A reverse water gas shift catalyst, its preparation method and application

Abstract

The application provides a reverse water gas shift catalyst, a preparation method and application thereof, and the reverse water gas shift catalyst prepared by the preparation method has excellent catalytic activity and high CO selectivity in a reverse water gas shift reaction. The preparation method comprises the following steps: contacting a precipitating salt solution with a precipitant aqueous solution and performing co-precipitation, and simultaneously controlling the reaction temperature to be 40-80 DEG C and the pH to be 6-8; optionally performing aging after the co-precipitation is completed; filtering the obtained precipitate to obtain a filter cake, washing the filter cake, then drying the filter cake, and calcining the filter cake at 300-500 DEG C to obtain the reverse water gas shift catalyst; wherein the precipitating salt solution is a mixed aqueous solution of a soluble salt of divalent metal ions and a soluble salt of trivalent metal ions, the divalent metal ions are selected from divalent ions of Mg and / or Zn, and the trivalent metal ions are selected from trivalent ions of Al, In and / or Ga.

Description

Technical Field

[0001] This invention relates to catalyst technology applicable to reverse water-gas shift reaction, specifically to a method for preparing a reverse water-gas shift catalyst and the application of the obtained catalyst. Background Technology

[0002] Carbon dioxide (CO2) is a globally recognized greenhouse gas, with its concentration reaching 413.2 ppm in 2020, 149% of pre-industrial levels. Resource utilization of carbon dioxide is currently a hot research topic. Reverse water-gas shift reaction (RWGS) is one of the effective ways to achieve carbon dioxide resource utilization, with the reaction equation CO2 + H2 = CO + H2O. The catalyst plays a crucial role in RWGS. Some research on RWGS catalysts has been reported.

[0003] CN103183346A discloses a method for using a reverse water gas shift catalyst in a reverse water gas shift reaction. The method is as follows: (1) Activation of the catalyst: using a 60-100 mesh nickel-cerium catalyst as the reverse water gas shift catalyst, and activating the nickel-cerium catalyst with high-purity carbon dioxide gas at 600-800℃ for 1-2 hours; (2) Reverse water gas shift reaction: mixing the activated nickel-cerium catalyst with 60-100 mesh quartz sand at a weight ratio of 1:2.5-3, passing reverse water gas feedstock gas, and catalytically reacting at 600-800℃ to obtain water gas.

[0004] CN106732743A discloses a mesoporous reverse water gas shift catalyst and its preparation method, which uses a vacuum calcination method to prepare the mesoporous reverse water gas shift catalyst.

[0005] CN106881084A discloses a noble metal catalyst for reverse water-gas shift reaction and its preparation method. The active component of the catalyst is Pt; the promoter is any one or more oxides of Li, Na, K, Rb, and Cs; and the support is mullite.

[0006] CN107051573A discloses a catalyst for reverse water-gas shift reaction and its preparation method. The method includes the following steps: 1) Ni(NO3)2·6H2O and P123 are placed in deionized water and magnetically stirred until completely dissolved; 2) SBA15 is added to the solution obtained in step 1) and adsorbed by stirring at room temperature; 3) The solution obtained after adsorption in step 2) is heated in a water bath and evaporated to a viscous state; 4) The viscous substance obtained in step 3) is dried, and the dried sample is calcined in a muffle furnace, wherein the calcination process includes heating, holding and cooling. Summary of the Invention

[0007] This invention provides a reverse water gas shift catalyst, its preparation method, and its application. The reverse water gas shift catalyst obtained by the preparation method of this invention exhibits good catalytic activity and high CO selectivity in the reverse water gas shift reaction.

[0008] To achieve its objective, the present invention provides the following technical solution:

[0009] This invention provides a method for preparing a reverse water-gas shift catalyst, comprising the following steps:

[0010] The salt solution for precipitation is contacted with the aqueous solution of the precipitant for co-precipitation, while the reaction temperature is controlled at 40-80℃ and the pH is controlled at 6-8. After the co-precipitation is completed, aging is optionally carried out. The obtained precipitate is filtered to obtain a filter cake, the filter cake is washed, and then the filter cake is dried and calcined at 300-500℃ to obtain the reverse water gas shift catalyst.

[0011] The precipitation salt solution is a mixed aqueous solution of a soluble salt of a divalent metal ion and a soluble salt of a trivalent metal ion, wherein the divalent metal ion is selected from divalent ions of Mg and / or Zn, and the trivalent metal ion is selected from trivalent ions of Al, In and / or Ga.

[0012] In a preferred embodiment, the molar ratio of divalent metal ions to trivalent metal ions in the salt solution for precipitation is 0.8-1.2:2.

[0013] In a preferred embodiment, the reaction temperature is 50-75°C and the pH is 6-7.

[0014] In a further preferred embodiment, the reaction temperature is 55-65°C and the pH is 6-6.7.

[0015] Preferably, the precipitant is a weak base, preferably selected from carbonates and / or bicarbonates.

[0016] In some specific embodiments, the calcination is carried out at 300-500°C for 3-5 hours.

[0017] In some specific embodiments, the washed filter cake is washed until the conductivity of the washing liquid is less than 100 μS / cm.

[0018] In some specific embodiments, the salt solution for precipitation and the aqueous solution of the precipitant are added to the reaction vessel in a parallel dripping manner.

[0019] The present invention also provides a reverse water gas shift catalyst prepared by the preparation method described above.

[0020] Another aspect of the present invention provides the application of the above-described reverse water gas shift catalyst, which is used to catalyze the hydrogenation of carbon dioxide to perform a reverse water gas shift reaction to produce carbon monoxide.

[0021] In some embodiments, the reaction conditions for the reverse water-gas shift reaction include: a hydrogen to carbon dioxide volume ratio of 1-10; a reaction pressure of 2-10 MPa; a reaction temperature of 280-600°C; and a mass hourly space velocity of 3000-20000 h⁻¹. -1 .

[0022] The technical solution provided by this invention has the following beneficial effects:

[0023] The reverse water gas shift catalyst prepared by the method of the present invention has excellent catalytic activity for reverse water gas shift reaction. Based on this catalyst, the reverse water gas shift reaction exhibits excellent catalytic performance and high selectivity for the product CO. Detailed Implementation

[0024] To facilitate understanding of the present invention, the following description, in conjunction with embodiments, will further illustrate the invention. It should be understood that the following embodiments are merely for a better understanding of the invention and do not imply that the invention is limited to these embodiments.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The term "and / or" may be used herein to include any and all combinations of one or more of the associated listed items.

[0026] Where specific experimental steps or conditions are not specified in the examples, the corresponding conventional experimental steps or conditions in this technical field can be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0027] This invention provides a method for preparing a reverse water-gas shift catalyst, which mainly includes the following steps:

[0028] The salt solution for precipitation and the aqueous solution of the precipitant are contacted in a reactor for co-precipitation, while the reactor temperature is controlled at 40-80°C and the pH is controlled at 6-8. After co-precipitation, aging is optional. The obtained precipitate is filtered to obtain a filter cake, which is then washed. The obtained filter cake is then dried and calcined at 300-500°C to obtain the reverse water gas shift catalyst.

[0029] The salt solution used for precipitation is a mixed aqueous solution of soluble salts of divalent metal ions and soluble salts of trivalent metal ions. The divalent metal ions are selected from divalent ions of Mg and / or Zn, and the trivalent metal ions are selected from trivalent ions of Al, In and / or Ga.

[0030] In some embodiments, the molar ratio of divalent metal ions to trivalent metal ions in the salt solution for precipitation is 0.8-1.2:2. The preferred molar ratio is used to prepare the reverse water-gas shift catalyst. The resulting catalyst has good catalytic activity and can obtain CO with high selectivity in the catalytic reverse water-gas shift reaction.

[0031] In some preferred embodiments, during the co-precipitation process, the reaction temperature is preferably controlled at 50-75°C and the pH at 6-7. Using these preferred conditions for co-precipitation results in a catalyst with superior catalytic activity, exhibiting improved CO selectivity in the catalytic reverse water-gas shift reaction while maintaining a relatively high reaction conversion rate. In some even more preferred embodiments, during the co-precipitation process, the reaction temperature is preferably controlled at 55-65°C and the pH at 6-6.7. Using these preferred conditions for co-precipitation further achieves a superior balance between high CO selectivity and high reaction conversion rate.

[0032] In some preferred embodiments, the molar ratio of divalent metal ions to trivalent metal ions in the salt solution for precipitation is 0.8-1.2:2, the reaction temperature is 50-75℃, and the pH is 6-7; in some more preferred embodiments, the molar ratio of divalent metal ions to trivalent metal ions in the salt solution for precipitation is 0.8-1.2:2, the reaction temperature is 55-65℃, and the pH is 6-6.7; the catalyst prepared using the preferred method exhibits superior catalytic performance in the reverse water-gas shift reaction.

[0033] In the preparation method of the present invention, the precipitant is preferably a weak base, such as a carbonate (e.g., sodium carbonate, potassium carbonate) and / or a bicarbonate (e.g., sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate). The inventors have found that using a weak base as a precipitant prevents the reaction process from being too violent and is beneficial for obtaining a reverse water gas shift catalyst with good catalytic performance.

[0034] This invention employs co-precipitation technology to prepare a reverse water-gas shift catalyst. Unless otherwise specified, the co-precipitation process can be performed according to conventional methods. In some embodiments, the salt solution and the aqueous solution of the precipitant are added to the reactor in a parallel-flow dripping manner. In some preferred embodiments, aging is performed after co-precipitation, for example, for 0.5-10 hours, preferably 0.5-1 hour. After complete co-precipitation, the filter cake obtained is washed, specifically with water, preferably until the conductivity of the washing liquid is less than 100 μS / cm.

[0035] In the preparation method of the present invention, the soluble salts of divalent metal ions and trivalent metal ions used in the salt solution for precipitation can be, but are not limited to, the corresponding nitrates, carbonates, chloride salts, sulfates and their hydrates, etc. The specific selection of soluble salts can adopt the types conventionally used in coprecipitation technology, which will not be elaborated in detail.

[0036] In the preparation method of this invention, the purpose of drying the obtained filter cake is to remove free water. Preferably, the cake is dried until the moisture content is less than 1 wt%. Drying can be carried out under conventional drying conditions in the art, such as at around 110°C, for example, for 10-16 hours. After drying, the cake is calcined at 300-500°C. The inventors have found that calcination at this temperature is beneficial for obtaining a reverse water-gas shift catalyst with good catalytic activity and excellent CO selectivity. The calcination time is, for example, 3-5 hours.

[0037] This invention also provides a reverse water-gas shift catalyst prepared by the method described above. The catalyst obtained by the method described above has porous microstructures and a high specific area, making it particularly suitable for application in reverse water-gas shift reactions. It exhibits good catalytic activity and excellent CO selectivity.

[0038] This invention also provides the application of the aforementioned reverse-flow gas shift catalyst, which is particularly suitable for catalyzing the hydrogenation of carbon dioxide to produce carbon monoxide via a reverse-flow gas shift reaction. Specific process conditions for the reverse-flow gas shift reaction can be referred to existing processes in the art; in some embodiments, the reaction conditions for the reverse-flow gas shift reaction using the catalyst of this invention include: a hydrogen to carbon dioxide volume ratio of 1-10; a reaction pressure of 2-10 MPa; a reaction temperature of 280-600°C; and a mass hourly space velocity of 3000-20000 h⁻¹. -1 A small amount of nitrogen gas can also be introduced into the reaction system, for example, nitrogen gas with a volume fraction of about 6%.

[0039] In some embodiments, the catalyst provided by the present invention is used to carry out the reverse water-gas shift reaction, and the CO2 single-pass conversion rate reaches 20-36%, and the product CO selectivity is as high as 80-100%.

[0040] The present invention will be further illustrated below with reference to embodiments:

[0041] Example 1

[0042] Weigh out 828g of zinc nitrate hexahydrate and 2087g of aluminum nitrate nonahydrate (Zn). 2+ With Al 3+The molar ratio of sodium carbonate to sodium carbonate is 1:2. Add water to prepare a 4L aqueous solution for later use, which is called salt solution A for precipitation. Weigh 960g of sodium carbonate and add water to prepare a 4L aqueous solution for later use, which is called aqueous solution B for precipitation.

[0043] In a 10L reactor, a salt solution A and an aqueous solution B for precipitation were added dropwise in a parallel flow, maintaining a uniform rate of addition. The reaction temperature was controlled at 80℃, and the pH was maintained at 8 during precipitation. After precipitation, stirring was continued at the same temperature for 1 hour. The mixture was filtered to obtain a filter cake, which was then washed with water repeatedly until the conductivity of the washings was less than 100 μS / cm. The filter cake was then dried at 110℃ to remove free water, forming a precursor with a water content of less than 1 wt%. This precursor was then transferred to a muffle furnace for calcination at 350℃ for 4 hours to obtain the target catalyst.

[0044] The catalyst obtained in Example 1 was subjected to a reverse water-gas shift reaction under the following conditions:

[0045] The volumetric composition of the feed gas was: H2 71%, CO2 23%, N2 6%; the reaction pressure was 3 MPa, the reaction temperature was 400℃, and the mass hourly space velocity was 3000 h⁻¹. -1 Gas chromatography analysis yielded the following reaction results: CO2 single-pass conversion rate of 30%, and CO selectivity of 87%.

[0046] Example 2

[0047] The same procedure was followed as in Example 1. Similarities will not be repeated here; only the differences will be explained: Zn in salt solution A used for precipitation... 2+ With Al 3+ The molar ratio was 1.2:2, and the precipitant aqueous solution B was a 2.5 mol / L potassium carbonate aqueous solution; the reaction temperature was controlled at 40℃, and the pH value was controlled at 7.5 during the precipitation process. The calcination temperature was 400℃, and the calcination time was 3 hours.

[0048] The catalyst obtained in Example 2 was subjected to a reverse water-gas shift reaction under the following conditions:

[0049] The volumetric composition of the feed gas was: H2 71%, CO2 23%, N2 6%; the reaction pressure was 3 MPa, the reaction temperature was 400℃, and the mass hourly space velocity was 3000 h⁻¹. -1 Gas chromatography analysis yielded the following reaction results: CO2 single-pass conversion rate 21.5%, and CO selectivity 80.2%.

[0050] Example 3

[0051] Weigh out 828g of zinc nitrate hexahydrate and 2087g of aluminum nitrate nonahydrate (Zn). 2+ With Al3+ The molar ratio of sodium carbonate to sodium carbonate is 1:2. Add water to prepare a 4L aqueous solution for later use, which is called salt solution A for precipitation. Weigh 960g of sodium carbonate and add water to prepare a 4L aqueous solution for later use, which is called aqueous solution B for precipitation.

[0052] In a 10L reactor, a salt solution A and an aqueous solution B for precipitation were added dropwise in a parallel flow, maintaining a uniform rate of addition. The reaction temperature was controlled at 70℃, and the pH was maintained at 7 during precipitation. After precipitation, stirring was continued at the same temperature for 1 hour. The mixture was filtered to obtain a filter cake, which was then washed with water repeatedly until the conductivity of the washings was less than 100 μS / cm. The filter cake was then dried at 110℃ to remove free water, forming a precursor with a water content of less than 1 wt%. This precursor was then transferred to a muffle furnace for calcination at 350℃ for 4 hours to obtain the target catalyst.

[0053] The catalyst obtained in Example 3 was subjected to a reverse water-gas shift reaction under the following conditions:

[0054] The volumetric composition of the feed gas was: H2 71%, CO2 23%, N2 6%; the reaction pressure was 3 MPa, the reaction temperature was 400℃, and the mass hourly space velocity was 3000 h⁻¹. -1 Gas chromatography analysis yielded the following reaction results: CO2 single-pass conversion rate of 31%, and CO selectivity of 100%.

[0055] Example 4

[0056] The same process was carried out as in Example 3. The similarities will not be repeated here. Only the differences will be explained below: the reaction temperature was controlled at 63°C and the pH value was controlled at 6.3 during the precipitation process.

[0057] The catalyst obtained in Example 4 was subjected to a reverse water-gas shift reaction under the following conditions:

[0058] The volumetric composition of the feed gas was: H2 71%, CO2 23%, N2 6%; the reaction pressure was 3 MPa, the reaction temperature was 400℃, and the mass hourly space velocity was 3000 h⁻¹. -1 Gas chromatography analysis yielded the following reaction results: CO2 single-pass conversion rate of 35.2% and CO selectivity of 100%.

[0059] Example 5

[0060] The procedure was carried out in accordance with Example 3. Similarities will not be repeated here; only the differences are described: the precipitant aqueous solution B was a 2.7 mol / L potassium carbonate aqueous solution; the reaction temperature was controlled at 75°C, and the pH value was controlled at 6.8 during precipitation. The calcination temperature was 300°C, and the calcination time was 5 hours.

[0061] The catalyst obtained in Example 5 was subjected to a reverse water-gas shift reaction under the following conditions:

[0062] The volumetric composition of the feed gas was: H2 71%, CO2 23%, N2 6%; the reaction pressure was 3 MPa, the reaction temperature was 400℃, and the mass hourly space velocity was 3000 h⁻¹. -1 Gas chromatography analysis yielded the following reaction results: CO2 single-pass conversion rate of 33.6% and CO selectivity of 99.7%.

[0063] Example 6

[0064] The procedure was carried out in accordance with Example 3. Similarities will not be repeated here; only the differences will be explained: In the precipitant salt solution A, zinc nitrate hexahydrate was replaced with magnesium chloride hexahydrate, wherein Mg... 2+ With Al 3+ The molar ratio was 0.8:2, and the precipitant aqueous solution B was a sodium carbonate aqueous solution with a concentration of 2.8 mol / L; the reaction temperature was controlled at 70℃, and the pH value was controlled at 7 during the precipitation process. The calcination temperature was 400℃, and the calcination time was 4 hours.

[0065] The catalyst obtained in Example 6 was subjected to a reverse water-gas shift reaction under the following conditions:

[0066] The volumetric composition of the feed gas was: H2 71%, CO2 23%, N2 6%; the reaction pressure was 2 MPa, the reaction temperature was 400℃, and the mass hourly space velocity was 5000 h⁻¹. -1 Gas chromatography analysis yielded the following reaction results: CO2 single-pass conversion rate of 34.9% and CO selectivity of 97.3%.

[0067] Example 7

[0068] The procedure was carried out in accordance with Example 1, except that the Zn in the salt solution A used for precipitation was different. 2+ With Al 3+ The molar ratio was 0.9:2, and the precipitant aqueous solution B was a 2.5 mol / L sodium bicarbonate aqueous solution; the reaction temperature was controlled at 50℃, and the pH value was controlled at 7.9 during the precipitation process. The calcination temperature was 400℃, and the calcination time was 3 hours.

[0069] The catalyst obtained in this embodiment was subjected to a reverse water-gas shift reaction under the following conditions:

[0070] The volumetric composition of the feed gas was: H2 71%, CO2 23%, N2 6%; the reaction pressure was 3 MPa, the reaction temperature was 350℃, and the mass hourly space velocity was 20000 h⁻¹. -1 Gas chromatography analysis yielded the following reaction results: CO2 single-pass conversion rate of 20.6% and CO selectivity of 90%.

[0071] Example 8

[0072] The procedure was carried out in accordance with Example 1, except that the Zn in the salt solution A used for precipitation was different. 2+ With Al 3+ The molar ratio was 1.1:2, and the precipitant aqueous solution B was a 2.5 mol / L sodium bicarbonate aqueous solution; the reaction temperature was controlled at 45℃, and the pH value was controlled at 8 during the precipitation process. The calcination temperature was 300℃, and the calcination time was 5 hours.

[0073] The catalyst obtained in Example 2 was subjected to a reverse water-gas shift reaction under the following conditions:

[0074] The volumetric composition of the feed gas was: H2 71%, CO2 23%, N2 6%; the reaction pressure was 3 MPa, the reaction temperature was 400℃, and the mass hourly space velocity was 10000 h⁻¹. -1 Gas chromatography analysis yielded the following reaction results: CO2 single-pass conversion rate 25.6%, and CO selectivity 94.7%.

[0075] Table 1 Summary of Experimental Results

[0076]

[0077]

[0078] In summary, the reverse water-gas shift catalyst prepared by the method of this invention exhibits good catalytic activity and achieves high CO selectivity in the reverse water-gas shift reaction. In Examples 3-6, controlling the reaction temperature of the coprecipitation reaction at 50-75℃ and the pH at 6-7 allows for better CO selectivity at a relatively high conversion rate. More preferably, Example 4 differs from Example 3 mainly in that the reaction temperature of the coprecipitation reaction is controlled at 55-65℃ and the pH at 6-6.7, which better balances relatively high conversion rate and CO selectivity.

[0079] It is readily understood that the above embodiments are merely illustrative examples for clear explanation and do not imply that the invention is limited thereto. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. An application of a reverse water gas shift catalyst, characterized in that, The reverse water-gas shift catalyst is used to catalyze the hydrogenation of carbon dioxide to produce carbon monoxide via a reverse water-gas shift reaction. The preparation method of the catalyst includes the following steps: The salt solution for precipitation is contacted with the aqueous solution of the precipitant for co-precipitation, while the reaction temperature is controlled at 55-65℃ and the pH is controlled at 6-6.

7. After the co-precipitation is completed, aging is optionally carried out. The obtained precipitate is filtered to obtain a filter cake, the filter cake is washed, and then the filter cake is dried and calcined at 300-400℃ to obtain the reverse water gas shift catalyst. The precipitation salt solution is a mixed aqueous solution of a soluble salt of a divalent metal ion and a soluble salt of a trivalent metal ion, wherein the divalent metal ion is selected from divalent ions of Mg and / or Zn, and the trivalent metal ion is selected from trivalent ions of Al, In and / or Ga.

2. The application according to claim 1, characterized in that, In the salt solution used for precipitation, the molar ratio of divalent metal ions to trivalent metal ions is 0.8-1.2:

2.

3. The application according to any one of claims 1-2, characterized in that, The precipitant is a weak base.

4. The application according to claim 3, characterized in that, The precipitant is selected from carbonates and / or bicarbonates.

5. The application according to any one of claims 1-2, characterized in that, The roasting is carried out at 300-400℃ for 3-5 hours.

6. The application according to any one of claims 1-2, characterized in that, The washed filter cake is washed until the conductivity of the washing liquid is less than 100 µS / cm.

7. The application according to any one of claims 1-2, characterized in that, The salt solution for precipitation and the aqueous solution of the precipitant are added to the reaction vessel in a parallel dripping manner.

8. The application according to any one of claims 1-2, characterized in that, The reaction conditions for the reverse water-gas shift reaction include: a hydrogen to carbon dioxide volume ratio of 1-10; a reaction pressure of 2-10 MPa; a reaction temperature of 280-600℃; and a mass hourly space velocity of 3000-20000 h⁻¹. -1 .

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