GaZrOx catalyst, preparation method thereof and application of GaZrOx catalyst in reaction of catalyzing hydrogenation of carbon dioxide to prepare methanol and dimethyl ether

Abstract

The invention provides a GaZrOx catalyst, a preparation method thereof and application of the GaZrOx catalyst in a reaction for catalyzing hydrogenation of carbon dioxide to prepare methanol and dimethyl ether, and relates to the technical field of catalysts. The preparation method comprises the following steps: carrying out Ga element atomic layer deposition on a t-ZrO2 carrier to obtain a GaZrOx catalyst; the number of atomic layer deposition is 1-50, and single atomic layer deposition comprises a first half reaction (taking trimethyl gallium as a precursor) and a second half reaction (taking water vapor as a precursor) which are sequentially carried out. A Ga element is deposited on the surface of a t-ZrO2 carrier by adopting an atomic layer deposition technology; and the dispersion state of Ga species on the surface of t-ZrO2 can be regulated and controlled by controlling the number of times of atomic layer deposition. Although the GaZrOx catalyst prepared by the method disclosed by the invention is extremely low in Ga content (0.60-6.50 wt%), the GaZrOx catalyst has excellent catalytic performance in a reaction for preparing methanol and dimethyl ether through CO2 hydrogenation, and the utilization rate of the Ga element is high.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst preparation, and in particular to a GaZrO x A catalyst, a preparation method thereof and application in the catalytic hydrogenation of carbon dioxide to produce methanol and dimethyl ether. Background Art

[0002] CO2 is a typical greenhouse gas. Converting CO2 into high-value-added chemicals and energy can not only effectively mitigate the greenhouse effect, but also promote the sustainable use of natural resources. Research suggests that CO2 hydrogenation to methanol is an effective way to mitigate the greenhouse effect caused by the continued growth of CO2 in the environment. A typical reaction is the hydrogenation of carbon dioxide to produce methanol and dimethyl ether.

[0003] GaZrO x The catalyst exhibits excellent catalytic performance in the process of CO2 hydrogenation to methanol and dimethyl ether. GaZrO prepared by solvent evaporation self-assembly (EISA) method x The catalyst has excellent catalytic activity and selectivity, which makes it one of the catalytic systems that researchers focus on. x The reaction performance is optimal when the Ga content in the catalyst is 27%. However, due to the high price of Ga reagents (scarcity and complex purification technology), the GaZrO x Industrial application of catalysts. At the same time, due to the EISA preparation method, the Ga element is evenly dispersed in the catalyst. In addition to being dispersed on the surface of the catalyst (where the reactants can access it), it also has a high content in the supporting structure of the catalyst (where the reactants cannot access it), which reduces the utilization rate of the Ga element. Therefore, how to improve the effective utilization rate of the Ga element has become a key issue in improving the performance of GaZrO x A key issue in catalyst economics and efficiency. Summary of the Invention

[0004] In view of this, the object of the present invention is to provide a GaZrO x Catalyst and its preparation method and application in catalytic carbon dioxide hydrogenation to methanol and dimethyl ether reaction. The present invention adopts atomic layer deposition technology to prepare GaZrO x The catalyst has an extremely low Ga content (0.60-6.50 wt%), but has excellent catalytic performance in the reaction of carbon dioxide hydrogenation to produce methanol and dimethyl ether, and has a high Ga element utilization rate.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a GaZrO xThe preparation method of the catalyst comprises the following steps:

[0007] Atomic layer deposition of t-ZrO2 was performed to obtain GaZrO x Catalyst; the number of atomic layer deposition is 1 to 50 times, and a single atomic layer deposition includes sequentially performing a first half reaction and a second half reaction, wherein the first half reaction uses trimethylgallium as a precursor, and the second half reaction uses water vapor as a precursor.

[0008] Preferably, the temperature of the atomic layer deposition is 200-240° C., and the vacuum degree is 0.1-100 Torr.

[0009] Preferably, the trimethylgallium and water vapor are respectively carried by a carrier gas, and the flow rate of the carrier gas is 20 sccm.

[0010] Preferably, in the single atomic layer deposition, the time of the first half reaction is 0.01 to 1 s, and the time of the second half reaction is 0.01 to 1 s.

[0011] Preferably, nitrogen purge is performed after the first half reaction and the second half reaction are completed, and the nitrogen flow rate during the nitrogen purge is 500 sccm and the purge time is 40 s.

[0012] Preferably, the preparation method of the t-ZrO2 carrier comprises the following steps:

[0013] zirconyl nitrate, urea and an alcohol solvent are mixed to carry out a solvothermal reaction to obtain a solvothermal product;

[0014] calcining the solvent thermal product under a protective atmosphere to obtain the t-ZrO2 carrier;

[0015] The molar ratio of zirconyl nitrate to urea is 1 / 10; the temperature of the solvent thermal reaction is 160-230° C., and the time is 20-72 hours; the temperature of the calcination is 300-500° C., and the time is 3-6 hours.

[0016] The present invention provides GaZrO prepared by the preparation method described in the above technical solution. x catalyst, the GaZrO x The catalyst comprises a t-ZrO2 carrier and a Ga element deposited on the surface of the t-ZrO2 carrier, wherein the Ga element exists in at least one of the following forms: monodisperse, oligomer and cluster. x The content of Ga element in the catalyst is 0.60-6.50 wt%.

[0017] Preferably, the GaZrO x The specific surface area of the catalyst is 40.5~65.4m 2 / g.

[0018] The present invention provides the GaZrO x Application of catalyst in catalytic carbon dioxide hydrogenation to produce methanol and dimethyl ether.

[0019] Preferably, the raw gas for the reaction comprises hydrogen, carbon dioxide and argon, the volume ratio of hydrogen to carbon dioxide is 2 / 1 to 5 / 1, and the volume percentage of argon in the raw gas is 1 to 5%; the pressure of the reaction is 2 to 5 MPa, the temperature is 240 to 380°C, and the raw gas space velocity is 12000 to 36000 mL·g cat -1 ·h -1 .

[0020] The present invention provides a GaZrO x The preparation method of the catalyst comprises the following steps: performing atomic layer deposition on a t-ZrO2 carrier to obtain GaZrO x Catalyst; the number of atomic layer depositions is 1 to 50 times, and a single atomic layer deposition includes sequentially performing a first half reaction and a second half reaction, wherein the first half reaction uses trimethylgallium as a precursor, and the second half reaction uses water vapor as a precursor. The present invention adopts atomic layer deposition (ALD) technology to deposit Ga elements on the surface of the t-ZrO2 carrier. Since the main process of the catalytic reaction usually occurs on the surface of the catalyst (this is because the reactant molecules first need to be adsorbed on the catalyst surface and interact with the active sites on the catalyst surface), therefore, loading Ga on the carrier surface can effectively improve the utilization rate of Ga elements; and by controlling the number of atomic layer depositions, the dispersion state of Ga species on the t-ZrO2 surface can be regulated (monodispersed, oligomeric and clustered), thereby constructing catalytic reaction active sites that match the CO2 hydrogenation reaction to produce methanol and dimethyl ether. GaZrO prepared by the method of the present invention x Although the Ga content of the catalyst is extremely low (0.60-6.50 wt%), it has excellent catalytic performance in the CO2 hydrogenation reaction to methanol and dimethyl ether (GaZrO x -8C catalyst at 340℃, 3MPa, H2 / CO2=3 / 1, GHSV=24000mL·g cat -1 ·h -1 Under the reaction conditions, the yield of methanol and dimethyl ether reached 5.40%, and the apparent TOF value reached 11815s -1 ), the utilization rate of Ga element is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The atomic layer deposition method of the present invention is used to prepare GaZrO xSchematic diagram of the catalyst process;

[0022] Figure 2 GaZrO prepared by different atomic layer deposition times x Powder X-ray diffraction patterns of the catalyst and comparative catalysts Ga2O3 and t-ZrO2;

[0023] Figure 3 GaZrO obtained with different deposition times x Nitrogen adsorption-desorption isotherms of the catalyst and comparative catalysts Ga2O3 and t-ZrO2;

[0024] Figure 4 GaZrO with different deposition cycles x HAADF-STEM and EDS mapping images of the catalyst, Figure 4 (a) is GaZrO x -1C HAADF-STEM and EDS mappings images, (b) GaZrO x -5C HAADF-STEM and EDSmappings images, (c) GaZrO x -8C HAADF-STEM and EDS mapping images, (d) GaZrO x -50C HAADF-STEM and EDS mapping images;

[0025] Figure 5 Ga2O3, t-ZrO2, GaZrO x -1C, GaZrO x -5C, GaZrO x -H2-TPR spectrum of 8C catalyst;

[0026] Figure 6 GaZrO statistics for ToF-SIMS x -1C, GaZrO x -5C, GaZrO x Ga-8C catalyst with different Ga atoms x Zr y O z - percentage of fragmentation;

[0027] Figure 7 Ga2O3, t-ZrO2, GaZrO x -1C, GaZrO x -5C, GaZrO x -XPS spectrum of 8C catalyst;

[0028] Figure 8 GaZrO x -1C, GaZrO x -5C, GaZrO x -In situ DRIFT spectra of 8C catalyst at different temperatures;

[0029] Figure 9 GaZrO x -1C, GaZrO x -5C, GaZrO x -Integral data of Ga-H species peak area of 8C catalyst at different temperatures;

[0030] Figure 10 GaZrO x -1C, GaZrO x -5C, GaZrO x -8C catalyst 13 CO2 hydrogenation 13 C CPMAS NMR spectrum;

[0031] Figure 11 GaZrO x -1C, GaZrO x -5C, GaZrO x -8C catalyst 13 CO2 hydrogenation 13 C HPDEC NMR spectrum;

[0032] Figure 12 GaZrO with different cycle times x Product selectivity of the catalyst in CO2 hydrogenation reaction, Figure 12 (a) is the selectivity of (CH3OH+CH3OCH3), and (b) is the selectivity of CO;

[0033] Figure 13 GaZrO with different cycle times x The trend of CO2 conversion rate of catalysts in the CO2 hydrogenation to CH3OH and CH3OCH3 reactions with temperature;

[0034] Figure 14 GaZrO with different cycle times x The trends of CH3OH and CH3OCH3 yields of the catalysts as a function of temperature;

[0035] Figure 15 GaZrO with different deposition cycles x Apparent TOF value of the catalyst;

[0036] Figure 16GaZrO with different cycle times x The apparent activation energy of the catalyst, Figure 16 (a) is the apparent activation energy fitting curve, and (b) is the solution of the Arrhenius equation for GaZrO x -1C, GaZrO x -3C, GaZrO x -5C, GaZrO x -8C、GaZrO x -10C, GaZrO x -25C、GaZrO x -50C catalyst apparent activation energy value plotted curve;

[0037] Figure 17 GaZrO with different deposition cycles x The kinetic test results of the catalyst, Figure 17 (a) to (c) are catalysts GaZrO x -1C, GaZrO x -5C and GaZrO x -8C generates (CH3OH+CH3OCH3) and the relationship between CO and CO2 partial pressures, (d) to (f) are catalysts GaZrO x -1C, GaZrO x -5C and GaZrO x -8C formation (CH3OH+CH3OCH3) and the relationship between CO and H2 partial pressures;

[0038] Figure 18 GaZrO x -50C catalyst stability test. DETAILED DESCRIPTION

[0039] The present invention provides a GaZrO x The preparation method of the catalyst comprises the following steps:

[0040] Atomic layer deposition of t-ZrO2 was performed to obtain GaZrO x Catalyst; the number of atomic layer deposition is 1 to 50 times, and a single atomic layer deposition includes sequentially performing a first half reaction and a second half reaction, wherein the first half reaction uses trimethylgallium as a precursor, and the second half reaction uses water vapor as a precursor.

[0041] The present invention has no special requirements on the source of the t-ZrO2 (tetragonal ZrO2) carrier, and it can be prepared by using commercial products or methods well known to those skilled in the art. xAmong the catalysts, the reactivity of t-ZrO2 is higher than that of m-ZrO2 (monoclinic ZrO2). In an embodiment of the present invention, the preparation method of the t-ZrO2 carrier preferably includes the following steps:

[0042] zirconyl nitrate, urea and an alcohol solvent are mixed to carry out a solvothermal reaction to obtain a solvothermal product;

[0043] The solvent thermal product is calcined under a protective atmosphere to obtain the t-ZrO2 carrier.

[0044] In the present invention, the molar ratio of zirconyl nitrate to urea is preferably 1 / 10. In an embodiment of the present invention, the zirconyl nitrate is added in the form of ZrO(NO3)2·xH2O. In the present invention, urea serves as a precipitant. In the present invention, the alcohol solvent is preferably methanol. The present invention has no particular requirements for the amount of the alcohol solvent used, as long as it can completely dissolve the zirconyl nitrate and urea. In the present invention, the mixing temperature can be 30°C and the mixing time can be 3 hours. The mixing is preferably carried out under stirring.

[0045] In the present invention, the temperature of the solvent thermal reaction is preferably 160 to 230°C, and can be 190 or 200°C. The time is preferably 20 to 72 hours, and can be 36 or 48 hours. The solvent thermal reaction is specifically carried out in a polytetrafluoroethylene-lined reactor. During the solvent thermal reaction, urea decomposes to produce NH3 and CO2. The released NH3 dissolves in the reaction system to form an alkaline environment. This alkaline condition promotes the hydrolysis of zirconium oxynitrate (crystallization water carried by the Zr salt) to produce ZrO(OH)2. ZrO(OH)2 undergoes intermolecular coupling and dehydration to produce oligomeric -Zr-O-Zr- species. After the solvent thermal reaction is completed, the present invention preferably cools the obtained solvent thermal reaction liquid to room temperature, washes and dries it in sequence to obtain a powdery hydrothermal product; the washing is preferably performed by centrifugation washing with methanol three times; the drying temperature is preferably 110°C, and the time is preferably 12 hours.

[0046] In the present invention, the protective atmosphere is preferably argon, and the argon flow rate is preferably 10 mL / min. The calcination temperature is preferably 300-500°C, and may be 300, 400, or 500°C. The calcination time is preferably 3-6 hours, and may be 3, 4, 5, or 6 hours. The heating rate from room temperature to the calcination temperature is preferably 2°C / min. In an embodiment of the present invention, the calcination is carried out in a tube furnace. During the calcination process, the oligomeric -Zr-O-Zr- species gradually crystallize to form tetragonal ZrO2.

[0047] Figure 1 The present invention uses atomic layer deposition to prepare GaZrO xThe schematic diagram of the catalyst process is shown below. Figure 1 Provide detailed explanation.

[0048] In the present invention, the temperature of the atomic layer deposition is preferably 200-240°C, and can be 200, 210, 220, 230 or 240°C. The vacuum degree is preferably 0.1-100 torr, and more preferably 0.1-10 torr. The present invention preferably places the t-ZrO2 carrier powder in a vacuum chamber (i.e., a deposition chamber) of an atomic layer deposition apparatus, heats it to 200-240°C, and begins deposition after the temperature stabilizes.

[0049] In the present invention, the number of atomic layer deposition is 1 to 50 times, which can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40 or 50 times. In the present invention, the single atomic layer deposition includes sequentially performing a first half reaction and a second half reaction. In the present invention, the first half reaction uses trimethylgallium (Ga(CH3)3, TMGa) as a precursor, and the trimethylgallium is preferably carried into the deposition chamber by a carrier gas, and the carrier gas is preferably nitrogen, and the flow rate of the carrier gas is preferably 20 sccm; during the process of introducing the trimethylgallium, the deposition chamber is preferably rotated at a speed of 30 r / min to ensure uniform distribution of the trimethylgallium. In the present invention, the time of the first half reaction (i.e., the time of introducing trimethylgallium) is preferably 0.01 to 1 s, and can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1 s. After the completion of the first half reaction, nitrogen purge is preferably performed to remove excess Ga(CH3)3 and by-product methane. The nitrogen flow rate during the nitrogen purge is preferably 500 sccm, and the purge time is preferably 40 s. Then, the second half reaction is performed. In the present invention, water vapor is used as a precursor for the second half reaction. The water vapor is preferably carried into the deposition chamber by a carrier gas. The flow rate of the carrier gas is preferably 20 sccm. In the present invention, the time of the second half reaction (i.e., the time of introducing water vapor) is preferably 0.01 to 1 s, and can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1 s. After the second half reaction is completed, nitrogen purge is preferably performed to remove excess water vapor and by-product methane. The nitrogen flow rate during the nitrogen purge is preferably 500 sccm, and the purge time is preferably 40 s. In the present invention, when atomic layer deposition is carried out for the first time, during the first half reaction, Ga(CH3)3 gas diffuses into the gaps between the t-ZrO2 carrier particles and reacts with the -OH groups on the t-ZrO2 surface to form a (CH3)2Ga-O- structure; then water vapor is introduced through the second half reaction, and the water molecules react with the CH3 groups in the Ga source deposited on the t-ZrO2 carrier, resulting in the CH3 groups being replaced by -OH; when the atomic layer deposition cycle continues, the -OH that has replaced the CH3 group continues to react with Ga(CH3)3 to form a (CH3)2Ga-O- structure and reacts with water molecules to replace the CH3 groups in the (CH3)2Ga-O- structure with -OH.

[0050] The present invention uses atomic layer deposition (ALD) technology to deposit Ga on the surface of the t-ZrO2 support (i.e., Ga is enriched on the surface of the t-ZrO2 support). The main process of the catalytic reaction usually occurs on the surface of the catalyst. This is because the reactant molecules first need to adsorb on the catalyst surface and interact with the active sites on the catalyst surface. Therefore, changing the synthesis strategy to load Ga on the support surface is an effective method to improve the utilization rate of Ga element.

[0051] In the present embodiment, in order to study the effect of different atomic layer deposition times on the catalyst performance, GaZrO was prepared with deposition times of 1, 3, 5, 8, 10, 25 and 50 times. x Catalyst: GaZrO obtained by deposition once x The Ga element in the catalyst is highly dispersed; the GaZrO obtained by 5 depositions x The catalyst has oligomeric Ga sites, which can produce more active hydrogen. Therefore, the catalytic activity of oligomeric Ga species is better than that of monodisperse Ga species. x The oligomeric Ga species on the catalyst surface reaches saturation and begins to generate Ga x O y The saturated oligomeric Ga species can provide sufficient active hydrogen species in the reaction process, greatly promoting the catalytic reaction, thereby improving the performance of the catalyst. When the deposition times are further increased, the catalytic performance of the obtained catalyst reaches a stable state and no longer increases, that is, the newly generated Ga x O y Clusters have no significant promoting effect on the catalytic reaction of CO2 hydrogenation. This shows that the present invention can regulate the dispersion state of Ga species on the t-ZrO2 surface by controlling the number of depositions during atomic layer deposition, thereby establishing a correlation between the dispersion of Ga species (monodisperse, oligomeric, and clustered) and the reactivity of CO2 hydrogenation to produce methanol and dimethyl ether, thereby better regulating the CO2 hydrogenation reaction to produce methanol and dimethyl ether.

[0052] The present invention provides GaZrO prepared by the preparation method described in the above technical solution. x catalyst, the GaZrO x The catalyst comprises a t-ZrO2 carrier and a Ga element deposited on the surface of the t-ZrO2 carrier. In the present invention, the Ga element is specifically Ga x O y Species phase exists, Ga x O yIn the present invention, the Ga element exists in at least one of the following forms: monodisperse, oligomers and clusters. In the embodiment of the present invention, the GaZrO obtained by deposition once is x The Ga element in the catalyst is highly dispersed; the GaZrO obtained by 5 depositions x The catalyst contains oligomeric Ga oligomers; GaZrO obtained by 8 depositions x The content of oligomeric Ga species on the catalyst surface reaches saturation and generates Ga x O y In the present invention, the GaZrO x The content of Ga element in the catalyst is 0.60-6.50wt%, which can be 0.60wt%, 0.96wt%, 1.16wt%, 2.28wt%, 2.73wt%, 4.16wt%, 6.50wt%. x The Ga content in the catalyst is extremely low, thereby improving the utilization rate of the Ga element.

[0053] In the present invention, the GaZrO x The specific surface area of the catalyst is preferably 40.5 to 65.4 m 2 / g, can be 40.5, 42.2, 42.4, 42.7, 55.5, 64.2 or 65.4m 2 / g.

[0054] The present invention provides the GaZrO x Application of catalyst in catalytic carbon dioxide hydrogenation to methanol and dimethyl ether.

[0055] In the present invention, the raw gas for the reaction preferably includes hydrogen, carbon dioxide and argon. The volume ratio of hydrogen to carbon dioxide is preferably 2 / 1 to 5 / 1, and can be 2 / 1, 3 / 1, 4 / 1 or 5 / 1. The volume percentage of argon in the raw gas is preferably 1 to 5%, and can be 4%. The pressure of the reaction is preferably 2 to 5 MPa, and can be 2, 3, 4 or 5 MPa. The temperature is preferably 240 to 380°C, and can be 240, 260, 280, 300, 320, 330, 340, 360 or 380°C. The raw gas space velocity (GHSV) is preferably 12000 to 36000 mL·g cat -1 ·h -1 , which can be 12000, 24000 or 36000 mL·g cat -1 ·h -1 .

[0056] Before use, the present invention preferablyx The catalyst is pretreated, and the pretreatment method is preferably: x The catalyst is heat-treated in a hydrogen atmosphere; the hydrogen flow rate can be 30 mL / min, the heat treatment temperature is preferably 340°C, and the holding time is preferably 2 hours; the pretreatment can be carried out at normal pressure. The present invention removes water molecules adsorbed on the catalyst surface through the pretreatment, generates oxygen vacancies, and converts Ga-OH on the catalyst surface into GaO x .

[0057] GaZrO prepared by the present invention x The Ga element of the catalyst is mainly enriched on the surface of the catalyst. Since Ga is a rare metal and is expensive, the enrichment of Ga on the surface of the catalyst can significantly improve the utilization rate of Ga. x The catalyst is used in the catalytic hydrogenation of carbon dioxide to methanol and dimethyl ether. The apparent turnover frequency (TOF) of (CH3OH+CH3OCH3) is high (significantly higher than that of GaZrO prepared by solvent evaporation self-assembly (EISA) method). x The catalyst has a high utilization rate of Ga and can achieve excellent catalytic performance for the CO2 hydrogenation to methanol and dimethyl ether reaction at an extremely low Ga content (0.60-6.50 wt%).

[0058] In order to further illustrate the present invention, the following examples are used to illustrate the GaZrO x The catalyst, its preparation method and its application in the catalytic hydrogenation of carbon dioxide to produce methanol and dimethyl ether are described in detail, but they should not be understood as limiting the scope of protection of the present invention.

[0059] Example

[0060] GaZrO x Preparation of catalyst:

[0061] (1) Preparation of t-ZrO2

[0062] Dissolve 10.8708 g of ZrO(NO₃)₂·xH₂O (0.04 mol) and 24.0240 g of urea in 100 mL of methanol and stir at 30°C for 3 hours to dissolve. The resulting solution is then transferred to a 250 mL polytetrafluoroethylene-lined hydrothermal reactor and heated at 190°C for 48 hours. After cooling the hydrothermal reactor to room temperature, the product is centrifuged and washed three times with anhydrous methanol and then dried at 110°C for 12 hours. The dried powder is then placed in a tube furnace and heated at a rate of 2°C / min to 400°C under Ar (10 mL / min) and maintained for 4 hours to obtain a t-ZrO₂ carrier powder.

[0063] (2) Preparation of GaZrO by atomic layer deposition x catalyst

[0064] First, 6g of t-ZrO2 carrier powder was placed in a vacuum chamber (vacuum degree 0.1 torr) and heated to 220℃. After the temperature stabilized, deposition began. During the deposition process, an alternating sequence of Ga(CH3)3, N2, H2O, and N2 purge was used. Figure 1 As shown, first, the precursor trimethylgallium Ga(CH3)3 is introduced into the vacuum chamber with 20sccm of N2. N2 can ensure its uniform distribution. When the Ga(CH3)3 gas diffuses into the gaps between the carrier particles, it reacts with the -OH groups on the surface of t-ZrO2 to form a (CH3)2Ga-O- structure. After 0.1s, the introduction of Ga(CH3)3 is stopped and N2 is used for purging to remove excess Ga(CH3)3 and by-products such as CH4. The purge flow rate is 500sccm and the purge time is 40s. After the purge is completed, water vapor is introduced with 20sccm of N2. The water molecules react with the CH3 groups in the Ga source deposited on the t-ZrO2 carrier, causing the CH3 groups to be replaced by -OH to generate GaO x layer; after 0.1s, the introduction of water vapor was stopped, and N2 was used again to purge to remove excess water vapor and by-product methane. The nitrogen purge flow rate was 500sccm and the purge time was 40s. The above is a complete deposition reaction. After a complete deposition reaction is completed, it is considered an ALD cycle. The obtained GaZrO x The catalyst is named GaZrO x In order to study the effect of different atomic layer deposition cycles on the catalyst performance, GaZrO with 1, 3, 5, 8, 10, 25 and 50 cycles were prepared respectively. x The catalyst was named GaZrO x -nC, where n represents the number of deposition cycles (i.e., GaZrO x -1C, GaZrO x -3C, GaZrO x -5C, GaZrO x -8C、GaZrO x -10C, GaZrO x -25C、GaZrO x -50C).

[0065] (3) Preparation of Ga2O3.

[0066] Take a certain amount of Ga(NO3)3·xH2O, heat it to 500℃ at a heating rate of 2.5℃ / min, and calcine it for 5h.

[0067] The prepared GaZrOx The catalyst was structurally characterized as follows:

[0068] (1) PXRD characterization

[0069] The structural characteristics of the catalyst were studied by powder X-ray diffraction analysis. Figure 2 GaZrO prepared by different atomic layer deposition times x The powder X-ray diffraction patterns of the catalyst and the comparative catalysts Ga2O3 and t-ZrO2 clearly show that the prepared t-ZrO2 (tetragonal ZrO2) is completely consistent with the standard card (JCPDS 50-1089), indicating that t-ZrO2 was successfully prepared. When trimethylgallium (Ga(CH3)3) was deposited onto the t-ZrO2 support using atomic deposition technology, the resulting catalyst did not show the characteristic peaks of Ga species at different deposition cycles. This indicates that the Ga species is highly dispersed on the catalyst or that the size of the Ga species is below the detection limit of XRD.

[0070] (2) Nitrogen physical adsorption-desorption experiment

[0071] The specific surface area and pore structure of the catalyst were further studied through nitrogen adsorption-desorption experiments. Figure 3 As shown ( Figure 3 GaZrO obtained with different deposition times x The nitrogen adsorption and desorption isotherms of the catalyst and the comparative catalysts Ga2O3 and t-ZrO2 are shown in Table 1. The catalysts after pure t-ZrO2 support and its Ga source deposition all show type IV isotherms with H3 type hysteresis loops, and these catalysts have slit pore structures. In addition, Ga2O3 metal oxide also shows H3 type hysteresis loops, but does not have a slit pore structure. The specific surface area data of the catalysts are summarized in Table 1. The specific surface areas of pure Ga2O3 and t-ZrO2 are 74.2 and 65.0 m 2 / g, after Ga source deposition, the specific surface area of the catalyst does not change significantly. When the number of Ga source deposition cycles is 1 and 3, the specific surface area of the catalyst is 64.2m 2 / g and 65.4m 2 / g, which is similar to that of pure t-ZrO2 support, indicating that the initial deposition of Ga source has little effect on the specific surface area. However, when the number of deposition cycles increases to 5 times, the specific surface area decreases to 55.5m 2 / g, and when the deposition times reached 8 times, the specific surface area of the catalyst further decreased to 42.4m 2 / g. This trend shows that with the increase of Ga source deposition, the specific surface area of the catalyst gradually decreases, which may be due to the fact that the deposited Ga species blocks some of the pores of the carrier ZrO2. It is worth noting that after the deposition times reach a certain level, the specific surface area of the catalyst tends to be stable and basically maintains at 42m 2 / g. The performance change of the catalyst may be closely related to the change of specific surface area.

[0072] (3) ICP-OES characterization

[0073] The changes in the Ga element content in the catalyst were analyzed by ICP-OES testing. The test results are shown in Table 1. As the number of deposition cycles increases, the Ga element content in the catalyst gradually increases. The experiment found that the surface Ga / Zr ratio obtained by XPS testing was significantly higher than the overall metal content of the catalyst obtained by ICP-OES testing. This difference indicates that the Ga element is enriched on the surface of the t-ZrO2 carrier. Since Ga is a rare metal and is expensive, the enrichment of Ga on the catalyst surface can significantly improve the utilization rate of Ga. This further shows that the atomic layer deposition preparation method can solve the problem of low utilization of Ga due to entrapment caused by traditional catalyst preparation methods such as co-precipitation and solvent-induced self-volatilization.

[0074] Table 1 t-ZrO2, Ga2O3 and different deposition cycles of GaZrO x Catalyst physical and chemical properties

[0075]

[0076] Note: In Table 1, a is the actual metal ratio of the sample determined by ICP-OES; b is the surface Ga / Zr atomic ratio obtained by XPS test; c is undetermined.

[0077] (4) AC-HAADF-STEM characterization

[0078] The GaZrO was characterized by high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM) corrected for spherical aberration. x -1C, GaZrO x -5C, GaZrO x -8C and GaZrO x The microstructure of the -50C catalyst was characterized in depth. Figure 4 As shown, Figure 4 GaZrO with different deposition cycles x HAADF-STEM and EDS mapping images of the catalyst, Figure 4 (a) (i.e. the first row) is GaZrOx -1C HAADF-STEM and EDS mappings images, (b) (i.e., the second row) is GaZrO x -5C HAADF-STEM and EDS mappings images, (c) (i.e. the third row) is GaZrO x -8C HAADF-STEM and EDSmappings images, (d) (i.e. the fourth row) is GaZrO x -50C HAADF-STEM and EDS mapping images. Figure 4 In the figure, the second graph in each row is a curve plotted based on the atomic heights measured by the five curves in the first graph.

[0079] In GaZrO x In the -1C catalyst, the Ga content is relatively low, and the Ga atoms are surrounded by a large number of Zr sites. This feature indicates that the Ga atoms are highly dispersed in the 1C catalyst. x -1C catalyst performance, it is speculated that this extremely small amount of Ga may be detrimental to the catalytic reaction. x -5C catalyst, more Ga-Zr adjacent sites were observed (due to the low contrast of O element in STEM mode, Ga-O-Zr was simplified to Ga-Zr adjacent). At the same time, Ga-Ga adjacent sites (Ga-O-Ga) were observed, indicating that there are some oligomeric Ga sites on the catalyst surface. Combined with the reaction activity test results ( Figure 14 ) and experimental results of reaction kinetics ( Figure 17 ), it is speculated that this Ga-Ga adjacent site may contribute to the overflow of active hydrogen and promote the hydrogenation process of the reaction intermediates. x In the -8C catalyst, the number of oligomeric Ga species increased, and some Ga x O y The formation of these clusters may be due to the local aggregation of the high loading of Ga element on the catalyst surface. x More Ga appeared in the -50C catalyst x O y Combined with the catalytic performance data, it is speculated that the appearance of Ga clusters may change the distribution of surface active sites of the catalyst, thereby affecting its performance in the CO2 hydrogenation to methanol reaction. x -1C, GaZrO x -5C and GaZrO xThe difference in the microstructure of the -8C catalysts, especially the dispersion state of Ga element, may be the important reason for their different catalytic performance in CO2 hydrogenation to methanol. x The highly dispersed Ga sites on the surface of the -1C catalyst are not conducive to the overflow of active hydrogen, and the local active hydrogen supply around the reaction intermediates is insufficient or very slow; (2) GaZrO x The oligomeric Ga sites on the -5C catalyst can produce more active hydrogen, but the content of oligomeric Ga species is insufficient, so the overflow of active hydrogen is still not sufficient; (3) GaZrO x The oligomeric Ga species content on the surface of the -8C catalyst reached saturation and began to generate Ga x O y Clusters and saturated oligomeric Ga species can provide sufficient active hydrogen species during the reaction process, greatly promoting the catalytic reaction, thus making GaZrO x -8C catalyst has the best performance. When the number of Ga deposition is further increased, the catalytic performance reaches a stable state and no longer increases, indicating that the newly generated Ga x O y The clusters have no promoting effect on the catalytic reaction of CO2 hydrogenation. These results provide important clues for a deeper understanding of the structure-activity relationship of catalysts and also provide a theoretical basis for optimizing catalyst design.

[0080] (5)H2-TPR

[0081] The reduction characteristics of the catalyst and its structure-performance relationship were studied by hydrogen temperature-programmed reduction technique. Figure 5 As shown, Figure 5 Ga2O3, t-ZrO2, GaZrO x -1C, GaZrO x -5C, GaZrO x H2-TPR spectrum of -8C catalyst.

[0082] The H2-TPR spectrum of pure Ga2O3 shows three characteristic reduction peaks at 335, 507 and 648℃. Among them, the low-temperature reduction peak at 335℃ can be attributed to the removal process of oxygen species adsorbed on the surface of Ga2O3; the reduction peak at 507℃ corresponds to the removal of oxygen species adsorbed on the surface of Ga2O3; 3+ →Ga + The high temperature reduction peak at 648℃ reflects the partial reduction reaction of Ga + →Ga 0 The complete reduction process of pure t-ZrO2 is shown in Figure 2. The pure t-ZrO2 has only a single reduction peak at 686℃, which corresponds to the bulk reduction of t-ZrO2. After the deposition of Ga element, GaZrO xThe reduction peak of the catalyst at 500-550℃ is mainly related to Ga2O3 species, while the high-temperature reduction peak above 600℃ contains contributions from both Ga2O3 and t-ZrO2. x -1C and GaZrO x Ga-5C catalyst 3+ The reduction peak temperature increased from 507°C to 534°C and 526°C, respectively, which is about 20-30°C higher than that of pure Ga2O3. Combined with the XPS analysis results (see below), this increase in reduction temperature can be attributed to the strong metal-support interaction between Ga species and t-ZrO2 support, which leads to a decrease in the electron cloud density of Ga and an increase in the difficulty of reduction. In contrast, GaZrO x The reduction characteristics of the -8C catalyst are highly similar to those of pure Ga2O3, indicating that its Ga species may be mainly Ga x O y The clusters exist and have weak interactions with the carrier. This is consistent with AC-HAADF-STEM ( Figure 4 ) showed the same catalyst structure.

[0083] (6)ToF-SIMS

[0084] The surface structure of the catalyst was characterized in depth using time-of-flight secondary ion mass spectrometry. Through highly sensitive surface analysis, a variety of Ga-Zr-O composite oxide fragment ions were detected on the catalyst surface, as shown in Table 2. In order to quantitatively analyze the distribution characteristics of Ga species on the catalyst surface, the intensities of all detected negative ion fragments were normalized and integrated based on Ga x Zr y O z - The number of Ga atoms in the structural unit (x = 1, 2, 3) is used to classify and count the fragment ions. Figure 6 As shown ( Figure 6 GaZrO statistics for ToF-SIMS x -1C, GaZrO x -5C, GaZrO x Ga-8C catalyst with different Ga atoms x Zr y O z - By comparing the contents of different Ga species, it was found that GaZrO x The percentages of Ga1, Ga2, and Ga3 species on the surface of the -8C catalyst are significantly higher than those on the surface of GaZrO x -5C and GaZrO x -1C catalyst. Of particular note is that GaZrO x-8C catalyst surface Ga3 species relative content increased significantly (compared to GaZrO x -5C catalyst increased by 55.3%), which indicates that there are some Ga x O y This finding is consistent with the previous AC-HAADF-STEM characterization results ( Figure 4 ) and H2-TPR( Figure 5 ) results corroborate each other, further confirming that GaZrO x The presence of Ga clusters on the surface of the -8C catalyst suggests that this surface structural difference may be one of the key factors contributing to the performance differences between different catalysts, providing important experimental evidence for a deeper understanding of the structure-activity relationship of catalysts.

[0085] Table 2GaZrO x -1C, GaZrO x -5C, GaZrO x Ga-8C catalyst x Zr y O z - Fragment Summary

[0086]

[0087] (7) XPS characterization

[0088] X-ray photoelectron spectroscopy, as a surface-sensitive analytical technique, can reveal the oxidation state and content of elements on the catalyst surface. Figure 7 As shown ( Figure 7 Ga2O3, t-ZrO2, GaZrO x -1C, GaZrO x -5C, GaZrO x -8C catalyst XPS spectrum), the Zr 3d orbital of pure t-ZrO2 presents a characteristic double peak, corresponding to Zr 4+ 3D 3 / 2 and 3D 5 / 2 , and its spin-orbit splitting energy is 2.4eV. It is worth noting that the half-height width of the Zr 3d spectrum peak of the catalyst increases after Ga deposition, and a new characteristic peak appears at 182.8eV through peak fitting. Combined with the results of ToF-SIMS, there is Ga on the catalyst surface. x Zr y O z - The fragments were identified as Zr-O-Ga structures. And with the increase of Ga loading, the relative content of Zr-O-Ga species gradually increased.

[0089] In Ga 2p3 / 2 In orbital analysis, the characteristic peak of pure Ga2O3 is located at 1118.0eV, while that of GaZrO x The binding energy of the -5C catalyst is significantly reduced to 1117.3 eV (a decrease of 0.7 eV), indicating that Ga species obtain electrons from the support, confirming the existence of electronic interaction at the Ga-O-Zr interface. x Ga 2p of -8C catalyst 3 / 2 The binding energy (1117.9eV) is close to that of pure Ga2O3. Combined with the AC-HAADF-STEM observation results, it is speculated that Ga x O y The interaction between nanoclusters and supports is weak.

[0090] O 1s analysis showed the presence of three oxygen species on the catalyst surface: lattice oxygen (O 2- ), defective oxygen and hydroxyl at 531.5eV, and surface adsorbed organic matter and water at 532.5eV. The corresponding contents of GaZrO were calculated using the peak areas of the three oxygen species as shown in Table 3. x -1C and GaZrO x The content of defective oxygen and hydroxyl groups on the surface of the -5C catalyst (~16.1%) is comparable to that of pure t-ZrO2 (16.9%), while the content of defective oxygen and hydroxyl groups on the surface of GaZrO2 is x -8C significantly increases the defective oxygen and hydroxyl content to 21.61%, proving that GaZrO x -8C catalyst can produce more defective oxygen and hydroxyl groups.

[0091] Table 3Ga2O3, t-ZrO2, GaZrO x -1C, GaZrO x -5C, GaZrO x -8C catalyst O1s fitting data

[0092] catalyst Lattice oxygen content Defective oxygen and hydroxyl content Surface adsorbed organic matter and water content <![CDATA[Ga2O3]]> 72.30％ 22.23％ 5.47％ <![CDATA[ZrO2]]> 76.69％ 16.99％ 6.32％ <![CDATA[GaZrO x -1C]]> 75.04％ 16.05％ 8.91％ <![CDATA[GaZrO x -5C]]> 75.38％ 16.13％ 8.49％ <![CDATA[GaZrO x -8C]]> 70.26％ 21.61％ 8.13％

[0093] (8) Study on catalytic reaction mechanism

[0094] In situ DRIFT was used to study the formation of Ga-H species and the activation mechanism of H2. The results show that Ga species can effectively promote the dissociation of H2 in catalytic reactions to form surface Ga-H species. In order to further explore the activation sites of H2 and its reaction mechanism, H2 was used as a probe molecule in the temperature range of 100-380℃, combined with in situ diffuse reflectance Fourier transform infrared spectroscopy, to investigate the formation of Ga-H species and the activation mechanism of H2 on GaZrO. x The catalyst surface was systematically studied. During the experiment, at 1981 cm -1 A significant infrared absorption peak was observed near Figure 8 As shown ( Figure 8 GaZrO x -1C, GaZrO x -5C, GaZrO x In situ DRIFT spectra of the -8C catalyst at different temperatures (test conditions: H2 (30 mL / min, 3.0 MPa, 100-380°C)). This peak is attributed to Ga-H species. The intensity of this peak gradually increases with increasing reaction temperature, indicating that Ga sites effectively promote the dissociation of H2 and stabilize the formation of Ga-H species. This result confirms the key role of Ga sites in the H2 activation process.

[0095] In order to further compare the GaZrO x The performance difference of the catalyst is x -1C, GaZrO x -5C and GaZrO x The infrared absorption peak areas of Ga-H species of the three catalysts were integrated and analyzed. Figure 9 As shown ( Figure 9 GaZrO x -1C, GaZrO x -5C, GaZrO x -8C catalyst Ga-H species peak area integration data at different temperatures), GaZrO x -1C, GaZrO x -5C and GaZrO x The peak area of Ga-H species of the -8C catalyst continued to increase in the entire temperature range (100-380 ° C), and the GaZrO x The peak area of the -8C catalyst is significantly higher than that of the other two catalysts, indicating that its surface can produce more Ga-H species, thereby providing sufficient active hydrogen species to promote the further conversion of reaction intermediates into methanol. From the kinetic test results, it can be seen that the activation of H2 or the supply of active hydrogen species has a greater impact on the formation of methanol and dimethyl ether. Therefore, GaZrO x The -8C catalyst produces more Ga-H species, which can make it more active in the catalytic reaction of CO2 hydrogenation to methanol.

[0096] Solid-state NMR technology was used to explore the reaction intermediates. 13 C cross-polarization magic angle spinning nuclear magnetic resonance ( 13 CCPMAS NMR) technology was used to characterize GaZrO x Catalyst in 13 The reaction intermediates in the CO2 hydrogenation process were detected. Figure 10 As shown ( Figure 10 GaZrO x -1C, GaZrO x -5C, GaZrO x -8C catalyst for CO2 hydrogenation 13 C CPMAS NMR spectrum, reaction conditions: 15 mbar 13 CO2+45mbar H2, heating at 250℃ for 20min, * represents spin sideband), in GaZrO x On the surface of the -8C catalyst, characteristic signals of various surface species were detected: bicarbonate (δ 13C =162.5ppm), formate (δ 13C =168.5-169.5ppm), methoxy (δ 13C =56.1ppm), methanol (δ 13C =53.1ppm) and a small amount of dimethyl ether (δ 13C =63.3ppm). By comparing and analyzing the three spectra, we found that the three catalysts have different contents of reaction intermediates. Specifically, compared with GaZrO x Compared with the GaZrO-1C catalyst x The content of formate reaction intermediates on the surface of the -5C catalyst showed a sudden increase, while the content of formate reaction intermediates on the surface of GaZrO x -8C catalyst and GaZrO x -5C catalyst increases the content of formate reaction intermediates more slowly. x The content of methoxy species on the -8C catalyst is significantly higher than that on the GaZrO x -5C and GaZrO x -1C catalyst, and showed GaZrO x -8C>GaZrO x -5C>GaZrO x -1C obvious gradient change.

[0097] In addition, GaZrO x catalyst 13 C high power decoupled magic angle spinning nuclear magnetic resonance spectroscopy (HPDEC MASNMR), such as Figure 11 As shown ( Figure 11 GaZrO x -1C, GaZrO x -5C, GaZrO x -8C catalyst for CO2 hydrogenation 13 C HPDECNMR spectrum, reaction conditions: 15 mbar 13CO2+45mbar H2, heating at 250℃ for 20min). It was found that the evolution of methoxy species is similar to 13 The C CPMAS NMR spectra showed high consistency. With the increase of Ga content in the catalyst (1C→8C), the peak areas of formate and methoxy species showed a significant increasing trend.

[0098] Conclusion: The kinetic analysis (see below) shows that H2 has a great influence on the CO2 hydrogenation reaction to produce methanol and dimethyl ether. Combined with the performance change trend of the catalyst, it is speculated that in GaZrO x Since the Ga element in the -1C catalyst is highly dispersed and has a low content, there is not enough active hydrogen species to undergo hydrogenation after the intermediate species are generated, so the activity of producing methanol and dimethyl ether is very low; GaZrO x The oligomeric Ga species in the -5C catalyst can greatly increase the supply of active hydrogen, so the catalytic performance is significantly improved, while GaZrO x The oligomeric Ga species in the -8C catalyst reach saturation. The sufficient oligomeric Ga species make the catalyst surface have enough active hydrogen species, and the reaction intermediates are quickly converted, with the highest activity in producing methanol and dimethyl ether.

[0099] Application Examples

[0100] Example: GaZrO with different deposition times was prepared by atomic layer deposition (ALD) x -nC (n = 1, 3, 5, 8, 10, 25, 50) catalysts, the catalytic activity of CO2 hydrogenation to methanol and dimethyl ether was tested below.

[0101] The catalyst performance test was carried out on a fixed bed reactor device. The catalyst was first pressed into tablets and then sieved to obtain a catalyst of 40-65 mesh. 0.3g of the catalyst was mixed with 0.7g of quartz sand of the same particle size, and then fixed in the quartz lining tube (inner diameter 6mm) of the stainless steel reaction tube with the help of quartz wool. First, under normal pressure, it was pretreated with 30mL / min of H2 at 340℃ for 2h, and then the reaction temperature was lowered to the starting temperature after the pretreatment. Then, the gas was switched to the reaction gas, and the reaction gas was introduced into the reaction system through a mass flow meter at a ratio of V(H2) / V(CO2) / V(Ar)=72 / 24 / 4. The system pressure was maintained at 3MPa by a back pressure valve. The reaction was then carried out at different temperatures, each temperature lasting 3h, and sampling was carried out continuously within 3h. Unless otherwise specified, the catalysts were all at T=240-380℃, P=3MPa, GHSV=24000mL·g cat -1 ·h -1The reaction was carried out under 37°C conditions. The reaction products primarily consisted of CH₃OH and CH₃OCH₃, with CO as a by-product. The products were analyzed using an online gas chromatograph (Fuli 9790Ⅱ) equipped with both a thermal conductivity detector (TCD) and a flame ionization detector (FID). The FID was an Agilent HP-Plot Q capillary column, 30 m × 0.53 mm × 40 μm, primarily designed for the detection of hydrocarbons such as CH₄, CH₃OH, and CH₃OCH₃. The TCD was a packed column, TDX-01, 2 m × 3 mm, primarily designed for the analysis of gases such as CH₄, Ar, CO, and CO₂. Both the TCD and FID detectors can detect CH₄, so CH₄ was used as a bridge between the TCD and FID for quantitative product analysis. During the reaction, all heating zones in the fixed bed were maintained at 130°C to ensure that all substances were present in gaseous form. The carbon balance for all data was 100 ± 4%.

[0102] Figure 12 Shows different cycle times of GaZrO x Product selectivity of the catalyst in CO2 hydrogenation reaction (reaction conditions: P = 3MPa, T = 240 ~ 380 ° C, H2 / CO2 = 3 / 1, GHSV = 24000mL·g cat -1 ·h -1 ), Figure 12(a) represents the selectivity for (CH3OH + CH3OCH3), and (b) represents the selectivity for CO. The primary products of the reaction include CH3OH, CH3OCH3, and CO; no other byproducts were observed. Analysis of changes in product selectivity reveals that within the reaction temperature range of 240–380°C, the selectivity for (CH3OH + CH3OCH3) decreases with increasing temperature, while the selectivity for CO increases with increasing temperature. This phenomenon is primarily due to the thermodynamic properties of the reaction. The hydrogenation of CO2 to produce CH3OH and CH3OCH3 is an exothermic reaction, which is inhibited by increasing temperature. The formation of CO, on the other hand, is an endothermic process, which is favored by increasing temperature. Therefore, as the temperature increases, the selectivity for methanol and dimethyl ether decreases, while the selectivity for carbon monoxide increases. Furthermore, the number of catalyst deposition cycles also plays a significant role in product selectivity. When the number of atomic layer deposition cycles is less than or equal to 8 and the reaction temperature is within 330°C, the selectivity of (CH3OH+CH3OCH3) gradually increases with the increase in the number of cycles and reaches a maximum value at 8 times. However, when the number of Ga deposition cycles increases further, the selectivity of the catalyst no longer increases significantly, which means that the dispersion of Ga elements on the catalyst surface has reached saturation. Further increasing the Ga loading will generate new Ga species on the surface of t-ZrO2, and this Ga species has a weaker effect on the improvement of reaction activity. Therefore, there is a critical value for the optimal number of catalyst cycles. After exceeding this value, the selectivity of the catalyst tends to stabilize.

[0103] Figure 13 Shows different cycle times of GaZrO x Temperature-dependent trends in CO2 conversion over catalysts for CO2 hydrogenation to CH3OH and CH3OCH3 (reaction conditions: P = 3 MPa, T = 240-380 °C, H2 / CO2 = 3 / 1, GHSV = 24000 mL·g cat -1 ·h -1 ). By analyzing this figure, several key observations can be made: First, the CO2 conversion rate shows a monotonically increasing trend with increasing reaction temperature. This phenomenon can be attributed to the fact that the increase in temperature promotes the activation process of CO2 on the catalyst surface, thereby significantly improving the reaction kinetics. Second, when the number of cycles is 1, 3, 5, and 8, the CO2 conversion rate gradually increases with the increase in the number of cycles; however, when the number of cycles reaches 25 and 50, the conversion rate decreases instead. It is worth noting that although GaZrO x -25C and GaZrO xThe -50C catalyst has a higher Ga content, but the newly generated Ga species exhibit lower catalytic activity. This phenomenon indicates that after eight atomic layer deposition cycles, the active sites of the catalyst have reached saturation, and further increases in the number of cycles will not further improve the catalytic activity.

[0104] GaZrO with different atomic layer deposition cycles x The yield of the product (CH3OH+CH3OCH3) under different catalyst temperatures showed a similar trend, such as Figure 14 As shown ( Figure 14 GaZrO with different cycle times x The trend of CH3OH and CH3OCH3 yields of the catalyst with temperature. Reaction conditions: P = 3 MPa, T = 240-380 °C, H2 / CO2 = 3 / 1, GHSV = 24000 mL·g cat -1 ·h -1 ). The (CH3OH+CH3OCH3) yield of all catalysts first increased and then decreased with the increase of temperature, reaching a maximum at 340°C. This trend shows that the increase in temperature can promote the reaction, especially at 340°C, the catalytic efficiency of the reaction system reached the best state. When the number of cycles reached 8, the yield of the catalyst reached the maximum, and with the increase of the number of subsequent cycles, the performance of the catalyst no longer improved significantly. This means that the 8-cycle GaZrO x The catalyst achieved optimal catalytic performance at 340°C, with a yield of 5.40% for (CH3OH+CH3OCH3). This result, consistent with other performance test results, demonstrates the effectiveness of atomic layer deposition technology in regulating catalyst performance.

[0105] The apparent turnover frequency (TOF) of the catalysts at different deposition cycles was calculated to evaluate the intrinsic activity of Ga in the catalyst. Figure 15 As shown ( Figure 15 GaZrO with different deposition cycles x The apparent TOF value of the catalyst, Figure 15 1C, 3C, 5C, 8C, 10C, 25C, and 50C represent GaZrO x -1C, GaZrO x -3C, GaZrO x -5C, GaZrO x -8C、GaZrO x -10C, GaZrO x -25C、GaZrO x-50C. 1C, 3C, 5C, 8C, 10C, 25C, and 50C in the other figures have the same meaning. Reaction conditions: P = 3 MPa, T = 340°C, H2 / CO2 = 3 / 1, GHSV = 24000 mL·g cat -1 ·h -1 ). The experimental results show that as the weight percentage of metallic Ga in the catalyst increases, its apparent TOF value of (CH3OH+CH3OCH3) shows a gradual downward trend, which indicates that when the Ga element content in the catalyst is low, the apparent activity of Ga atoms is higher and the conversion efficiency is the best. Since the reaction of CO2 hydrogenation to produce methanol and dimethyl ether is a dual-site reaction. The Ga site is responsible for H2 activation, and the Zr site is responsible for CO2 activation. As the Ga content increases, the apparent activity of Ga atoms gradually decreases. This may be because after the Ga loading is increased, some Ga species cannot participate in the formation reaction of methanol and dimethyl ether (there are no Zr species around), thereby reducing the apparent reaction efficiency of the catalyst.

[0106] The calculation formula for TOF is as follows:

[0107]

[0108] In the formula, GHSV is the volume space velocity of the reaction, Yield is the molar yield of (CH3OH+CH3OCH3), m cat is the mass of the catalyst, Ga wt% is the weight percentage of Ga in the catalyst, M Ga is the relative atomic mass of Ga.

[0109] GaZrO with different deposition cycles x The Ga content, (CH3OH+CH3OCH3) yield and apparent TOF data of the catalysts are summarized in Table 4.

[0110] Table 4 GaZrO with different deposition cycles x Ga content of catalyst, (CH3OH+CH3OCH3) yield and TOF

[0111]

[0112]

[0113] Apparent activation energy is a key parameter in the study of catalytic reaction kinetics. Its numerical value directly reflects the sensitivity of the reaction system to temperature, and provides an important basis for in-depth understanding of the catalytic mechanism and optimization of reaction conditions. Based on the Arrhenius equation, five temperature points (260-330°C) with CO2 conversion rates below 10% were selected for kinetic analysis. The specific experimental method is as follows: first, the reaction rate r at each temperature point is measured, and then the Arrhenius relationship curve of ln r and 1000 / T is constructed, and a linear regression analysis is performed. Finally, the apparent activation energy (E a = -k × R, where R = 8.314 J·mol -1 ·K -1 ). The calculation results are as follows Figure 16 As shown ( Figure 16 GaZrO with different cycle times x The apparent activation energy of the catalyst, Figure 16 (a) is the apparent activation energy fitting curve, and (b) is the solution of the Arrhenius equation for GaZrO x -1C, GaZrO x -3C, GaZrO x -5C, GaZrO x -8C、GaZrO x -10C, GaZrO x -25C、GaZrO x The curve is drawn from the apparent activation energy of the -50C catalyst. Reaction conditions: P = 3 MPa, T = 260-330 °C, H2 / CO2 = 3 / 1, GHSV = 24000 mL·g cat -1 ·h -1 ), the error bars in the figure are derived from the statistical deviation of the slope of the Arrhenius curve fitting. x For the -1C catalyst, the fitting slope is -9.2±0.52, and the corresponding activation energy error is ±4.3 kJmol -1 (0.52×8.314). Figure 16 It can be seen that with the increase of Ga content, the apparent activation energy of the catalyst shows a significant downward trend: GaZrO x -1C catalyst has the highest activation energy, while GaZrO x -5C and GaZrO x -8C catalyst activation energy decreases in sequence. This regular change is consistent with the x The results are highly consistent with the excellent catalytic performance of the -8C catalyst, indicating that the introduction of Ga species effectively reduces the energy barrier of the CO2 hydrogenation reaction, thereby significantly improving the catalytic activity.

[0114] Apparent activation energy (E a )Calculation process:

[0115]

[0116] Substituting in and taking the logarithm we get: Right now

[0117] r A Calculation formula:

[0118] In the above formula, k is the reaction rate constant, A0 is the pre-exponential factor, A1 and A2 are constants, and E a is the apparent activation energy, R is the molar gas constant, T is the temperature, r A is the reaction rate, P CO2 and P H2 are the partial pressures of CO2 and H2, m and n represent the reaction orders of CO2 and H2, respectively. CO2 is the CO2 conversion rate, CO2% is the content of CO2 in the reaction system, S (CH3OH+CH3OCH3) The selectivity is (CH3OH+CH3OCH3).

[0119] Plot ln r against 1000 / T, select five temperature points (260-330°C) where the CO2 conversion rate is less than 10%, and find the slope to calculate E. a .

[0120] GaZrO with different cycle times x The calculated values of the apparent activation energies of the catalysts are listed in Table 5.

[0121] Table 5 GaZrO with different cycle times x Calculated values of the apparent activation energy of the catalyst

[0122] catalyst <![CDATA[E a / kJ mol -1 ]]> <![CDATA[GaZrO x -1C]]> 76.3±4.3 <h2 style=";text-align:left;direction:ltr"><![CDATA[GaZrO <h2 style=";text-align:left;direction:ltr"> x <h2 style=";text-align:left;direction:ltr"> -3C]]><h2 style=";text-align:left;direction:ltr"> 72.5±4.2 <![CDATA[GaZrO x -5C]]> 69.8±4.3 <![CDATA[GaZrO x -8C]]> 66.3±4.8 <![CDATA[GaZrO x -10C]]> 68.6±4.0 <![CDATA[GaZrO x -25C]]> 71.4±3.7 <![CDATA[GaZrO x -50C]]> 70.0±3.6

[0123] The reaction order of different catalysts was determined by controlling the partial pressures of the reactants. The experiments were conducted at a constant temperature of 340°C. By varying the partial pressure ratio of CO₂ and H₂ (see Table 6 for specific parameters), the effect of reactant concentration on catalytic performance was systematically investigated. By analyzing the relationship between the reaction rate and partial pressure, the reaction order of each catalyst for CO₂ and H₂ was determined.

[0124] Table 6 Gas ratio in reaction order test experiment

[0125]

[0126] In Table 6, a is the theoretical flow rate. During operation, the actual flow rate should be calculated according to the working curve of the flow meter. The unit is mL / min.

[0127] GaZrO x -1C, GaZrO x -5C and GaZrO x The reaction order test results of the -8C catalyst are as follows Figure 17 As shown, Figure 17 GaZrO with different deposition cycles x Kinetic test results of the catalyst (reaction conditions: P = 3MPa, T = 340 ° C, GHSV = 24000mL·g cat -1 ·h -1 ), Figure 17 (a) to (c) are catalysts GaZrO x -1C, GaZrO x -5C and GaZrO x -8C generates (CH3OH+CH3OCH3) and the relationship between CO and CO2 partial pressures, (d) to (f) are catalysts GaZrO x -1C, GaZrO x -5C and GaZrO x -8C generation (CH3OH+CH3OCH3) and the relationship between CO and H2 partial pressures. Figure 17 The trend of the reaction order of (CH3OH+CH3OCH3) and CO formation and the partial pressure of CO2 and H2 is shown (the specific gas ratio is detailed in Table 6). As the number of catalyst preparation and deposition increases (Ga loading increases), the effect of CO2 partial pressure on the formation rate of (CH3OH+CH3OCH3) gradually increases (reaction order 0.19→0.32, Figure 17 In (a) to (c), this may be because the newly introduced Ga species increases the supply of active hydrogen, accelerates the consumption of CO2 adsorbed species on the catalyst surface, and reduces the CO2 content adsorbed on the catalyst surface. The CO2 reaction order of the CO generation rate on the three catalysts is basically the same (0.27 to 0.31). This means that the effect of CO2 partial pressure on the CO generation rate is similar among the three catalysts. x -1C, GaZrO x -5C and GaZrO x -8C three catalysts ( Figure 17In (d) to (f), the reaction order of (CH3OH+CH3OCH3) corresponding to the H2 partial pressure all showed a large positive value (1.60 to 1.88), indicating that the increase in H2 partial pressure has a significant promoting effect on the generation rate of (CH3OH+CH3OCH3). At the same time, the above results also show that the coverage of active *H on the catalyst surface is relatively low under the reaction conditions. With the increase in the number of depositions, the reaction order gradually increases, indicating that GaZrO x The -8C catalyst has a stronger effect on the formation rate of (CH3OH + CH3OCH3). This is likely due to the presence of more H2 activation sites on the catalyst surface, which more effectively promotes the reaction between H2 and CO2 or its carbon-containing intermediates, thereby increasing the formation rate of (CH3OH + CH3OCH3). When the H2 partial pressure is varied, the CO formation rates corresponding to the three catalysts all exhibit negative reaction orders (-0.17 to -0.05), indicating that increasing H2 concentration inhibits CO formation.

[0128] In order to further evaluate the stability of the catalyst, GaZrO x The stability test of -50C catalyst was conducted at 340℃ for 240h (10 days). The main purpose of the stability test is to check whether the performance of the catalyst will decline during the long-term reaction process, so as to ensure that it can maintain good catalytic activity and selectivity in practical applications. Figure 18 As shown ( Figure 18 GaZrO x Stability test of -50C catalyst. Reaction conditions: P = 3MPa, T = 340℃, H2 / CO2 = 3 / 1, GHSV = 24000mL·g cat -1 ·h -1 ), the catalyst's CO2 conversion, (CH3OH + CH3OCH3) selectivity, and yield remained unchanged throughout the test. This demonstrates the catalyst's excellent durability under the reaction conditions. This result lays a solid foundation for the catalyst's application in practical industrial reactions.

[0129] Comparative Example

[0130] Table 7 shows the catalysts GaZrO prepared by different methods. x Comparison of catalytic performance of CO2 hydrogenation to methanol and dimethyl ether, reaction conditions: T = 340 ° C, P = 3 MPa, H2 / CO2 = 3 / 1, GHSV = 24000 mL g cat -1 ·h -1 .

[0131] Table 7 Catalysts GaZrO prepared by different methods xCatalytic performance for CO2 hydrogenation to methanol and dimethyl ether

[0132]

[0133] In Table 7, [1] Feng W.-H., Yu M.-M., Wang L.-J., et al. Insights into bimetallic oxide synergy during carbon dioxide hydrogenation to methanol anddimethyl ether over GaZrO x oxide catalysts[J].ACS Catalysis,2021,11:4704-4711.

[0134] [2] Miao Yuting. Effect of ZrO2 crystal form in Ga2O3 / ZrO2 catalyst on CO2 hydrogenation performance [Master's thesis]. Lanzhou: Lanzhou University. 2023.

[0135] It can be seen from Table 7 that when the weight percentage of Ga is similar, the GaZrO prepared by atomic layer deposition x The apparent TOF value of the -25C catalyst is similar to that of the catalyst prepared by solvent thermal + impregnation method, and both are significantly higher than that of the catalyst prepared by EISA method, which greatly improves the apparent reaction efficiency of the site. x The weight percentage of Ga in the -8C catalyst is only 2.28wt%, which is comparable to that of GaZrO x -25C catalyst has the same yield, and GaZrO x The TOF values of the -8C catalysts are GaZrO prepared by EISA method. x The catalyst activity was 2.3 and 1.8 times that of the GTZ-5 catalyst prepared by the solvothermal method, respectively, which also proves the advantages of the catalyst prepared by the present invention.

[0136] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation thereto. It should be noted that those skilled in the art may make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications shall also be considered within the scope of protection of the present invention.

Claims

1. A GaZrO x The method for preparing a catalyst is characterized in that: The following steps are involved: Atomic layer deposition of t-ZrO2 was performed to obtain GaZrO x Catalyst; the number of atomic layer deposition is 1 to 50 times, and a single atomic layer deposition includes sequentially performing a first half reaction and a second half reaction, wherein the first half reaction uses trimethylgallium as a precursor, and the second half reaction uses water vapor as a precursor.

2. The preparation method according to claim 1, characterized in that The temperature of the atomic layer deposition is 200-240° C., and the vacuum degree is 0.1-100 torr.

3. The preparation method according to claim 1, characterized in that The trimethylgallium and water vapor are respectively carried by carrier gas, and the flow rate of the carrier gas is 20 sccm.

4. The preparation method according to any one of claims 1 to 3, characterized in that In the single atomic layer deposition, the first half reaction time is 0.01 to 1 s, and the second half reaction time is 0.01 to 1 s.

5. The preparation method according to claim 4, characterized in that After the first half reaction and the second half reaction were completed, nitrogen purging was performed respectively. The nitrogen flow rate during the nitrogen purging was 500 sccm and the purging time was 40 s.

6. The preparation method according to claim 1, characterized in that The preparation method of the t-ZrO2 carrier comprises the following steps: zirconyl nitrate, urea and an alcohol solvent are mixed to carry out a solvothermal reaction to obtain a solvothermal product; calcining the solvent thermal product under a protective atmosphere to obtain the t-ZrO2 carrier; The molar ratio of zirconyl nitrate to urea is 1 / 10; the temperature of the solvent thermal reaction is 160-230° C., and the time is 20-72 hours; the temperature of the calcination is 300-500° C., and the time is 3-6 hours.

7. GaZrO prepared by the preparation method according to any one of claims 1 to 6 x catalyst, the GaZrO x The catalyst comprises a t-ZrO2 carrier and a Ga element deposited on the surface of the t-ZrO2 carrier, wherein the Ga element exists in at least one of the following forms: monodisperse, oligomer and cluster. x The content of Ga element in the catalyst is 0.60-6.50 wt%.

8. GaZrO according to claim 7 x A catalyst characterized in that The GaZrO x The specific surface area of the catalyst is 40.5~65.4m 2 / g.

9. GaZrO according to claim 7 or 8 x Application of catalyst in catalytic carbon dioxide hydrogenation to methanol and dimethyl ether.

10. The use according to claim 9, characterized in that The raw gas for the reaction includes hydrogen, carbon dioxide and argon, the volume ratio of hydrogen to carbon dioxide is 2 / 1 to 5 / 1, and the volume percentage of argon in the raw gas is 1 to 5%. The pressure of the reaction is 2 to 5 MPa, the temperature is 240 to 380°C, and the raw gas space velocity is 12000 to 36000 mL·g cat -1 ·h -1 .

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