Method of modifying an aluminosilicate using gas supply

Abstract

The present invention provides a method of modifying an aluminosilicate, using an aqueous solution of carbon dioxide that is formed by passing a supply of carbon dioxide through water. The reaction conditions of this efficient method are mild, advantageously requiring less energy and avoiding the use of strong acids. The method yields a modified aluminosilicate having excellent textural and catalytic properties, to which the invention also relates, and which may beneficially be further transformed by impregnation with a metal.

Description

[0001] METHOD OF MODIFYING AN ALUMINOSILICATE USING GAS SUPPLY

[0002] Field of the Invention

[0003] The present invention relates to a method of modifying an aluminosilicate, such as a zeolite, by using an aqueous solution of CO2. The method produces a modified aluminosilicate that is particularly suitable for use as a catalyst or an adsorbent surface, such as in a cracking process or in the treatment of exhaust gas.

[0004] Background

[0005] Solid catalysts such as aluminosilicates are used in heterogeneous catalysis, typically involving a cycle of molecular adsorption of a gas-phase reactant, followed by a reaction and then desorption, which occur at the catalyst surface.

[0006] Zeolites are crystalline aluminosilicates that possess well-defined porous systems of varying sizes and tuneable physicochemical properties. Due to these properties, zeolites are used extensively as solid catalysts in various refining and petrochemical industrial applications, such as cracking, alkylation of aromatics, reforming, dewaxing, isomerisation of xylenes, and the synthesis of various organic molecules.

[0007] Recently, attention has been devoted to the generation of zeolites with improved diffusional properties, either by the creation of wider porous structures or by decreasing the diffusional paths. This aids in reducing mass transfer constraints of reactants and products to and from the active centre, particularly when dealing with bulkier molecules. Additionally, it prevents undesired side reactions caused by the microporous channels of zeolite, which can lead to coking, catalyst deactivation and most significantly, the wastage of zeolite materials and energy. As a result, zeolites with such characteristics are appealing for many catalytic applications, e.g. Friedel-Crafts alkylation of arenes, cracking of plastics to liquid fuels, Fischer-Tropsch synthesis (FTS) process for the production of clean hydrocarbon fuels or chemicals from syngas, and direct oxidation of benzene to phenol.

[0008] Therefore, ongoing research and development efforts have been focused on improving the accessibility of the active sites within zeolite frameworks via the formation of ultra-large pore zeolites (ULP), zeolite nanocrystals with shorter diffusion paths and hierarchically modified zeolites with combined micro- and mesopores. However, the poor structural stability, loss of acidity and high synthesis cost of ULP zeolites have limited their practical applicability. Similarly, the synthesis of nanocrystal zeolites also faces many obstacles, since it involves the use of hazardous and costly templates, with serious implications to the environment [M. Usman Azam et al. (2023)]. On the other hand, hierarchical zeolites incorporate the benefits of multi-level porosity [S. Mitchell et al. (2015)]] that assist in the mobility of bulky molecules and decrease the probability for the catalyst to deactivate owing to the reduction of molecules retention time within the structure, while presenting comparable crystallinity and functionality to their parent counterparts [L. H. Chen et al. (2020)]. Hierarchical zeolites can be obtained either by bottom-up (soft or hard templating) or top-down methodologies (i.e. desilication or dealumination). Among all, the top-down technique based on the dealumination of zeolite is affordable and considered as a promising approach with practical applications [L.H. Chen et al. (2020); P. Peng et al. (2020)]. It consists of a post-synthesis procedure, utilising organic or inorganic acids or through hydrothermal treatment with water vapour (steaming), where mesoporosity is generated by the elimination of aluminium, either framework and / or extra-framework species, from the zeolite [Z. Zhu et al. (2021)].

[0009] Despite the significant advantages towards the affordability and formation of mesoporosity, removal of framework and / or extra-framework aluminium may be accompanied by a significant loss in the number of Bnansted and Lewis acid sites if dealumination conditions are not tightly controlled, which for some catalytic applications is not advantageous. Moreover, conventional dealumination methods, such as steaming or acid leaching, limit the sustainable properties of the resulting dealuminated zeolites [S. Abdulridha et al. (2021)].

[0010] Steaming generally takes places at high temperatures, and is therefore an energy-intensive and timeconsuming process (e.g. up to 500-600 °C for 5-6 hours). Also, despite the harsh operating conditions, the steaming process may undergo channelling, which results in insufficient dealumination by just removing extra-framework aluminium species due to the formation of dense layers or surface blockage. This may also lead to limited access to active sites (i.e. strong acidic sites) and reduced catalytic performance.

[0011] Meanwhile, conventional acid leaching techniques use strong acids (such as using HCI, H2SO4 and / or HNO3) at elevated temperatures (i.e. 60-100 °C), and generate large quantities of acidic and toxic effluent.

[0012] Thus, it is desirable to improve upon these methods, and strike a balance between degree of dealumination and acidity with retained crystallinity, while ideally using chemistry that is more environmentally friendly.

[0013] The present invention has been devised in light of the above considerations.

[0014] Summary of the Invention

[0015] A first aspect of the invention is a method of modifying an aluminosilicate, the method comprising passing a supply of carbon dioxide through water to form aqueous solution of CO2, and exposing the aluminosilicate to the aqueous solution of CO2 to produce a modified aluminosilicate.

[0016] As is known in the art, an aluminosilicate is a material containing anionic Si-O-AI linkages. Thus, the aluminosilicate comprises at least silicon (Si), aluminium (Al) and oxygen (O). The aluminosilicate may be described as a solid catalyst. Suitably, the aluminosilicate is a crystalline aluminosilicate.

[0017] Suitably, the aluminosilicate is modified to impart a hierarchical structure. Unlike known techniques to achieve this, which require the use of strong acids or high-temperature steaming or the inclusion of additives, the present invention surprisingly demonstrates the provision of a leaching approach that is free of strong acids and which can be carried out at ambient conditions, thus requiring less energy and less harsh conditions. The present invention uses a mildly acidic aqueous solution of CO2, which is conveniently produced as part of the method by passing a supply of carbon dioxide through water. As will be appreciated the person skilled in the art, a solution of carbon dioxide in water will contain the acidic species, carbonic acid (H2CO3). In the present invention, beneficially, the carbon dioxide may subsequently be removed (such as by aeration or heating) and captured, and may then be utilised in further runs of the method, providing a cyclic method that minimises waste of resources.

[0018] The resultant modified catalyst may have comparable or superior textural and catalytic properties, as described herein, with preserved structure crystallinity.

[0019] In some embodiments, exposing the aluminosilicate to the aqueous solution of CO2 causes dealumination of the aluminosilicate. By “dealumination”, it is meant that the aluminosilicate is chemically and structurally modified to remove from the framework a portion of the aluminium species that the aluminosilicate comprises, thus resulting in a modified aluminosilicate that has a hierarchical structure and typically modified catalytic properties. The removed aluminium may remain on the structure of the modified aluminosilicate, as so-called extra-framework aluminium. Suitably, the hierarchical structure comprises micropores (pores having a diameter of less than 2 nm) and mesopores (pores having a diameter of from 2 to 50 nm).

[0020] In some embodiments, the aluminosilicate is a zeolite.

[0021] In some embodiments, the zeolite is selected from a faujasite, beta zeolite, ZSM-5 zeolite or HZSM-5 zeolite.

[0022] In some embodiments, the zeolite is a faujasite.

[0023] In some embodiments, the zeolite is faujasite type Y.

[0024] In some embodiments, the zeolite (such as faujasite, e.g. faujasite type Y) is a hydrogen form of zeolite.

[0025] The “Si / AI ratio” is a term of art used to describe the proportion of silicon species (i.e. atoms or ions) to aluminium species in a solid structure. This ratio is generally expressed as a single number, signifying the number of silicon species relative to a single aluminium species (e.g. if the proportion of Si species to Al species is 80:20, the “Si / AI ratio” is expressed as 4). Generally, the Si / AI ratio refers to the solid structure as a whole, considering all Si and Al atoms present, including framework and extra-framework positions (this may be alternatively denoted as the “global Si / AI ratio”). A “framework Si / AI ratio” may also be expressed, referring to the Si / AI ratio in the crystalline framework of the solid structure (e.g. of an aluminosilicate or a modified aluminosilicate).

[0026] In some embodiments, the aluminosilicate comprises silicon and aluminium in an Si / AI ratio or a framework Si / AI ratio of at least 1 , or at least 2, or at least 5, or at least 10, or at least 15, or at least 20, or at least 25, or at least 30, or at least 40, or at least 50. In some embodiment, the aluminosilicate comprises silicon and aluminium in an Si / AI ratio or a framework Si / AI ratio of at most 80, or at most 70, or at most 60, or at most 50, or at most 40, or at most 30, or at most 25, or at most 20, or at most 15, or at most 10.

[0027] In some embodiments, the aluminosilicate comprises silicon and aluminium in an Si / AI ratio or a framework Si / AI ratio of between 1 and 80. In some embodiments, the aluminosilicate comprises silicon and aluminium in an Si / AI ratio or a framework Si / AI ratio of between 50 and 80. In some embodiments, the aluminosilicate comprises silicon and aluminium in an Si / AI ratio or a framework Si / AI ratio of between 2 and 50. In some embodiments, the aluminosilicate comprises silicon and aluminium in an Si / AI ratio or a framework Si / AI ratio of between 2 and 40. In some embodiments, the aluminosilicate comprises silicon and aluminium in an Si / AI ratio or a framework Si / AI ratio of between 15 and 40. In some embodiments, the aluminosilicate comprises silicon and aluminium in an Si / AI ratio or a framework Si / AI ratio of between 2 and 10.

[0028] In some embodiments, the framework Si / AI ratio of the modified aluminosilicate is greater than the framework Si / AI ratio of the aluminosilicate (i.e. the aluminosilicate before modification).

[0029] In some embodiments, the framework Si / AI ratio of the modified aluminosilicate is at least 1 .05 times greater, or at least 1 .20 times greater, or at least 1 .50 times greater than the framework Si / AI ratio of the aluminosilicate before modification.

[0030] In some embodiments, the framework Si / AI ratio of the modified aluminosilicate is at least 2, or at least 4, or at least 10, or at least 20, or at least 30, or at least 40, or at least 50, or at least 60, or at least 80, or at least 100.

[0031] In some embodiments, the framework Si / AI ratio of the modified aluminosilicate is at least 20.

[0032] In some embodiments, the framework Si / AI ratio of the modified aluminosilicate is at least 30.

[0033] In some embodiment, the framework Si / AI ratio of the modified aluminosilicate is at most 160, or at most 140, or at most 120, or at most 100, or at most 80, or at most 60, or at most 50, or at most 40, or at most 30, or at most 20.

[0034] In some embodiments, the external surface area (Sext) of the modified aluminosilicate is greater than the Sext of the aluminosilicate before modification.

[0035] In some embodiments, the micropore volume (Vmicro) and / or the mesopore volume (Vmeso) in the modified aluminosilicate is greater than in the aluminosilicate before modification.

[0036] In some embodiments, the micropore volume (Vmicro) in the modified aluminosilicate is greater than in the aluminosilicate before modification. However, alternatively, the Vmicro in the modified aluminosilicate may be less than in the aluminosilicate before modification - for example, this may be due to the presence of debris and / or EFAI.

[0037] In some embodiments, the mesopore volume (Vmeso) in the modified aluminosilicate is greater than in the aluminosilicate before modification. In some embodiments, the micropore volume (Vmicro) and the mesopore volume (Vmeso) in the modified aluminosilicate are greater than in the aluminosilicate before modification.

[0038] In some embodiments, the mesopore volume (Vmeso) in the modified aluminosilicate is greater than in the aluminosilicate before modification, and the micropore volume (Vmicro) in the modified aluminosilicate is less than in the aluminosilicate before modification.

[0039] The micropore volume and / or mesopore volume affect the activity and performance of the modified aluminosilicate, and so these volumes may be approximately tailored depending on the intended end use of the modified aluminosilicate.

[0040] In some embodiments, the Vmicro in the modified aluminosilicate is at least 0.210 cm3g-1. In some embodiments, the Vmicro in the modified aluminosilicate is at least 0.220 cm3g-1. In some embodiments, the Vmicro in the modified aluminosilicate is at least 0.225 cm3g-1.

[0041] In some embodiments, the Vmicro in the modified aluminosilicate is at most 0.300 cm3g-1. In some embodiments, the Vmicro in the modified aluminosilicate is at most 0.280 cm3g-1. In some embodiments, the Vmicro in the modified aluminosilicate is at most 0.260 cm3g-1.

[0042] In some embodiments, the Vmicro in the modified aluminosilicate is from 0.220 to 0.280 cm3g-1.

[0043] In some embodiments, the Vmeso in the modified aluminosilicate is at least 0.240 cm3g-1. In some embodiments, the Vmeso in the modified aluminosilicate is at least 0.250 cm3g-1. In some embodiments, the Vmeso in the modified aluminosilicate is at least 0.255 cm3g-1.

[0044] In some embodiments, the Vmeso in the modified aluminosilicate is at most 0.320 cm3g-1. In some embodiments, the Vmeso in the modified aluminosilicate is at most 0.300 cm3g-1. In some embodiments, the Vmeso in the modified aluminosilicate is at most 0.290 cm3g-1.

[0045] In some embodiments, the Vmeso in the modified aluminosilicate is from 0.250 to 0.290 cm3g-1.

[0046] In some embodiments, the Vmicro in the modified aluminosilicate is from 0.220 to 0.280 cm3g-1and the Vmeso in the modified aluminosilicate is from 0.250 to 0.290 cm3g-1.

[0047] In some embodiments, the aluminosilicate is exposed to the water and then the supply of carbon dioxide is passed through the water, forming the aqueous solution of CO2 to which the aluminosilicate is exposed.

[0048] In some embodiments, the supply of carbon dioxide is passed through the water, forming the aqueous solution of CO2, and then the aluminosilicate is exposed to the aqueous solution. In some embodiments, the supply of carbon dioxide continues as the aluminosilicate is exposed to the aqueous solution.

[0049] In some embodiments, the supply of carbon dioxide is passed through the water, forming the aqueous solution of CO2, simultaneously as the aluminosilicate is exposed to the aqueous solution.

[0050] In some embodiments, the aqueous solution of CO2 is formed in a container and the aluminosilicate is exposed to the aqueous solution in the same container. Thus, the method may be a “one-pot” process, at least for the steps of forming the aqueous solution of CO2 and exposing the aluminosilicate to the aqueous solution of CO2. In alternative embodiments, the aqueous solution of CO2 is formed in a first container and the aluminosilicate is exposed to the aqueous solution of CO2 in a second container.

[0051] The container (e.g. the first or second container) may be any container (i.e. a receptacle or enclosure) that is suitable for carrying out the steps of the method of the invention.

[0052] The supply of carbon dioxide may be provided by any means of supply suitable for containing and passing carbon dioxide through water, such as a canister or tank with an outlet (e.g. a tube or pipe).

[0053] The carbon dioxide may be passed through water by any suitable way to form an aqueous solution of CO2, such as by bubbling the carbon dioxide in the water.

[0054] The aluminosilicate may be exposed to the aqueous solution of CO2 by any suitable way to produce the modified aluminosilicate. In some embodiments, the aluminosilicate is (at least partly) immersed in the aqueous solution of CO2. Therefore, where the aluminosilicate is exposed to the water and then the supply of carbon dioxide is passed through the water, the aluminosilicate may be (at least partly) immersed in the water, which may result in the aluminosilicate being (at least partly) immersed in the aqueous solution of CO2 as it is formed.

[0055] Suitably, the carbon dioxide is supplied as gaseous carbon dioxide. Suitably, the aqueous solution of CO2 comprises carbonic acid.

[0056] In some embodiments, the water is deionised water.

[0057] In some embodiments, the aqueous solution of CO2 has a pH of at least 2.5, or at least 2.8, or at least 3.0, or at least 3.2, or at least 3.5, or at least 3.7. In some embodiments, the aqueous solution of CO2 has a pH of at least 2.8.

[0058] In some embodiments, the aqueous solution of CO2 has a pH of at most 4.5, or at most 4.2, or at most 4.0, or at most 3.8. In some embodiments, the aqueous solution of CO2 has a pH of at most 4.0.

[0059] In some embodiments, the aqueous solution of CO2 has a pH of from 2.5 to 4.5, or from 2.8 to 4.5, or from 3.0 to 4.5, or from 3.2 to 4.5, or from 3.5 to 4.5, or from 3.7 to 4.5, or from 2.5 to 4.2, or from 2.8 to 4.2, or from 3.0 to 4.2, or from 3.2 to 4.2, or from 3.5 to 4.2, or from 3.7 to 4.2, or from 2.5 to 4.0, or from 2.8 to 4.0, or from 3.0 to 4.0, or from 3.2 to 4.0, or from 3.5 to 4.0, or from 3.7 to 4.0, or from 2.5 to 3.8, or from 2.8 to 3.8, or from 3.0 to 3.8, or from 3.2 to 3.8, or from 3.5 to 3.8.

[0060] In some embodiments, the aqueous solution of CO2 has a pH of from 2.8 to 4.0.

[0061] In some embodiments, the aluminosilicate is exposed to the aqueous solution of CO2 for at least 0.5 hours, or at least 1 hour, or at least 1 .5 hours, or at least 2 hours.

[0062] In some embodiments, the aluminosilicate is exposed to the aqueous solution of CO2 for at most 12 hours, or at most 10 hours, or at most 7 hours, or at most 5 hours, or at most 3 hours, or at most 2 hours.

[0063] In some embodiments, the aluminosilicate is exposed to the aqueous solution of CO2 for 0.5 to 12 hours, or 0.5 to 10 hours, or 0.5 to 7 hours, or 0.5 to 5 hours, or 0.5 to 3 hours, or 0.5 to 2 hours, or 1 to 12 hours, or 1 to 10 hours, or 1 to 7 hours, or 1 to 5 hours, or 1 to 3 hours, or 1 to 2 hours, or 1 .5 to 12 hours, or 1 .5 to 10 hours, or 1 .5 to 7 hours, or 1 .5 to 5 hours, or 1 .5 to 3 hours, or 1 .5 to 2 hours, or 2 to 12 hours, or 2 to 10 hours, or 2 to 7 hours, or 2 to 5 hours, or 2 to 3 hours.

[0064] In some embodiments, the aluminosilicate is exposed to the aqueous solution of CO2 for 0.5 to 10 hours.

[0065] In some embodiments, the aluminosilicate is exposed to the aqueous solution of CO2 for 0.5 to 5 hours.

[0066] In some embodiments, the aluminosilicate is exposed to the aqueous solution of CO2 for 0.5 to 2 hours.

[0067] In some embodiments, the aluminosilicate is exposed to the aqueous solution of CO2 at a temperature of at most 100 °C, or at most 80 °C, or at most 60 °C, or at most 50 °C, or at most 40 °C, or at most 30 °C, or at most 25 °C.

[0068] In some embodiments, the aluminosilicate is exposed to the aqueous solution of CO2 at a temperature of at most 60 °C. In some embodiments, the aluminosilicate is exposed to the aqueous solution of CO2 at a temperature of at most 25 °C.

[0069] In some embodiments, the aluminosilicate is exposed to the aqueous solution of CO2 at a temperature of at least 10 °C, or at least 20 °C, or at least 30 °C.

[0070] In some embodiments, the aluminosilicate is exposed to the aqueous solution of CO2 at a temperature of between 10 °C and 100 °C.

[0071] In some embodiments, the aluminosilicate is exposed to the aqueous solution of CO2 at a temperature of between 10 °C and 60 °C.

[0072] In some embodiments, the aluminosilicate is exposed to the aqueous solution of CO2 at a temperature of between 10 °C and 25 °C.

[0073] In some embodiments, the aluminosilicate is exposed to the aqueous solution of CO2 at approximately room temperature.

[0074] The temperature values and ranges disclosed herein for the step of the aluminosilicate being exposed to the aqueous solution of CO2 may also apply for the step of passing the supply of carbon dioxide through water to form the aqueous solution of CO2.

[0075] In some embodiments, the aluminosilicate is exposed to the aqueous solution of CO2 at the same temperature as that at which the supply of carbon dioxide is passed through the water to form the aqueous solution of CO2.

[0076] In some embodiments, the aluminosilicate is exposed to the aqueous solution of CO2 at a different temperature from that at which the supply of carbon dioxide is passed through the water to form the aqueous solution of CO2.

[0077] Varying the temperature and / or the time at which the aluminosilicate is exposed to the aqueous solution of CO2 generally affects the extent of modification of the aluminosilicate. For example, where exposing the aluminosilicate to the aqueous solution of CO2 causes dealumination of the aluminosilicate, increasing the thermal energy can overcome activation energy barriers, making the dealumination process more feasible. However, this is balanced against the fact that the solubility of carbon dioxide decreases as the temperature is raised. Moreover, a greater degree of dealumination may be achieved by increasing the time while keeping the temperature constant. An optimum temperature and time may be found that maximises the modification of the aluminosilicate and the efficiency of the modification process.

[0078] A further factor to consider is the pressure at which the step of forming the aqueous solution of CO2 and / or exposing the aluminosilicate to the aqueous solution of CO2 takes place. In particular, this is because changes in the pressure can affect the pH of the aqueous solution of CO2 that is achieved. Generally, higher pressures lead to greater solubility of carbon dioxide and therefore lower pH values.

[0079] The pressure may be at most 200 atm, or at most 150 atm, or at most 100 atm, or at most 50 atm, or at most 30 atm, or at most 20 atm, or at most 10 atm, or at most 5 atm, or at most 2 atm, or at most 1 atm.

[0080] The pressure may be at least 0.5 atm, or at least 1 atm, or at least 2 atm, or at least 5 atm, or at least 10 atm, or at least 20 atm, or at least 30 atm, or at least 50 atm, or at least 100 atm, or at least 150 atm.

[0081] The pressure may be approximately ambient pressure. This may be preferred for reasons of convenience, such as to minimise energy consumption.

[0082] The temperature, time and / or pressure may be selected according to several factors, including the Si / AI ratio of the aluminosilicate. For instance, a aluminosilicate having a relatively high Si / AI ratio may require exposure to the aqueous solution of CO2 for a longer amount of time and / or at a lower pH (e.g. achieved by higher pressure), because such aluminosilicates are generally more difficult to dealuminate (due to the lower Al content). Conversely, an aluminosilicate having a relatively low Si / AI ratio may undergo exposure to the aqueous solution of CO2 at a lower temperature and / or for a lower amount of time and / or at a higher pH, because such aluminosilicates are generally easier to dealuminate (due to the greater Al content).

[0083] For example, an aluminosilicate having an Si / AI ratio of at most 20 may be exposed to the aqueous solution of CO2 at a temperature of at most 25 °C (such as approximately room temperature) and / or for a time of at most 2 hours (such as at most 1 .5 hours or at most 1 hour) and / or at a pH of at least 3.5 (such as at least 3.7). Meanwhile, an aluminosilicate having an Si / AI ratio of at least 50 may be exposed to the aqueous solution of CO2 at a temperature of at least 20°C (such as at least 30 °C) and / or for a time of at least 2 hours and / or at a pH of at least 2.8 (such as at most 3.5).

[0084] The steps of passing a supply of carbon dioxide through water, and exposing the aluminosilicate to the aqueous solution of CO2 represent a run (i.e. a cycle) of modifying the aluminosilicate.

[0085] In some embodiments, the method comprises one run.

[0086] In other embodiments, the method comprises two or more runs (such as two, three or four). These multiple runs effectively represent multiple cycles of modifying the aluminosilicate (e.g. dealumination). The multiple runs may be carried out at the same temperature and / or time, or at different temperatures and / or times. Multiple runs may be preferred for aluminosilicates having a relatively high Si / AI ratio (e.g. at least 50). In some embodiments, the method further comprises a step of removing carbon dioxide from the aqueous solution of CO2. For example, the carbon dioxide may be removed by aeration or heating. The removed carbon dioxide may be captured. The removed carbon dioxide (i.e. the captured carbon dioxide) used as the supply of carbon dioxide in a subsequent run of the method, or in a separate method or separate application.

[0087] Therefore, this beneficially allows for a cyclic method in which waste of resources is minimised.

[0088] Additionally or alternatively, the method may further comprise a step of impregnating the modified aluminosilicate with a metal to produce a metal-impregnated modified aluminosilicate.

[0089] Such impregnation may improve the overall activity of the catalyst. For example, a metal-impregnated modified aluminosilicate may beneficially be multifunctional. The added metal may result in a catalyst having multiple active sites. For instance, the metal-impregnated modified aluminosilicate may be bifunctional and have two active sites, such as one for cracking and one for hydrogenation / dehydrogenation.

[0090] In some embodiments, the step of impregnating the modified aluminosilicate with the metal comprises adding to the modified aluminosilicate an aqueous solution comprising the metal, optionally followed by drying, optionally followed by calcining.

[0091] In some embodiments, the step of impregnating the modified aluminosilicate with the metal comprises adding to the modified aluminosilicate an aqueous solution comprising the metal, and then drying and calcining.

[0092] In some embodiments, the metal-impregnated modified aluminosilicate comprises at least 1 wt%, or at least 2 wt%, or at least 3 wt%, or at least 4 wt%, or at least 5 wt% of the metal.

[0093] In some embodiments, the metal-impregnated modified aluminosilicate comprises at most 20 wt%, or at most 18 wt%, or at most 16 wt%, or at most 14 wt%, or at most 12 wt%, or at most 10 wt%, or at most 8 wt% of the metal.

[0094] In some embodiments, the metal-impregnated modified aluminosilicate comprises from 2 to 10 wt% of the metal.

[0095] In some embodiments, the metal-impregnated modified aluminosilicate comprises about 5 wt% of the metal.

[0096] Suitably, the metal is not aluminium.

[0097] In some embodiments, the metal is selected from nickel, palladium, platinum and ruthenium.

[0098] In some embodiments, the metal is nickel. Hence, in these embodiments, metal-impregnated modified aluminosilicate is a Ni-impregnated modified aluminosilicate. As described herein, it is found that nickel improves the overall activity of a zeolite catalyst, which consequently has two active sites: one active site for cracking originating from the modified zeolite structure, and another active site for (de)hydrogenation originating from the nickel. A second aspect of the invention provides a modified aluminosilicate produced by the method of the first aspect, or a metal-impregnated modified aluminosilicate produced by the method of the first aspect.

[0099] A third aspect of the invention provides use of the modified aluminosilicate or the metal-impregnated modified aluminosilicate of the second aspect as a catalyst or an adsorbent surface.

[0100] For example, the modified aluminosilicate or the metal-impregnated modified aluminosilicate may be used as a catalyst or an adsorbent surface in a cracking process (including a hydrocracking or fluid catalytic cracking process), in the treatment of exhaust gas, in the treatment of waste water, in molecular sieves, or in a chemical sensor. Furthermore, the modified aluminosilicate or the metal-impregnated modified aluminosilicate may be used in oil refineries, in biomedical applications, in cation exchange applications, as well as other adsorption and separation processes.

[0101] The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided. Preferred features mentioned in relation to the first aspect of the invention may apply equally to the other aspects.

[0102] Summary of the Figures

[0103] Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

[0104] Figure 1 depicts a scheme showing dealumination of zeolite using a supply of carbon dioxide passed through water;

[0105] Figure 2 depicts a graph showing product selectivity based on carbon number of n-heptane soluble liquid obtained by hydrocracking;

[0106] Figure 3 shows an impact assessment of different dealumination techniques on global warming (in graph (a)) and on freshwater aquatic ecotoxicity (in graph (b)).

[0107] Detailed Description of the Invention

[0108] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference.

[0109] In the following examples, faujasite (FAU) type Y zeolite is utilised as a benchmark catalyst because of its industrial application in petroleum refineries for fluid catalytic cracking (FCC) and hydrocracking. Dealumination

[0110] Dealumination of the type Y zeolite was carried out by exposure to an aqueous solution of CO2, formed by passing a supply of carbon dioxide gas through water, and compared to a conventional dealumination procedure.

[0111] The conventional dealumination of a parent type Y zeolite involved hierarchical modification through strong acid leaching. Specifically, 1 g of a commercial HY zeolite (hydrogen form, Si / AI ~30, available from Alfa Aesar) was added in a dilute solution of 33 mL 0.5 M HCI and stirred for 1 hour at 60 °C in a conical flask. After 1 hour, the sample was filtered and washed several times with deionised (DI) water, followed by drying in an oven at 100 °C overnight. The dried sample was then calcined in a tubular furnace at 500 °C for 6 hours under airflow of 60 mL min-1g-1. The resultant (comparative) modified aluminosilicate solid catalyst, specifically a hierarchical dealuminated sample, is denoted as “DAHY-HCI”.

[0112] Meanwhile, in the CO2 process, 100 mL min-1of carbon dioxide was absorbed in 33 mL of DI water for 15 minutes, followed by the addition of 1 g of the commercial HY zeolite. The sample was then stirred for 1 hour at room temperature over a continuous flow of carbon dioxide in a closed vessel. After 1 hour, the sample was filtered, dried in an oven at 100 °C for 12 hours and calcined at 500 °C for 6 hours under airflow of 60 mL min-1g-1. A scheme of this process is shown in Figure 1 . The resultant (inventive) modified aluminosilicate catalyst, specifically a hierarchical dealuminated sample, is denoted as “DAHY- CO2”.

[0113] The elemental analysis based on the Si / AI ratio of parent and dealuminated Y zeolites was calculated by ICP-OES and the results are presented in Table 1 below.

[0114] As shown in Table 1 , the uncontrolled strong acid leaching using HCI significantly removed aluminium from the structure, resulting in a prominent change in the framework Si / AI (39) and crystallinity (87%).

[0115] Contrary to this, the controlled and milder conditions during CO2 treatment results in a smaller elimination of FAI (framework aluminium species) with an addition of EFAI (extra-framework aluminium species) and a little change in framework Si / AI (33) and relative crystallinity (93%). This is due to the presence of debris and / or significant EFAI within the structure of the zeolite [see L. H. Chen et al. (2020)]. As a result, the CO2 modification technique appears to be a more controlled way to dealuminate zeolite (considering the medium Si / AI ratio of the zeolite) without significantly compromising the crystallinity and number of Bnansted acid sites.

[0116] Similarly, compared to the HY zeolite starting material, DAHY-CO2 showed a milder change in the porosity and external surface area (Sext), whereas DAHY-HCI showed a significant increase in the porosity and surface area, due to the method of modification (i.e. use of relatively strong acid treatment), which is following the calculations of framework Si / AI, FAI and EFAI. Table 1 - Physicochemical properties of the zeolite samples

[0117] Table 1 compares physicochemical properties of the HY aluminosilicate, the comparative modified aluminosilicate DAHY-HCI and the inventive modified aluminosilicate DAHY-CO2.

[0118] Crystallinity is estimated from XRD data by comparison of the peaks area for 2 theta range from 5° to 30° of dealuminated zeolite samples to that of the parent zeolite. X-Ray diffraction (XRD) patterns of calcined samples were obtained from a PANalytical X'Pert X-ray Powder diffractometer (PIXcel 1 D detector) with Cu Ka radiation with a step size of 0.047s and operating at 40 kV and 40 mA. Based on the area under the peaks, the relative intensities of the powdered samples were compared to that of the parent HY zeolite. Additionally, NaCI was used as an internal standard to locate the exact diffraction positions, and Bragg’s Law was used to calculate the unit cell parameter (ao) of the pristine and various dealuminated HY zeolites.

[0119] Si / AI ratio is calculated using Global Si / AI determined from elemental analysis (ICP-OES). Si / Ahv denotes the framework Si / AI ratio, calculated from the unit cell parameter using the Breck-Flanigen equation [see W. Lutz (2014)]. FAI and EFAI denote framework aluminium species and extra-framework aluminium species respectively.

[0120] Sext denotes external surface area. Vmicro and Vmeso denote micropore volume and mesopore volume respectively. The textural properties of the calcined zeolite samples were measured by N2-physisorption in a Tristar-3000 apparatus (Micromeritics) at -196 °C. Before the adsorption, for the fresh catalyst, a calculated amount of sample was degassed at 350 °C for 6 h under N2. The spent catalysts were degassed at 120 °C for 2 h to avoid any removal of coke. The total pore volume (Vtotai) was estimated from the amount of N2 adsorbed at a relative pressure (P / Po) of 0.97, while the microporosity (Vmicro) and external surface area (Sext) were computed using the t-plot method. The difference between Vtotai and Vmicro WaS USed tO Calculate Vmeso.

[0121] Metal impregnation

[0122] Metal-impregnated modified aluminosilicates were prepared by incipient wetness impregnation using 5 wt% of nickel [see M. Usman Azam et al. (2023)]. A calculated volume of an aqueous solution of the metal precursor (nickel nitrate hexahydrate) was added dropwise to the dried HY zeolite support. The Ni- impregnated zeolite samples were calcined at 500 °C for 6 h under dry airflow of 60 ml min1g1after being dried at 100 °C for 12 h in an oven.

[0123] The Ni-loaded samples were denoted as “Ni-DAHY-HCI” (5% Ni-impregnated dealuminated Y zeolite through conventional strong acid leaching), and “Ni-DAHY-CCh” (5% Ni impregnated dealuminated Y zeolite through CO2 treatment).

[0124] Both Ni-loaded dealuminated Y zeolites were compared for the hydrocracking of virgin high density polyethylene (HDPE) at different reaction temperatures (275-400 °C), 20 bar initial cold H2 pressure for 60 min residence time.

[0125] As shown in Table 2 below, comparative Ni-DAHY-HCI showed better conversion than inventive Ni-DAHY-CC>2 at lower reaction temperatures (275 °C). However, interestingly the conversion and overall product distribution remained comparable at elevated temperatures (i.e. 325-400 °C). However, the small difference in the product selectivities is ascribed to the textural properties of different dealuminated samples. This shows the similar cracking ability of both Ni-loaded dealuminated samples.

[0126] Table 2 - Performance comparison and product distribution of catalytic hydrocracking of HDPE, using different Ni-loaded dealuminated catalysts at different reaction temperatures

[0127] Moreover, Figure 2 shows the effect of reaction temperature on the product distribution of lighter oils. Specifically, the graph of Figure 2 depicts product selectivity based on carbon number of the n-heptane soluble liquids obtained by the hydrocracking of virgin HDPE in a 300 mL autoclave reactor, 20 bar initial cold H2 pressure, feed to catalyst ratio of 20:1 (by weight) for 60 min residence time at different reaction temperatures. Both Ni-loaded hierarchical Y zeolite samples show comparable selectivity for gasoline range fuels (i.e.

[0128] C5-C12) and diesel range fuels (C -Cia) at different temperatures. This shows the better cracking ability of dealuminated zeolites with significantly different textural properties.

[0129] However, for a better comparison of both Ni-loaded dealuminated Y zeolite samples, calculation of kinetic parameters, i.e. activation energy (EA) and frequency factor (A), at different reaction temperatures (i.e. 275 to 375 °C) and by employing the Arrhenius equation. Based on the calculations, Ni-DAHY-CC>2 requires 81 kJ / mol, while Ni-DAHY-HCI shows an activation energy of 75 kJ / mol. This shows the similar cracking ability of the CO2 modification technique, compared with traditional strong acid leaching.

[0130] The hydrocracking experiments were performed in a 300 mL cylindrical Parr reactor (Series 4560 mini reactors). The feed of catalyst and virgin HDPE pellets (MW 155,000 g / mol, melting point 140 °C, density 0.95 g / cm3, obtained from Sigma-Aldrich) were completely dried in an oven at 100 °C for 2 h before being used in the reactor. Afterwards, a known quantity of feed (5 g) and catalyst (20:1 , g / g) were introduced in a glass liner, and the reactor vessel was tightly closed. The reactor was purged with nitrogen (3 times) followed by hydrogen (3 times), and the system was checked for any leaks. A desired initial H2 pressure (10-30 bar) and a temperature setpoint (275, 325, 350, 375 and 400 °C) were given to the reactor. When the temperature reached 225 °C, the agitator was set at 500 rpm. This is to ensure that HDPE (melting point 140 °C) melts completely before being mixed with the catalyst. The reaction time was initiated when the temperature reached the desired setpoint. The reaction was run for 45 min and / or 1 h and then the agitation and heating were turned off. The reactor was placed in an ice bath for cooling down. After that, gaseous products were collected from the gas release valve, whereas liquids and solids were collected from the reaction vessel.

[0131] The liquid and solid reaction products were collected from the reactor using a solvent extraction approach. A known quantity of n-heptane was added to the reaction vessel containing the liquids and solids. The lighter liquid products, identified as "lighter oils", were extracted using n-heptane, and the “heavier oils” were dissolved in tetrahydrofuran (THF). The total fraction of lighter and heavier oils is categorised as liquids. Any remaining insoluble part was completely dried and referred to as solids.

[0132] The n-heptane fraction of oils was analysed by GC analysis using an Agilent DB-1 capillary column of 50 m length and a flame ionisation detector (FID). In detail, a known quantity of lighter oils was combined with a known quantity of n-heptane as an internal standard and analysed by gas chromatography. The chromatograph was calibrated using in-house prepared standards of hydrocarbons (C5-C20).

[0133] The overall conversion (C) of different products were calculated using the following equation:

[0134] The selectivity of the products was calculated using the following equation: 100

[0135] C is the conversion, mHDPEis the mass of feed, S and Y correspond to the selectivity and yield% of product respectively (i.e., / represents the gaseous / oils or heavier oils). Table 3 - Inventory data for the modification of dealuminated Y zeolites

[0136] Moreover, the environment profiles of different modification methods for the dealuminated Y zeolite samples were studied using a simple life-cycle assessment, as per ISO standards and systems. The primary goal of this assessment is to determine the environmental impacts associated with the hierarchical modification of Y zeolites with a functional unit of 1 g of each catalyst. The inputs related to energy utilisation and different materials used calculated based on laboratory studies and the LCI (lifecycle inventory) data are shown in Table 3 above.

[0137] Figure 3 illustrates the overall LCIA midpoint characterisation results for the Y zeolite modification using different methods in terms of global warming potential (kg of CO2 eq.) [see graph (a) of Figure 3] and freshwater aquatic ecotoxicity (FWAE, kg 1 ,4-DB eq.) [see graph (b) of Figure 3], using CML-IA baseline method.

[0138] Overall, DAHY-HCI showed a more negative impact on the environment (15.9 kg CO2 eq. / FU), whereas DAHY-CO2 showed a slightly lower impact (15.3 kg CO2 eq. / FU). A similar trend was seen over FWAE, where DAHY-HCI showed a greater impact (4.12 kg, 1 ,4-DB eq.), due to higher usage of resources (electricity, water and HCI), whereas DAHY-CO2 showed comparatively lower impact on FWAE (3.66 kg, 1 ,4-DB eq.).

[0139] These results highlight the importance of the catalysts of the invention with regard to sustainability principles and minimising environmental impacts. As such, the potential of using an aqueous solution of CO2 for the modification of aluminosilicate catalysts provides an opportunity to develop innovative processes for producing hierarchical modified aluminosilicate catalysts that are highly energy-efficient with the least environmental impacts and significant relevance on an industrial scale.

[0140] In summary, the method of the invention surprisingly achieves modification of an aluminosilicate under mild conditions (including at ambient temperature and pressure), to produce a modified aluminosilicate that retains crystallinity and shows enhanced porosity and external surface area, and does not compromise the textural and catalytic properties observed.

[0141] The catalysts are suitable for a range of adsorption and separation processes. The catalysts may be used in petroleum industries including in oil refineries, such as for cracking (e.g. hydrocracking or fluid catalytic cracking) of heavy hydrocarbons to produce valuable fuels and petrochemical feedstocks. In particular, plastics are difficult to recycle due to their bulky and complex chain molecular structure, but the catalysts of the invention can be used to crack long-chain polymers into value-added chemicals. The catalysts may also be used in the automotive industry for catalytic exhaust gas treatment, as well as in fine chemicals and pharmaceuticals. Further and specific applications include use in the treatment of waste water (and other environmental remediation treatments to remove heavy metals, etc.), in molecular sieves, in cation exchange applications, in chemical sensors, and in biomedical applications.

[0142] The features disclosed in the foregoing description, or in the following claims, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

[0143] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

[0144] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0145] Any section headings used herein are for organisational purposes only and are not to be construed as limiting the subject matter described.

[0146] Throughout this specification, including the claims which follow, unless the context requires otherwise, the words “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0147] It must be noted that, as used in the specification and the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and / or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about”, it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means, for example, + / - 10%.

[0148] References

[0149] A number of publications are cited above in order to more fully describe and disclose the invention and the state of the art to which the invention pertains. Full citations for these references are provided below. The entirety of each of these references is incorporated herein. M. Usman Azam et al., Hydrocracking of surgical face masks over Y Zeolites: Catalyst development, process design and life cycle assessment, Fuel, (2023), 349, 128704. https: / / doi.Org / 10.1016 / J.FUEL.2023.128704

[0150] S. Mitchell et al., Structural analysis of hierarchically organized zeolites, Nat. Commun. (2015), 6, 8633. https: / / doi.Org / 10.1038 / ncomms9633

[0151] L. H. Chen et al., Hierarchically structured zeolites: From design to application, Chem. Rev. (2020), 120, 11194. https: / / doi.org / 10.1021 / acs.chemrev.0c00016

[0152] P. Peng et al., Diffusion and catalyst efficiency in hierarchical zeolite catalysts, Natl. Sci. Rev. (2020), 7, 1726. https: / / d0i.0rg / l 0.1093 / nsr / nwaa184

[0153] Z. Zhu et al., Insight into tri-coordinated aluminum dependent catalytic properties of dealuminated Y zeolites in oxidative desulfurization, Appl Catal. B. (2021), 288, 120022. https: / / doi.Org / 10.1016 / J.APCATB.2021 .120022

[0154] S. Abdulridha et al., An efficient microwave-assisted chelation (MWAC) post-synthetic modification method to produce hierarchical Y zeolites, Microporous and Mesoporous Materials (2021), 311 , 110715. https: / / doi.Org / 10.1016 / J.MICROMESO.2020.110715

[0155] W. Lutz, Zeolite Y: synthesis, modification, and properties - a case revisited, Adv. Mater. Sci. Eng. (2014), article ID 724248. https: / / doi.org / 10.1155 / 2014 / 724248

Claims

Claims:1 . A method of modifying an aluminosilicate, the method comprising passing a supply of carbon dioxide through water to form an aqueous solution of CO2, and exposing the aluminosilicate to the aqueous solution of CO2 to produce a modified aluminosilicate.

2. The method of claim 1 , wherein exposing the aluminosilicate to the aqueous solution of CO2 causes dealumination of the aluminosilicate.

3. The method of either claim 1 or claim 2, wherein the aluminosilicate is a crystalline aluminosilicate.

4. The method of claim 3, wherein the aluminosilicate is a zeolite.

5. The method of claim 4, wherein the zeolite is selected from a faujasite, beta zeolite, ZSM-5 zeolite or HZSM-5 zeolite.

6. The method of claim 5, wherein the zeolite is a faujasite, optionally faujasite type Y.

7. The method of any one of claims 1 to 6, wherein the aluminosilicate comprises silicon and aluminium in an Si / AI ratio of between 15 and 40.

8. The method of any one of claims 1 to 7, wherein the framework Si / AI ratio of the modified aluminosilicate is greater than the framework Si / AI ratio of the aluminosilicate before modification.

9. The method of any one of claims 1 to 8, wherein the micropore volume (Vmicro) and / or the mesopore volume (Vmeso) in the modified solid catalyst is greater than in the solid catalyst before modification.

10. The method of any one of claims 1 to 9, wherein the micropore volume (Vmicro) in the modified aluminosilicate is from 0.220 to 0.280 cm3g-1, and / or the mesopore volume (Vmeso) in the modified aluminosilicate is from 0.250 to 0.290 cm3g-1.11 . The method of any one of claims 1 to 10, wherein the aqueous solution of CO2 has a pH of from 2.8 to 4.0.

12. The method of any one of claims 1 to 11 , wherein the aqueous solution of CO2 is formed in a container and the aluminosilicate is exposed to the aqueous solution of CO2 in the same container.

13. The method of any one of claims 1 to 12, wherein the aluminosilicate is immersed in the aqueous solution of CO2.

14. The method of any one of claims 1 to 13, wherein the aluminosilicate is exposed to the aqueous solution of CO2 for 0.5 to 10 hours, or 0.5 to 5 hours, or 0.5 to 2 hours.

15. The method of any one of claims 1 to 14, wherein the aluminosilicate is exposed to the aqueous solution of CO2 at a temperature of at most 60 °C, or at most 25 °C.

16. The method of any one of claims 1 to 15, further comprising a step of removing carbon dioxide from the aqueous solution of CO2, optionally by aeration or heating.

17. The method of claim 16, wherein the removed carbon dioxide is used as the supply of carbon dioxide in a subsequent run of the method according to any one of claims 1 to 16.

18. The method of any one of claims 1 to 17, further comprising a step of impregnating the modified aluminosilicate with a metal to produce a metal-impregnated modified aluminosilicate.

19. The method of claim 18, wherein the step of impregnating the modified aluminosilicate with the metal comprises adding to the modified aluminosilicate an aqueous solution comprising the metal, and then drying and calcining.

20. The method of either claim 18 or claim 19, wherein the metal-impregnated modified aluminosilicate comprises from 2 to 10 wt% of the metal.

21. The method of any one of claims 18 to 20, wherein the metal is selected from nickel, palladium, platinum and ruthenium.

22. The method of claim 21 , wherein the metal is nickel.

23. A modified aluminosilicate produced by the method of any one of claims 1 to 17.

24. A metal-impregnated modified aluminosilicate produced by the method of any one of claims 18 to 22.

25. Use of the modified aluminosilicate of claim 23 or the metal-impregnated modified aluminosilicate of claim 24 as a catalyst or an adsorbent surface, optionally in a cracking process, in the treatment of exhaust gas, in the treatment of waste water, in molecular sieves, or in a chemical sensor.

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