KR20240024007A - Catalyst for reverse water gas shift reaction comprising gas-permeable amorphous shell formed from copper-based strong metal-support interaction - Google Patents

Abstract

The present invention relates to a catalyst for reverse water gas reaction comprising a gas-permeable amorphous shell formed by strong copper-based metal-support attraction. The present inventors synthesized a copper-ceria solid solution and then adjusted the surface defect sites of the solid solution to prepare a catalyst in which an amorphous and gas-permeable shell structure was formed on copper particles eluted with enhanced surface defect sites. . When using the catalyst preparation method according to the present invention, it is possible to synthesize a catalyst containing a structure consisting only of very small-sized CuO particles fixed in the surface shell and Cu sites inserted into the CeO2 lattice structure, and use this in the RWGS reaction. When used, it exhibits superior reactivity at low temperatures, high reactivity, and durability compared to existing noble metal catalysts. In addition, even when the catalyst of the present invention is supported on a monolith and the RWGS reaction is performed at a bench scale, it shows the same high reactivity, CO ₂ conversion rate, and durability as at the laboratory scale, so it is expected to be applicable to actual processes. It is expected.

Description

Catalyst for reverse water gas reaction comprising a gas-permeable amorphous shell formed by copper-based strong metal-support attraction

The present invention relates to a catalyst for reverse water gas reaction comprising a gas-permeable amorphous shell formed by strong copper-based metal-support attraction.

In the case of the reverse water gas shift reaction (RWGS reaction), reaction at high temperature is required to achieve high carbon dioxide conversion rate and carbon monoxide selectivity. In the above reaction, which produces carbon monoxide and water by injecting carbon dioxide and hydrogen, a side reaction to methane occurs predominantly at low temperatures, and the reaction site collapses in a high reducing atmosphere at high temperatures. Therefore, it is difficult to achieve high reactivity and high selectivity to carbon monoxide at the same time. Therefore, in order to be used in an actual process, the reaction site must have high temperature durability and durability in a reducing atmosphere, or a reaction that simultaneously achieves high reactivity and selectivity at low temperature. It is essential to make this happen.

Controlling the interface between metal nanoparticles and oxide supports has been actively studied to develop heterogeneous catalysts that are effective in various surface reactions. Small nanoparticles, typically ≤10 nm in size, were dispersed in the support, but these nanoparticles easily sintered into larger particles during the reaction. To solve this durability problem, strong metal-support interaction (SMSI) has received much attention because it can often form an oxide shell on metal nanoparticles, preventing sintering.

The oxide shell is formed when surface oxygen species are activated. After extracting mobile surface oxygen species, the resulting sub-stoichiometric metal oxide species migrate to the metal nanoparticles to form an overlayer. Typically, this process takes place in a high temperature reducing environment. However, metal nanoparticles are often sintered before the shell is formed. Additionally, the shell is generally so crystalline that it is not permeable to gases and thus loses catalytic activity.

However, the gas-permeable shell structure of small nanoparticles was observed only for noble metal nanoparticles, which may be because oxygen species can be efficiently activated only at the interface between noble metal nanoparticles and metal oxide support. Since non-noble metal catalysts with an amorphous shell structure may be particularly promising for large-scale industrial processes, there is a need to develop non-noble metal catalysts with an amorphous shell structure.

Republic of Korea Patent No. 10-1682117 (registration date: November 28, 2016)

The present inventors made extensive research efforts to develop a non-precious metal catalyst with an amorphous shell structure that can be used in large-scale industrial processes. As a result, when Cu-doped CeO ₂ is used, the Cu nanoparticles deposited on CeO ₂ can form an amorphous shell with gas permeability without sintering, and the catalyst prepared in this way has excellent reactivity and durability in the reverse gas shift reaction. was confirmed and the present invention was completed.

Therefore, the purpose of the present invention is to provide a composite oxide catalyst containing a metal oxide support such as CeO ₂ and copper. In particular, according to the present invention, a complex oxide catalyst that shows high reactivity and selectivity while satisfying favorable temperature conditions in large-scale industrial processes can be provided.

Another object of the present invention is to provide a catalyst ink composition containing the complex oxide catalyst.

Another object of the present invention is to provide a method for producing a complex oxide catalyst.

However, the purpose of the present invention is not limited to the above-described content, and will become clearer from the content described in the following specification.

According to one embodiment of the present invention, the present invention provides a complex oxide catalyst including a metal oxide support and copper.

In this case, in one embodiment of the present invention, the metal oxide may be TiO ₂ or CeO ₂ .

Meanwhile, in one embodiment of the present invention, the copper exists as particles on the surface of the catalyst.

In one embodiment of the present invention, the particles are nanoparticles.

In one embodiment of the invention, the particles have a size of 1 to 150 nm, 1 to 100 nm, 1 to 80 nm, 1 to 50 nm, 1 to 40 nm, 1 to 30 nm, 1 to 20 nm, or 1 to 20 nm. It has an average particle diameter of 10 nm, but is not limited thereto.

In one embodiment of the present invention, the copper in the particles includes copper oxide. The copper oxide is Cu ₂ O, CuO, or Cu ₂ O ₃ .

In one embodiment of the present invention, the particles are encapsulated with a shell made of the metal oxide support. In one embodiment of the invention, the shell exhibits gas permeability.

In one embodiment of the present invention, the copper may exist in a CeO ₂ lattice structure.

In one embodiment of the present invention, the complex oxide is used for Reverse Water Gas Shift (RWGS), but is not limited thereto.

According to another aspect of the present invention, the present invention provides a catalyst composition including the complex oxide catalyst.

In one embodiment of the present invention, the catalyst composition further includes a stabilizer, an accelerator, or a binder.

The stabilizer is polyvinylpyrrolidone (PVP), polyvinylalcohol (PVA), or cetyltrimethyl ammonium bromide (CTAB), and may be included without limitation as long as it is a stabilizer for a catalyst known in the art (Ott, L. S., & Finke , R. G. (2007). Transition-metal nanocluster stabilization for catalysis: a critical review of ranking methods and putative stabilizers. Coordination Chemistry Reviews, 251(9-10), 1075-1100.

The promoter is a reducible transition metal oxide, such as La ₂ O ₃ , or MoOx; an oxygen-friendly metal such as Re (Rhenium); Or it may be an alkali metal, such as Li (Lithium), Na (Sodium), Na ₂ O, K (Potassium), K ₂ O, or KO _x , but is not necessarily limited thereto.

The binder may be an inorganic binder or an organic binder, but is not necessarily limited thereto. For example, the inorganic binder can be clay, water glass, silica, titania, or zirconia. As another example, the organic binder may be polyvinyl alcohol, polyurethane, acrylic resin, melamine resin, or epoxy resin. For another example, the binder may be silica, siloxane polymer, silicone resin, aluminum phosphate, acrylic binder, zeolite, rare earth oxide, glass fine powder, or polymer. The rare earth may be Sc, Y, or La.

In one embodiment of the present invention, the catalyst composition includes aluminum oxide particles. The aluminum oxide particles are used as a binder.

In one embodiment of the present invention, the catalyst composition contains aluminum oxide particles in an amount of 50 to 80% (w/w), 60 to 80% (w/w), 65 to 80% (w/w), 70 to 80% (w/w), 72 to 80% (w/w), or 75 to 80% (w/w). The aluminum oxide particles have an average diameter of 20 to 50 μm.

In one embodiment of the present invention, the catalyst composition includes sodium oxide.

In one embodiment of the present invention, the catalyst composition may be a catalyst ink composition and may be used to coat a specific article to provide a catalyst function.

According to another aspect of the present invention, the present invention provides a reverse water gas shift (RWGS) method comprising contacting the catalyst composition according to an embodiment with a mixed gas containing carbon dioxide gas and hydrogen gas. Provides a method for selectively producing carbon monoxide through reaction.

In one embodiment of the present invention, the mixed gas includes nitrogen gas, carbon dioxide gas, and hydrogen gas.

In one embodiment of the present invention, the volume ratio of carbon dioxide gas and hydrogen gas is 1:1 to 1:4.

In another embodiment of the present invention, the volume ratio of carbon dioxide gas and hydrogen gas is 1:1, 1:2, 1:3, or 1:4.

In another embodiment of the present invention, the volume ratio of carbon dioxide gas and hydrogen gas is 1:3.

In another embodiment of the present invention, the volume ratio of carbon dioxide gas and hydrogen gas is 1:1.

According to another aspect of the present invention, the present invention provides a method for producing a complex oxide catalyst comprising the following steps:

(a) dissolving the metal oxide precursor and copper oxide in water;

(b) adjusting the pH of the solution to 8 to 9 and stirring it to precipitate it;

(c) drying the precipitate to prepare a solid solution;

(d) calcining the solid solution; and

(e) reducing the calcined solid solution under hydrogen conditions.

In one embodiment of the present invention, steps (a) and (b) are steps in which co-precipitation is performed.

In one embodiment of the present invention, the metal oxide is cerium oxide or titanium oxide. The cerium oxide is CeO ₂ . The titanium oxide is TiO ₂ .

In one embodiment of the present invention, the copper oxide is dissolved in an amount of 3 mg to 31 mg based on 90 mL of water, but is not limited thereto. For example, the copper oxide may be dissolved in amounts of 3 mg, 5 mg, 14 mg, 23 mg, and 31 mg based on 90 mL of water, or the content (mg) between the above values may be dissolved.

In one embodiment of the present invention, the stirring in step (b) is performed for 3 to 10 hours.

In one embodiment of the present invention, the precipitate in step (c) is filtered before drying.

In one embodiment of the present invention, the drying in step (c) is performed for 6 hours to 12 hours, 6 hours to 10 hours, 6 hours to 8 hours, 8 hours to 12 hours, or 8 hours to 10 hours. will be.

In one embodiment of the present invention, the calcination step (d) is a step of oxidizing the metal oxide support and copper.

In one embodiment of the present invention, the firing in step (d) is performed at 400 to 600°C, 400 to 550°C, 400 to 500°C, 450 to 600°C, 450 to 550°C, 450 to 500°C, 500 to 600°C. It is carried out at ℃, or 500 to 550 ℃, but is not limited thereto.

In one embodiment of the present invention, the firing in step (d) is 2 hours to 6 hours, 2 hours to 5 hours, 2 hours to 4 hours, 2 hours to 3 hours, 3 hours to 6 hours, 3 hours to It is performed for 5 hours, or 3 to 4 hours, but is not limited thereto.

In one embodiment of the present invention, the reduction step (e) is a step in which the metal oxide forms a shell structure on the surface of the copper particle.

The reduction step may be performed together with heat treatment.

The reduction heat treatment is 200°C to 700°C, 200°C to 600°C, 200°C to 500°C, 200°C to 400°C, 200°C to 300°C, 300°C to 700°C, 300°C to 600°C, 300°C to 500°C. °C, 300 °C to 400 °C, 400 °C to 700 °C, 400 °C to 600 °C, 400 °C to 500 °C, 500 °C to 700 °C Performed under hydrogen gas and inert gas at 500 °C to 600 °C or 600 °C to 700 °C do.

In another embodiment of the present invention, the reduction heat treatment is performed at 500°C under hydrogen gas and an inert gas.

In one embodiment of the present invention, the volume percentage of the hydrogen gas relative to the inert gas is 5% (v/v) to 20% (v/v).

In another embodiment of the present invention, the volume percentage of the hydrogen gas relative to the inert gas is 5% (v/v) to 20% (v/v), 5% (v/v) to 15% (v) /v), 5% (v/v) to 10% (v/v), 10% (v/v) to 20% (v/v), 10% (v/v) to 15% (v/v) ), or 15% (v/v) to 20% (v/v).

In one specific embodiment of the present invention, the volume percentage of the hydrogen gas relative to the inert gas is 10% (v/v).

After synthesizing a copper-ceria solid solution, the researchers manufactured a catalyst in which an amorphous and gas-permeable shell structure was formed on copper particles eluted with enhanced surface defect sites by controlling the surface defect sites of the solid solution. . When using the catalyst preparation method according to the present invention, it is possible to synthesize a catalyst containing a structure consisting only of very small-sized CuO particles fixed in the surface shell and Cu sites inserted into the CeO ₂ lattice structure, which can be used in the RWGS reaction. When used, it exhibits superior reactivity at low temperatures, high reactivity, and durability compared to existing noble metal catalysts. In addition, even when the catalyst of the present invention is supported on a monolith and the RWGS reaction is performed at a bench scale, it shows the same high reactivity, CO ₂ conversion rate, and durability as at the laboratory scale, so it is expected to be applicable to actual processes. It is expected.

Figure 1 is a schematic diagram of a complex oxide catalyst according to an embodiment of the present invention.
Figure 2 is a diagram for explaining the hydrogenation mechanism of CO ₂ according to an embodiment of the present invention.
Figure 3 shows the results of measuring surface oxygen mobility in a ceria shell doped with Cu, Ni, Co, and Fe. Upon Cu doping, a large reduction peak appeared at low temperature, indicating that surface oxygen species can be easily activated by reduction. 23CC, 23NiC, 23CoC, and 23FeC represent 23 atomic% of CeO ₂ doped with Cu, Ni, Co, and Fe, respectively.
Figure 4 shows the results of X-ray diffraction (XRD) and high-resolution X-ray scattering (HR-XRS) in each step of synthesizing the complex oxide catalyst according to an embodiment of the present invention and a schematic diagram of the shell structure. (a) shows the XRD and HR-XRS results of CC and CeO ₂ in solid solution state. (b) Results obtained after firing in air at 500°C for 4 hours. (c) Results obtained after reduction with 10% H ₂ (balance N ₂ ) for 2 hours at 500°C. (d) XRD and HR-XRS results at 23C/C after calcination and further reduction. In this case, 3CC, 5CC, 14CC, 23CC, and 31CC indicate that 3, 5, 14, 23, and 31 at% (atomic weight percent) of copper was doped, respectively.
Figure 5 is a diagram showing the results of a long-term durability test of a complex oxide catalyst according to an embodiment of the present invention at 600°C for 150 hours. The reactions of 23CC and 23C/C were carried out at a gas composition of CO ₂ :H ₂ = 1:1 and WHSV = 48000 mL/g _cat ·h.
Figure 6 is a diagram showing the characteristics of surface oxygen species in a complex oxide catalyst according to an embodiment of the present invention. (a) H ₂ -TPR results and (b) Raman spectra obtained before reduction, (c) H ₂ -TPR results and (d) Raman spectra obtained after reduction for CC catalyst, 23C/C catalyst and CeO ₂ support.
Figure 7 is a diagram showing a TEM image showing the amorphous shell of Cu nanoparticles. (a) TEM image of 23CC, (b) enlarged TEM image of the particle circled in yellow in (a), (c) corresponding EDS mapping of Cu and Ce. Images were collected after durability testing for 150 hours at 600°C in a gas composition of CO ₂ :H ₂ = 1:1. Acquired simultaneously by bright field (BF), dark field (DF) and secondary electron (SE) modes.
Figure 8 is a graph showing hydrogenation activity according to an embodiment of the present invention. In particular, Figure 8 shows CO ₂ conversion and _CO selectivity for (a) 23CC and (b) 23C/C performed at various CO 2 :H ₂ ratios. (c) CC catalyst, (d) 23C/C, _CO2 conversion and CO2 selectivity over _CeO2 and CuO. In this case, the reaction was carried out at a gas composition of CO ₂ :H ₂ :N ₂ = 1:1:2 and WHSV = 48000 mL/g _cat ·h.
Figure 9 is a diagram showing the characterization of surface intermediates of 23CC and 23C/C according to an embodiment of the present invention. (a) and (b) are in situ DRIFT spectra collected at a gas composition of CO ₂ :H ₂ = 1:3 for 23CC and 23C/C. in this case. Gas injection started at 25°C, increased to 300°C at 5°C/min, and then maintained at 300°C for 30 minutes. Spectra were acquired every minute. (c) is the in situ DRIFT spectrum collected during gas control for 23CC. In this case, the catalyst was heated to 300°C in 100% Ar and then the gas was changed to 10% CO ₂ /Ar (grey). Gaseous CO ₂ was removed and then the gas was changed to 10% H ₂ /Ar (red). The temperature was then increased to 400°C (blue).
Figure 10 is a graph showing surface oxygen species characterization of 23CC and 23C/C according to an embodiment of the present invention. In this case, (a) is the NAP-XPS result of O 1 second for 23CC and 23C/C obtained at room temperature, 150°C, 250°C, 350°C, and 450°C, and the position and area ratio of each peak are indicated. The total pressure is 1 Torr, and the gas composition is CO ₂ :H ₂ = 1:3. (b) and (c) are graphs showing changes in the oxygen peak ratio of O _ads and O _w as temperature increases, respectively.
Figure 11 is a diagram showing the bench scale performance of 23CC according to an embodiment of the present invention. (a) is an image of a honeycomb monolith and a bench reactor, and the monolith was coated with a 23CC catalyst. In the bench reactor, the reaction occurred in the left furnace and the gas inlet was preheated in the right furnace. (b) is the CO ₂ hydrogenation performance of 23CC in a bench reactor for three repeated reactions, and (c) is a graph comparing the CO production rates of 23CC for a laboratory scale reactor and a bench reactor. Numbers in the legend represent WHSV at laboratory scale. The WHSV for these conditions was estimated to be 48507 mL/g _cat ·h, which was similar to the conditions used in the laboratory scale reactor (48000 mL/g _cat ·h).

Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various different forms. The examples below make the disclosure of the present invention complete, and provide those of ordinary skill in the art with the scope of the invention. It is provided to provide complete information. Additionally, for convenience of explanation, the sizes of components may be exaggerated or reduced in the drawings.

However, the following examples are provided to enable those skilled in the art to fully understand the present invention, and may be modified into various other forms, and the scope of the present invention is limited to the examples described below. It doesn't work.

Meanwhile, throughout the specification, when a part is said to “include” a certain component, this means that it does not exclude other components but may further include other components, unless specifically stated to the contrary.

The above-mentioned purpose, features and advantages will become clearer through the following detailed description in relation to the attached drawings, and accordingly, those skilled in the art in the technical field to which the invention pertains will be able to easily implement the technical idea of the invention. .

In this specification, the term “catalytic complex” may also be used for a complex comprising a support and a catalytic amount of metal partially or fully deposited on the support. The term catalyst complex may be used interchangeably with catalyst. The catalyst complex may be a supported metal catalyst.

Additionally, in this specification, the term “metal-support interaction” refers to the direct influence of the support on the chemisorption and catalytic properties of the supported metal. The metal-support interaction of the present invention is specifically SMSI.

In addition, the term "SMSI (strong metal-support interaction)" in this specification is meant to encompass changes in chemical adsorption properties and catalytic activity that occur when reducing metal supported on a support at high temperature. . Specifically, in the present invention, SMSI is meant to include the reversible surface migration phenomenon of partially reduced oxide species.

As used herein, the term “solid solution” refers to a solution in which one or more solutes in a solvent are mixed and exist in a solid state. Specifically, in the present invention, the solid solution may be a solvent in which a copper solute exists in a ceria solvent.

In this specification, the term "Reverse Water Gas Shift (RWGS) reaction" refers to carbon dioxide (CO ₂ ) and hydrogen (H ₂ ) as reactants, and carbon monoxide (CO) and water (H ₂ O) as products. refers to an endothermic reaction that produces carbon monoxide, water, and methane as products. Products may be selected depending on thermodynamic equilibrium. The main reaction of the reverse water gas conversion reaction is CO ₂ (g) + H ₂ (g) ↔ CO (g) + H ₂ O (g), and a methanation reaction occurs as a side reaction.

As used herein, the term “calcination” means heating to high temperatures in air or oxygen. In the present invention, heat treatment, that is, calcination, was performed to oxidize the catalyst through air at high temperature.

The inventors of the present invention discovered that when Cu nanoparticles are uniformly present on the surface of the CuCeO _x solid solution, an amorphous shell can be formed on the Cu nanoparticles upon hydrogenation of CO ₂ . On the other hand, nanoparticles deposited on bare CeO ₂ did not form such an amorphous shell. In addition, the conventional Cu/CeO ₂ catalyst is formed at a temperature near ~600°C, which reaches the thermochemically possible conversion limit of CO ₂ , but the catalyst with the amorphous shell formed as described above is capable of CO ₂ activation and H ₂ It was found that the outflow was intensified and the _CO2 conversion limit was reached at a much lower temperature, around ~350°C. The amorphous shell of the present invention maintained high reactivity while preserving Cu nanoparticles. Additionally, it was found that these non-precious metal catalysts can be used in large-scale processes.

Hereinafter, with reference to FIG. 1, a complex oxide catalyst according to an embodiment of the present invention will be described.

Referring to FIG. 1, the complex oxide catalyst according to an embodiment of the present invention is a metal oxide solid solution containing a metal oxide support 100 and copper, wherein the copper is formed as copper nanoparticles 200 on the surface of the metal oxide support. This metal oxide solid solution has oxygen defect sites (300, O _v ), and an amorphous shell 400 is formed on the surface of the copper nanoparticles to encapsulate the surface of the copper nanoparticles.

The metal oxide support 100 may be cerium oxide or titanium oxide, and the copper nanoparticles 200 on the surface may preferably have a size of 10 nm or less.

The amorphous shell 400 is preferably a metal oxide support encapsulating copper nanoparticles on the surface, and may be induced by formate, an intermediate in the reverse water gas shift reaction. Additionally, the amorphous shell 400 may exhibit gas permeability.

Additionally, copper nanoparticles 200 may exist within the lattice structure of the metal oxide support.

Hereinafter, with reference to FIG. 2, the hydrogenation mechanism of carbon dioxide according to an embodiment of the present invention will be described.

First, in Figure 2 (a), when carbon dioxide is adsorbed to the oxygen defect site (O _v ) of a metal oxide support, for example, cerium oxide or titanium oxide, it reacts with OH on the adjacent surface as shown in Figure 2 (b) to form bicarbonate. (Bicarbonate) is formed on the surface of the metal oxide support. In this case, H ₂ molecules diffuse and dissociate on the copper nanoparticles 200 on the surface of the metal oxide support 100. At this time, the dissociated H atoms move on the amorphous shell 400. (Figure 2(c))

Afterwards, referring to (d) of FIG. 2, formates are formed by the dissociated hydrogen atoms supplied by moving through the amorphous shell 400, and as shown in (e) of FIG. 2, formates are formed. It is converted to carbon monoxide and separated from the metal oxide support. Finally, hydrogen is supplied again to OH at the site where carbon monoxide was separated, forming water, which leaves the metal oxide support and forms an oxygen defect site (O _v ) again.

Through repetition of the cycle of (a) to (f) of FIG. 2, the reverse water gas conversion reaction continues to occur.

Hereinafter, an example of a complex oxide catalyst according to an embodiment of the present invention will be described.

Example

Throughout this specification, “%” used to indicate the concentration of a specific substance means (weight/volume)% for solid/solid, (weight/volume)% for solid/liquid, and Liquid/liquid may mean (volume/volume)%.

Experimental materials and experimental methods

Catalyst Syntheses

Cu-doped CeO ₂ catalyst, denoted as xCC (x represents atomic percent of Cu), was synthesized by the co- _{precipitation} method. 4.5 g of Ce(NO ₃ ) ₃ ·6H ₂ O (99.99%, Kanto chemical) and an appropriate amount of Cu(NO ₃ ) ₂ ·3H 2 O (≥98%, Sigma-Aldrich) were dissolved in 90 mL of deionized water. This solution was stirred for 30 minutes, and ammonia water (30%, Deoksan) was added dropwise until the pH reached 8.5. After stirring the solution for more than 4 hours, the color changed to dark green. This green slurry was filtered, washed with deionized water and dried at 80°C overnight. The dried sample was finely ground to make a fine powder and then calcined in air at 500°C for 4 hours. Ni, Co and Fe-doped CeO ₂ catalysts also produced Ni(NO ₃ ) ₂ ·6H ₂ O, Co(NO ₃ ) ₂ ·6H ₂ O and Fe(NO ₃ ) ₃ ·9H ₂ O (≥99%, Sigma- Aldrich) was synthesized using the same method as a metal precursor.

As a control sample, Cu/CeO ₂ containing 23 atomic% Cu, expressed as 23C/C, was synthesized by a wet-impregnation method. The bare CeO ₂ support was synthesized using the same method without using Cu precursor. CeO ₂ was dispersed in deionized water, and an aqueous solution containing an appropriate amount of CuCl ₂ (≥99.99%, Sigma-Aldrich) was added dropwise. The final solution was vigorously stirred, dried at 80°C overnight, ground well, and then heat-treated (calcined) in air at 500°C for 4 hours in a furnace.

C.O. ₂ Hydrogenation (CO ₂ Hydrogenation)

CO ₂ hydrogenation was performed in a U-shaped quartz glass fixed-bed reactor loaded with 50 mg of catalyst. Reduction pre-treatment was performed in 10% H ₂ (N ₂ balance) at 500°C for 2 hours. All reactions were carried out at atmospheric pressure with various CO ₂ :H ₂ ratios. N ₂ flowed with the calibration gas at a flow rate of 20 sccm. The total flow rate was 40 sccm and the weight hourly space velocity (WHSV) was 48,000 mL/gcat·h. The gaseous products were analyzed using an online gas chromatograph (Younglin GC 6500) equipped with a packed Carboxen 1000 column and a thermal conductivity detector (TCD). For the bench-scale reaction, a catalyst ink consisting of 35% by weight of catalyst, 3% by weight of binder (Disperal P2, Sasol), and the balance of deionized water was prepared after ball milling 30g of 23CC. Using this ink, 23CC catalyst was coated on a honeycomb monolith (1 inch in diameter, 1 inch in height) at a catalyst dosage of 125 g/L. The monolith was dried in a convection oven at 120°C for 4 hours and annealed at 500°C for 4 hours in air. This monolith was placed in the reactor, and then gases (CO ₂ 325 sccm, H ₂ 325 sccm, N ₂ 650 sccm) were injected into the reactor. The inlet gas was introduced through a preheated furnace to avoid temperature drop.

In the present specification, in the synthesis method, the catalyst in the state after drying at 80°C for 8 hours and before heat treatment is Dry, the catalyst in the state after heat treatment and before reduction treatment is Oxi or Oxide, and the catalyst in the state after reduction treatment is Red, or It is marked as Reduced.

Characterizations

TEM (Hitachi HF 5000) images in BF, DF, and SE modes were obtained to investigate the exact morphology of the catalyst at 200 kV. EDS mapping images were also obtained with the same equipment. The crystal structure of the catalyst was investigated using powder XRD (SmartLab, RIGAKU). The peak shift of the XRD pattern was monitored by HR-XRS at the 8D beamline at Pohang Light Source (PLS). H ₂ -TPR was performed on a BELCAT II (MicrotracBEL) equipped with a TCD. Samples were pretreated with Ar at 150 °C for 1 h and then the temperature was increased to 800 °C at a ramping rate of 10 °C/min. DRIFTS (Nicolet iS-50, Thermo Scientific) was performed with a ZnSe window. 20 mg of catalyst reduced at 500°C for 2 hours was mixed well with 180 mg of KBr powder and placed in a DRIFTS sample cup. After pretreatment with Ar at 100°C for 30 min, a gas mixture (4% CO ₂ , 12% H2, balance Ar) was flowed and the temperature was increased to 300°C at a ramp rate of 5°C/min and maintained at 300°C for 30 min. maintained. TPSR was performed on a BELCAT II using a mass spectrometer (BELMASS; MicrotracBEL). 50 mg of the catalyst reduced at 500°C for 2 hours was pretreated with Ar at 150°C for 1 hour, and then the gas mixture (4% CO ₂ , 4% H ₂ , balance Ar) was heated to 600°C at a ramping rate of 10°C/min. Flowed to ℃. Raman spectra were collected by a FT-Raman spectrometer (Bruker) using a beam at 514 nm. In situ Raman spectra were obtained with the same equipment using a gas mixture (4% CO ₂ , 4% H ₂ , balance Ar) at a ramping rate of 20°C/min.

Example 1: Formation of amorphous shell of Cu nanoparticles

In the case of reducible metal oxides such as CeO ₂ and TiO ₂ , surface oxygen mobility can be improved by doping heteroatoms. Doping with transition metals such as Ni, Co and Fe resulted in improved surface oxygen transport. Here, CeO ₂ doped with a transition metal was prepared by the coprecipitation method described in the experimental method above. Surface redox properties were investigated by H ₂ temperature-programmed reduction (H ₂ -TPR).

As shown in Figure 3, a large reduction peak appeared at the lowest temperature when doped with Cu among Cu, Ni, Co, and Fe, indicating that surface oxygen species can be easily activated by reduction.

This Cu-doped CeO ₂ was prepared as a solid solution with various Cu contents and was expressed as xCC (x: 3, 5, 14, 23, 31), where x represents the atomic percent of Cu. The results are shown in Figure 4.

As shown in Figure 4 (a), when these CC materials were examined by X-ray diffraction (XRD) and high-resolution X-ray scattering (HR-XRS) without calcination or reduction, ceria (CeO ₂ It can be seen that only the peak of ) is observed. As Cu content increased, the peak shift became larger. Even 31 atomic% of Cu was able to form a solid solution with a CeO ₂ crystal structure.

These CC materials were calcined in air and then reduced in H ₂ at 500ºC. As shown in Figure 4 (b), even though the Cu content increased after firing, the CeO ₂ (111) peak moved back to its original position.

After reduction, as the amorphous shell 400 was formed, as shown in (c) of FIG. 4, a small CuO or Cu peak appeared at 40 CC, but no Cu peak appeared when the Cu content was 23 CC.

On the other hand, bare CeO ₂ was first prepared, and then Cu (23 atomic%) was deposited on CeO ₂ by a wet impregnation method. This material was labeled 23C/C.

As shown in Figure 4 (d), when 23C/C was calcined and reduced under the same conditions, a very large and sharp CuO peak appeared in XRD. When this was reduced, a very large Cu peak appeared, meaning that large bulk Cu particles were formed on the surface.

That is, in the case of the catalyst of the present invention, it can be confirmed through the above XRD that copper particles are very uniformly mixed with CeO ₂ . Looking at (a) of Figure 4, no peak for copper is visible, which means that copper is mainly well mixed into the CeO ₂ lattice structure. This is also explained by the shift of the Ce (111) peak in the dry XRD results. Looking at (b) of FIG. 4, when firing was performed in air at 500°C for 4 hours, small copper particles were separated and separated to the surface, and in this process, the CeO ₂ (111) peak moved again. In the case of 31CC, a peak was observed in XRD because large copper particles were exposed on the surface. Looking at (c) of Figure 4, in the case of 23CC, the peak was not revealed even after reduction, and in the case of 31CC, the peak for copper oxide changed to a peak for copper. In other words, it can be seen that the Cu nanoparticles are uniformly present in the vicinity of 23CC. That is, according to the experiment, it was found that Cu nanoparticles existed most uniformly at 14 CC or more and 31 CC or less, preferably 23 CC.

Among all catalysts, the catalyst synthesized by our research team showed only peaks for very small copper particles. On the other hand, in the case of the control C/C catalyst synthesized similarly to previous studies (synthesis method: copper supported on CeO ₂ ), the concentration was very large even though the same amount of copper was used. In the case of this research team, it was possible to synthesize a catalyst with uniformly small particles as shown above because it was synthesized by a method of eluting very small copper particles on the surface.

Figure 5 shows the results of CO ₂ hydrogenation using 23CC and 23C/C at 600ºC for 90 hours. As shown in Figure 5, 23CC showed higher CO ₂ conversion rate and better durability than 23C/C.

Surface reducibility was investigated by H ₂ -TPR for various Cu contents after calcination at 500ºC.

The results are shown in Figure 6.

As shown in Figure 6 (a), three reduction peaks (α, β and γ) appeared in the H ₂ -TPR results. Peak α at ~190ºC is assigned to the reduction of small CuOx clusters, peak β at ~210ºC is assigned to the reduction of surface lattice oxygen next to Cu sites in Cu-Ce solid solution, and peak γ at ≥ 400ºC by bulk Assigned to reduction of CuOx species. The 23C/C catalyst exhibits peak γ, while the CC catalyst has only peaks α and β. Depending on the Cu content, the peak positions and areas varied; 23CC showed a decrease peak at the lowest temperature with a large amount of H ₂ consumption.

H ₂ -TPR was performed again after reducing the CC catalyst under H ₂ at 500ºC for 2 hours. As shown in Figure 6(c), 23CC showed a large reduction peak at ~230 ºC, indicating that surface oxygen was still being extracted, while 23C/C showed almost no reduction peak. The BET surface areas of 23CC and 23C/C obtained after reduction were similar, with values of 32.3 m ² /g and 25.3 m ² /g, respectively.

Looking at the H ₂ -TPR results in (a) of Figure 6, it can be seen that as the amount of copper doping increases, a peak is formed at a very relatively low temperature compared to the existing CeO ₂ . As shown in (a) of Figure 7, in the case of CC catalysts according to the present invention, the peak ended below 200°C. α, β, and γ peaks appear. In the case of the α peak, it is a reduction peak for _CuO , the γ peak, which appears only in the control catalyst, is a reduction peak for large CuO. Through the peak that appeared only in the control group, it was confirmed again that nano-sized copper nanoparticles could not be synthesized through catalyst synthesis through support. Figure 6(c) shows the results of re-measurement of H ₂ -TPR after reduction of the catalyst at 500°C. Since the reduction was performed once, the oxygen species were already consumed to some extent and the size of the peak decreased, but the position of the peak did not change significantly. This means that the size of the copper particles present on the surface did not increase, and that the copper particles existed uniformly even after reduction.

Additionally, Raman spectroscopy was performed on CC and 23C/C to investigate surface oxygen vacancy.

As shown in Figure 6 (b), the peak at 465 cm ^-1 represents the octahedrally symmetrical vibration mode (F _2g ) and the peak at 600 cm ^-1 represents the defect-induced mode of ceria. , D) occurs. To compare the amount of surface oxygen vacancy in various samples, the ratio of peak areas (I _D /I _F2g ) was estimated. As a result, all CCs showed much higher values than 23C/C or bare ceria.

Raman spectra were obtained again after reduction at 500 °C.

As shown in Figure 6(d), the I _D /I _F2g ratio decreased significantly after reduction, but CC still retained a significant amount of defect sites, unlike 23C/C. The surface oxygen of CC could be removed much more easily, and CC clearly had more surface defect sites, leading to shell formation.

Figures 6 (b) and (d) are Raman spectra results for confirming surface oxygen defect sites. The F peak is a peak that appears as a reference in CeO ₂ , and the D peak is a peak that appears due to surface oxygen defect sites in CeO ₂ . By comparing the intensities of the F peak and D peak, the concentration of surface oxygen defect sites can be compared. Looking at (d) of Figure 6, as can be seen from the oxide results, when doped with copper (3CC I _D /I _F = 0.20; 5CC I _D /I _F = 0.38; 14CC I _D /I _F = 1.23; 23CC I _D /I _F = 1.75; and 31CC I _D /I _F = 1.81) Very large I _D /I _F value even compared to a typical CeO ₂ carrier (I _D /I _F = 2.0 × 10 ^-2 ) can confirm. If you check the results of the reduced sample after reduction, you can see that the surface oxygen defect sites have been greatly reduced, which proves that the oxygen defect sites act as a very important mediator in the formation of the shell.

Meanwhile, the catalyst obtained after 150 hours at 600ºC for 23CC, in which Cu nanoparticles were observed most uniformly and the amorphous shell was well formed, was examined using bright field (BF), dark field (DF), and secondary electron ( It was investigated by transmission electron microscopy (TEM) using secondary electron (SE) mode and energy dispersive spectroscopy (EDS) mapping.

The results are shown in Figure 7. Figure 7 (a) is a TEM image of 23CC, Figure 7 (b) is an enlarged TEM image of 23CC, and Figure 7 (c) is an EDS mapping image of Cu and Ce.

As shown in Figure 7, for 23CC, small Cu nanoparticles with a size of 10 nm or less were observed. Interestingly, Cu nanoparticles (200) were encapsulated in an amorphous shell (400). The SE mode in Figure 7(b) showed the shape of the shell more clearly. Even when the presence of the shell was ambiguous in the implicit mode, the shell was clearly observed in the SE mode.

Referring to (c) of FIG. 7, the EDS mapping image confirmed that the interior of the metal oxide support was composed of Ce and Cu, and that Cu was mainly located inside the cell.

Example 2: CO ₂ Hydrogenation performance (Performance for CO ₂ hydrogenation)

CO ₂ hydrogenation (CO ₂ + H ₂ → CO + H ₂ O) was performed using a CC catalyst. This reaction has recently received much attention as a scalable method for _CO2 reduction, which is essential for achieving a carbon neutral cycle. In these CO ₂ hydrogenation reactions, noble metal-based catalysts often produced CH ₄ , whereas CC or 23C/C catalysts only produced CO. Thermodynamic equilibrium compositions were calculated using HSC chemistry software, considering CO as the only product.

Thermodynamically, the highest CO ₂ conversion depends on the CO ₂ :H ₂ ratio. For example, the highest CO ₂ conversion value at 600ºC is 38.4% for CO ₂ :H ₂ = 1:1 but 66.2% for CO ₂ :H ₂ = 1:4. In general, CO ₂ conversion rates are high when excessive amounts of H ₂ are used. However, using four times as much H2 may not be advantageous because _H2 , a valuable chemical, is wasted.

Referring to Figure 8, when CO ₂ hydrogenation was performed with a gas composition of CO ₂ :H ₂ = 1:1, the CC catalyst was the best, reaching 18.0%, which is the thermodynamic limit of CO 2 conversion at 350°C for 23CC. Performance was shown, and CO ₂ conversion followed the thermodynamic limit at temperatures above 350°C.

However, 23 C/C showed significantly lower activity with a _CO2 conversion of 4.4% at 350ºC. The same trend was observed at various CO ₂ :H ₂ ratios. Although 23CC followed the thermodynamic limit above 350°C regardless of the CO ₂ :H ₂ ratio, 23 C/C showed very poor performance at low temperatures, showing only significantly small conversions, especially at lower temperatures below 500°C. showed.

Meanwhile, the durability of 23CC and 23C/C was tested through long-term reaction at 600°C for 150 hours. Since the catalyst decomposes more under highly reducing conditions, long-term reactions were performed with CO ₂ :H ₂ = 1:4 in addition to CO ₂ : H ₂ = 1:1. 23CC demonstrated excellent durability by maintaining the CO ₂ conversion rate at 66.2% in the case of CO ₂ : H ₂ = 1:4. However, at 23C/C, the CO ₂ conversion rate decreased from 60.8% to 54.0% for CO ₂ :H ₂ = 1:4. CO selectivity was 100% and no coking was observed in all cases. To perform the reaction under conditions that were not close to equilibrium, the durability reaction was also performed at lower temperatures. Durability testing for 23CC was performed at 300°C and for 23C/C at 400°C, as no activity was observed at 300°C. The durability of 23CC was once again proven as there was no decrease in reactivity even at low temperatures.

Example 3: CO ₂ Activate and H ₂ Spillover (CO ₂ activation and H ₂ spillover)

CO ₂ activation ability was first evaluated for 23CC and 23C/C through CO ₂ -TPD analysis. More CO ₂ molecules were attached to 23CC with stronger bonds compared to 23C/C. CO ₂ hydrogenation at 23CC and 23C/C was also monitored using in situ DRIFTS while co-flowing CO 2 _and H ₂ (see Figures 9(a) and (b)).

The peak of formate or carbonate appeared at 1700 ~ 1200 cm ^-1 . When spectra were obtained while the temperature was increased from 25°C to 300°C and maintained at 300°C, the peaks of formate or carbonate were larger at 23 CC than at 23 C/C. This behavior can be observed more clearly in the two-dimensional demonstration (see Figure 9(c)). Bicarbonate peaks first appeared at 1609 cm ^-1 , 1420 cm ^-1 , and 1288 cm ^-1 at 23CC, showing that CO ₂ was being activated efficiently at the surface, and as the temperature increased, carbonate and formate peaks increased at 1530 cm -1 ^. It increased further at ¹ and 1367 cm ^-1 . The bicarbonate intermediate is known to appear before the formate intermediate. Additionally, the absorbance of 23CC became negative at 2900 to 3500 cm ^-1 in the temperature range of 100 to 200 ºC, meaning that surface hydroxyl groups and water molecules were removed.

To further clarify the reaction intermediates on the catalyst surface, DRIFTS was performed at 300°C by first flowing CO ₂ to remove gaseous CO ₂ and then flowing H ₂ as the temperature increased (see Figure 9(c)). . When CO ₂ was flowed, the peak at 1700~1200 cm ^-1 was larger at 23CC than at 23C/C. For H ₂ flow, additional peaks at 2852 cm ^-1 , 2122 cm ^-1 and 1760 cm ^-1 appeared at 23CC, indicating formate, CO adsorbed on metallic Cu, and H ₂ outflow, respectively. This peak was not observed at 23C/C. When the temperature was further increased to 400ºC, the formate peak disappeared and the CO peak remained. The surface intermediate formed upon CO ₂ adsorption at 23CC was converted to formate and CO upon H ₂ efflux. CO ₂ is adsorbed to form bicarbonate, and then this intermediate becomes formate and finally produces CO.

Meanwhile, surface oxygen species at 23CC and 23C/C were investigated by near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS).

Referring to Figure 10, as the temperature increased, the XPS O 1s spectrum of the catalyst was obtained at a gas composition of CO ₂ :H ₂ = 1:3. The peaks are lattice oxygen (O _latt , ~ 530.1 eV), surface adsorbed oxygen (O _ads , ~ 532.2 eV), which typically represents defect oxygen on the surface, and hydroxyl oxygen species (O _w , ~), including surface hydroxyl groups, reaction intermediates, and water. 533.6 eV) was resolved into three peaks. With increasing temperature, for 23CC the O _ads ratio decreases from 59.7% at room temperature to 34.2% at 150°C and O _w increases from 6.0% at room temperature to 19.0% at 150°C, while for 23C/C there is a much smaller change. It seemed. Compared to 23C/C, 23CC had a higher concentration of surface oxygen species, which promoted more efficient H ₂ spillover. As a result, a greater number of surface hydroxyl groups and reactive intermediates were formed. 23CC significantly improved both CO ₂ activation and H ₂ spillover compared to 23C/C, leading to high levels of CO ₂ hydrogenation.

Example 4: Bench-scale reaction

To test the applicability of 23CC in larger processes, _CO2 hydrogenation was performed in a bench-scale reactor. First, 30g of 23CC was ball milled into fine powder. Afterwards, a catalyst slurry was prepared to coat the catalyst on a honeycomb monolith with a diameter and height of 1 inch. The catalyst loading was 125 g/L, and the actual catalyst capacity of the monolith was 1.6 g/L. This monolith was placed in a bench scale tube reactor and CO ₂ hydrogenation was performed using feed gases of 325 sccm CO ₂ , 325 sccm H ₂ and 650 sccm N ₂ (Figure 11(a)). The WHSV for these conditions was estimated to be 48507 mL/g _cat ·h, which was similar to the conditions used in the laboratory scale reactor (48000 mL/g _cat ·h). 23CC showed high activity and durability even in bench-scale responses (Figure 11 (b)). _CO2 conversion was very close to the thermodynamic limit above 350ºC. Although differences between laboratory-scale reactions and bench-scale reactions are often observed, the 23CC catalyst showed almost identical performance, proving that it has high potential for practical application. Carbon dioxide was produced with 100% selectivity, and no change was observed even after the reaction was repeated three times up to 600°C. To increase actual CO production, CO2 hydrogenation was performed by tripling the reactant feed at both laboratory and bench scales. The actual CO productivity of 23CC was compared between the laboratory scale response and the bench scale response (Figure 11(c)). It increased 32-fold from 30.8 mmol/g _cat ·h at the laboratory scale to 984.9 mmol/g _cat ·h at the bench scale, and was measured at a similar WHSV of 144000 mL/g _cat ·h. CO production rates were also compared with literature values (Table 1). 23CC represents an all-time high in terms of actual CO production rate. This non-precious metal catalyst, synthesized in a facile and scalable method, may be promising for thermal CO2 reduction in large-scale processes.

Ref Catalysts H ₂ /CO ₂ ratio Reaction tempera-
ture WHSV (mL/g _cat ·h) _CO2 conversion (%) CO ₂ conversion rate CO ₂ conversion rate
(mmol·g _cat ^-1 h ^-1 ) CO flow _out
(mmolCO ₂ conversion rate (mmol*g _cat ^-1 h ^-1 ) lab bench lab bench lab bench This work 23CC One 250 144000
(for bench reaction, 145521) 3.0 2.1 47.7 34.1 2.4 54.6 300 7.4 6.6 118.5 108.0 5.9 172.7 350 16.7 13.7 268.5 224.4 13.4 359.0 400 22.7 21.4 365.1 348.7 18.2 557.9 450 27.1 25.8 436.2 420.5 21.8 672.8 500 31.3 30.4 502.9 495.6 25.1 793.0 550 35.0 34.3 562.6 560.1 28.1 896.1 600 38.4 37.7 616.9 615.6 30.8 984.9 2 PtCo/ _CeO2 2.8 300 3000 9.1 - 48.7 - 4.9 - 3 Pt/ _TiO2 1.4 12000 10 - 3.5 - 1.7 - 4 0.3CuMgAl-LDH 4 6000 21 - 8.4 - 1.7 - 5 CuCeO _x 3 - 18 - 6.6 - 1.3 - 6 1Rh/10FC One 350 240000 13.2 - 217.8 - 10.9 - 7 Ni/a-TiO ₂ 4 15000 5 - 6.4 - 2.5 - 8 Pt-K/Mullite One 30000 8.5 - 45 - 4.5 - 9 _NiFe0.9 / _ZrO2 2 400 24000 18.6 - 24.9 - 2.5 - 10 1Pd-La ₂ O ₃ /MWCNT 3 72000 19.5 - 22.3 - 1.1 - 11 Pd/TiO ₂ -0.01 4 11000 20.1 - 18.0 - 0.9 - 12 Pt/CeO ₂ -AA 3 450 72000 33 - 169.2 - 8.5 - 13 0.75Fe 0.25Cu/CeO ₂ -Al ₂ O ₃ 4 500 30000 56 - 114.5 - 5.7 - 14 CuSiO/ _CuOx 3 60000 17.8 - 114.4 - 2.3 - 15 In ₂ O ₃ -CeO ₂ 0.5 48000 30 - 107.1 - 5.35 - 6 1Rh/10FC One 600 240000 38.3 - 992.4 - 49.6 - 16 Pd-In/SiO ₂ One 60000 30 - 146.4 - 7.3 - 17 Cu-Cs- _Mo2C 4 12000 64 - 64.3 - 16.1 - 18 Cu-Al spinel 2 30000 47 - 644.4 - 6.4 - 19 Cuβ- _Mo2C 2 300000 38 - 1696.3 - 36.6 - 20 BaZr _0.8 Y _0.16 Zn _0.04 O ₃ One 2400 38 - 20.1 - 10.0 - 21 Ni/ _nSiO2 4 400000 60 - 164.3 - 2.5 -

As shown in Table 1 above, 23CC showed a record-high CO production rate. Synthesized in a facile and scalable manner, this non-precious metal catalyst may be promising for thermal _{CO 2 reduction} in large-scale processes.

The advantage of a shell-structured catalyst is that it exhibits high durability because the shell maintains the small copper structure. In the case of the RWGS reaction, it is carried out in a reducing atmosphere using hydrogen, which causes agglomeration of metal particles on a typical supported catalyst. The shell structure prevents this clumping.

discussion

Cu-doped CeO ₂ (CC) greatly promotes surface oxygen transfer, forming oxygen defects more easily than Cu deposited on bare CeO ₂ (C/C). Upon reduction, an amorphous shell is formed on small Cu nanoparticles in CC, whereas Cu sinters into large particles in C/C. Although oxide shell formation of metal nanoparticles has previously only been reported for noble metal catalysts, this behavior was observed for this non-noble metal catalyst by enhancing surface oxygen transfer. The CO ₂ hydrogenation reaction was performed on a CC catalyst and only CO was produced. In particular, 23CC, which contains 23 at% Cu, showed a high CO production rate in all temperature ranges along the thermodynamic equilibrium limit of over 350°C. This catalyst also showed high durability for long-term reactions at 600°C for 150 hours. Promoted surface defects enabled more efficient CO ₂ activation and H ₂ efflux as confirmed by in-situ DRIFTS and TPSR. The 23CC catalyst was also applied to a bench-scale reactor, achieving record-high CO production rates. It is expected that this encapsulated non-precious metal catalyst can be applied on a large scale for _CO2 reduction.

Although embodiments of the present invention have been described in more detail with reference to the accompanying drawings, the present invention is not necessarily limited to these embodiments, and various modifications may be made without departing from the technical spirit of the present invention. . Accordingly, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention, but are for illustrative purposes, and the scope of the technical idea of the present invention is not limited by these embodiments. Therefore, the embodiments described above should be understood in all respects as illustrative and not restrictive. The scope of protection of the present invention should be interpreted in accordance with the claims below, and all technical ideas within the equivalent scope should be construed as being included in the scope of rights of the present invention.

Claims (14)

A composite oxide catalyst containing a metal oxide support and copper.
The composite oxide catalyst of claim 1, wherein the metal oxide is TiO ₂ or CeO ₂ .
The composite oxide catalyst according to claim 1, wherein the copper exists as particles on the surface of the catalyst.
The composite oxide catalyst according to claim 3, wherein the copper of the particles includes copper oxide.
The composite oxide catalyst according to claim 3, wherein the particles are encapsulated in a shell made of the metal oxide support.
The composite oxide catalyst according to claim 5, wherein the shell exhibits gas permeability.
The composite oxide catalyst according to claim 1, wherein the copper exists in a CeO ₂ lattice structure.
A catalyst ink composition comprising the complex oxide catalyst of any one of claims 1 to 7.
Method for preparing a complex oxide catalyst comprising the following steps:
(a) dissolving the metal oxide precursor and copper oxide in water;
(b) adjusting the pH of the solution to 8 to 9 and stirring it to precipitate it;
(c) drying the precipitate to prepare a solid solution;
(d) calcining the solid solution; and
(e) reducing the calcined solid solution under hydrogen conditions.
The method of claim 9, wherein the metal oxide is cerium oxide or titanium oxide.
The method of claim 9, wherein 5 to 50 mg of the copper oxide is dissolved based on 90 mL of water.
The manufacturing method according to claim 9, wherein the stirring in step (b) is performed for 3 to 10 hours.
The manufacturing method according to claim 9, wherein the baking in step (d) is performed at 400 to 600°C.
The manufacturing method according to claim 9, wherein the baking in step (d) is performed for 2 to 6 hours.