An inverse water gas shift catalyst, its preparation method and application

Abstract

The present invention discloses a reverse water-gas shift catalyst, a preparation method thereof, and an application thereof. The catalyst is a confined nickel phosphide catalyst Ni x P y @A, wherein Ni x P y is nickel phosphide and A is a mesoporous silica support; the preparation method of the catalyst is as follows: H3PO4 and Ni(NO3)2·6H2O are dissolved in pure water, and then the aqueous solution is added to n-hexane containing the support A; then, the mixed solution is sealed and stirred evenly, and then the sealing condition is removed and continuous stirring is carried out until all the n-hexane volatilizes; finally, the remaining material after volatilization is subjected to temperature-programmed reduction to obtain the reverse water-gas shift catalyst Ni x P y @A; the catalyst prepared by the present invention is used for the selective hydrogenation of CO2 by thermal catalysis to produce CO, which can not only treat the greenhouse gas CO2, but also produce syngas with high industrial value, and has good environmental and economic benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and particularly to a reverse water-gas shift catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] With the large emission of CO 2 greenhouse gases, global warming has become increasingly serious, triggering a series of environmental problems, such as the melting of glaciers and permafrost, the rise of sea level, the redistribution of global precipitation, etc., posing a great threat to the biosphere and human beings. Carbon capture and utilization (CCU) technology can catalytically convert CO in waste gas 2 into value-added products, which can not only reduce the carbon footprint but also generate economic benefits. The thermal catalytic reduction of CO 2 with renewable hydrogen is considered a feasible method for large-scale application. Under atmospheric pressure, CO 2 can be hydrogenated to CH 4 through the Sabatier reaction, or hydrogenated to CO through the reverse water-gas shift reaction. The highly selective hydrogenation of CO 2 to produce CO is considered a promising approach because CO and excess hydrogen as syngas can produce a variety of high-value-added chemicals and fuels through Fischer-Tropsch synthesis.

[0003] Generally, active metals such as Ni, Ru, and Rh are beneficial to the production of CH 4 , while Cu, Pd, and Pt are highly selective for CO. However, noble metal-based catalysts are limited in use due to high costs, and copper-based catalysts have poor stability due to easy sintering in a high-temperature H 2 atmosphere. A strategy for designing a reverse water-gas shift catalyst is to control the particle size of the metal, because larger nanoparticles are beneficial to the formation of CH 4 , while single atoms and nanoclusters contribute to the formation of CO. However, it is difficult to precisely control the size, and nanoclusters are prone to sintering at high temperatures. Constructing dual-metal active sites is another widely used strategy. However, the temperature dependence and inhomogeneity of the dual-metal structure may hinder perfect CO selectivity.

[0004] Nickel phosphide has a crystal structure in which Ni atoms are effectively dispersed by P atoms. Among the numerous crystal forms of nickel phosphide, Ni 12 P 5 and Ni 2 P have high thermal stability and have been widely studied in the catalytic field. Recently, Ni 12 P 5 has been found to have almost 100% CO selectivity as a photothermal catalyst for photocatalytic hydrogenation of CO 2 . It is worthy of further confirmation that Ni 12 P5 Whether it is an ideal active species and study the effect of different nickel phosphide crystal forms on CO 2 hydrogenation.

[0005] The traditional method for preparing nickel phosphide is the impregnation method. This method is simple and convenient but cannot effectively confine the Ni source and P source in the pores of the mesoporous material and cannot effectively control the size of the nickel phosphide nanoparticles. Mesoporous silica SBA-15 has a regular mesoporous structure and a large specific surface area, making it suitable as the carrier of the confined catalyst. The confined active species often exhibit higher activity and stability due to the confinement effect. The main problem at present is how to effectively introduce the Ni source and P source into the pores of SBA-15 to prepare a confined nickel phosphide catalyst, so as to effectively improve the reaction activity on the basis of high CO selectivity. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a reverse water-gas shift catalyst, its preparation method and application.

[0007] The technical solution of the present invention is: a reverse water-gas shift catalyst, the catalyst is a confined nickel phosphide catalyst Ni x P y @A, where Ni x P y is nickel phosphide and A is a mesoporous silica carrier. The weight percentage composition of the catalyst is: Ni: 5-10 wt%, P: 0.5-2.5 wt%, and the balance is A.

[0008] Further, the nickel phosphide Ni x P y is selected from Ni 12 P 5 、Ni 2 P or Ni 3 P.

[0009] Note: The activities and CO selectivities of the above nickel phosphides with different crystal forms are different, and the corresponding reverse water-gas shift catalyst can be selected according to actual usage requirements.

[0010] Further, the mesoporous silica carrier A is selected from SBA-15, MCM-41, HMS, KIT-6 or SBA-16.

[0011] Note: The above-listed mesoporous silicas can all be used in the preparation of the reverse water-gas shift catalyst of the present invention. These mesoporous silicas all have mesoporous channels and can confine nickel phosphide nanoparticles.

[0012] The present invention also provides a preparation method of the reverse water-gas shift catalyst as described in claim 1, which is characterized by including the following steps:

[0013] S1. Dissolve H 3 PO 4 and Ni(NO 3 ) 2 ·6H 2 O in pure water, and then add the aqueous solution to n-hexane containing support A to obtain a mixed solution;

[0014] S2. Seal and stir the mixed solution for 3 h, then remove the sealing condition and continue stirring until all the n-hexane has evaporated to obtain the material for absorbing the aqueous solution;

[0015] S3. Reduce the material for absorbing the aqueous solution by temperature-programmed reduction in H 2 at 650 °C for 4 h to obtain the reverse water-gas shift catalyst.

[0016] Note: The reverse water-gas shift catalyst is prepared by the double-solvent method. Compared with the impregnation method, this method can effectively confine the Ni source and P source in the pores of the mesoporous material, and the nickel phosphide nanoparticles have uniform and fine particle sizes.

[0017] Furthermore, the mass concentration of H 3 PO 4 is 85%, and the mass ratio of H 12 P 5 in the aqueous solution to Ni(NO 3 ) 4 ·6H 3 O is 0.16:1 when preparing Ni 2 ·6H 2 O, the mass ratio of H 2 P in the aqueous solution to Ni(NO 3 ) 4 ·6H 3 O is 0.32:1 when preparing Ni 2 ·6H 2 O, and the mass ratio of H 3 P in the aqueous solution to Ni(NO 3 ) 4 ·6H 3 O is 0.12:1 when preparing Ni 2 ·6H 2 O; the mass ratio of the aqueous solution, support A and n-hexane is 1:1:20.

[0018] Note: Different nickel phosphide crystal forms will be prepared with different precursor ratios, showing different catalytic effects. The corresponding precursor ratio can be selected according to the actual usage requirements.

[0019] Further, during the temperature-programmed reduction process, the heating rate from room temperature to 300 °C is 5 °C / min, and the heating rate from 300 °C to 650 °C is 2 °C / min.

[0020] Note: Reduction does not occur below 300 °C, so rapid heating can save time and cost. Reduction starts above 300 °C, and slow heating is beneficial to crystal growth.

[0021] The present invention also provides an application of the reverse water-gas shift catalyst as described in claim 1, using the catalyst for thermocatalytic CO 2 hydrogenation to produce CO. Before the reaction, the catalyst is reduced in an H 2 atmosphere for 1 h to activate the material; wherein, the H 2 flow rate is 30 mL / min, and the temperature is 600 °C.

[0022] Note: By adopting the above treatment method and parameters, and reducing the catalyst in an H 2 atmosphere before the reaction, the catalyst can be effectively activated.

[0023] Further, the specific method for the catalyst to thermocatalytically hydrogenate CO 2 to produce CO is as follows: Add the catalyst to a fixed-bed reactor, and then mix CO 2 , H 2 and N 2 in a flow rate ratio of 1:4:1 and introduce them into the fixed-bed reactor for continuous reaction; wherein, the space velocity of the mixed gas is 43200 mL h -1 g -1 , and the reaction temperature is 200-600 °C.

[0024] Note: By adopting the above treatment parameters for thermocatalytically hydrogenating CO 2 to produce CO, the prepared reverse water-gas shift catalyst can be efficiently utilized for CO 2 conversion to produce CO, which can effectively improve the conversion rate of greenhouse gas CO 2 and thus improve economic benefits.

[0025] The beneficial effects of the present invention are as follows:

[0026] (1) The present invention provides a novel nickel phosphide confinement strategy, that is, the double-solvent method is used to effectively introduce Ni source and P source into the pores of SBA-15, and then the confined nickel phosphide catalyst is prepared by temperature-programmed reduction. The loading of nickel phosphide is relatively high and the nickel phosphide nanoparticles have uniform and fine particle sizes, which improves the problems that the Ni source and P source cannot be effectively confined in the pores of the mesoporous material and the uneven size of the nickel phosphide nanoparticles when preparing the catalyst by the traditional impregnation method.

[0027] (2) Using the catalyst prepared by the present invention for thermocatalytic CO 2 hydrogenation reaction can achieve a CO selectivity close to 100% and relatively high activity, and the catalyst has good stability, and the catalytic effect is superior to most catalysts in the same industry.

[0028] (3) The catalyst prepared by the present invention is used for thermocatalytic CO 2 selective hydrogenation to prepare CO, which can not only treat the greenhouse gas CO 2 , but also produce syngas with relatively high industrial value, and has good environmental and economic benefits. Description of the Drawings

[0029] Figure 1 is the XRD pattern of Ni 12 P 5 @SBA-15 prepared by the double-solvent method and Ni 12 P 5 / SBA-15, Ni 12 P 5 / SiO 2 、Ni 2 P / SiO 2 and Ni / SiO 2 ;

[0030] Figure 2 is the (a, c, d) TEM images and (b) particle size distribution diagram of Ni 12 P 5 @SBA-15 prepared by the double-solvent method;

[0031] Figure 3 is the (a, c, d) TEM images and (b) particle size distribution diagram of Ni 12 P 5 / SBA-15 prepared by the impregnation method;

[0032] Figure 4 is the (a) TEM image and (b) particle size distribution diagram of Ni / SiO 2 prepared by the impregnation method; (c) TEM image and (d) particle size distribution diagram of Ni 12 P 5 / SiO 2 ; (e) TEM image and (f) particle size distribution diagram of Ni 2 P / SiO 2 ;

[0033] Figure 5 is Ni 12 P 5 @SBA-15 prepared by the double-solvent method and Ni 12 P5 / SBA-15, Ni 12 P 5 / SiO 2 、Ni 2 P / SiO 2 and Ni / SiO 2 XPS spectra in the Ni 2p region;

[0034] Figure 6 NiP@SBA-15 prepared by the dual-solvent method and NiP 12 P 5 / SBA-15 prepared by the impregnation method, and the 12 P 5 / SBA-15, Ni 12 P 5 / SiO 2 (a) Activity comparison chart and (b) selectivity comparison chart of the catalysts;

[0035] Figure 7 NiP 12 P 5 / SiO 2 、Ni 2 P / SiO 2 and Ni / SiO 2 (a) Activity comparison chart and (b) selectivity comparison chart of the catalysts;

[0036] Figure 8 NiP@SBA-15 catalyst prepared by the dual-solvent method, the 12 P 5 stability test chart of the @SBA-15 catalyst. Detailed implementation manners

[0037] The present invention will be further described in detail below in combination with the specific implementation manners to better reflect the advantages of the present invention.

[0038] Example 1

[0039] A reverse water-gas shift catalyst, the catalyst is a confined nickel phosphide catalyst Ni 12 P 5 @SBA-15, the weight percentage composition of the catalyst is: Ni: 9.8 wt%, P: 1.7 wt%, and the balance is SBA-15;

[0040] The preparation method of the above-mentioned reverse water-gas shift catalyst Ni 12 P 5 @SBA-15 includes the following steps:

[0041] Mix H 3 PO 4 (85%) and Ni(NO3 ) 2 ·6H 2 O is dissolved in pure water, and then this aqueous solution is added to n - hexane containing SBA - 15 to obtain a mixed solution; where the mass ratio of H 3 PO 4 , Ni(NO 3 ) 2 ·6H 2 O to pure water is 0.16:1:0.84, and the mass ratio of the aqueous solution, SBA - 15 and n - hexane is 1:1:20; then, the mixed solution is sealed and stirred for 3 h, and then the sealing condition is removed and stirring is continued until all the n - hexane has evaporated, obtaining a material that absorbs the aqueous solution; finally, the material that absorbs the aqueous solution is reduced by temperature - programmed reduction at 650 °C for 4 h in H 2 . The temperature - programmed reduction is specifically as follows: the heating rate from room temperature to 300 °C is 5 °C / min, and the heating rate from 300 °C to 650 °C is 2 °C / min.

[0042] The Ni 12 P 5 @SBA - 15 prepared by the double - solvent method in Example 1 above is subjected to relevant experimental tests, and the following comparative examples are set:

[0043] 1) Comparative Example 1: This comparative example describes the process of preparing Ni 12 P 5 / SBA - 15. The weight percentage composition of the catalyst is: Ni: 9.7 wt%, P: 1.7 wt%, and the balance is SBA - 15;

[0044] SBA - 15, H 3 PO 4 (85%) and Ni(NO 3 ) 2 ·6H 2 O are added to pure water and stirred for 2 h. The mass ratio of H 3 PO 4 , Ni(NO 3 ) 2 ·6H 2 O, SBA - 15 to pure water is 0.16:1:2:40; then it is evaporated to dryness in a 90 °C water bath and dried in an oven at 105 °C; finally, the material is reduced by temperature - programmed reduction at 650 °C for 4 h in H 2 . The heating rate from room temperature to 300 °C is 5 °C / min, and the heating rate from 300 °C to 650 °C is 2 °C / min.

[0045] 2) Comparative Example 2: This comparative example describes the process of preparing Ni 12 P5 / SiO 2 In the process of, the weight percentage composition of the catalyst is: Ni: 9.8 wt%, P: 1.7 wt%, and the balance is SiO 2 ;

[0046] Add SiO 2 , H 3 PO 4 (85%) and Ni(NO 3 ) 2 ·6H 2 O to pure water and stir for 2 h. The mass ratio of H 3 PO 4 , Ni(NO 3 ) 2 ·6H 2 O, SiO 2 to pure water is 0.16:1:2:40; then evaporate to dryness in a water bath at 90 °C and dry in an oven at 105 °C; finally, reduce the material by temperature-programmed reduction in H 2 at 650 °C for 4 h, with a heating rate of 5 °C / min from room temperature to 300 °C and a heating rate of 2 °C / min from 300 °C to 650 °C.

[0047] 3) Comparative Example 3: This comparative example describes the process of preparing Ni 2 P / SiO 2 The weight percentage composition of the catalyst is: Ni: 9.4 wt%, P: 2.2 wt%, and the balance is SiO 2 ;

[0048] Add SiO 2 , H 3 PO 4 (85%) and Ni(NO 3 ) 2 ·6H 2 O to pure water and stir for 2 h. The mass ratio of H 3 PO 4 , Ni(NO 3 ) 2 ·6H 2 O, SiO 2 to pure water is 0.32:1:2:40; then evaporate to dryness in a water bath at 90 °C and dry in an oven at 105 °C; finally, reduce the material by temperature-programmed reduction in H 2 at 650 °C for 4 h, with a heating rate of 5 °C / min from room temperature to 300 °C and a heating rate of 2 °C / min from 300 °C to 650 °C.

[0049] 4) Comparative Example 4: This comparative example describes the process of preparing Ni / SiO2 In the process, the weight percentage composition of the catalyst is: Ni: 10.0 wt%, and the balance is SiO 2 ;

[0050] Add SiO 2 and Ni(NO 3 ) 2 ·6H 2 O to pure water and stir for 2 h. The mass ratio of Ni(NO 3 ) 2 ·6H 2 O, SiO 2 to pure water is 1:2:40; then evaporate to dryness in a water bath at 90 °C and dry in an oven at 105 °C; finally, reduce the material in H 2 at 500 °C for 2 h.

[0051] The characterization results are as follows:

[0052] The XRD patterns of Ni 12 P 5 @SBA-15 prepared by the dual-solvent method and Ni 12 P 5 / SBA-15, Ni 12 P 5 / SiO 2 , Ni 2 P / SiO 2 and Ni / SiO 2 are shown as Figure 1 . The broad diffraction scattering at about 23° in all catalysts belongs to amorphous silica. For Ni / SiO 2 , the characteristic peaks at 44.5°, 51.8° and 76.4° belong to face-centered cubic Ni (JCPDS No. 04-0850). Similarly, the tetragonal Ni 12 P 5 / SiO 2 and Ni 12 P 5 / SBA-15 and the hexagonal Ni 12 P 5 crystal form (JCPDS No. 22-1190) and the hexagonal Ni 2 P / SiO 2 are determined. In addition, for the Ni 2 P 12 P 5 @SBA-15 catalyst, no diffraction peaks of Ni 12 P 5 are observed, which is caused by the small size of the nanoparticles and the surface passivation layer.

[0053] Ni prepared by the double-solvent method 12 P 5 @SBA-15 and its particle size distribution diagram are shown as Figure 2 follows. It can be seen that in the Ni 12 P 5 @SBA-15 catalyst, almost all Ni 12 P 5 nanoparticles are located in the pores of SBA-15, and they are small in size, with an average particle size of 5.8 nm and a relatively concentrated size distribution. This indicates that the double-solvent method is an effective method to confine metal phosphide nanoparticles in the carrier pores. The TEM image and particle size distribution diagram of Ni 12 P 5 / SBA-15 prepared by the double-solvent method are shown as Figure 3 follows. It can be seen that in the Ni 12 P 5 / SBA-15 catalyst, part of the Ni 12 P 5 nanoparticles are outside the pores of SBA-15, and part are inside the pores of SBA-15. Moreover, the sizes of the Ni 12 P 5 nanoparticles are uneven, and the average particle size is relatively large, being 11.9 nm. The TEM images and particle size distribution diagrams of Ni / SiO 2 、Ni 12 P 5 / SiO 2 and Ni 2 P / SiO 2 prepared by the impregnation method are shown as Figure 4 follows. It can be seen that the size distribution of the active nanoparticles is relatively wide, and the average particle size is relatively large. The average particle sizes of Ni / SiO 2 、Ni 12 P 5 / SiO 2 and Ni 2 P / SiO 2 are 13.8 nm, 13.1 nm, and 13.3 nm respectively.

[0054] Ni 12 P 5 @SBA-15 prepared by the double-solvent method and Ni 12 P 5 / SBA-15、Ni 12 P 5 / SiO 2 、Ni 2 P / SiO 2 and Ni / SiO 2The XPS pattern in the Ni 2p region is as shown in Figure 5 . The peak at 852.5 eV in Ni / SiO 2 belongs to zero-valent nickel. In addition, the peak at 852.9 - 853.0 eV in the Ni 12 P 5 catalyst is assigned to nickel with partial positive charge (δ+, 0 < δ < 2), while the binding energy of Ni 2 P / SiO 2 shifts to 853.4 eV for the Ni δ+ species. These results indicate that there is an electron transfer from Ni to P in nickel phosphide, and the electron transfer in Ni 2 P is more than that in Ni 12 P 5 . For all the above catalysts, the peaks in the ranges of 855.5 - 857.1 eV and 860.6 - 862.2 eV correspond to the Ni 2+ species and its satellite peaks respectively. There is Ni 2+ because the catalyst is passivated by air.

[0055] Example 2

[0056] This example describes the application of the catalyst prepared in Example 1 in the thermal catalytic CO 2 selective hydrogenation catalyst. The catalyst is used for the thermal catalytic CO 2 hydrogenation reaction to produce CO. Before the reaction, the catalyst is reduced in an H 2 atmosphere for 1 h; among them, the flow rate of H 2 is 30 mL / min and the temperature is 600 °C. The specific operation of the catalyst for the thermal catalytic CO 2 hydrogenation reaction to produce CO is as follows: Add the catalyst to a fixed-bed reactor, and then mix CO 2 , H 2 and N 2 in a flow rate ratio of 1:4:1 and introduce them into the fixed-bed reactor for continuous reaction; among them, the space velocity of the mixed gas is 43200 mL h -1 g -1 , and the reaction temperature rises from 200 °C to 600 °C, and data is measured once every 50 °C and stabilized for 1 h.

[0057] The Ni 12 P 5 @SBA-15 prepared in the above Example 1 and the Ni 12 P 5 / SBA-15, Ni 12 P 5 / SiO 2 , Ni 2 P / SiO 2and Ni / SiO 2 Perform the thermal catalytic CO 2 hydrogenation reaction of Example 2, with the catalyst dosage being 50 mg each, and the results of the catalytic reaction are as Figure 6 - 7 and Table 1 below show:

[0058] Table 1 Results of the thermal catalytic CO 2 hydrogenation reaction of each catalyst at 600 °C

[0059] Group <![CDATA[CO 2 conversion rate]]> CO Selectivity <![CDATA[Ni 12 P 5 @SBA-15 (Example 1)]]> 51.6％ 99.7％ <![CDATA[Ni 12 P 5 / SBA-15 (Comparative Example 1)]]> 45.4％ 99.1％ <![CDATA[Ni 12 P 5 / SiO 2 (Comparative Example 2)]]> 36.8％ 99.5％ <![CDATA[Ni 2 P / SiO 2 (Comparative Example 3)]]> 6.9％ 100％ <![CDATA[Ni / SiO 2 (Comparative Example 4)]]> 62.7％ 57.5％

[0060] Combined with Example 1 and Comparative Examples 1-2, as Figure 6 and shown in Table 1 above, the CO selectivities of the confined catalyst Ni 12 P 5 @SBA-15, the supported catalyst Ni 12 P 5 / SBA-15 and Ni 12 P 5 / SiO 2 are all close to 100%. While Ni 12 P 5 @SBA-15 has the highest CO 2 conversion rate because the growth of nanoparticles in the SBA-15 pores is restricted by space, thus maintaining a smaller particle size and exposing more active sites. Ni 12 P 5 / SBA-15 only has some Ni 12 P 5 nanoparticles located in the SBA-15 pores, so the activity is lower; while Ni 12 P 5 / SiO 2 has all Ni 12 P 5 nanoparticles located on the SiO 2 surface, resulting in lower activity.

[0061] Combined with Example 1 and Comparative Examples 3-4, as Figure 7 and shown in Table 1 above, although the traditional Ni-based catalyst has high activity, its selectivity for CO is poor and cannot meet the requirements. While the Ni 2 P species shows 100% CO selectivity, but its activity is very low and it is not ideal. Overall, the Ni 12 P 5 species has almost 100% CO selectivity and good activity, verifying that it is an ideal active species for the catalytic reverse water-gas shift reaction. This is because Ni 12 P 5The unique geometric structure of the active species, which has a weak adsorption to the carbonyl group of the reaction intermediate and thus rapidly desorbs to generate CO.

[0062] Meanwhile, in order to further test the Ni 12 P 5 @SBA-15 catalyst for stability, the above catalyst was used for the CO 2 hydrogenation reaction in Example 2. The catalyst dosage was 50 mg, the reaction temperature was 600 °C, and the reaction was continuously carried out for 36 h under unchanged conditions. The stability test results are as Figure 8 and Table 2 below:

[0063] Table 2 Stability test results of the thermal catalytic CO 2 hydrogenation reaction of the catalyst at 600 °C

[0064] Group <![CDATA[CO 2 Conversion rate]]> CO Selectivity <![CDATA[Ni 12 P 5 @SBA-15(1h)]]> 51.6％ 99.7％ <![CDATA[Ni 12 P 5 @SBA-15(36h)]]> 46.6％ 99.8％

[0065] It can be seen from the results in Table 2 above that the Ni 12 P 5 @SBA-15 catalyst after 36 h of reaction, the CO 2 conversion rate slightly decreased from 51.6% to 46.6%, while the CO selectivity remained between 99.6% and 99.9%. The Ni 12 P 5 @SBA-15 showed good stability at a very high reaction temperature, because the structural stability of Ni 12 P 5 and the confinement effect of the SBA-15 pore channels can effectively inhibit the sintering of Ni 12 P 5 nanoparticles.

[0066] Example 3

[0067] This example is basically the same as Example 1, except that the weight percentage composition of the catalyst is: Ni: 5.1 wt%, P: 0.9 wt%, and the balance is SBA-15. And the mass ratio of H 3 PO 4 , Ni(NO 3 ) 2 ·6H 2 O and pure water is 0.08:0.5:1.42, and the mass ratio of the aqueous solution, SBA-15 and n-hexane is 1:1:20.

[0068] Example 4

[0069] This example is basically the same as Example 1, except that the weight percentage composition of the catalyst is: Ni: 7.4 wt%, P: 1.3 wt%, and the balance is SBA-15. And the mass ratio of H3 PO 4 、Ni(NO 3 ) 2 ·6H 2 O and pure water have a mass ratio of 0.12:0.75:1.13, and the mass ratio of the aqueous solution, SBA-15 and n-hexane is 1:1:20.

[0070] Perform the thermal catalytic CO 12 P 5 @SBA-15 prepared in Examples 3 and 4 above for the hydrogenation reaction in Example 2. The amount of the catalyst used is 50 mg each. At 600 °C, the results of the catalytic reaction are shown in Table 3 below: 2 Hydrogenation reaction, the amount of the catalyst used is 50 mg each. At 600 °C, the results of the catalytic reaction are shown in Table 3 below:

[0071] Table 3 Results of the thermal catalytic CO 2 hydrogenation reaction of each catalyst at 600 °C

[0072] Group <![CDATA[CO 2 Conversion rate]]> CO Selectivity <![CDATA[Ni 12 P 5 @SBA-15 (Example 1)]]> 51.6％ 99.7％ <![CDATA[Ni 12 P 5 @SBA-15 (Example 3)]]> 35.4％ 99.8％ <![CDATA[Ni 12 P 5 @SBA-15 (Example 4)]]> 44.7％ 99.7％

[0073] It can be seen from the results in Table 3 above that the Ni 12 P 5 loading has a certain influence on the activity of the confined catalyst Ni 12 P 5 @SBA-15 in the thermal catalytic CO 2 hydrogenation reaction. The higher the loading, the higher the activity. The catalyst in Example 1 has the highest CO 2 conversion rate, while the Ni 12 P 5 loading has little influence on the CO selectivity.

[0074] Example 5

[0075] This example is basically the same as Example 1, except that the catalyst is the confined nickel phosphide catalyst Ni 2 P@SBA-15. The weight percentage composition of the catalyst is: Ni: 9.5 wt%, P: 2.3 wt%, and the balance is SBA-15. And in the aqueous solution, H 3 PO 4 、Ni(NO 3 ) 2 ·6H 2 O and pure water have a mass ratio of 0.32:1:0.68, and the mass ratio of the aqueous solution, SBA-15 and n-hexane is 1:1:20.

[0076] Example 6

[0077] This example is basically the same as Example 1, except that the catalyst is the confined nickel phosphide catalyst Ni 3P@SBA-15, the weight percentage composition of the catalyst is: Ni: 9.8 wt%, P: 1.3 wt%, and the balance is SBA-15. And in the aqueous solution, the mass ratio of H 3 PO 4 , Ni(NO 3 ) 2 ·6H 2 O and pure water is 0.12:1:0.88, and the mass ratio of the aqueous solution, SBA-15 and n-hexane is 1:1:20.

[0078] Carry out the thermal catalytic CO 2 P@SBA-15, Ni 3 P@SBA-15 prepared in the above Examples 5 and 6 for the hydrogenation reaction in Example 2. The dosage of the catalyst is 50 mg each. At 600 °C, the results of the catalytic reaction are shown in Table 4 below: 2 The results of the thermal catalytic CO

[0079] hydrogenation reaction of each catalyst at 600 °C 2 are as follows

[0080] Group <![CDATA[CO 2 Conversion rate]]> CO Selectivity <![CDATA[Ni 12 P 5 @SBA-15 (Example 1)]]> 51.6％ 99.7％ <![CDATA[Ni 2 P@SBA-15 (Example 5)]]> 11.7％ 100％ <![CDATA[Ni 3 P@SBA-15 (Example 6)]]> 59.4％ 95.9％

[0081] It can be seen from the results in Table 4 above that different nickel phosphide crystal forms confined in SBA-15 have a great influence on the CO 2 hydrogenation reaction. When the crystal form of nickel phosphide is Ni 2 P, the CO selectivity is 100% but the activity is low, while the Ni 3 P crystal form shows a high CO 2 conversion rate but the CO selectivity is not ideal enough. Generally speaking, the Ni 12 P 5 crystal form has relatively high activity and almost 100% CO selectivity. Therefore, Ni 12 P 5 @SBA-15 is a reverse water gas shift catalyst with better comprehensive performance.

Claims

1. A reverse water-gas shift catalyst, characterized in that, The catalyst is a confined nickel phosphide catalyst Ni x P y @A, where Ni x P y is nickel phosphide and A is a mesoporous silica support. The weight percentage composition of the catalyst is: Ni: 5-10 wt%, P: 0.5-2.5 wt%, and the balance is A; the preparation method of the reverse water-gas shift catalyst comprises the following steps: S1. Dissolve H 3 PO 4 and Ni(NO 3 ) 2 ·6H 2 O in pure water, and then add this aqueous solution to n-hexane containing carrier A to obtain a mixed solution; S2. Seal and stir the mixed solution for 3 h, then remove the sealing condition and continue stirring until all of the n-hexane has evaporated to obtain the material that absorbs the aqueous solution; S3. The material that absorbs the aqueous solution is reduced by temperature-programmed reduction at 650 °C for 4 h in H 2 to obtain a reverse water-gas shift catalyst; During the process of the programmed temperature reduction, the heating rate from room temperature to 300 °C is 5 °C / min, and the heating rate from 300 °C to 650 °C is 2 °C / min.

2. The reverse water-gas shift catalyst according to claim 1, characterized in that, The nickel phosphide Ni x P y is selected from Ni 12 P 5 , Ni 2 P or Ni 3 P.

3. The reverse water-gas shift catalyst according to claim 1, characterized in that, the mesoporous silica support A is selected from SBA-15, MCM-41, HMS, KIT-6 or SBA-16.

4. The reverse water-gas shift catalyst according to claim 1, characterized in that, The mass concentration of said H 3 PO 4 is 85%. When preparing Ni 12 P 5 , the mass ratio of H 3 PO 4 in the aqueous solution to Ni(NO 3 ) 2 ·6H 2 O is 0.16:

1. When preparing Ni 2 P, the mass ratio of H 3 PO 4 in the aqueous solution to Ni(NO 3 ) 2 ·6H 2 O is 0.32:

1. When preparing Ni 3 P, the mass ratio of H 3 PO 4 in the aqueous solution to Ni(NO 3 ) 2 ·6H 2 O is 0.12:1; the mass ratio of the aqueous solution, carrier A and n-hexane is 1:1:

20.

5. The reverse water-gas shift catalyst according to claim 1, characterized in that, The reduction is carried out in H 2 .

6. An application of the reverse water-gas shift catalyst according to claim 1, characterized in that, Use the catalyst for the thermal catalytic CO 2 hydrogenation reaction to produce CO. Before the reaction, reduce the catalyst in an H 2 atmosphere for 1 h; wherein, the H 2 flow rate is 30 mL / min and the temperature is 600 °C.

7. The application of the reverse water-gas shift catalyst according to claim 6, characterized in that, Catalyst for thermal catalytic CO 2 The specific method for hydrogenation reaction of CO to produce CO is as follows: Add a catalyst to a fixed-bed reactor, and then mix CO 2 , H 2 and N 2 in a flow rate ratio of 1:4:1 and introduce them into the fixed-bed reactor for continuous reaction; among them, the space velocity of the mixed gas is 43200 mL h -1 g -1 , and the reaction temperature is 200 - 600 °C.

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