Shaped dehydrogenation catalyst and method for converting paraffins to corresponding olefins using the same

Abstract

Disclosed herein is a dehydrogenation catalyst having single-atom cobalt supported on a silica-based shaped carrier, a preparation method thereof, and a method for preparing olefins by dehydrogenating corresponding paraffins, especially light paraffins, in the presence of the dehydrogenation catalyst.

Description

Technical Field

[0001] The present invention relates to a shaped dehydrogenation catalyst and a method for converting paraffin into olefin using the same. More specifically, the present invention relates to a dehydrogenation catalyst having a single atomic cobalt supported on a silica-based shaped carrier, a method for preparing the same, and a method for preparing olefin by dehydrogenating the corresponding paraffin, especially light paraffin, in the presence of the dehydrogenation catalyst. Background Art

[0002] Light olefins, such as ethylene, propylene, butene, etc., are major chemical raw materials used as base materials for chemical products (oxo alcohols, acrylonitrile, propylene oxide, butanol, acrylic acid, etc.) and plastic products (polypropylene, ethylene propylene rubber, etc.), and find wide application in the petrochemical industry. In particular, propylene, a colorless compound with a low boiling point, is usually traded as polymer grade (purity of at least about 99.5%), chemical grade (purity of about 90-96%), and refinery grade (purity of about 50-70%).

[0003] Generally, light olefins are prepared by thermal cracking of naphtha or kerosene under steam supply (i.e., steam cracking). However, with the growth of demand for light olefins, thermal cracking methods are difficult to meet the growing demand. In response to this demand, various synthesis methods (e.g., catalytic cracking processes of light fractions, etc.) have been proposed. The products obtained by steam cracking, catalytic cracking, etc. are generally mixtures of various hydrocarbons, including methane, ethane, propane, and C5 / C6+ paraffins and olefins (ethylene, propylene, etc.).

[0004] The composition of the hydrocarbon mixture can be adjusted by changing the operating conditions of the process. However, such changes are not a sufficient strategy when the market demand for a specific product is higher than other co-products. For example, in many regions, the market demand for propylene, in particular, is growing rapidly relative to the demand for ethylene. Such low olefin yields with conventional commercial processes require catalyst reaction technology to maximize the selectivity to olefins.

[0005] Examples of commercial dehydrogenation technologies currently in use are summarized in Table 1 below.

[0006] Table 1

[0007]

[0008] For the commercial process illustrated above, the feedstock is provided in the form of a mixed gas, while primarily using a chromium-based or platinum-based (e.g., Pt-Sn) catalyst. It is also known that iron oxide-based catalysts and gallium / zeolite catalysts can be used for the dehydrogenation of paraffins. In addition, although usually undergoing a regeneration process after deactivation due to the formation of coke during the reaction, the dehydrogenation catalyst is required to maintain catalytic activity during multiple regeneration cycles.

[0009] In recent years, there has been increasing interest in catalyst technologies that utilize all metal elements supported on a support. Conventional metal-supported catalysts have catalytic metal particles assembled on a support. Given the wide size distribution and irregular morphology, the assembled metal particles cannot fully utilize the metal active sites, thus having an adverse effect on catalyst activity or selectivity. In contrast, single-atom catalysts offer the advantage that catalyst activity can be maximized by reducing the size of metal nanostructures to the extent that metal active sites are distributed at the atomic level.

[0010] In this regard, there is a known technology for converting propane into propylene by dehydrogenation in the presence of a catalyst having a single-atom type active metal (e.g., zinc) supported on a carrier such as silica (e.g., ACS Catal. 2014, 4, 4, 1091-1098). In this document, a mixed gas containing 3% propane and the remainder of an inert gas argon (Ar) is used as a reactant, with the aim of selectively converting paraffins into corresponding olefins while suppressing the formation of by-products. However, from a commercial point of view, raw materials containing low levels of paraffins are not suitable. In addition, the catalyst may be thermally unstable in a high temperature reaction of about 500°C-600°C and in a dehydrogenation process performed at high temperature and under regeneration conditions because the heat treatment temperature of the catalyst is as low as 300°C.

[0011] Therefore, there is a need for better catalytic activity that is highly stable and shows the greatest advantages of single-atom catalysts. In particular, single-atom catalysts are difficult to commercialize because shaped catalysts cannot guarantee single-atom properties. Summary of the invention

[0012] According to an embodiment of the present invention, a dehydrogenation catalyst supported with single-atom cobalt (Co) and a method for preparing the same are provided, wherein the dehydrogenation catalyst not only exhibits excellent catalytic stability but is also made of a shaped body suitable for commercialization.

[0013] According to an embodiment of the present invention, there is provided a dehydrogenation method which can achieve a high paraffin conversion rate and excellent selectivity to the corresponding olefins even for a feedstock containing a high concentration of paraffins.

[0014] According to a first aspect of the present invention, there is provided a method for preparing a cobalt-based shaped single-atom catalyst, the method comprising the following steps:

[0015] Mixing a silica binder and a carrier material with silica powder in an aqueous medium to prepare a molding paste;

[0016] shaping the paste into a silica-based shaped carrier;

[0017] contacting a silica-based shaped support with an alkali metal salt in an aqueous medium to form an alkali-treated silica-based shaped support, either before or after pH adjustment with a base, wherein at least a portion of the alkali metal ions are electrostatically adsorbed on the surface of the silica-based shaped support;

[0018] contacting the alkali metal-treated silica-based shaped support with an aqueous solution of a first cobalt precursor to form a first silica-based shaped support containing cobalt and alkali metal, adjusting the pH of the aqueous solution of the first cobalt precursor by adding a base to the solution, wherein the first cobalt precursor has an oxidation number of 3+, wherein at least a portion of the cobalt ions with an oxidation number of 3+ are electrostatically adsorbed on the alkali metal-treated silica-based shaped support, and

[0019] heat treating a first silica-based shaped support containing cobalt and alkali metal,

[0020] Thus, the cobalt with an oxidation number of 2+ and the alkali metal with an oxidation number of 1+ are respectively present in the form of isolated single atoms on the silica-based shaped support, and the cobalt with an oxidation number of 2+ is tetrahedrally coordinated on the three-membered siloxane ring, which is present on the surface of the silica-based shaped support.

[0021] According to an exemplary embodiment, the method may further include the steps of: contacting the first silica-based shaped support containing cobalt and an alkali metal with an aqueous solution of a second cobalt precursor having an oxidation number of 3+ to form a second silica-based shaped support containing cobalt and an alkali metal, adjusting the pH thereof by adding a base to the aqueous solution of the second cobalt precursor; and

[0022] The second cobalt and alkali metal-containing silica-based shaped support is heat treated.

[0023] According to a second aspect of the present invention, there is provided a method for preparing a cobalt-based shaped single-atom catalyst, the method comprising the following steps:

[0024] mixing a silica binder and a carrier material with silica powder in an aqueous medium to prepare a molding paste;

[0025] shaping the paste into a silica-based shaped carrier;

[0026] contacting a silica-based shaped support with an alkali metal salt in an aqueous medium to form an alkali-treated silica-based shaped support, either before or after pH adjustment with a base, wherein at least a portion of the alkali metal ions are electrostatically adsorbed on the surface of the silica-based shaped support;

[0027] contacting the alkali metal-treated silica-based shaped support with an aqueous solution of a first cobalt precursor to form a first silica-based shaped support containing cobalt and alkali metal, adjusting the pH of the aqueous solution of the first cobalt precursor by adding a base to the solution, wherein the first cobalt precursor has an oxidation number of 3+, wherein at least a portion of the cobalt ions with an oxidation number of 3+ are electrostatically adsorbed on the alkali metal-treated silica-based shaped support;

[0028] contacting the first silica-based shaped support containing cobalt and an alkali metal with an aqueous solution of a second cobalt precursor to form a second silica-based shaped support containing cobalt and an alkali metal, the pH of the aqueous solution of the second cobalt precursor being adjusted by adding a base to the solution, the oxidation number of the second cobalt precursor being 3+;

[0029] heat treating the second cobalt- and alkali-metal-containing silica-based shaped support,

[0030] Thus, the cobalt with an oxidation number of 2+ and the alkali metal with an oxidation number of 1+ exist on the silica-based shaped support in the form of isolated single atoms, respectively, and the cobalt with an oxidation number of 2+ is tetrahedrally coordinated on the three-membered siloxane ring, which exists on the surface of the silica-based shaped support.

[0031] According to a third aspect of the present invention, there is provided a dehydrogenation catalyst comprising:

[0032] A silica-based shaped support having an alkali metal adsorbed thereon; and

[0033] Cobalt, which is supported as an active metal on a silica-based shaped support,

[0034] The dehydrogenation catalyst is a cobalt-based shaped single-atom catalyst, in which cobalt with an oxidation number of 2+ and alkali metal with an oxidation number of 1+ exist in the form of isolated single atoms on a silica-based shaped support, respectively, and cobalt with an oxidation number of 2+ is tetrahedrally coordinated on a ternary siloxane ring, which exists on the surface of the silica-based shaped support.

[0035] According to a fourth aspect of the present invention, there is provided a method for preparing olefins, the method comprising the following steps:

[0036] Providing a feedstock containing light paraffins;

[0037] In the presence of the above catalyst, the feedstock is dehydrogenated at a temperature of 500° C. to 700° C. and a pressure of 0.3 to 2 bar; and

[0038] Olefins corresponding to light paraffins are recovered from the dehydrogenated product. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The above and other aspects, features and advantages of the present invention will become more apparent from the following detailed description in conjunction with the accompanying drawings, in which:

[0040] Figure 1 is a schematic diagram showing a series of methods for preparing a silica-based shaped support and a single atom catalyst having cobalt supported on the support according to an exemplary embodiment;

[0041] Figure 2 1 is an EXAFS spectrum showing the cobalt single atom catalyst and the shaped cobalt single atom catalyst prepared in Preparation Example 2 and Comparative Preparation Examples 2 to 5;

[0042] Figure 3 : is a graph showing the results of propane dehydrogenation using a molded cobalt single atom catalyst and a powdered cobalt single atom catalyst. DETAILED DESCRIPTION

[0043] The present invention can be completed in full by the following description. It should be understood that the following description shows the preferred embodiments of the present invention, but the present invention is not necessarily limited thereto. It should also be understood that the accompanying drawings are included to provide a further understanding of the present invention and are not intended to limit the scope of the present invention.

[0044] The terms used herein are defined as follows.

[0045] The term "heterogeneous catalyst" refers to a catalyst that exists in a different phase from the reactants during the catalytic reaction. For example, the heterogeneous catalyst may remain undissolved in the reaction medium. When a heterogeneous catalyst is given, the start of the reaction occurs with the diffusion and adsorption of the reactants on the surface of the heterogeneous catalyst. After the reaction is completed, it is necessary to desorb the product from the surface of the heterogeneous catalyst.

[0046] As used herein, the term "support" refers to a material (usually a solid phase material) having a high specific surface area to which catalytically active components are attached, and the support may or may not participate in the catalytic reaction.

[0047] As used herein, the term "crystalline" generally refers to any solid material in which atoms are arranged in a lattice structure (e.g., three-dimensional order), while the term "amorphous" refers to any solid material that does not have such a lattice structure. These materials can be identified by X-ray diffraction (XRD), nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), or a combination thereof.

[0048] As used herein, the term "light paraffin" refers to an alkane having 2 to 5 carbon atoms, more particularly, an alkane having 3 or 4 carbon atoms, such as ethane, propane, n-butane and pentane. In addition, the "corresponding olefin" refers to an olefin obtained by removing hydrogen molecules from the light paraffin in the feedstock by dehydrogenation and thus having the same number of carbon atoms as the paraffin.

[0049] As used herein, the term "silicon dioxide" refers to a tetrahedrally coordinated substance in which four oxygen atoms are bonded to one silicon atom.

[0050] As used herein, the term "porous silica" refers to a three-dimensional network silica having porosity, which may be composed of aggregates of primary silica particles.

[0051] As used herein, the term "single-atom catalyst" generally refers to a catalytic material in which the active component for a specific catalytic reaction is dispersed in the form of single atoms on the surface of any framework or support (e.g., metal oxide). Generally, single-atom catalysts can be characterized using any analytical equipment with atomic-level resolution (e.g., HAADF-STEM (high-angle annular dark-field scanning transmission electron microscope)).

[0052] Cobalt-based shaped single-atom catalyst

[0053] According to an embodiment of the present invention, a cobalt-based shaped single-atom catalyst is provided, which is not only suitable for converting a feedstock containing a high concentration of paraffins (especially light paraffins) into corresponding olefins with high conversion rate and selectivity, but also shows remarkable thermal stability even when exposed to high temperature during the dehydrogenation process, and finds suitable application in commercial methods.

[0054] According to an embodiment, the catalyst may be a heterogeneous catalyst in which a single-site (atom) cobalt as an active metal is supported (or fixed) on a silica-based shaped support having an alkali metal fixed (adsorbed) thereon in a single-atom form (i.e., treated with an alkali metal). In this regard, the silica-based shaped support according to an exemplary embodiment may include a combination of a silica powder for a support (e.g., wet-process (hydrated) silica) and a silica binder (e.g., colloidal silica).

[0055] In the silica-based shaped carrier adsorbed with alkali metal, the alkali metal (or alkali metal ion) with positive charge and oxidation number 1+ on the silica binds to the negatively charged SiO on the surface of the silica-based shaped carrier in the form of isolated single atoms. --The bonding is carried out by electrostatic interaction (or adsorption). In addition, cobalt (Co(II)) or cobalt ions with an oxidation number of 2+ are present on the surface of the silica-based molded support in the form of isolated single atoms. The cobalt in the form of single atoms is tetrahedrally coordinated on the three-membered siloxane ring, which is present on the surface of the silica-based molded support.

[0056] Thus, before cobalt is loaded (or loaded) onto the support, an alkali metal in the form of a single atom is introduced into the silica-based shaped support to define sites available for loading cobalt, whereby the alkali metal is inserted between the cobalt atoms, thereby effectively suppressing aggregation caused by polymerization such as dimerization between cobalt atoms.

[0057] In addition, by introducing an alkali metal therein, the catalyst according to the present embodiment shows enhanced resistance to the reduction of the oxidized cobalt to the elemental state by hydrogen generated during dehydrogenation, and thus advantageously resists a sharp decrease in activity during the reaction. In this regard, conceptually, the functions generated by the introduction of the alkali metal into the molded catalyst are different from the use of the alkali metal as a promoter in the conventional catalyst to provide the following functions: control of the strong acid sites present in the support rather than the central metal component, inhibition of the dissociation of carbon-carbon bonds in the paraffin or the formation of coke induced by the strong acid sites to increase the selectivity of the catalytic reaction, and prevention of catalyst deactivation caused by coke.

[0058] In the present embodiment, the introduction of alkali metal is intended to control the deposition (e.g., impregnation) site and / or amount of cobalt as the central metal, and alkali metal is locally concentrated, so it is easy to aggregate, but does not act as a promoter like conventional dehydrogenation catalysts. Therefore, in theory, alkali metal may interfere with the catalytic reaction. However, in this embodiment, the introduction of alkali metal is considered to have the advantage of providing increased catalyst stability by minimizing those shortcomings while ultimately suppressing the reduction and / or aggregation of cobalt metal. Specifically, during the dehydrogenation reaction, cobalt loaded in the form of single atoms without alkali metal treatment experiences the formation and aggregation of Co-O-Co dimers. In particular, when the catalyst is exposed to high temperature as the reaction proceeds, or when dehydrogenation is carried out using a raw material containing a high concentration of paraffin, the above-mentioned problem is particularly evident, thereby reducing the catalytic activity.

[0059] According to an exemplary embodiment, the alkali metal may be at least one selected from sodium (Na), potassium (K) and cesium (Cs). More specifically, the alkali metal may be potassium (K), because potassium has an ion size that enables it to be located around cobalt bonded to the three-membered siloxane ring, thereby being able to coordinate with cobalt to achieve effective stabilization.

[0060] In this regard, the content of alkali metal in the catalyst can be, for example, in the range of about 0.00001-1% by weight, particularly about 0.005-1% by weight, more particularly about 0.01-0.5% by weight. According to an exemplary embodiment, the dehydrogenation catalyst in a shaped form comprises, for example, about 0.5-5% by weight, particularly about 0.7-3% by weight, more particularly about 1-2.5% by weight of cobalt. The loading amount can vary slightly depending on the properties of the silica-based shaped support, etc., but can be controlled by considering the maximum amount of cobalt present in the form of a single atom, typically about 2-3% by weight.

[0061] In an exemplary embodiment, the weight ratio of cobalt (Co) / alkali metal in the catalyst can be, for example, in the range of about 1 to 1000, particularly about 10 to 800, more particularly about 50 to 600, and most particularly about 100 to 500, relative to the alkali metal, and the excessive loading of cobalt causes the presence of excess cobalt ions in the local restricted area. In this case, the lack of alkali metal components may cause the reduction or aggregation of cobalt ions on the catalyst surface, thereby causing the cobalt single atom catalyst to be deactivated. On the other hand, when the relative loading of cobalt relative to the alkali metal is too small, the alkali metal occupies a relatively large space and acts as a barrier to prevent the reactant light paraffin from entering the catalyst, thereby greatly reducing the conversion rate. In view of this, the weight ratio of cobalt (Co) / alkali metal can be advantageously adjusted within this range.

[0062] As long as the cobalt-based shaped catalyst is suitable for commercial methods, catalyst is not limited to specific shape and / or size (or size). In exemplary embodiments, the shape of catalyst can be cylinder, particle, pellet, tablet, spherical or trilobal. In this regard, the diameter of cylindrical catalyst can be in the range of, for example, about 0.1-5mm (especially about 0.5-4mm, more particularly about 1-3mm), length such as about 0.5-20mm (especially about 1-15mm, more particularly about 3-10mm). In addition, when catalyst has particle, pellet, tablet or spherical shape, its average size can be, for example, about 0.1-10mm (especially about 0.5 to 7mm, more particularly about 1-5mm).

[0063] In order to reduce the pressure drop at the front and rear ends, which is one of the important process variables in commercial processes (especially for the production of propylene) where high temperature reactions and frequent gas changes occur, the catalyst as described above may advantageously have a uniform shape with sufficient pores when loaded into the reactor.

[0064] Preparation method of cobalt-based shaped single-atom catalyst

[0065] exist Figure 1A series of methods are described in which a silica-based shaped support is prepared and cobalt is loaded or loaded onto the support to prepare a single atom catalyst according to an embodiment of the present invention. The embodiments given are given for illustrative purposes only and are not intended to limit the present invention.

[0066] -Preparation of silica-based shaped carriers

[0067] According to an exemplary embodiment, the silica binder and the carrier material are mixed with silica powder to form a molding paste.

[0068] As one of the main components of the forming paste, the silicon dioxide powder is not limited to a specific type, but can advantageously adopt high-purity silicon dioxide with as low an impurity content as possible. According to exemplary embodiments, silicon dioxide can be amorphous silicon dioxide, particularly porous amorphous silicon dioxide, for example, wet (hydrated) silicon dioxide (silica gel and precipitated silica). The lower the crystallinity, the more favorable it is for the catalyst. As fine powder, silicon dioxide has a large amount of silanol groups and siloxane groups on its molecular surface. The silanol (hydroxyl) groups on the silicon dioxide surface can exist in three types: isolated (Si-OH), ortho (connected by hydrogen bonds) and original (germinal) (HO-Si-OH), or may be rich in a combination of isolated type: ortho type composition of 2:1. Meanwhile, when amorphous dry-process silica (fumed silica, pyrogenic silica) is incorporated at a level exceeding a certain level (e.g., in an amount of about 20 wt % or more of the silica powder for the support material), the supported monatomic cobalt is exposed to high temperatures at which dehydrogenation occurs, and the stability of the cobalt may deteriorate (e.g., the cobalt grows in the form of oxides to promote coke formation).

[0069] According to a specific embodiment, the silica has a thickness of, for example, at least about 100 m 2 / g, especially about 200-1500m 2 / g, more particularly about 300-1000m 2 The pore volume of silica can be, for example, about 0.1-10 cm 3 / g, especially about 0.3-5cm 3 / g, more particularly about 0.5-3cm 3 In the range of 100 nm to 500 nm, the pore size (average diameter) may be, for example, in the range of about 0.5-200 nm, particularly about 1-100 nm, more particularly about 3-30 nm. However, it should be understood that the numerical range is given for illustrative purposes.

[0070] At the same time, the silica binder that can be used to prepare the molding paste can bind the support material with silica. In addition, the silica molded support prepared using the silica binder should allow cobalt as a central metal to be stably maintained in a single atomic form.

[0071] According to an exemplary embodiment, the silica binder can be colloidal silica. The term "colloidal silica" refers to a suspension of silica particles. Colloidal silica can generally be prepared by wet chemical synthesis (particularly by hydrolysis of organic silicates in organic solvents such as alcohols). The particle size of the colloidal silica can be, for example, about Especially about In addition, the purity of the silica binder can be, for example, at least about 95%, particularly at least about 99%, and more particularly at least about 99.9%. The silica binder can be commercially available, for example, under the trade name LUDOX AS-40. However, the sodium form (e.g., trade name LUDOX HS-40) may result in reduced catalytic activity. In order to limit the functions other than the intended function of the binder itself, the ammonium form of the silica binder may be advantageous. In this regard, the ammonium form of the silica binder may contain, for example, less than about 1% by weight, particularly less than about 0.1% by weight of sodium.

[0072] refer to Figure 1 , providing silica powder for carrier material to prepare a shaped carrier, and at the same time preparing an aqueous dispersion containing a silica binder.

[0073] It can be seen that the aqueous dispersion containing the silica binder can contain the silica binder alone or in combination with a lubricant (optional ingredient). The lubricant can generally be a hydrolyzable polymer. The lubricant increases the adhesion between the silica powder for the carrier material and the silica binder in subsequent steps such as the kneading process to facilitate the formation of a paste.

[0074] According to an exemplary embodiment, the lubricant may be polyvinyl alcohol, polyacrylate, polyvinyl pyrrolidone, cellulose, cellulose ether (eg, hydroxyethyl cellulose, methyl cellulose, etc.), starch, polyamino acid, polytetrahydrofuran, polyethylene glycol, and polyethylene glycol copolymers. They may be used alone or in combination.

[0075] According to an exemplary embodiment, a lubricant can be added to an aqueous medium (particularly water) to form a lubricant emulsion. Then, a silica binder is added to the lubricant emulsion to prepare an emulsion containing a silica binder. For uniform dispersion, the silica binder can be added to the lubricant emulsion in the form of an aqueous dispersion. The content of the lubricant in the lubricant emulsion containing the silica binder can be, for example, about 0.1-20% by weight, particularly about 0.5-10% by weight, but is not limited thereto.

[0076] According to an alternative embodiment, an aqueous dispersion containing a silica binder may be prepared by adding the silica binder to water instead of the lubricant emulsion, and this may be used to prepare the molding paste.

[0077] According to an exemplary embodiment, the content of the silica binder in the emulsion containing the silica binder or the aqueous dispersion containing the silica binder, wherein the silica binder can be used as a crosslinking agent, can be adjusted within a range from a minimum ratio to a maximum ratio relative to the silica for the carrier material, wherein the content is, for example, within a range of about 10-60 wt %, in particular within a range of about 20-40 wt %.

[0078] According to the described embodiment, colloidal silica may be used as the silica binder as described above. Considering that cobalt is loaded (or impregnated) by electrostatic adsorption after forming a shaped support, it is advantageous that the colloidal silica may not contain additional cations and anions.

[0079] refer to Figure 1 , after obtaining, the emulsion or aqueous dispersion containing the silica binder is combined with the silica powder for the carrier material to prepare a silica-based molding paste. According to an exemplary embodiment, the silica powder for the carrier material may have a size of, for example, about 30 μm or less, particularly about 20 μm or less, and more particularly about 15 μm or less. However, the numerical range is understood to be illustrative. In order to provide a powder form of the silica for the carrier material, a comminution step such as grinding may be performed.

[0080] According to an exemplary embodiment, the mixing ratio (weight) of silica binder: silica powder for carrier material can be, for example, 1 (about 0.1-10), particularly 1: (about 0.5-6), more particularly 1: (about 0.6-4). Considering the influence on the cobalt loading of the molding carrier itself and the thermal stability of cobalt, it is preferred to adjust the mixing ratio within the above range. The molding paste can be prepared using methods known in the art, such as a kneader.

[0081] Then, the molded paste can be used to prepare a silica-based molded support. The molding method is not limited to a specific method, but any catalyst molding method known in the art can be applied, such as extrusion, granulation, etc. The formation and molding of the paste can be carried out in each separate step. Alternatively, the paste formation and molding can be carried out simultaneously in the molding method.

[0082] In a particular embodiment, the shaped support can be obtained by extrusion. As used herein, the term "extrusion" refers to a process for forming an object having a predetermined shape, usually by pushing a material (or paste) through a die or orifice. The silica-based shaped product can be prepared to have a variety of shapes (e.g., cylinders, granules, pellets, tablets, spheres, trilobes, etc.) and sizes (or dimensions).

[0083] The molded product obtained in the molding process can be subjected to a drying step as required. The drying step can be carried out for about 1-24 hours (especially about 2-12 hours) at, for example, about 15-70°C (especially about 20-50°C, more especially room temperature). In addition, the molded product can be subjected to subsequent heat treatment. The heat treatment can be carried out in an oxygen-containing atmosphere (such as a pure oxygen atmosphere or air). The temperature of the heat treatment can be adjusted at, for example, about 100-800°C, especially about 150-700°C, more especially 500-650°C. In addition, the heat treatment can be carried out for example for about 1-24 hours, especially about 1.5-12 hours, more especially about 2-5 hours. In this regard, the heat treatment can be carried out in multiple stages. The heat treatment can be carried out at a relatively low temperature (for example, about 100-300°C, especially about 120-200°C), followed by a higher temperature (for example, about 400-800°C, especially about 500-700°C). The above-described drying and heat treatment conditions are to be understood as illustrative.

[0084] - Preparation of the first silica-based shaped catalyst containing cobalt and alkali metal

[0085] According to an embodiment, the silica-based shaped support prepared above is first contacted with an alkali metal to form an alkali metal-treated silica-based shaped support.

[0086] In particular, the alkali metal treatment can be carried out by adding the silica-based shaped support to an aqueous medium and dissolving the alkali metal salt in the medium. The aqueous medium can be water, especially distilled water. The silica-based shaped support can be added, for example, in an amount of about 1-30 wt %, in particular about 3-20 wt %, more particularly about 5-10 wt %, based on the weight of the aqueous medium.

[0087] The alkali metal salt may be at least one selected from hydroxides, nitrates, chlorides, carbonates and sulfates of alkali metals, but is not limited thereto. More particularly, alkali metal hydroxides and / or nitrates may be used because these salts are advantageous in pH control and do not cause coprecipitation of the cobalt precursor.

[0088] In an exemplary embodiment, the alkali metal may be dissolved in an amount of about 0.001-3 wt %, specifically about 0.005-1 wt %, and more specifically about 0.01-0.8 wt %, based on the weight of the silica-based shaped support in the aqueous medium.

[0089] In an exemplary embodiment, the pH of the aqueous medium may be adjusted by adding a base before or after the silica-based shaped support is contacted with the alkali metal salt in the aqueous medium.

[0090] By adding a base, the pH of the aqueous medium can be adjusted to, for example, at least about 9, particularly at least about 9.5, and more particularly about 10-12. The reason for increasing the pH of the aqueous medium containing the shaped support when treated with an alkali metal is to deprotonate the surface of the silica-based shaped support. In particular, the surface of the silica-based shaped support can be deprotonated by removing hydrogen ions (H 2 O) from the silanol groups (Si-OH) present on the surface. + ) makes the surface negatively charged. That is, at the point of zero charge (PZC) of the silica shaped support, ions are not adsorbed, but silanol groups (hydroxyl groups) are retained. Therefore, the surface of the silica-based shaped support is negatively charged by deprotonation through pH adjustment.

[0091] As a result, the alkali metal ions can be fixed (or immobilized) or grafted to the silica in a single-atom form by electrostatic interaction (i.e., by electrostatic adsorption) with the silanol anions (SiO-) on the surface of the deprotonated silica-based shaped support. In addition, siloxanes, especially ternary siloxanes, coexisting with silanol on the surface of the silica-based shaped support form three silanol anions in an alkaline aqueous medium, which are believed to provide sites on which cobalt can be fixed or immobilized in a subsequent step.

[0092] According to an exemplary embodiment, the base (i.e., the alkaline component) can be at least one selected from, for example, sodium hydroxide, potassium hydroxide, ammonium hydroxide, cesium hydroxide, and lithium hydroxide, and can be particularly an ammonium-containing base, more particularly ammonium hydroxide (aqueous ammonia). Advantageously, the added base will not precipitate in a subsequent step in which an aqueous solution of a cobalt precursor is combined or mixed therewith.

[0093] refer to Figure 1 The alkali metal-treated silica-based shaped support can be contacted with a pH-adjusted aqueous solution of a cobalt precursor to form a first silica-based shaped support containing cobalt and alkali metal. To this end, an aqueous solution of a cobalt precursor can be prepared separately from the preparation step for the alkali metal-treated silica-based shaped support, and a base (alkaline component) can be added to provide a pH-adjusted aqueous solution of a cobalt precursor.

[0094] In this regard, the cobalt precursor may include a cobalt (Co(III)) complex ion having an oxidation number of 3+. For example, Co(NH 3 ) 6 Cl 3 , or at least one selected from Co(NO 3 ) 2 、CoCl 2 and Co(acac) 3 The cobalt compound (precursor) of (cobalt acetylacetonate) was treated with aqueous ammonia and filtered to obtain a precursor including a cobalt complex ion. Co(NH 3 ) 6 Cl 3 The use of is advantageous for the easy formation of cobalt single-atom catalysts because it can minimize the preparation steps.

[0095] In an exemplary embodiment, the aqueous precursor solution may include the cobalt precursor at a concentration of, for example, about 0.1-20 wt %, specifically about 0.5-10 wt %, and more specifically about 1-7 wt %.

[0096] In addition, the pH of the cobalt precursor solution can be adjusted with an alkali (alkaline component). As described above, the pH adjustment allows the surface of the silica-based shaped support to stably maintain a deprotonated state (i.e., modified to have a negative charge) in the subsequent step of contacting the silica-based shaped support treated with an alkali metal. The positively charged cobalt ions (Co) of the precursor are thus 3 +) can be fixed or attached to the surface of silica by electrostatic adsorption. In this regard, the alkaline component added to the cobalt precursor solution can be at least one of the alkaline components selected from the preparation of the silica-based shaped carrier treated with alkali metal. For example, the alkaline component or alkaline compound used in the alkali metal treatment step and the cobalt fixing (loading) step can be the same or different. Even in this case, it is preferred that the alkaline component does not cause precipitation when mixed with the aqueous solution of the cobalt precursor. In addition, the addition of the alkaline component can adjust the pH of the aqueous solution of the cobalt precursor to, for example, at least about 9, particularly at least about 9.5, and more particularly about 10-12.

[0097] Likewise, a pH adjusted aqueous solution of a Co(III) precursor (e.g., an aqueous solution of a first cobalt precursor) is contacted with an alkali metal-treated silica-based shaped support (typically contained in a pH adjusted aqueous medium) to form a first cobalt- and alkali metal-containing silica-based shaped support.

[0098] The mixing (combination) ratio between the pH-adjusted aqueous solution of the cobalt precursor and the alkali-treated silica-based shaped support can be determined by considering the amount of cobalt ions in the aqueous solution of the cobalt precursor that can be fixed in a single-atom form (especially a single-atom form of a monolayer) on the surface of the alkali-treated support. In this regard, the cobalt ions can be loaded on the surface of the silica-based support in an amount of up to about 2-3% by weight. However, in practice, not all cobalt precursors used can be fixed on the surface of the silica-based support. Therefore, an excess of cobalt (Co(III)) precursor greater than the theoretical amount can be dissolved.

[0099] In an exemplary embodiment, the amount of the cobalt precursor can be controlled within a range of about 1-100 wt %, particularly within a range of about 5-50 wt %, and more particularly within a range of about 10-30 wt %, based on the weight of the silica shaped support. In addition, the weight ratio of cobalt: alkali metal during mixing can fall within a range of, for example, about 1000:1 to 1:1, particularly about 800:1 to 10:1, more particularly about 600:1 to 50:1, and most particularly 500:1 to 100:1.

[0100] After the above process, at least a portion of the cobalt ions can be electrostatically adsorbed on the surface of the silica shaped support adsorbed with the alkali metal ions. + ions) and cobalt ions (Co 3+ ions) can be independently fixed or immobilized on the shaped support in the form of single atoms. Specifically, since the alkali metal ions have been introduced into the silica-based shaped support by alkali treatment, the cobalt (or Co) with an oxidation number of 3+ as a precursor 3+ ) can only be strongly bound to the support surface sites where the three-membered siloxane ring is present, while preventing the deposition of cobalt at other sites. In other words, the pretreatment of the silica-based shaped support with an alkali metal limits the sites available for cobalt deposition.

[0101] In contrast, when cobalt is supported without alkali metal treatment, cobalt ions are weakly attached to undesirable surface sites of the silica-based molded body, for example, sites where isolated silanol groups exist. The cobalt supported in this manner undergoes polymerization (dimerization) with other cobalt in the subsequent dehydrogenation reaction and aggregates, causing a particle formation phenomenon and becoming a factor in reducing catalytic activity.

[0102] According to an exemplary embodiment, the aqueous cobalt precursor solution and the alkali metal treated silica-based shaped support (generally contained in an aqueous medium) can be mixed while stirring. The stirring can be carried out at a speed of, for example, about 200-500 rpm, particularly about 250-400 rpm, and can last, for example, at least about 3 minutes, particularly about 5-40 minutes, more particularly about 10-30 minutes, but not limited thereto. The temperature of the mixing can be set to, for example, about 10-40°C, particularly about 20-30°C, more particularly room temperature, but not limited thereto.

[0103] Then, the following step may be performed as a post-treatment process: the alkali metal and cobalt that are not fixed in the form of single atoms to the surface of the first cobalt- and alkali metal-containing silica-based shaped support may be removed as much as possible from the mixed aqueous medium. This process makes the method of the present invention different from the conventional impregnation method, which is a method in which only the alkali metal (or alkali metal ion) and cobalt (or Co) fixed in the form of single atoms are removed by electrical interaction. 3+ ) remain on the surface of silica, while eliminating other alkali metals and cobalt. As in conventional impregnation methods, for example, during dehydrogenation, a large amount of cobalt precursor attached to the surface of silica causes reduction, aggregation, etc., thereby reducing catalytic activity.

[0104] With full consideration of the above, the first silica-based molding carrier containing cobalt and alkali metals can be quickly separated from the liquid (e.g., by sedimentation, filtration, etc.), and the separated molding carrier can be subjected to repeated cycles of adding water (especially distilled water), stirring and separation according to the exemplary embodiment as needed. In addition, the separated molding carrier can be washed with water (especially distilled water) at least once, especially twice or more times, to remove as many alkali metals and cobalt precursors as possible that remain unattached. Next, the first cobalt- and alkali-metal-containing (fixed or immobilized) molding carrier can be obtained by drying at a temperature of, for example, about 50-200°C, especially, for example, about 70-150°C for about 3-24 hours, especially about 6-12 hours, but is not limited thereto. At this time, the cobalt ion still maintains an oxidation number of +3.

[0105] return Figure 1 As a subsequent step, the first cobalt- and alkali-metal-containing (fixed or immobilized) silica-based shaped support may be converted into a catalyst by heat treatment. The heat treatment may be carried out, for example, at about 250-700° C., particularly about 200-600° C., more particularly about 300-550° C. in an oxygen-containing atmosphere. Any heat treatment time may be used as long as it is sufficient to change the oxidation number of cobalt from 3+ to 2+. For example, the heat treatment may last for about 2-24 hours, particularly about 2.5-12 hours, more particularly about 3-6 hours.

[0106] In this embodiment, when the (fixed or immobilized) silica adsorbed with alkali metals and cobalt is heat-treated, the oxidation number of the cobalt adsorbed on the silica changes from 3+ to 2+. However, in the optional drying step performed before the heat treatment, a portion of the cobalt may be reduced from an oxidation number of 3+ to 2+, and then most of the cobalt is reduced to an oxidation number of 2+. Without being bound by a particular theory, the reason why the cobalt maintains an oxidation number of 2+ after heat treatment is explained as follows.

[0107] For cobalt with an oxidation number of 3+, only an octahedral structure is possible because six electrons occupy the outermost orbital, thereby being able to form six bonds. When cobalt is reduced to 2+, there are seven electrons in the outermost orbital, so a tetrahedral structure is mainly formed, and an octahedral structure like that in CoO is also possible. According to the present embodiment, it is believed that cobalt is reduced to 2+ to form a tetrahedral structure because it should be structurally bound to the ternary siloxane group. On the other hand, in order to return to 3+, cobalt should cooperate with its surroundings to form an octahedron. At this time, silicon (Si) essentially does not have any structure other than a tetrahedron, which is inconsistent with the octahedral structure of cobalt, making it difficult to convert the reduced cobalt into an oxidation state 3+. On the contrary, when the bond (linkage) (connection) with Si is disconnected and the Co metal is aggregated alone, deactivation occurs. Therefore, it is believed that the oxide formed by contact with oxygen will cause Co containing cobalt with an oxidation number of 3+ to deactivate. 3 O 4 .

[0108] The cobalt with an oxidation number of 2+ obtained by heating conversion at a predetermined temperature or higher in the heat treatment step does not return to cobalt with an oxidation number of 3+ even if the heat treatment is continued in an oxygen-containing (or oxidizing) atmosphere (or calcining atmosphere). The reason is that the monoatomic cobalt needs to retain a tetrahedral structure. In addition, even when the catalyst is applied to dehydrogenation performed at a predetermined temperature or higher, the oxidation state remains unchanged, which means that the catalyst according to the present embodiment is resistant to reduction.

[0109] -Preparation of a second silica-based shaped catalyst containing cobalt and alkali metal

[0110] according to Figure 1In the embodiment shown, the carrier of the first silica-based shaped carrier catalyst containing cobalt and alkali metal prepared above is disadvantageous in loading single atomic cobalt thereon, so the loading capacity is relatively poor, so the catalyst exhibits lower catalytic activity compared to the powder form. In some cases, due to the competition between cobalt and alkali metals (especially potassium) for adsorption, the loading amount of cobalt may be relatively small, while the alkali metal may remain in large quantities, which has a negative impact on dehydrogenation. In view of this situation, according to an exemplary embodiment, a second cobalt loading step can be performed as needed. The loading amount of cobalt can be additionally increased by loading (applying) cobalt under alkaline (base) conditions to exchange the alkali metal with cobalt while washing off the alkali metal.

[0111] The second cobalt loading step may be performed after the heat treatment (first heat treatment) step performed after preparing the first cobalt and alkali metal-containing silica-based shaped supported catalyst. Alternatively, cobalt may be loaded for the second time without performing the first heat treatment step, followed by heat treatment.

[0112] from Figure 1 As can be seen in the figure, an alkaline component is added to an aqueous solution of a cobalt precursor to obtain a pH-adjusted aqueous solution of a cobalt precursor, which is then contacted with a first cobalt- and alkali-metal-containing silica-based shaped support (or catalyst) to deposit the central metal cobalt in an adsorbent manner. After the second cobalt loading step, as described above, the support is separated from the liquid phase, optionally subjected to a drying step, and then subjected to a heat treatment (second heat treatment) in a manner similar to the first heat treatment step.

[0113] The second cobalt loading step and the second heat treatment step share technical contents with the first cobalt loading step and the first heat treatment step, and thus descriptions thereof are omitted.

[0114] Dehydrogenation

[0115] According to another embodiment thereof, the present invention provides a method for converting paraffins, particularly light paraffins (more particularly light paraffins of 2 to 5 carbon atoms) into corresponding olefins by using the above-mentioned cobalt-based shaped single-atom catalyst. In particular, the light paraffins may contain propane. In this regard, the feedstock may be provided in a gas phase.

[0116] When applied to feedstocks containing high levels of paraffins, the catalyst can achieve better conversion and selectivity. For example, the content of paraffins in the feedstock can be, for example, at least about 50% by volume, particularly at least about 70% by volume, more particularly at least about 80% by volume, or even higher than about 99% by volume. This is different from experimental results in which up to about 20% by volume of the feedstock was dehydrogenated in the presence of a conventional single-atom catalyst (e.g., a Zn catalyst).

[0117] In the dehydrogenation according to the exemplary embodiment, the reaction temperature may be, for example, in the range of about 500-700° C., particularly about 550-650° C., more particularly about 570-620° C. In addition, a pressure of, for example, about 0.3-2 bar, particularly about 0.4-1.5 bar, more particularly about 0.5-1 bar may be set for dehydrogenation. As for the gas hourly space velocity (GHSV), the range thereof may be selected to be, for example, about 100-2000 h under standard conditions. -1 , especially about 200-1500 hours -1 , more particularly about 300-1000 hours -1 The dehydrogenation conditions may vary depending on the type of paraffin in the feedstock, the active metal in the catalyst, the loading amount and ratio of the alkali metal, etc.

[0118] According to exemplary embodiments, the conversion rate and selectivity of dehydrogenation may be, for example, at least about 30% (particularly at least about 40%) and at least about 70% (particularly at least about 80%), respectively.

[0119] The present invention may be better understood by the following examples, which are provided to illustrate but should not be construed as limiting the present invention.

[0120] -EXAFS

[0121] In order to study the single-atom cobalt in the cobalt single-atom catalyst and analyze the environment around the single-atom cobalt, the Co K-edge (7.709 keV) was measured and recorded at the Pohang Light Source (PAL PLS-II) 8C beamline (nano-XAFS (X-ray absorption spectroscopy), 4-20 keV and 1012 photons / second. The gas was controlled to transfer I 0 The absorbances of It and It+Ir were set to 15% and 85%, respectively. The monochromator was detuned to 70%. All samples except the reference sample (0.1 mm) were powdered, loaded into a 2 mm slit and planarized before measurements in transmission mode.

[0122] - Calculate conversion and selectivity

[0123] The conversion rate and selectivity of propane were calculated according to Equation 1 and Equation 2 below.

[0124] [Equation 1]

[0125]

[0126] [Equation 2]

[0127]

[0128] Preparation Example 1

[0129] Preparation of silica-based shaped (extruded) carriers

[0130] As a silica binder, 17.2 g of LUDOX AS-40 (Sigma-Aldrich) was mixed with 3.6 g of distilled water while stirring at 500 rpm to prepare a silica binder solution (dispersion). Separately, the carrier material was ground into a fine powder of 30 μm or less in size using a mortar grinder with silica. The finely ground silica powder weighed 10.28 g. The silica binder solution was added dropwise to the ground silica powder to obtain a silica-silica binder paste. The paste was fed into an extruder and extruded into a noodle form having a constant thickness (size: 1.5 mm). The extrudate thus obtained was fully dried at room temperature and introduced into a heating furnace, where it was heat treated at 150° C. for 2 hours in an air atmosphere and then heat treated at 600° C. for 2 hours to provide a shaped silica carrier.

[0131] Preparation Example 2

[0132] Preparation of silica-based shaped (extruded) single-atom catalysts loaded with alkali metal-cobalt (one-step cobalt loading)

[0133] First, 10 g of the silica-based support prepared according to Preparation Example 1 was dispersed in 100 ml of distilled water, and then 0.072 g of KOH (Samchun Chemicals) was added thereto. After stirring for 30 minutes, the pH of the dispersion was controlled to 11 by adding 28 wt % ammonia water (Samchun Chemicals) thereto. In another beaker, 2.5 g of a cobalt precursor (Co(NH 3 ) 6 Cl 3 TCI) was dissolved in 50 ml of distilled water. The cobalt precursor aqueous solution was controlled to have a pH of 11 by adding 28 wt % ammonia water (Samchun Chemicals) thereto.

[0134] Next, the aqueous solution of the cobalt precursor is immediately added to the dispersion containing the silica shaped support and the alkali metal, and then stirred at room temperature for 10 minutes. The stirred sample is placed for 5 minutes, and the supernatant thus formed is decanted. 200 ml of distilled water is added to the residue, and then stirred again for 10 minutes. The stirred sample is allowed to stand, and the supernatant thus formed is decanted. The residue is vacuum filtered and washed several times with distilled water. Afterwards, the washed filtrate is dried at room temperature and then dried at 125°C. The dried sample is heated to 300°C at a rate of 5°C / min and heat treated at this temperature for 3 hours to prepare a single-atom catalyst of cobalt supported on which cobalt and alkali metal are supported.

[0135] Preparation Example 3

[0136] Preparation of silica-based shaped (extruded) single-atom catalysts loaded with alkali metal-cobalt (two-step cobalt loading)

[0137] First, 10 g of the silica-based support prepared according to Preparation Example 1 was dispersed in 100 ml of distilled water, and then 0.072 g of KOH (Samchun Chemicals) was added thereto. After stirring for 30 minutes, the pH of the dispersion was controlled to 11 by adding 28 wt % ammonia water (Samchun Chemicals) thereto. In another beaker, 2.5 g of a cobalt precursor (Co(NH 3 ) 6 Cl 3 TCI) was dissolved in 50 ml of distilled water. The cobalt precursor aqueous solution was controlled to have a pH of 11 by adding 28 wt % ammonia water (Samchun Chemicals) thereto.

[0138] Next, the aqueous solution of cobalt precursor is immediately added to the dispersion containing the silica shaped support and the alkali metal, and then stirred at room temperature for 10 minutes. The stirred sample is placed for 5 minutes, and the supernatant thus formed is decanted. 200ml of distilled water is added to the residue, and then stirred again for 10 minutes. The stirred sample is allowed to stand, and the supernatant thus formed is decanted. The residue is vacuum filtered and washed several times with distilled water. Thereafter, the washed filtrate is dried at room temperature and then dried at 125°C. The dried sample is heated to 300°C at a rate of 5°C / min and heat treated at this temperature for 3 hours to prepare a single-atom primary catalyst of cobalt supported on which cobalt and alkali metal are supported.

[0139] In order to load cobalt onto the single-atom primary catalyst loaded with cobalt, first, 10 g of the single-atom primary catalyst loaded with cobalt was dispersed in 100 ml of distilled water. The pH of the dispersion was controlled to 11 by adding 28 wt % ammonia water (Samchun Chemicals). In another beaker, 2.5 g of cobalt precursor (Co(NH 3 ) 6 Cl 3 TCI) was dissolved in 50 ml of distilled water. The cobalt precursor aqueous solution was controlled to have a pH of 11 by adding 28 wt % ammonia water (Samchun Chemicals) thereto.

[0140] After this, the cobalt precursor aqueous solution is added immediately into the solution (dispersion) of the single-atom primary catalyst loaded with cobalt, then stirred at room temperature for 10 minutes. The stirred sample is placed for 5 minutes, and the supernatant thus formed is decanted. In the residue, 200ml of distilled water is added, and then stirred again for 10 minutes. The stirred sample is left to stand, and the supernatant thus formed is decanted. The residue is vacuum filtered, and washed with distilled water several times.

[0141] The washed filtrate was dried at room temperature and then further dried at 125° C. The dried sample was heated to 300° C. at a rate of 5° C. / min and heat-treated at the temperature for 3 hours to prepare a shaped cobalt single atom catalyst.

[0142] Comparative Preparation Example 1

[0143] Preparation of cobalt-loaded single-atom catalysts using commercial silica supports in extruded form

[0144] A single atom catalyst supported with cobalt was prepared in the same manner as in Preparation Example 2, except that 20 g of commercially available silica (SP100, Evonik) processed into an extrudate form was used as the silica-based shaped support.

[0145] Comparative Preparation Example 2

[0146] Preparation of cobalt single-atom catalyst formed from a mixture of powdered cobalt single-atom catalyst and silicon dioxide binder

[0147] First, 20 g of commercially available silica was dispersed in 200 ml of distilled water, and then 0.144 g of KOH was dissolved therein. The pH of the dispersion was controlled to 11 by adding ammonia water (Samchun Chemicals) having a concentration of 28 wt %.

[0148] In another beaker, 5 g of cobalt precursor (Co(NH 3 )6 Cl 3 TCI) was dissolved in 50 ml of distilled water. The cobalt precursor aqueous solution was controlled to have a pH of 11 by adding 28 wt % ammonia water (Samchun Chemicals) thereto.

[0149] Next, the aqueous solution of cobalt precursor is immediately added to the dispersion containing silica and alkali metal, and then stirred at room temperature for 10 minutes. The stirred sample is placed for 5 minutes, and the supernatant thus formed is decanted. 200ml of distilled water is added to the residue, and then stirred again for 10 minutes. The stirred sample is allowed to stand, and the supernatant thus formed is decanted. The residue is vacuum filtered and washed several times with distilled water. Afterwards, the washed filtrate is dried at room temperature and then dried at 125°C. The dried sample is heated to 300°C at a rate of 5°C / min and heat treated at this temperature for 3 hours to prepare a single atom catalyst loaded with cobalt.

[0150] The mixture of the prepared catalyst and silica binder was molded into a cobalt single atom catalyst. To this end, first, 0.52 g of lubricant PVA (Sigma-Aldrich, polyvinyl alcohol) was mixed with 2.0 g of distilled water and the mixture was stirred, while 8.58 g of silica binder LUDOX AS-40 was added dropwise.

[0151] The cobalt-loaded single-atom catalyst prepared above was ground to a size of less than 30 μm. Under stirring, a mixture of a lubricant and a silica binder was dripped into the resulting 5.18 g catalyst powder. Before drying, the resulting paste was introduced into an extruder and extruded into a noodle form with a constant thickness (size: 1.5 mm). The extrudate thus obtained was fully dried at room temperature and introduced into a heating furnace, where it was heat treated at 150° C. for 2 hours in an air atmosphere and then at 600° C. for 2 hours to obtain a shaped cobalt single-atom catalyst.

[0152] Comparative Preparation Example 3

[0153] Preparation of cobalt single-atom catalyst formed from a mixture of powdered cobalt single-atom catalyst and alumina binder

[0154] First, 20 g of commercially available silica was dispersed in 200 ml of distilled water, and then 0.144 g of KOH was dissolved therein, followed by stirring for 30 minutes. The pH of the dispersion was controlled to 11 by adding 28 wt % ammonia water (Samchun Chemicals) thereto.

[0155] In another beaker, 5 g of cobalt precursor (Co(NH 3) 6 Cl 3 TCI) was dissolved in 50 ml of distilled water. The cobalt precursor aqueous solution was controlled to have a pH of 11 by adding 28 wt % ammonia water (Samchun Chemicals) thereto.

[0156] Next, the aqueous solution of cobalt precursor is immediately added to the dispersion containing silica and alkali metal, and then stirred at room temperature for 10 minutes. The stirred sample is placed for 5 minutes, and the supernatant thus formed is decanted. 200ml of distilled water is added to the residue, and then stirred again for 10 minutes. The stirred sample is allowed to stand, and the supernatant thus formed is decanted. The residue is vacuum filtered and washed several times with distilled water. Thereafter, the washed filtrate is dried at room temperature and then dried at 125°C. The dried sample is heated to 300°C at a rate of 5°C / min and heat treated at this temperature for 3 hours to prepare a cobalt-loaded single atom catalyst.

[0157] The cobalt-supported single-atom catalyst prepared above was ground to a size of 30 μm or less. 12.5 g of the catalyst powder thus obtained was added to a PP container together with 12.5 g of an alumina binder boehmite (SASOL) and mixed in a roll mixer for 12 hours.

[0158] Weigh 60% nitric acid (Sigma-Aldrich) to an amount equivalent to 0.25g of pure nitric acid and dilute it with distilled water to obtain 10cc of nitric acid aqueous solution. Add the nitric acid solution dropwise to the cobalt single atom catalyst powder-boehmite mixture and mix thoroughly to obtain a paste of the mixed powder. The cobalt single atom catalyst powder-boehmite-nitric acid mixed paste is fully kneaded and then extruded into noodles of constant thickness (size: 1.5mm) in an extruder. The extrudate thus obtained is fully dried at room temperature and introduced into a heating furnace, where it is heat treated at 150°C for 2 hours in an air atmosphere and then heat treated at 600°C for 2 hours to obtain a shaped cobalt single atom catalyst.

[0159] Comparative Preparation Example 4

[0160] Preparation of powdered cobalt single atom catalyst

[0161] First, 20 g of commercially available silica was dispersed in 200 ml of distilled water, and then 0.144 g of KOH was dissolved therein, followed by stirring for 30 minutes. The pH of the dispersion was controlled to 11 by adding 28 wt % ammonia water (Samchun Chemicals) thereto.

[0162] In another beaker, 5 g of cobalt precursor (Co(NH 3) 6 Cl 3 TCI) was dissolved in 50 ml of distilled water. The cobalt precursor aqueous solution was controlled to have a pH of 11 by adding 28 wt % ammonia water (Samchun Chemicals) thereto.

[0163] Next, the aqueous solution of cobalt precursor is immediately added to the dispersion containing silica and alkali metal, and then stirred at room temperature for 10 minutes. The stirred sample is placed for 5 minutes, and the supernatant thus formed is decanted. 200ml of distilled water is added to the residue, and then stirred again for 10 minutes. The stirred sample is allowed to stand, and the supernatant thus formed is decanted. The residue is vacuum filtered and washed several times with distilled water. Thereafter, the washed filtrate is dried at room temperature and then dried at 125°C. The dried sample is heated to 300°C at a rate of 5°C / min and heat treated at this temperature for 3 hours to prepare a cobalt-loaded single atom catalyst.

[0164] EXAFS analysis

[0165] The EXAFS of the cobalt single atom catalyst and the shaped cobalt single atom catalyst prepared in Preparation Example 3 and Comparative Preparation Examples 1-4 were analyzed, and Figure 2 Give the spectrum.

[0166] It can be seen from the figure that Co foil A strong peak appears near the Co-Co bond of cobalt metal. 3 O 4 and CoO, two peaks were observed: the first peak of Co-O and the second peak of Co-Co In the particles, the oxide forms crystals in which the unit cell structure repeats, which explains the appearance of the second peak.

[0167] At the same time, the cobalt single atom catalyst powder (Comparative Preparation Example 4) and the molded catalyst (Preparation Example 3 and Comparative Preparation Examples 1-3) all show a well-formed first peak, but the second peak is significantly attenuated, indicating that the Co atoms are far away from each other and no bonds are formed between them. Considering the Si-O bond supporting Co, it is believed that this weak peak comes from the Co-Si bond.

[0168] The above analysis results show that the prepared shaped catalyst exists in the form of single atom.

[0169] Catalyst composition analysis

[0170] The compositions of cobalt and potassium in the catalysts prepared in Preparation Example 2 and Comparative Preparation Examples 1 to 4 were analyzed using ICP-AES and are summarized in Table 2 below.

[0171] Table 2

[0172]

[0173]

[0174] The catalyst (Preparation Examples 2 and 3) prepared using the single atom-loaded cobalt catalyst of the silica shaped carrier prepared according to the preparation example is compared with the catalyst prepared in the comparative preparation example. As can be seen from the data of Table 2, the cobalt loading exhibited by the catalyst prepared in Preparation Example 2 is 36% of the cobalt loading in the conventional powdered catalyst (conventional powdered catalyst is conducive to cobalt single atom loading), which is similar to the cobalt loading on the catalyst on the commercially available extruded silica loaded with cobalt. However, when comparing the amount of potassium, the catalyst of Preparation Example 2 still retains a spare space in which cobalt can be loaded. In addition, the cobalt loading in the catalyst prepared according to Preparation Example 3 is similar to the catalyst formed by a mixture of 70% powdered catalyst and binder. All three catalysts are considered to have cobalt occupying most of the sites available for cobalt (that is, cobalt and potassium are loaded on similar sites, so the amount of potassium is significantly reduced).

[0175] Based on the above characteristics, catalysts with similar cobalt contents were compared and observed. In addition, Preparation Examples 2 and 3, which were loaded with cobalt in one step and two steps, respectively, were compared. Potassium that still occupies the active sites that have not yet been loaded with cobalt in the first step of loading is replaced by cobalt in the second step, thereby increasing the active sites that can perform dehydrogenation.

[0176] Experimental Example 1

[0177] In this experimental example, a reaction gas containing a high content of paraffin was dehydrogenated in the presence of the cobalt-supported single atom catalyst prepared in Preparation Example 3 and Comparative Preparation Examples 2-4 to synthesize olefins.

[0178] Dehydrogenation for catalyst evaluation was performed using a 3 / 4 inch quartz tube reactor (3 / 4 inch diameter in the catalyst loading area and 1 / 4 inch diameter in other tube areas). The flow rate of the gas was controlled using a mass flow controller, and the product gas from the reactor was analyzed using an online gas chromatograph (50 m HP-PLOT column).

[0179] The shaped catalyst was crushed to a L / D and D / d ratio suitable for placement in the reactor. Only particles with a size of 16 to 40 mesh were selected. Among them, 6 cc (about 3 g) was weighed and supported with quartz wool in a reaction tube, and then N 2(99.999%, Dacheng Industrial Gas Co., Ltd.) was passed through the tube at a flow rate of 100 cc / min and the temperature was increased from room temperature to 590° C. at a rate of 5° C. / min. Subsequently, the conditions were kept stable for 1 hour, during which the pressure in the reaction tube was reduced to about 0.5 bar using a micro air pump installed at the rear of the reactor.

[0180] In order to dehydrogenate the paraffins, a reaction gas (regas) containing 99.5% propane was introduced into the reactor at a flow rate of 20 cc / min. The composition of the gas in the reactor was analyzed using a FID (flame ionization detector). The results are shown in Figure 3 middle.

[0181] refer to Figure 3 , the catalyst in which cobalt was loaded onto commercially available extruded silica showed low dehydrogenation activity, as expected from the relatively low cobalt loading, whereas the catalyst prepared in Preparation Example 2 had high dehydrogenation activity despite the low cobalt loading. In addition, it was observed that the catalyst prepared in Preparation Example 3 (with an increased cobalt loading level) dehydrogenated at the same level as the powder type catalyst.

[0182] In contrast, both catalysts prepared in the comparative preparations had low conversions (Comparative Preparation 2; formed with a silica binder) or low selectivities (Comparative Preparation 3; formed with an alumina binder), despite cobalt loadings similar to those in the catalyst prepared in Preparation 3.

[0183] As described above, even when exposed to high temperatures (e.g., about 500° C. or higher) during the dehydrogenation of chain alkanes corresponding to olefins, especially light chain alkanes, the single-atom catalyst using the silica-based shaped support according to an embodiment of the present invention is effectively prevented from undergoing aggregation or sintering of cobalt by the action of the alkali metal fixed in the form of a single atom on the surface of the silica-based shaped support, thereby maintaining catalytic activity for a long period of time.

[0184] Furthermore, the catalyst according to an embodiment of the present invention can maintain the central metal cobalt in a single atom form even when a shaped support suitable for commercialization is used, and thus can ensure a dehydrogenation activity comparable to that of a powder type catalyst.

[0185] In particular, when dehydrogenation is performed in the presence of the catalyst according to an embodiment of the present invention, the catalyst according to an embodiment of the present invention can achieve excellent conversion and excellent selectivity to olefins for a feedstock containing a high content of paraffins.

[0186] Therefore, it should be understood that simple modifications and variations of the present invention can be easily used by those skilled in the art, and such modifications or variations can fall within the scope of the present invention.

Claims

1. A method for preparing a cobalt-based shaped single-atom catalyst, the method The following steps are involved: Mixing a silica binder and silica powder for a carrier material in an aqueous medium to prepare a molding paste, wherein the silica powder for a carrier material is amorphous silica; shaping the paste into a silica-based shaped carrier; contacting the silica-based shaped support with an alkali metal salt in an aqueous medium to form an alkali-treated silica-based shaped support, either before or after pH adjustment with a base, wherein at least a portion of the alkali metal ions are electrostatically adsorbed on the surface of the silica-based shaped support; contacting the alkali metal-treated silica-based shaped support with an aqueous solution of a first cobalt precursor to form a first silica-based shaped support containing cobalt and alkali metal, wherein the pH of the aqueous solution of the first cobalt precursor is adjusted by adding a base to the solution, wherein the oxidation number of the first cobalt precursor is 3+, wherein at least a portion of the cobalt ions with an oxidation number of 3+ are electrostatically adsorbed on the alkali metal-treated silica-based shaped support; and heat treating the first cobalt- and alkali-metal-containing silica-based shaped support, Thus, the cobalt with an oxidation number of 2+ and the alkali metal with an oxidation number of 1+ are respectively present in the form of isolated single atoms on the silica-based shaped support, and the cobalt with an oxidation number of 2+ is tetrahedrally coordinated on the three-membered siloxane ring, which is present on the surface of the silica-based shaped support.

2. A method for preparing a cobalt-based shaped single-atom catalyst, the method The following steps are involved: Mixing a silica binder and silica powder for a carrier material in an aqueous medium to prepare a molding paste, wherein the silica powder for a carrier material is amorphous silica; shaping the paste into a silica-based shaped carrier; contacting the silica-based shaped support with an alkali metal salt in an aqueous medium to form an alkali-treated silica-based shaped support, either before or after pH adjustment with a base, wherein at least a portion of the alkali metal ions are electrostatically adsorbed on the surface of the silica-based shaped support; contacting the alkali metal-treated silica-based shaped support with an aqueous solution of a first cobalt precursor to form a first silica-based shaped support containing cobalt and alkali metal, wherein the pH of the aqueous solution of the first cobalt precursor is adjusted by adding a base to the solution, wherein the oxidation number of the first cobalt precursor is 3+, wherein at least a portion of the cobalt ions with an oxidation number of 3+ are electrostatically adsorbed on the alkali metal-treated silica-based shaped support; contacting the first silica-based shaped support containing cobalt and an alkali metal with an aqueous solution of a second cobalt precursor to form a second silica-based shaped support containing cobalt and an alkali metal, wherein the pH of the aqueous solution of the second cobalt precursor is adjusted by adding a base to the solution, the oxidation number of the second cobalt precursor being 3+; heat treating the second cobalt- and alkali-metal-containing silica-based shaped support, Thus, the cobalt with an oxidation number of 2+ and the alkali metal with an oxidation number of 1+ are respectively present in the form of isolated single atoms on the silica-based shaped support, and the cobalt with an oxidation number of 2+ is tetrahedrally coordinated on the three-membered siloxane ring, which is present on the surface of the silica-based shaped support.

3. The method of claim 2, further comprising the step of heat treating the first silica-based shaped support containing cobalt and alkali metals before the step of forming the second silica-based shaped support containing cobalt and alkali metals.

4. The method of claim 1 or 2, wherein the amorphous silicon dioxide comprises wet-process hydrated silicon dioxide.

5. The method according to claim 1 or 2, wherein the silica binder is colloidal silica.

6. The method according to claim 1 or 2, wherein the weight ratio of the silica binder to the silica powder for the carrier material is 1:0.1 to 1:

10.

7. The method according to claim 1 or 2, in, The steps of preparing the molding paste include: preparing (i) a lubricant emulsion containing a silica binder or (ii) an aqueous dispersion containing a silica binder; and The lubricant emulsion containing the silica binder or the aqueous dispersion containing the silica binder is mixed with the silica powder for the carrier material, The lubricant emulsion containing a silica binder or the aqueous dispersion containing a silica binder contains the silica binder in an amount of 10 to 60% by weight.

8. The method according to claim 7, in, The lubricant emulsion containing a silica binder contains a lubricant in an amount of 0.1 to 20% by weight.

9. The method according to claim 1 or 2, in, The silica-based shaped carrier has at least one shape selected from the group consisting of a cylinder, a granule, a pellet, a tablet, a sphere, and a trilobal shape.

10. The method according to claim 1 or 2, wherein the alkali metal is at least one selected from sodium (Na), potassium (K) and cesium (Cs), and The alkali metal salt is at least one selected from the group consisting of hydroxides, nitrates, chlorides, carbonates and sulfates of alkali metals.

11. The method according to claim 1 or 2, wherein the step of forming the alkali metal-treated silica-based shaped support employs the silica-based shaped support in an amount of 1-30 wt % based on the weight of the aqueous medium, and The amount of the alkali metal salt is 0.001-3 wt % based on the weight of the silica-based shaped support in the aqueous medium.

12. The method according to claim 1 or 2, in, In the step of forming the alkali metal treated silica-based shaped support, the base is an ammonium-containing base and is used to adjust the pH to at least 9.

13. The method according to claim 1, in, The first cobalt precursor in the aqueous solution is a precursor of a complex ion containing cobalt (Co(III)) having an oxidation number of 3+, and the first cobalt precursor in the aqueous solution is contained at a concentration of 0.1 to 20 wt %.

14. The method according to claim 1 or 2, wherein in the step of forming the first cobalt- and alkali-metal-containing silica-based shaped support, the cobalt precursor is used in an amount of 1-100 wt% based on the weight of the silica shaped support.

15. The method according to claim 1 or 2, in, The heat treatment is performed at a temperature of 250° C. to 700° C. in an oxygen-containing atmosphere.

16. A dehydrogenation catalyst comprising: a silica-based shaped carrier having an alkali metal adsorbed thereon, the silica-based shaped carrier consisting of a silica binder and an amorphous silica powder; and Cobalt, which is supported as an active metal on the silica-based shaped support; The dehydrogenation catalyst is a cobalt-based shaped single-atom catalyst, in which cobalt with an oxidation number of 2+ and alkali metal with an oxidation number of 1+ are respectively present in the form of isolated single atoms on the silica-based shaped carrier, and the cobalt with an oxidation number of 2+ is tetrahedrally coordinated on the ternary siloxane ring, and the ternary siloxane ring is present on the surface of the silica-based shaped carrier. 17 . The dehydrogenation catalyst according to claim 16 , wherein the cobalt and the alkali metal are contained in contents of 0.5-3 wt % and 0.00001-1 wt %, respectively, and a weight ratio of cobalt (Co) / alkali metal is in the range of 1 to 1000.

18. A method for preparing olefins, the method comprising: The following steps are involved: Providing a feedstock containing light paraffins; Dehydrogenating the feedstock in the presence of the catalyst of claim 16 or 17 at a temperature of 500°C to 700°C and a pressure of 0.3 to 2 bar; as well as Olefins corresponding to the light paraffins are recovered from the dehydrogenated product.

19. The method according to claim 18, in, The feedstock contains at least 50% by volume of light paraffins having 2 to 5 carbon atoms.

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