxide-based catalyst and at least one metal oxide-based catalyst is an unsupported metal oxide-based catalyst. In some preferred embodiments, the at least one first metal oxide-based catalyst is a supported metal oxide-based catalyst and at the at least one second metal oxidebased catalyst is an unsupported metal oxide-based catalyst. In some preferred embodiments, the at least one first metal oxide-based catalyst is an unsupported metal oxide-based catalyst and at the at least one second metal oxide-based catalyst is a supported metal oxide-based catalyst.

[0134] In the event that the solid catalyst composition as described herein comprises at least one supported metal oxide-based catalyst and at least one unsupported metal oxide-based catalyst, the method for preparing the solid catalyst composition as described herein may comprise the steps of: preparing at least one metal oxide-based supported catalyst, wherein the synthesis procedure comprises forming a synthesis slurry by mixing a metal source, a solid catalyst support, a solvent, and optionally a basic precipitating agent, thereby precipitating the metal oxide-based catalyst on the solid catalyst support; preparing at least one metal oxide-based unsupported catalyst, wherein the synthesis procedure comprises forming a synthesis mixture by mixing a metal source, a solvent, and optionally a basic precipitating agent, thereby precipitating the metal oxide-based catalyst; and, mixing the metal oxide-based supported catalyst and the metal oxide-based unsupported catalyst, thereby obtaining the solid catalyst composition.

[0135] Preferably, the solid catalyst support is a porous solid catalyst support, more preferably a mesoporous solid catalyst support.

[0136] In some embodiments, the solid catalyst support is a particulate solid catalyst support. Preferably, suitable particulate solid catalyst supports comprise carbon-containing materials like silicon carbide, petroleum coke, black carbon, activated carbon, char and / or graphite and / or carbon nanotubes, and any mixture thereof.

[0137] In some embodiments, the solid catalyst support comprises activated carbon, biochar, graphite, graphene oxide, carbon black, and / or carbon nanotubes, preferably having at least 1 wt.% of oxygen atoms and / or at least 80 wt.% of carbon atoms. Preferably, the solid catalyst support comprises acidic and / or basic oxygen surface species. Acidic oxidic surface groups on the solid catalyst support may include hydroxyl groups, carbonyl groups, phenol groups, lactone groups, lactol groups, and carboxyl groups. Basic oxidic surface functionalities may comprise chromene structures, diketone or quinone groups, and / or pyrone-like groups. Preferably, the solid catalyst support comprises basic nitrogen surface species, provided by amino-N, pyrrolic-N, pyridinic-N, and quaternary nitrogen surface groups.

[0138] In some embodiments, suitable particulate solid catalyst supports are refractory oxides such as alumina (AI2O3), silica (SiC>2), titania (TiC>2), ceria (CeC>2), zirconia (ZrC>2), magnesia (MgO), yttria (Y2O3), hafnia (HfC>2), lanthania (La2Os), and any mixture thereof, more preferably alumina, silica, ceria, zirconia, magnesia, and any mixture thereof. A typical example of an amorphous mixed oxide is ASA (amorphous silica-alumina).

[0139] In some embodiments, the solid catalyst support comprises a crystalline mixed oxide, preferably selected from the list comprising: one or more oxides having a cubic fluorite structure optionally being at least partially substituted with one or more lower-valent cations, preferentially selected from Sm, Gd, Y, Sc, Yb, Mg, Ca, La, Dy, Er, Eu; and / or one or more ABOs-perovskites with A and B tri-valent cations, optionally being at least partially substituted in A position with one or more lower-valent cations, preferentially selected from Ca, Sr, or Mg, and comprising at least one of Ni, Ga, Co, Cr, Mn, Sc, Fe, and / or a mixture thereof in B position; and / or one or more ABOs-perovskites with A bivalent cation and B tetra-valent cation, optionally being at least partially substituted with one or more lower-valent cations, preferentially selected from magnesium (Mg), scandium (Sc), yttrium (Y), neodymium (Nd) or ytterbium (Yb) in the B position or with a mixture of different B elements in the B position; and / or. one or more A2B2O?-pyroch lores with A trivalent cation and B tetra-valent cation optionally being at least partially substituted in A position with one or more lower-valent cations, preferentially selected from Ca or Mg, and comprising at least one of Sn, Zr and Ti in B position; and / or one or more AB2O4-spinel with A divalent cation and B tri-valent cation (for example MgAhO4, CaAl2O4, BaAl2O4, SrAl2O4, FeAl2O4, and ZnAI2O4) comprising at least one of Al or Fe in B position; and / or one or more hydrotalcite, a double layered lamellar clay, comprising brucite-like positively charged layers, with an anionic layer sandwiched between them with general formula [Alli-xBlll(OH)2]x+[Cn-]x / n-yH2O (for example Mg6AI2(OH)i6CO3-4H2O) with A divalent cation and B tri-valent cation.

[0140] In some embodiments, suitable particulate solid catalyst supports are microporous or mesoporous oxides such as molecular sieves, including silica-alumina, silica-boria, silica- germania, alumina-phosphate, silica-alumina-phosphate zeolites, and any mixture thereof. Examples of such molecular sieves are MFI (ZSM-5, silicalite-1 , boralite C, TS-1 ), MEL (ZSM- 11 , silicalite-2, boralite D, TS-2, SSZ-46), clinoptilolite, MSA (mesoporous silica-alumina, MCM-41 , MCM-48, SBA-15, SBA-16), FER (Ferrierite, FU-9, ZSM-35), MTT (ZSM-23), ZSM- 21 , ZSM-42, ZSM -57, MWW (MCM-22, PSH-3, ITQ-1 , MCM-49), TON (ZSM-22, Theta-1 , NU-10), EUO (ZSM-50, EU-1 ), MFS (ZSM-57), ZSM- 48, MTW, MAZ, BETA, FAU (zeolite X, Y or SAPO-37), LTL, MOR, zeolite Omega, AFI (SAPO-5), AFO (SAPO-41 ) and AEL (SAPO- 11 ).

[0141] In some embodiments, said solid catalyst support further comprises a specific surface area ranging between 5 m2 / g and 1000 m2 / g as determined by N2adsorption measurement, more preferably between 50 m2 / g and 900 m2 / g, even more preferably between 100 m2 / g and 800 m2 / g, most preferably between 200 m2 / g and 700 m2 / g.

[0142] In some preferred embodiments, the solid catalyst support concentration in the synthesis slurry comprises at least 1 weight percent and at most 50 weight percent of solid catalyst support, for example about 10 weight percent.

[0143] In some preferred embodiments, the solid catalyst support concentration in the synthesis slurry comprises at least 1 weight % to at most 50 weight %, preferably at least 2 weight% to at most 30 weight %, preferably at least 3 weight% to at most 20 weight %, preferably at least 4 weight% to at most 10 weight %, of solid catalyst support, for example about 5 weight %.

[0144] In some embodiments, the amount of metal oxide-based catalyst on the solid catalyst support in the final catalyst is preferably between 1 and 50 weight percent of metal in the final catalyst, meaning that 100 gram of supported metal oxide-based catalyst comprises between 1 and 50 grams of metal, more preferably between 5 and 35 weight percent of metal and most preferable between 10 and 20 weight percent of metal (10 weight percent metal in the final catalyst corresponds to about 15,5 weight percent as metal-oxide (dry basis) and 50 weight percent of metal corresponds to 77 weight percent as metal-oxide (dry basis).

[0145] In a third aspect, the present invention relates to the use of the solid catalyst composition according to a first aspect of the present invention, or embodiments thereof, or obtained or obtainable by means of the method according to a second aspect of the present invention, or embodiments thereof, in a process for CO2 desorption from an absorbent, preferably comprising one or more nitrogen compounds such as amines.

[0146] It should be noted that (preferred) embodiments of the first aspect and second aspect of the present invention and any associated advantages thereof are also (preferred) embodiments of the third aspect of the present invention and vice versa.

[0147] It should be clear that in the context of the process for CO2 desorption as described herein, the absorbent is contacted with the solid catalyst composition after CO2 absorption. Hence, the absorbent is a CC>2-containing absorbent that may be subjected to CO2 desorption, thereby releasing the captured CC^ and regenerating the absorbent.

[0148] A particular advantage of using the present solid catalyst composition in a process for CO2 desorption are reduced costs for regenerating absorbents in the overall absorption / desorption process. Moreover, use of a solid catalyst composition as described herein allows to reduce the circulating flow rate of the absorbent and to reduce the temperature of CO2 desorption, which in turn leads to lower energy requirements (OPEX), and / or less solvent degradation. For example, desorption at lower temperatures allows for less degradation of amine(s).

[0149] Experimentation of the present inventors has revealed that the present solid catalyst composition is particularly productive in an industrial process for CO2 desorption from an absorbent. The productivity and efficiency of the catalytic action may be measured herein by how many kilograms of feed (i.e., CC>2-containing absorbent) is processed per kilogram of solid catalyst composition per hour. This parameter is typically expressed as the weight hourly space velocity (WHSV) according to the following formula:

[0150] In some preferred embodiments, the catalyst composition is contacted with the absorbent in a process for CO2 desorption at a weight hourly space velocity of between 0.01 and 2000 h’1, preferably between 1 and 500 h’1.

[0151] In some preferred embodiments, the solid catalyst composition acts as a non-solubilized heterogeneous catalyst composition. The solid catalyst composition is typically stable and insoluble in the absorbent, which makes it easy to be separated and regenerated.

[0152] In some preferred embodiments, the absorbent comprises an amine compound, preferably an alkanolamine, comprising a primary amine group, secondary amine group, and / or tertiary amine group. Examples of suitable amines include but are not limited to: monoethanolamine (MEA), 2-amino-2-methyl-1 -propanol (AMP), diethanolamine (DEA), diglycolamine (DGA), methyldiethanolamine (MDEA), piperazine (PZ), ammonia, amines, alkanolamines, derivatives and / or combinations thereof. Preferably, the amine solvent comprises monoethanolamine (MEA) or 2-amino-2-methyl-1 -propanol (AMP), preferably monoethanolamine (MEA).

[0153] The mechanism of CO2 absorption in different amine compounds is shown as follows:

[0154] Primary / secondary amine group:

[0155] CO2+ 2R1R2NH 2R1R2NH2++ R^NCOCT

[0156] Tertiary amine group:

[0157] CO2+ RtR2R3N + H2O R1R2R3NH++ HC03~

[0158] Preferably, the present absorbent comprises monoethanolamine (MEA). The present inventors have found that monoethanolamine (MEA) is particularly advantageous because of its high CO2 absorption rate, high capacity, high mass-transfer performance, and low-price properties. Absorption of CO2 in MEA solvent follows a Zwitterion mechanism. One CO2 is absorbed and forms one carbamate (anion) and one neutralizing protonated MEA (cation).

[0159] Without willing to be bound to any theory, the presently described CO2 desorption process may consist of a series of chemical step(s) and physical transport steps. The present catalyst composition is particular efficient for catalysing one or more of the chemical steps of the desorption route. For instance, in the event that the absorber comprises an amine compound, preferably an alkanolamine, a carbamate is typically formed upon CO2 absorption. Next, the carbamate can be decomposed into the amine compound and dissolved CO2 as schematically shown in FIG. 1. This decomposition step involves a proton transfer from a suitable proton donor (e.g., a hydronium ion). The dissolved CO2 can move to the liquid-gas interphase and the dissolved CO2 escapes from the liquid solvent into the gas phase. While the physical transport steps can be enhanced by increasing turbulence and in particular by increasing the liquid-gas interphase area, the carbamate decomposition step requires a minimum activation energy to occur. Such minimum activation energy can be attained by using the present solid catalyst composition.

[0160] In some embodiments, the amine compound comprises a combination of two or more amines, for example 2-amino-2-methyl-1 -propanol (AMP) and piperazine (PZ). A combination of amines can increase absorption rate and cyclic capacity to reduce energy of regeneration (heat duty), and minimize degradation. An AMP / PZ (3 M / 1 .5 M) ratio is considered to be a preferred ratio. The proper ratio of AMP / PZ can increase the absorption rate and the cyclic capacity while avoiding the precipitation of PZ.

[0161] In some embodiments, the amine compound is present in the absorber at a molar concentration of at least a 1 M to at most a 10 M, preferably of at least a 2 M to at most an 8 M, preferably of at least a 4 M to at most a 6 M, for example at about a 5 M concentration. These concentrations were found to provide optimal results, as illustrated in the example section.

[0162] CO2 as used herein is typically provided as a CO2 rich gas, which is a gas having a CO2 concentration being substantially higher than the CO2 concentration in air, i.e. a concentration substantially higher than 0.04%, such as higher than 1%, 2%, 5%, or even higher than 10%. The CO2 rich gas, as used herein, is usually an exhaust gas from combustion of carbonaceous fuels, and more specifically fossil fuels. However, the present invention may also be used for desorbing CO2 obtained from exhaust gas from combustion of non-fossil fuels, combination of fossil and non-fossil fuels, such as waste, or from CO2 capture from any industrial waste gas comprising CO2, and where the remaining waste gas may be released into the surroundings after CO2 capture.

[0163] The present invention further encompasses a process for CO2 desorption from an absorbent, preferably comprising one or more nitrogen compounds such as amines. The process preferably comprising the steps of: providing a CC>2-containing absorbent, preferably comprising CO2 absorbed in an amine compound; supplying a solid catalyst composition according to a first aspect of the present invention, or embodiments thereof, to the CC>2-containing absorbent; heating the CC>2-containing absorbent comprising the solid catalyst composition to a desorption temperature Td; and, desorbing CO2 from the absorbent comprising the solid catalyst composition during a residence time t.

[0164] In some embodiments, the desorption temperature Td is at most 200°C, preferably at most 160°C, preferably at most 130°C, preferably at most 100°C.

[0165] The present invention has the significant advantage that the desorption temperature can be kept low. The boosting of CO2 desorption rate with the catalyst composition makes it possible for the absorbent regeneration process to run under a lower temperature which can significantly decrease the energy cost of post-combustion capture (PPC) and prevent the absorbent from degradation and evaporation.

[0166] In some preferred embodiments, the residence time is at least 4 hours and at most 168 hours, preferably at least 8 hours and at most 72 hours, preferably at least 16 hours and at most 48 hours, preferably at least 20 hours and at most 36 hours, for example about 24 hours.

[0167] These residence times were found to provide optimal results, as illustrated in the example section.

[0168] The presently described process for CO2 desorption from an absorbent, in the presence of a solid catalyst composition as described herein, may be performed in suitable desorption equipment such as a desorption column of a carbon capture and storage (CCS) unit. An example of a desorption column is a stripper column, wherein CO2 may be released from the absorbent by stripping with hot steam in the presence of the catalyst composition, and steam and CO2 is withdrawn through a CO2 line for further treatment. Regenerated, or lean, absorbent is then collected at the bottom of the stripper column.

[0169] Use of a solid catalyst composition as described herein allows for obtaining a leaner absorbent, collected at the bottom of the stripper column, and hence having to circulate less absorbent between the absorption and stripping sections and hence requires less energy to regenerate the more lean absorbent.

[0170] Use of a solid catalyst composition as described herein allows for a reduction in size of the desorption column (e.g., stripper column) leading to lower CAPEX.

[0171] In some embodiments, the solid catalyst composition may have different shapes according to the location where it is best applied: a power-like solid material (typically having particle size of less than 0.1 millimetre) used in an agitated or stirred reactor vessel that can be operated batch-wise or continuously, a shaped solid material (typically having particle size of more than 0.1 millimetre) comprising crushed irregular particles, spherical particles, solid or open pellet, solid or open rods (extrudates), solid or open trilobed, solid or open quadrilobed shapes, honeycomb shapes, etc. Optionally, the power-like solid material can be circulated with the absorbent between an absorption and stripper column of a carbon capture and storage (CCS) unit. In case of shaped solid materials, the shaped solid material is located in fixed bed type of reactor sections. It is a preferred method of the present invention to operate the CO2 stripping in a continuous manner.

[0172] The solid catalyst composition may be used in different locations of a desorption section of the carbon capture and storage (CCS) unit. For instance, in the feed line supplying the CO2- containing absorbent from a heat exchanger to a stripper column, inside the stripper column on active area of trays, in a downcomer of the tray or as layered sections within a packed column or both, in a line between the bottom of the stripper column to a reboiler, in the reboiler or as a parallel reactor to the stripper column (withdrawing a liquid stream from the stripper column to be sent to the parallel reactor while the product is reinjected into the stripper column).

[0173] The present invention further encompasses a process for CO2 absorption and desorption. Preferably, the process comprises the steps of: absorbing CO2 in an absorbent, thereby obtaining a CC>2-containing absorbent; and, desorbing CO2 from the CC>2-containing absorbent using the process as described herein, or (preferred) embodiments thereof, thereby regenerating the absorbent.

[0174] The present invention allows to reduce the cost of regeneration of absorbents in the absorption / desorption process.

[0175] The present process for CO2 absorption and desorption may be performed in a carbon capture and storage (CCS) unit as schematically illustrated in FIG. 2. The present solid catalyst composition may be used in said process.

[0176] As shown in FIG. 2, the CO2 absorption and desorption process starts by introducing a CO2- containing flue gas stream into an absorber. Suitable absorbers include packed bed absorber columns. The flue gas stream may enter the absorber such that the absorbent flows counter- currently with respect to the flue gas stream to absorb CO2. After absorption, the CO2- containing absorbent is transferred to a stripper. Suitable strippers include stripper columns. Optionally, the CO2-containing absorbent is directed to a heat exchanger prior to being transferred to the stripper. In the stripper, the CO2-containing absorbent is heated to a temperature of from 50°C to 150°C by contacting the CO2-containing absorbent with steam. Next, the CO2-containing absorbent is contacted with the present solid catalyst composition at a temperature of from 50°C to 150°C and a pressure of from 0.5 bar to 7.0 bar, preferably of from 1 .0 to 4.0 bar to desorb CO2. At least a part of the desorbed CO2 is recovered from the partially regenerated absorbent at a total pressure of between 0.5 and 5.0 bara, preferably between 1.0 and 2.0 bara. Optionally, the at least partially regenerated absorbent is heated in a dedicated stripping equipment comprising a reboiler, thereby producing regenerated, or lean, absorbent. The regenerated absorbent may be recycled to the absorber to repeat the present process.

[0177] In some preferred embodiments, the contacting of the present catalyst composition and the CO2-containing absorbent is performed in an integral part of the stripper. In some embodiments, the process is a batch process. In some more preferred embodiments, the process is a continuous process.

[0178] In some embodiments, the process further comprises the step of: recycling the solid catalyst composition into the process.

[0179] The solid catalyst composition of the present invention has the advantage that it can be easily recycled, particularly since the catalyst typically acts as a non-solubilized heterogeneous catalyst.

[0180] In some embodiments, the step of recycling the solid catalyst composition comprises the step of: directly recycling the solid catalyst composition and absorbent into the process, by using the solid catalyst composition and absorbent in a re-absorption step without separation.

[0181] In some embodiments, the step of recycling the solid catalyst composition comprises the steps of: removing the solid catalyst composition from the absorbent, preferably through filtration; washing the solid catalyst composition with water; optionally, centrifuging the solid catalyst composition; drying the solid catalyst composition; and, adding the dried catalyst composition to an absorbent.

[0182] EXAMPLES

[0183] The following examples serve to merely illustrate the invention and should not be construed as limiting its scope in any way. While the invention has been shown in only some of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes and modifications without departing from the scope of the invention.

[0184] Experimental Methods

[0185] An experimental apparatus for solvent regeneration (CO2 desorption) is shown in FIG. 3. It consists of a 250 mL round-bottom flask equipped with a thermometer, a heater controlled by a temperature controller, a condenser, a magnetic field stirrer. For a typical CO2 desorption experiment run, 150 mL 5 M MEA solution with initial CO2 loading (0.52 mol / mol) and 3 g catalyst is mixed in the reactor under a 500 mL / min N2 flow from the top of the condenser. Then the solution was heated to 361.1 K in 50 ± 5 min and kept constant for 180 min with a stirring rate of 500 rpm. The time when the solution reached 361.1 K is noted as 0 min. For a long time (168 h) CO2 desorption experiment, 6 g of solid catalyst composition is used in 150 mL 5 M MEA. The CO2 concentration of the solution is analysed by Chittick equipment with the average absolute relative deviation less than 5%. Typically, 500 pL CO2 loaded amine solution was added to the flask by a pipette, then 1 mL of 1 .5 M H2SO4 was injected into the solution under a violent stirring. The volume of released CO2 is noted to further calculate the CO2 concentration of the sample. Every sample was tested three times, and the average value was adopted.

[0186] Solid catalyst compositions and metal oxide-based catalysts are evaluated in two aspects: CO2 deposition amount during the temperature ramping stage and the catalytic reaction rate constant (kcAi).

[0187] The kcAT is calculated as follows: kcAT—koverall " kblank koveraii is the overall reaction rate constant calculated through the CO2 concentration of 0 min, 30 min, 60 min, 90 min, 120 min and 180 min after the temperature gets stable ( isothermal stage), kbiank is calculated from the changes of the CO2 concentration in MEA solvent without any catalysts during the first 3 h desorption in the isothermal stage. Without specific description, the value of kbiank is considered to be -1.3 *10'4min-1.

[0188] X-ray powder diffraction (XRD) was conducted on a high-throughput STOE STADI P Combi diffractometer in the transmission mode with focusing Ge(111 ) monochromatic X-ray inlet beams (A=1.5406 A, Cu Ko source).

[0189] Thermogravimetric analysis (TGA) was conducted on TGA Q500 from TA Instruments. Typically, the TGA was performed under a 10 mL / min N2 atmosphere, with a temperature ramping from 50°C to 150°C for 30 min to make sure all free water is released, and then to 800°C. The temperature ramping rate was 10°C / min.

[0190] Zeta potential was tested on NanoPlus HD with an Auto-Titrator from Particulate Systems. Typically, 40 mg well-grinded sample powder was mixed with 40 g ultrapure water, followed by a 20 min ultrasonic treatment. The finely dispersed sample solution was used for the testing. The Zeta potential was tested under a pH from 3 to 12. 0.1 M HCI and 0.1 M NaOH were used for pH adjustment. N2 absorption measurements were performed using Micromeritics Instruments Tristar 3000 at 77 K. The samples were degassed under N2 flow at 250°C for 6 h prior to measurement. The relative nitrogen pressure varied between 0.01 and 0.99 (p / pO).

[0191] Example 1 : Mixture of zirconium oxide-based catalysts

[0192] In a first example, a solid catalyst composition according to the present invention was prepared by mixing two zirconium oxide-based catalysts, each having a different ratio of acidic hydroxyl groups to basic hydroxyl groups.

[0193] The solid catalyst composition (composition 1 ) was obtained by physically mixing a first metal oxide-based catalyst (catalyst A) and a second metal oxide-based catalyst (catalyst B) in a weight ratio of catalyst A to catalyst B of 0.8.

[0194] Catalyst A is a zirconium oxide-based catalyst comprising mainly weak basic sites (terminal OH groups having basic hydroxyl groups). Catalyst A was prepared by means of precipitation as described herein. More specifically, a NaOH solution was dripped into a ZrO(NOs)2 solution until pH reached 2 under constant stirring. After ageing for 3 h, the sediment was centrifuged and washed three times, then dried at 100°C for 48 h. The obtained zirconium oxide-based catalyst has the following chemical formula ZrOxHywith x and y being positive numbers.

[0195] Catalyst B is a zirconium oxide-based catalyst comprising mainly weak acidic sites (bridged OH groups having acidic hydroxyl groups). Catalyst B was prepared by means of precipitation as described herein. More specifically, a NaOH solution was dripped into a ZrO(NOs)2 solution until pH reached 8 under constant stirring. After ageing for 3 h, the sediment was centrifuged and washed three times, then dried at 100°C for 48 h. The obtained zirconium oxide-based catalyst has the following chemical formula ZrOtHzwith t and z being positive numbers.

[0196] The catalytic performance of catalyst A, catalyst B, and composition 1 for CO2 desorption from an amine solvent was determined as described in the experimental method section above. The desorption results and properties of catalyst A, catalyst B, and composition 1 are summarized in Table 1.

[0197] Table 1

[0198] CO2 desorption Performance and properties of catalyst A, catalyst B, and comp 1 Ratio

[0199] Bridged Terminal CO2kcAT / OH acidic Total OH

[0200] OH OH desorption amount

[0201] Sample OH content content content amount (*10'2min-1to basic (mmol / g) (mmol / g) (mmol / g) (mmol) mol'1)

[0202] OH

[0203] Catalyst A 0.4 12.3 3.5 8.8 9 0.03

[0204] Catalyst B 2.0 10.9 7.3 3.6 19 0.32

[0205] Composition 1 1.1 10.3 5.4 4.9 31 0.90

[0206] Reaction conditions: 3 g of catalysts, 150 mL CO2-saturated 5 M MEA, N2 flow of 0.5 L min'1from the top of the condenser, 88°C. The CO2 desorption amount is based on the isothermal reaction period.

[0207] As illustrated in FIG. 4, the solid catalyst composition, composition 1 with a CAT / OH amount of around 0.90*1 O'2min'1mol'1, exhibits a surprisingly better performance compared to the individual metal oxide-based catalysts, catalyst A and catalyst B with a CAT / OH amount of around 0.05*1 O'2min'1mol'1and 0.36*1 O'2min'1mol'1, respectively. Without willing to be bound to any theory, this unexpected result corroborates a synergy effect of the two metal-oxide- based catalysts but with little restriction in terms of the proximity of acidic and basic hydroxyl groups.

[0208] Example 2: Mixture of zirconium oxide-based catalyst and titanium oxide-based catalyst

[0209] In a second example, a solid catalyst composition according to the present invention was prepared by mixing two different metal oxide-based catalysts, each having a different ratio of acidic hydroxyl groups to basic hydroxyl groups.

[0210] The solid catalyst composition (composition 2) was obtained by physically mixing a zirconium oxide-based catalyst (catalyst C) and a titanium oxide-based catalyst (catalyst D) in a weight ratio of catalyst C to catalyst D of 2.5.

[0211] Catalyst C is a zirconium oxide-based catalyst comprising mainly weak basic sites (terminal OH groups having basic hydroxyl groups). Catalyst C was prepared by means of the same procedure as described herein for catalyst A in Example 1 .

[0212] Catalyst D is a titanium oxide-based catalyst comprising mainly weak acidic sites (bridged OH groups having acidic hydroxyl groups). Catalyst D was prepared by means of precipitation as described herein. More specifically, a titanium isopropoxide (Ti(O-iC3H7)4) solution was dripped into 2L of water under constant stirring to obtain a molar ratio of water:Ti(O-iCsH7)4 Of 1400:1. After stirring for 4 hours at 20°C, the obtained precipitate was then filtered, rinsed three times with distilled water and ethanol, and then dried at 100°C for 5 hours. The obtained titanium oxide-based catalyst has the following chemical formula TiOiHmwith I and m being positive numbers.

[0213] The catalytic performance of catalyst C, catalyst D, and composition 2 for CO2 desorption from an amine solvent was determined as described in the experimental method section above.

[0214] The desorption results and properties of catalyst C, catalyst D, and composition 2 are summarized in Table 2.

[0215] Table 2

[0216] CO2 desorption Performance and properties of catalyst C, catalyst D, and comp 2

[0217] Ratio

[0218] Bridged Terminal CO2kcAT / OH acidic Total OH

[0219] OH OH desorption amount

[0220] Sample OH content content content amount (*10'2min-1to basic (mmol / g) (mmol / g) (mmol / g) (mmol) mol'1)

[0221] OH

[0222] Catalyst C 0.4 12.3 3.5 8.8 0.03

[0223] Catalyst D 9.4 16.7 15.1 1.6 0.26

[0224] Composition 2 1.0 13.5 6.7 6.8 0.52 Reaction conditions: 3 g of catalysts, 150 mL CO2-saturated 5 M MEA, N2 flow of 0.5 L min-1from the top of the condenser, 88°C. The CO2 desorption amount is based on the isothermal reaction period.

[0225] As illustrated in FIG. 5, the solid catalyst composition, composition 2 with a CAT / OH amount of around 0.52*1 O'2min'1mol'1, exhibits a surprisingly better performance compared to the individual metal oxide-based catalysts, catalyst C and catalyst D with a CAT / OH amount of around 0.03*10'2min'1mol'1and 0.26*10'2min'1mol'1, respectively. This example further demonstrates the versatility of the present approach in terms of suitable metal oxide-based catalysts.

Claims

CLAIMS1 . A solid catalyst composition for CO2 desorption comprising at least one first metal oxide-based catalyst having a ratio of acidic hydroxyl groups to basic hydroxyl groups of at most 0.7; and, at least one second metal oxide-based catalyst having a ratio of acidic hydroxyl groups to basic hydroxyl groups of at least 1 .3; wherein the catalyst composition has a ratio of acidic hydroxyl groups to basic hydroxyl groups of from at least 0.7 to at most 2.0, preferably of from at least 0.8 to at most 1.3.

2. The solid catalyst composition according to claim 1 , wherein the at least one first metal oxide-based catalyst has a ratio of acidic hydroxyl groups to basic hydroxyl groups of at most 0.6, preferably at most 0.5.

3. The solid catalyst composition according to any one of claims 1 or 2, wherein the at least one second metal oxide-based catalyst has a ratio of acidic hydroxyl groups to basic hydroxyl groups of at least 1 .4, preferably at least 1 .5.

4. The solid catalyst composition according to any one of claims 1 to 3, wherein the metal oxide-based catalysts comprise zirconium, titanium, scandium, hafnium, aluminium, silicon, vanadium, chromium, manganese, iron, zinc, gallium, copper, nickel, cobalt, calcium, cadmium, lanthanum, lead, thallium, ytterbium, molybdenum, tungsten, indium, or a combination thereof; and preferably zirconium, titanium, a combination thereof, or a mixture thereof.

5. The solid catalyst composition according to any one of claims 1 to 4, wherein the at least one first metal oxide-based catalyst and the at least one second metal oxide-based catalyst comprise a different centre atom or ion; preferably wherein the different centre atoms or ions are zirconium and titanium.

6. The solid catalyst composition according to any one of claims 1 to 5, wherein the solid catalyst composition comprises from at least 5.0 to at most 95.0 wt.% of the first metal oxide-based catalyst; and from at least 5.0 to at most 95.0 wt.% of the second metal oxide-based catalyst; with wt.% relative to the total weight of the solid catalyst composition.

7. The solid catalyst composition according to any one of claims 1 to 6, wherein the metal oxide-based catalysts are supported metal oxide-based catalysts or unsupported metal oxide-based catalysts.

8. A method for preparing the solid catalyst composition according to any one of claims 1 to 7, wherein the method comprises the steps of: preparing at least one first metal oxide-based catalyst and at least one second metal oxide-based catalyst, wherein each preparation procedure comprises forming a synthesis mixture by mixing a metal source, a solvent, and optionally a basic precipitating agent, thereby precipitating each metal oxide-based catalyst; and mixing the at least one first metal oxide-based catalyst and at least one second metal oxide-based catalyst, thereby obtaining the solid catalyst composition.

9. The method according to claim 8, wherein the metal source is a metal complex comprising zirconium, titanium, scandium, hafnium, aluminium, silicon, vanadium, chromium, manganese, iron, zinc, gallium, copper, nickel, cobalt, calcium, cadmium, lanthanum, lead, thallium, ytterbium, molybdenum, tungsten, indium, or a combination thereof; and preferably further comprising nitrate, oxynitrate, halide, oxyhalide, sulphate, alkoxide, carboxylate or a combination thereof.

10. The method according to any one of claims 8 or 9, wherein the synthesis mixture comprises a basic precipitating agent, and wherein the basic precipitating agent comprises hydroxide, carbonate, bicarbonate, or carboxylate, and an alkali metal cation, alkaline earth metal cation, or ammonium cation and / or wherein the basic precipitating agent comprises an alkylamine, ammonia, dialkylamine, trialkylamine, alkanolamine, urea, or hydrazine.

11. The method according to any one of claims 8 to 10, wherein the metal oxide-based catalysts are supported metal catalysts, and wherein the method comprises the steps of: preparing at least one first metal oxide-based catalyst and at least one second metal oxide-based catalyst, wherein each synthesis procedure comprises forming a synthesis slurry by mixing a metal source, a solid catalyst support, a solvent, and optionally a basic precipitating agent, thereby precipitating each metal oxide-based catalyst on each solid catalyst support; and mixing the at least one first metal oxide-based supported catalyst and at least one second metal oxide-based supported catalyst, thereby obtaining the solid catalyst composition.

12. The method according to any one of claims 8 to 10, wherein the solid catalyst composition comprises at least one supported metal oxide-based catalyst and at least one unsupported metal oxide-based catalyst, wherein the method comprises the steps of: preparing at least one metal oxide-based supported catalyst, wherein the synthesis procedure comprises forming a synthesis slurry by mixing a metal source, a solid catalyst support, a solvent, and optionally a basic precipitating agent, thereby precipitating the metal oxide-based catalyst on the solid catalyst support; preparing at least one metal oxide-based unsupported catalyst, wherein the synthesis procedure comprises forming a synthesis mixture by mixing a metal source, a solvent, and optionally a basic precipitating agent, thereby precipitating the metal oxide-based catalyst; and, mixing the metal oxide-based supported catalyst and the metal oxide-based unsupported catalyst, thereby obtaining the solid catalyst composition.

13. The method according to claim 11 or 12, wherein the solid catalyst support is a porous solid catalyst support, preferably a mesoporous solid catalyst support.

14. Use of the solid catalyst composition according to any one of claims 1 to 7, or obtained or obtainable by means of the method according to any one of claims 8 to 12 in a process for CO2 desorption from a CC>2-containing absorbent, preferably wherein the CC>2-containing absorbent comprises one or more nitrogen compounds, such as amines.

15. The use according to claim 14, wherein the solid catalyst composition is contacted with the CC>2-containing absorbent at a temperature of from 50°C to 150°C and a pressure of from 0.5 bar to 7.0 bar, preferably of from 1.0 to 4.0 bar, and preferably wherein the contacting of the solid catalyst composition and the CC>2-containing absorbent is performed in a CO2 stripper.

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