Ni-ga based catalyst, its preparation method and application

Abstract

The application aims to provide a Ni-Ga based catalyst, a preparation method and application thereof, and belongs to the technical field of catalysts.The Ni-Ga based catalyst has a Ni-Ga alloy as an active phase and CeO2 as a carrier; the total content of the metal Ni-Ga accounts for 3-20 wt% of the weight of the catalyst. The catalyst preparation process comprises the following steps: a mixed solution of nickel and gallium metal salts is impregnated into the CeO2 carrier, rotary evaporation, drying and heat reduction treatment are carried out at a certain temperature to obtain the Ni-Ga / CeO2 catalyst. The Ni-Ga alloy phase effectively inhibits the occurrence of the methanation side reaction due to the unique surface properties, and exhibits excellent catalytic activity, CO selectivity and catalyst stability. The catalyst preparation method is simple, any noble metal is not used in the synthesis process, the production cost is low, and the industrial application is easy.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a Ni-Ga-based catalyst, its preparation method, and its application. Background Technology

[0002] The extensive use of fossil fuels has led to a continuous rise in atmospheric CO2 levels. The CO2 greenhouse effect induces a series of environmental and ecological problems, such as glacial melting, extreme weather, sea-level rise, ocean acidification, and global warming, seriously threatening human survival and sustainable social development. Furthermore, with the acceleration of industrialization, the large-scale extraction of fossil fuels has led to the increasing depletion of traditional energy sources. Against this backdrop of both environmental and energy challenges, new CO2 carbon capture and utilization (CCU) technologies have attracted widespread attention from researchers, especially CO2 hydrogenation catalytic conversion technology. This technology can not only synthesize high-value-added chemicals such as CO, CH4, CH3OH, higher hydrocarbons, and higher alcohols, but also effectively mitigate the greenhouse effect caused by excessive CO2 emissions.

[0003] With the rapid development of large-scale hydrogen production technologies utilizing renewable energy, discontinuous renewable energy sources can be converted into high-energy-density chemical products and fuels through CO2 catalytic hydrogenation technology. Reverse water-gas shift reaction (RWGS) can synthesize CO under mild conditions, and RWGS coupled with Fischer-Tropsch reactions can synthesize hydrocarbons, fuel oils, and other high-value-added chemicals. Therefore, developing high-performance RWGS catalysts is of great significance for carbon dioxide emission reduction, the synthesis of chemical raw materials, and the clean utilization of coal.

[0004] In reverse water-gas shift reaction (RWGS) systems, noble metals such as Pt, Au, Ag, and Pd, as well as non-noble metals such as Cu, Fe, Co, Ni, and Mn, are often used as active metals for supported catalysts. Among them, Cu-based catalysts are among the most promising catalysts for RWGS reactions due to their low cost and high catalytic efficiency. However, Cu particles are prone to agglomeration at high reaction temperatures, leading to severe deactivation even in the initial stages of the reaction. Chinese patent CN 109499577 A discloses a method for preparing and applying a Cu-Ni-based catalyst for RWGS reactions, which achieves high activity and high CO selectivity in CO2 hydrogenation by constructing a network structure of the metal catalyst. However, this catalyst exhibits severe deactivation in the first few hours.

[0005] Ni-based catalysts have been widely studied as inexpensive CO2 hydrogenation catalysts. Chinese patent CN 107570162A discloses a nickel-based catalyst for reverse water-gas shift reaction and its preparation method. The addition of lanthanum to the catalyst significantly improves nickel dispersion and reduces methanation side reactions. However, when the Ni loading exceeds 5%, lanthanum cannot promote Ni dispersion, resulting in poor CO selectivity. Chinese patent CN 112604699A discloses a Ni2P / CeO2 catalyst for improving the selectivity of the reverse water-gas shift reaction and its preparation method. This invention uses Ni2P as the active phase in the RWGS reaction, exhibiting good carbon dioxide conversion and high CO selectivity at high temperatures. However, at low temperatures, the catalyst shows poor CO selectivity. Chinese patent application number 201210538164.0 discloses a nickel-cerium catalyst for the reverse water-gas shift reaction, using metallic nickel as the active component and CeO2 as the support. While the prepared Ni / CeO2 catalyst exhibits good catalytic activity and thermal stability in the reverse water-gas shift reaction, the nickel-based catalyst is prone to methanation side reactions, reducing the selectivity of the nickel-cerium catalyst for CO. Therefore, more and more researchers are inclined to develop non-precious metal RWGS catalysts with high activity, high CO selectivity, high stability, and low cost. Summary of the Invention

[0006] The purpose of this invention is to provide a Ni-Ga-based catalyst, its preparation method, and its application. This catalyst has the characteristics of high activity, high CO selectivity, and high stability. The preparation method has the characteristics of simple experimental operation, good performance repeatability, and low synthesis cost.

[0007] The present invention adopts the following technical solution: A Ni-Ga-based catalyst, wherein the catalyst support is CeO2, the active phase is a Ni-Ga alloy phase, the total content of the Ni-Ga alloy phase is 3-20 wt% of the catalyst mass, and the molar ratio of Ni to Ga is 0.1:1-10:1.

[0008] A method for preparing a Ni-Ga-based catalyst includes the following steps: Preparation of S1 and CeO2 supports: CeO2 supports were prepared by calcining cerium source samples in a muffle furnace at high temperature. S2. Preparation of impregnation solution: Dissolve nickel salt and gallium salt in solvent in different proportions and stir until completely dissolved to obtain an impregnation solution containing metallic Ni-Ga. S3. Impregnation: Mix and stir the CeO2 support and impregnation solution for 1-24 hours until the metal Ni-Ga is fully impregnated to obtain the impregnated mixture. S4. Solvent Removal: The impregnated mixture is subjected to solvent rotary evaporation in a reduced pressure or vacuum environment at 50-100℃ until it becomes a paste. S5. Dry the paste-like sample obtained in S4 at 80-120℃. The dried powder is the catalyst precursor. S6. Activation: The catalyst precursor is reduced and activated to obtain the Ni-Ga / CeO2 catalyst.

[0009] Further, in S1, the cerium source is Ce(NO3)3·6H2O, and the calcination conditions are: the cerium source sample is heated from room temperature to 300-600℃ at a heating rate of 1-10℃ / min, and calcined for 2.0-10.0h.

[0010] Furthermore, the calcination conditions are as follows: the cerium source sample is heated from room temperature to 500°C at a heating rate of 2°C / min, and calcined for 4 hours.

[0011] Further, in S2, the nickel salt includes any one of nickel nitrate, nickel chloride, nickel acetate, and nickel acetylacetonate; the gallium salt includes any one of gallium nitrate, gallium chloride, gallium acetate, and gallium acetylacetonate.

[0012] Furthermore, in S2, the solvent includes any one of deionized water, ethanol, and acetone, with deionized water being preferred.

[0013] Furthermore, in S3, the mixing and stirring time is 12 hours.

[0014] Furthermore, in S4, the rotary evaporation conditions are rotary evaporation performed in a vacuum environment at 70°C.

[0015] Furthermore, in S5, the drying is carried out in still air at a drying temperature of 120°C for 12 hours.

[0016] Furthermore, in S6, the reducing gas used in the reduction and activation process is pure hydrogen gas with a purity greater than 99.999% or a hydrogen-containing mixture, wherein the hydrogen content in the mixture is 3%-100%, and the diluting gas other than hydrogen includes nitrogen, argon or helium.

[0017] Furthermore, the flow rate of the reducing gas is 5-80 mL / min, the reduction temperature is 300-700℃, preferably 400-600℃, the reduction time is 1-24 h, and the reduction pressure is atmospheric pressure; the reduction temperature is increased from room temperature to the target reduction temperature at a rate of 1-10℃ / min.

[0018] A Ni-Ga-based catalyst is applied to the reverse water-gas shift reaction.

[0019] A Ni-Ga-based catalyst is applied to a gas-solid phase catalytic reverse water-gas shift reaction. The reaction conditions are as follows: the reactant is a mixture of H2 and CO2, the feed molar ratio of H2 to CO2 is 0.5:1-5:1, the reaction temperature is 200-600℃, the pressure is atmospheric or near atmospheric pressure, and the mass hourly space velocity is 24-72 L / (g·h).

[0020] In this invention, the unique surface properties of the Ni-Ga alloy phase enable the Ni-Ga-based catalyst to significantly promote the reverse water-gas shift reaction while suppressing the methanation side reaction, thereby greatly improving CO selectivity and overcoming the poor selectivity of traditional nickel-based catalysts. The Ni-Ga-based catalyst of this invention has low synthesis cost, a simple preparation method, high catalytic activity, high CO selectivity, and stable reaction performance, making it easy to implement in industrial applications.

[0021] The beneficial effects of this invention are as follows: 1. The only reagents used in the method of this invention are nickel salt, gallium salt, cerium salt, and deionized water, without any other organic reagents, making the raw materials green and environmentally friendly.

[0022] 2. The preparation method of the Ni-Ga-based catalyst for reverse water-gas shift provided by the present invention is simple and reliable, the preparation process is easy to operate, and it is suitable for large-scale production.

[0023] 3. The Ni-Ga-based catalyst for reverse water-gas shift provided by this invention alloys Ni and Ga to form a Ni-Ga alloy phase through high-temperature reduction of the catalyst precursor, effectively suppressing Ni phase transformation and sintering. The unique surface properties of the Ni-Ga alloy phase can suppress the occurrence of methanation side reactions, significantly improving CO selectivity, with low-temperature CO selectivity approaching 100%. The lower Ni:Ga metal ratio exhibits excellent reverse water-gas shift performance, overcoming the shortcomings of poor selectivity and low activity of traditional nickel-based catalysts.

[0024] 4. This invention determines the preparation conditions of the Ni-Ga-based catalyst that are most favorable for improving CO selectivity. The key lies in determining the Ni:Ga ratio.

[0025] 5. Compared with catalysts containing precious metals, the Ni-Ga-based catalyst prepared by this invention has higher economic value and market prospects, and is suitable for industrial application. Attached Figure Description

[0026] Figure 1 XRD patterns of Ni-Ga / CeO2 catalysts with different nickel-gallium ratios; Figure 2 A comparison of the catalytic performance of Ni-Ga / CeO2 catalysts with different nickel-gallium ratios; Figure 3The results show the performance evaluation of Ni-2Ga / CeO2 catalysts under different feed ratios. Detailed Implementation

[0027] The present invention will be described below with reference to specific embodiments, but the implementation of the present invention is not limited thereto. Experimental methods not specifically described in the embodiments are generally performed under conventional conditions and conditions described in the manual, or according to the manufacturer's recommendations. The general equipment, materials, reagents, etc. used are commercially available unless otherwise specified. The raw materials required in the following embodiments and comparative examples are all commercially available.

[0028] Examples 1-5 illustrate the preparation of Ni-Ga / CeO2 catalysts with different nickel-gallium ratios. Example 1 0.7822 g of Ni(NO3)3·6H2O and 3 g of CeO2 support were weighed and added to a round-bottom flask to dissolve. The mixture was then impregnated for 8 h at room temperature (50 rpm) using a rotary evaporator. The slurry was then evaporated under vacuum at 65 °C to a paste-like solid state, and finally dried in a forced-air drying oven at 120 °C for 8 h to obtain the catalyst precursor. The obtained sample was sieved to 20-40 mesh. The catalyst precursor was then subjected to reduction activation treatment to obtain Ni / CeO2. The reduction activation process was as follows: the reduction temperature was increased from room temperature to 450 °C at a rate of 5 °C / min, the reducing atmosphere was hydrogen at a flow rate of 10 mL / min, and the reduction activation time was 1 h.

[0029] Example 2 Except for the amount of Ni(NO3)3·6H2O being 0.4662g and the amount of Ga(NO3)3·6H2O being 0.2048g, the preparation method was exactly the same as in Example 1, yielding 2Ni-Ga / CeO2.

[0030] Example 3 Except for the amount of Ni(NO3)3·6H2O being 0.3397g and the amount of Ga(NO3)3·6H2O being 0.2987g, the preparation method was exactly the same as in Example 1, yielding Ni-Ga / CeO2.

[0031] Example 4 Except for the amount of Ni(NO3)3·6H2O being 0.2329g and the amount of Ga(NO3)3·6H2O being 0.4097g, the preparation method was exactly the same as in Example 1, yielding Ni-2Ga / CeO2.

[0032] Example 5 Except for the amount of Ga(NO3)3·6H2O being 0.5502g, the preparation method was exactly the same as in Example 1, yielding Ga / CeO2.

[0033] The XRD patterns of the catalysts obtained in Comparative Examples 1-5 are shown in the attached figures. Figure 1 As shown, in the XRD pattern, besides the CeO2 diffraction peak, characteristic diffraction peaks belonging to the Ni-Ga alloy were observed at 2θ = 46.8° and 84.5°. Furthermore, the intensity of the Ni-Ga alloy diffraction peaks gradually increased with increasing Ni loading. In summary, during the high-temperature reduction process of the catalyst precursor, Ni and Ga species interact to form the Ni-Ga alloy phase.

[0034] Examples 6-10 illustrate the preparation of Ni-2Ga / CeO2 catalysts treated at different activation temperatures. Example 6 Weigh out 0.2329 g of Ni(NO3)3·6H2O, 0.4097 g of Ga(NO3)3·6H2O, and 3 g of CeO2 support. Add 25 mL of H2O to a round-bottom flask and mix to dissolve. Stir the solution using a rotary evaporator at room temperature (50 rpm) for 8 hours. Then, evaporate the slurry to a paste-like solid under vacuum at 65°C. Dry the paste-like solid in a forced-air drying oven at 120°C for 8 hours to obtain the catalyst precursor. Sieve the obtained sample to 20-40 mesh. The catalyst precursor undergoes reduction activation treatment to obtain the catalyst. The reduction activation process is as follows: the reduction temperature is increased from room temperature to 300°C at a rate of 10°C / min, the reducing atmosphere is hydrogen at a flow rate of 10 mL / min, and the reduction activation time is 1 hour. The catalyst is designated as Ni-2Ga / CeO2-300.

[0035] Example 7 Except for the activation temperature of 400℃, the other preparation methods are exactly the same as in Example 6, and Ni-2Ga / CeO2-400 activated at 400℃ is obtained.

[0036] Example 8 Except for the activation temperature of 450℃, the other preparation methods are exactly the same as in Example 6, and Ni-2Ga / CeO2-450 activated at 450℃ is obtained.

[0037] Example 9 Except for the activation temperature of 500℃, the other preparation methods are exactly the same as in Example 6, and Ni-2Ga / CeO2-500 activated at 500℃ is obtained.

[0038] Example 10 Except for the activation temperature of 600℃, the other preparation methods are exactly the same as in Example 6, and Ni-2Ga / CeO2-600 activated at 600℃ is obtained.

[0039] The catalysts obtained in Examples 1-5 were used in a reverse water-gas shift reaction, and their catalytic activities were compared. The catalytic reaction method was as follows: Step 1: Loading the catalyst precursor. Sieve the catalyst precursor, take 100 mg of 20-40 mesh catalyst precursor, and load it into a fixed-bed quartz tube reactor.

[0040] Step 2: Reduction and activation of the catalyst precursor. The reducing gas is pure hydrogen with a purity greater than 99.999%, at a flow rate of 10 mL / min. The temperature is increased from room temperature to the target reduction temperature at a rate of 10℃ / min, and the reduction time is 60 min.

[0041] Step 3: Catalyst Performance Testing. A mixture of H2 and CO2 was used, with a feed molar ratio of H2:1 to CO2 of 0.5:1–5:1. The mass hourly space velocity (HHSV) was 24–72 L / (g·h), the reaction temperature was 200–450℃, and the pressure was atmospheric or near-atmospheric. The resulting tail gas mixture was cold-trapped and then analyzed by an Agilent 4890D gas chromatograph using a thermal conductivity detector (TCD). H2 was used as the carrier gas, and a TDX-01 packed column was used. N2 was used as the internal standard. The CO2 conversion, CO selectivity, and CH4 selectivity were calculated using the correction factor obtained from the internal standard curve.

[0042] The test results are attached. Figure 2 and attached Figure 3 .

[0043] The CO2 hydrogenation performance of Ni-Ga / CeO2 catalysts with different nickel-gallium molar ratios is as follows: Figure 2 As shown. Under the conditions of normal pressure, a CO2:H2 molar ratio of 1:4, a reaction temperature of 200-400℃, and a mass hourly space velocity of 60 L / (g·h), the CO2 conversion rate of the catalyst is as follows. Figure 2 As shown in (a), the CO2 conversion rate of all Ni-containing catalysts increases with increasing temperature, reaching a maximum at 350-400℃. The CO2 conversion rate of Ni / CeO2 is significantly higher than that of bimetallic nickel-gallium-based catalysts across the entire temperature range (200-400℃), while the conversion rate of Ga / CeO2 is almost zero. This indicates that the dissociation of H2 by metallic Ni effectively promotes the improvement of CO2 hydrogenation performance; however, the introduction of metallic Ga to form a nickel-gallium alloy inhibits the dissociation of H2. Regarding product selectivity, as... Figure 2As shown in (b) and (c), the conversion product of Ni / CeO2 is almost entirely methane, indicating that the active metal Ni can effectively catalyze the methanation reaction. In the nickel-gallium-based catalyst, the selectivity for CO increases with increasing Ga content, while the conversion product of Ga / CeO2 is almost entirely CO. The addition of metallic Ga leads to the formation of the NiGa alloy phase, effectively promoting the reverse water-gas shift reaction. These results indicate that the introduction of metallic Ga alters the reaction pathway of CO2 hydrogenation, causing the CO2 hydrogenation reaction to shift from methanation to reverse water-gas shift reaction. The Ni / Ga ratio has a significant regulatory effect on CH4 selectivity; the higher the Ga content and the lower the Ni content, the stronger the selectivity of the reverse water-gas shift reaction. Figure 2 (d) shows the CO yield of different nickel-gallium-based catalysts within the test range. The CO yield of Ni-2Ga / CeO2 peaks at around 350℃ (approximately 20%), significantly higher than other nickel-gallium-based catalysts. The CO yields of Ni / CeO2 and Ga / CeO2 are almost zero. This indicates that Ni-2Ga / CeO2, obtained by optimizing the Ni / Ga ratio, is an advantageous catalyst for the reverse water-gas shift reaction. Its optimal Ni / Ga ratio and Ga content jointly contribute to the high CO generation efficiency.

[0044] To investigate the effect of feed gas composition (H2 / CO2 feed ratio) on reaction performance, the CO2 methanation reaction performance of Ni-2Ga / CeO2 under different feed ratios was examined. The test results are as follows: Figure 3 As shown, the CO2 conversion rate gradually increases as the H2 / CO2 ratio increases from 1 to 4. When the H2 / CO2 ratio is 3-4, the CH4 selectivity increases significantly and the CO selectivity decreases significantly. By optimizing the H2 / CO2 feed ratio, the reaction pathway and performance of CO2 hydrogenation can be controlled, thereby maximizing the CO yield. This provides a basis for the targeted optimization of CO2 hydrogenation products.

[0045] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A Ni-Ga-based catalyst, characterized in that: The catalyst is supported by CeO2, and the active phase is a Ni-Ga alloy phase. The total content of the Ni-Ga alloy phase is 3-20 wt% of the catalyst mass, wherein the molar ratio of Ni to Ga is 0.1:1-10:

1.

2. A method for preparing the Ni-Ga-based catalyst as described in claim 1, characterized in that: Includes the following steps: Preparation of S1 and CeO2 supports: CeO2 supports were prepared by calcining cerium source samples in a muffle furnace at high temperature. S2. Preparation of impregnation solution: Dissolve nickel salt and gallium salt in solvent in different proportions and stir until completely dissolved to obtain an impregnation solution containing metallic Ni-Ga. S3. Impregnation: Mix and stir the CeO2 support and impregnation solution for 1-24 hours until the metal Ni-Ga is fully impregnated to obtain the impregnated mixture. S4. Solvent Removal: The impregnated mixture is subjected to solvent rotary evaporation in a reduced pressure or vacuum environment at 50-100℃ until it becomes a paste. S5. Dry the paste-like sample obtained in S4 at 80-120℃. The dried powder is the catalyst precursor. S6. Activation: The catalyst precursor is reduced and activated to obtain the Ni-Ga / CeO2 catalyst.

3. The method for preparing a Ni-Ga-based catalyst according to claim 2, characterized in that: In S1, the cerium source is Ce(NO3)3·6H2O, and the calcination conditions are: the cerium source sample is heated from room temperature to 300-600℃ at a heating rate of 1-10℃ / min, and calcined for 2.0-10.0h.

4. The method for preparing a Ni-Ga-based catalyst according to claim 2, characterized in that: In S2, the nickel salt includes any one of nickel nitrate, nickel chloride, nickel acetate, and nickel acetylacetone; The gallium salt includes any one of gallium nitrate, gallium chloride, gallium acetate, and gallium acetylacetonate; The solvent includes any one of deionized water, ethanol, and acetone.

5. The method for preparing a Ni-Ga-based catalyst according to claim 2, characterized in that: In S5, the drying is carried out in still air at a temperature of 120°C for 12 hours.

6. The method for preparing a Ni-Ga-based catalyst according to claim 2, characterized in that: In S6, the reducing gas used in the reduction activation process is pure hydrogen gas with a purity greater than 99.999% or a hydrogen-containing mixture gas, wherein the hydrogen content in the mixture gas is 3%-100%, and the diluting gas other than hydrogen includes nitrogen, argon or helium.

7. The method for preparing a Ni-Ga-based catalyst according to claim 6, characterized in that: The reducing gas has a flow rate of 5-80 mL / min, a reduction temperature of 300-700℃, a reduction time of 1-24 h, and a reduction pressure of atmospheric pressure; the reduction temperature is increased from room temperature to the target reduction temperature at a rate of 1-10℃ / min.

8. A Ni-Ga-based catalyst as described in claim 1 applied to a reverse water-gas shift reaction.

9. The application of the Ni-Ga-based catalyst according to claim 8, characterized in that: The reverse water-gas shift reaction is a gas-solid phase catalytic reverse water-gas shift reaction. The reaction conditions are as follows: the reaction feedstock is a mixture of H2 and CO2, the feed molar ratio of H2 to CO2 is 0.5:1-5:1, the reaction temperature is 200-600℃, the pressure is atmospheric or near atmospheric pressure, and the mass hourly space velocity is 24-72 L / (g·h).

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