Doped catalyst NiC / Ni-CeO2 as well as preparation method and application thereof

Abstract

The invention provides a doped catalyst NiC / Ni-CeO2 as well as a preparation method and application thereof, aiming at solving the technical problems that the preparation process of the current reverse water gas shift reaction catalyst is complicated, and the activity and the CO selectivity cannot be obtained at the same time. The preparation method comprises the following steps: firstly, preparing a nanorod Ni-Ce (OH) 3 / CeO2 precursor with uniform morphology by a simple one-step hydrothermal method, then carrying out selective region reconstruction during calcination in a reducible atmosphere (such as a mixed atmosphere of 75 vol% H2 and 25 vol% CO2), converting Ce (OH) 3 into CeO2 with a stable porous structure, separating out Ni atoms doped in Ce (OH) 3 to form Ni clusters, and partially carbonizing the Ni clusters to form NiC so as to generate the catalyst NiC / Ni-CeO2.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal catalysis, and particularly relates to a doped catalyst NiC / Ni-CeO 2 and its preparation method and application. Background Art

[0002] In heterogeneous catalytic reactions, the rational design and synthesis of catalysts often play a crucial role in catalytic performance. However, in most current in-situ catalyst preparation processes, the process is complex and it is difficult to achieve both high catalyst activity and selectivity at the same time.

[0003] Currently, the reverse water-gas shift reaction (i.e., RWGS reaction) can utilize carbon dioxide to produce high-value-added CO, and the reaction temperature is relatively high. However, the catalysts used not only have a complex preparation process but also have difficulty in simultaneously achieving high activity and high selectivity for carbon monoxide. For example, although the Ni-SAs / N-CNTs catalyst has achieved the problem of CO selectivity in the reverse water-gas shift reaction, it has not solved the problem of 2 low CO conversion rate, and the preparation process of this catalyst is complex and its activity is not high. It can be seen that there is still a problem that high activity and high CO selectivity cannot be achieved simultaneously.

[0004] In view of this, the research team of the present invention believes that it is necessary to design a catalyst for the reverse water-gas shift reaction with a simple preparation process and capable of simultaneously achieving high activity and high CO selectivity. Summary of the Invention

[0005] The purpose of the present invention is to solve the technical problems that the current catalyst preparation process for the reverse water-gas shift reaction is complex and there is a problem that high activity and high CO selectivity cannot be achieved simultaneously, and to provide a doped catalyst NiC / Ni-CeO 2 and its preparation method and application.

[0006] Conception of the Present Invention

[0007] In view of the problems existing in the current catalysts for the reverse water-gas shift reaction, the research team of the present invention considered that in the design of catalysts for the reverse water-gas shift reaction, the following points need to be met:

[0008] 1) It can effectively activate small molecule CO 2 , improve the CO 2 conversion rate, and provide the possibility for further improving the activity of the RWGS reaction;

[0009] 2) Avoid the generation of by-product CH 2 produced by the hydrogenation of CO 4 , which causes a decrease in the purity of CO and limits its application in Fischer-Tropsch synthesis.

[0010] Therefore, in combination with the design requirements of the reverse water-gas shift reaction catalyst and the current bottlenecks, the research team intends to use the idea of dual-site activation. CeO 2 has unique and abundant oxygen vacancies on its surface, which can effectively activate small molecules such as H 2 , CO 2 , H 2 O, etc. In addition, hydrogen is easily activated by Ni. Therefore, the research team of this invention intends to prepare a doped catalyst NiC / Ni-CeO 2 , using the transition metal Ni and the carrier CeO 2 to activate H 2 and CO 2 simultaneously to achieve the application of a bifunctional catalyst. Although the introduction of Ni solves the problem of RWGS reaction activity, the strong adsorption of CO on Ni often leads to the formation of by-products CH 4 , which is kinetically unfavorable. Therefore, the research team of this invention optimizes the preparation process of the supported CeO 2 catalyst. First, the precursor Ni-Ce(OH) 3 / CeO 2 is prepared, and then the Ni-Ce(OH) 3 region is selectively reconstructed to form a doped catalyst NiC / Ni-CeO 2 with Ni clusters, solving the problems of poor CO 2 activity and low CO selectivity in the reverse water-gas shift reaction.

[0011] Based on the above inventive concept, to achieve the above object, the technical solution provided by this invention is:

[0012] A preparation method of a doped catalyst NiC / Ni-CeO 2 , which is characterized in that it includes the following steps:

[0013] 1) In a cooled strong base solution, a solution prepared from a Ce salt, a Ni salt, and ultrapure water is dropped, and a nanorod-shaped Ni-Ce(OH) 3 / CeO 2 precursor is prepared by a hydrothermal method, and the Ni loading in the precursor is less than 2.5 wt%; in this process, Ni can be doped into the Ce(OH) 3 / CeO 2 two phases in a uniform form, laying a foundation for the selective regional reconstruction of Ni-Ce(OH) 3 during subsequent calcination;

[0014] 2) The Ni-Ce(OH) 3 / CeO 2 precursor obtained in step 1) is placed in H 2and CO 2 Calcined in a mixed atmosphere of and at 450 - 600 °C for 2 - 4 h, and naturally cooled to obtain a nanorod-shaped porous nickel-doped cerium oxide catalyst NiC / Ni-CeO with uniform morphology 2 ; In this process, Ce(OH) 3 will be converted into CeO 2 , meanwhile, the Ni doped in the aforementioned Ce(OH) 3 will precipitate and reconstruct to form Ni clusters and be partially carbonized into NiC during the in-situ treatment process.

[0015] Furthermore, step 1) is specifically as follows:

[0016] Slowly add a strong base (as a precipitant in the co-precipitation method) to a glass bottle filled with ultrapure water and stir evenly to form a strong base solution. After the strong base solution cools down, slowly drip a solution prepared from Ce(NO 3 ) 3 ·6H 2 O, Ni(NO 3 ) 2 ·6H 2 O and ultrapure water (in order to reduce the influence of other impurity ions, nitrates are used here to avoid the influence caused by introducing other anions). After the dripping is completed and stirred evenly at room temperature, place it in a glass bottle and react at 100 - 120 °C for 12 - 24 h (the reaction temperature cannot be too high, otherwise it will affect the content of Ce(OH) 3 , preferably react at 100 °C for 24 h). After the reaction ends, wash it repeatedly with water and alcohol, and then dry it at 60 - 80 °C for 8 - 12 h to obtain the Ni-Ce(OH) 3 / CeO 2 precursor.

[0017] Furthermore, in step 1), the strong base is a strong base such as NaOH or KOH; the molar concentration of OH - in the reaction solution is 1 - 9 mol / L (that is, after adding the strong base solution to the solution prepared from Ce(NO 3 ) 3 ·6H 2 O, Ni(NO 3 ) 2 ·6H 2 O and ultrapure water, the molar concentration of OH - is 1 - 9 mol / L), and when the concentration is 6 mol / L, the performance is the best;

[0018] The molar ratio of Ni to Ce is 1:10 - 70 (preferably 1:50), and the molar concentration of Ce in the reaction solution is 40 - 60 mmol / L; thus, OH -The concentration of Ce is above 1M, which is one order of magnitude higher than that of Ce, which is beneficial to Ce(OH) 3 The generation of , paves the way for subsequent reconstruction.

[0019] Further, step 2) is specifically as follows:

[0020] The Ni-Ce(OH) obtained in step 1) 3 / CeO 2 The precursor is mixed evenly with quartz sand (Ni-Ce(OH) 3 / CeO 2 The precursor and quartz sand (volume ratio of 1:3) were placed in a fixed bed reactor under H 2 With CO 2 In a mixed atmosphere, the temperature was raised to 450-600 ° C, calcined for 2-4 hours, and naturally cooled to obtain a rod-shaped porous nickel carbide doped cerium oxide catalyst NiC / Ni-CeO with uniform morphology. 2 .

[0021] Further, in step 2), H 2 With CO 2 The mixed atmosphere is 75 vol% H 2 With 25 vol% CO 2 The mixed gas flow rate is 50 mL min -1 The present invention uses 75 vol% H 2 +25vol%CO 2 The mixed gas of Ce(OH) is used as the calcining atmosphere because of its good reducing property and the generated CO is easy to carbonize on Ni to form NiC. At the same time, the present invention found in the exploration process that Ce(OH) 3 The transition temperature is about 200°C. The temperature will affect the structure and morphology of the pores, and 600°C is the temperature point that maintains the best performance. Therefore, in step 2), it is preferred to increase the temperature to 600°C at a heating rate of 5°C / min as the calcination temperature. The product morphology can be stabilized after calcination for 2h, and finally naturally cooled to obtain the catalyst NiC / Ni-CeO with a regular porous rod-like morphology. 2 .

[0022] The present invention provides a doped catalyst NiC / Ni-CeO prepared by the above method. 2 , wherein the Ni loading is not higher than 2.5wt%, and the catalyst is used in the reverse water gas shift reaction. The catalyst can effectively solve the problems of the existing catalysts, such as the complicated preparation process and the difficulty in achieving both high selectivity and high activity, and can avoid the generation of methane under high temperature reaction conditions, thereby achieving the preparation of high-purity carbon monoxide.

[0023] Meanwhile, the present invention also provides a method for preparing CO through the reverse water-gas shift reaction, which is characterized in that the doped catalyst NiC / Ni-CeO prepared by the above preparation method is used as the catalyst for this reaction. The specific operation process is as follows: 2 Place the doped catalyst NiC / Ni-CeO in a fixed-bed reactor, with a WHSV of 72,000 mL·g

[0024] 2 ·h -1 -1 2 :CO 2: 2 =3:1:8, the reaction temperature is 200 - 550 °C (the performance of the catalyst is better at 500 - 550 °C), the reaction pressure is 0.1 Mpa, and high-purity carbon monoxide is obtained after the reaction is completed. During the reaction process, the tail gas of the fixed-bed reactor is connected to a gas chromatograph, and the gas components are analyzed online through the TCD and FID of the gas chromatograph to calculate the amount of substance of CH 4 and CO. When using this catalyst for the reaction, the selectivity of carbon monoxide in the product is > 97%.

[0025] Principle of the present invention:

[0026] First, the present invention prepares a uniformly shaped nanorod-like Ni-Ce(OH) precursor through a simple one-step hydrothermal method under a strong alkaline environment by controlling the reaction temperature and reaction time through low-pressure hydrothermal method. Then, it is calcined in a mixed atmosphere of H 3 / CeO 2 2 and CO 2 (such as: a mixed gas of 75 vol% H 2 + 25 vol% CO 2 ). During this process, Ce(OH) 3 is converted into stable CeO 2 , and at the same time, Ni precipitates and reconstructs to form Ni clusters and is partially carbonized into NiC. The overall design idea is to activate carbon dioxide and hydrogen at different sites by designing two sites, namely CeO 2 and NiC, that is, the CeO 2 and NiC double sites. CeO 2 is responsible for activating CO 2 , and NiC activates hydrogen.

[0027] The NiC / Ni-CeO catalyst selectively reconstructs Ni-Ce(OH) during the in-situ synthesis process 2 3 ​​​​​​, Ni precipitation forms Ni clusters, which can catalyze the reverse water-gas shift reaction. The Ni clusters are partially carbonized by CO to form NiC, reducing the CO adsorption capacity and improving the selectivity of the reverse water-gas shift reaction (the timely desorption of CO at the active sites can avoid over-hydrogenation to form CH 4 , thus enhancing the CO selectivity).

[0028] To enable the precipitation and reconstruction of Ni to form Ni clusters, the present invention selects strong base solutions such as sodium hydroxide, which is more conducive to the preparation of well-crystallized cerium hydroxide. This strong base condition is an essential condition for the selective area Ni-Ce(OH) 3 reconstruction; in addition, different calcination atmospheres will affect the degree of conversion of Ce(OH) 3 to CeO 2 , the number of surface oxygen vacancies, and the maintenance of the microstructure. Using pure H 2 as the calcination atmosphere can increase the number of surface oxygen vacancies, but the CO selectivity is poor; using pure CO as the calcination atmosphere can increase the CO selectivity, but the catalyst activity is poor. Therefore, the present invention explores and optimizes the Ni-Ce(OH) 3 / CeO 2 precursor in a mixed atmosphere (75 vol% H 2 + 25 vol% CO 2 ) and the calcination temperature (450 °C - 600 °C), realizing the preparation of a porous rod-shaped doped NiC / Ni-CeO 2 catalyst. Through transmission electron microscopy and nitrogen adsorption-desorption tests, it is found that the calcination at 600 °C has the best retention effect and remains a uniform porous rod-shaped structure. Finally, through performance tests, it is confirmed that the NiC / Ni-CeO 2 catalyst can indeed exhibit good catalytic activity in the reverse water-gas shift reaction.

[0029] The advantages of the present invention are as follows:

[0030] 1. The present invention provides a preparation strategy for a catalyst that can simultaneously activate CO 2 and H 2 , and effectively avoid the generation of methane in the reverse water-gas shift reaction. Using nanorod-shaped Ni-Ce(OH) 3 / CeO 2 as the precursor, Ni precipitation and reconstruction form Ni clusters and are partially carbonized to form NiC by in-situ calcination, finally generating a catalyst NiC / Ni-CeO 2 with a uniform porous rod-shaped structure. The whole operation is simple, requires less raw materials, has high economic benefits, and effectively solves the problems of low CO selectivity and low CO 2 conversion rate in the reverse water-gas shift reaction.

[0031] 2. The present invention designs dual active sites and activates H by using NiC 2 , CeO 2 to activate CO 2 . Based on this design concept, the NiC / Ni-CeO 2 catalyst is designed. The process flow is simple, and a precursor Ni-Ce(OH) 3 / CeO 2 with regular morphology is prepared. Meanwhile, by regulating the calcination atmosphere and temperature, the NiC / Ni-CeO 3+ with a high oxygen vacancy (the Ce 2 content is as high as over 35%, indicating a high oxygen vacancy on the surface) is prepared. During the reaction process, the oxygen vacancy can be maintained and not deactivated. Ni precipitates Ni clusters and is partially carbonized to form NiC, achieving the effect of bifunctional catalysis. During the preparation of the NiC / Ni-CeO 2 catalyst, no additional substances need to be added or post-treatment is required. The NiC / Ni-CeO 2 catalyst has a regular structure, is nanorod-shaped and has a porous structure.

[0032] 3. The NiC / Ni-CeO 2 catalyst prepared by the present invention has a high CO generation rate and a low CH 4 concentration (selectivity > 97%) in the reaction temperature range of 500 - 550 °C (the catalyst performance is better in the high-temperature section). That is, while accelerating the CO 2 conversion rate, the generation of by-product CH 4 is avoided, effectively solving the problem of CO purity and avoiding additional steps for further purification of subsequent gases, and further solving the bottleneck problem of the reverse water-gas shift reaction products in Fischer-Tropsch synthesis applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 are the preparation process and morphological characterization diagrams of the precursor Ni-Ce(OH) 3 / CeO 2 : a is the experimental preparation flow chart; b is the X-ray diffraction pattern; c is the high-resolution transmission electron microscopy image;

[0034] Figure 2 are the morphological characterization diagrams of the catalyst NiC / Ni-CeO 2 : a is the X-ray diffraction pattern; b is the high-angle annular dark field; c is the high-resolution transmission electron microscopy image; d is the partially enlarged high-angle annular dark field;

[0035] Figure 3 are the morphological characterization diagrams of CeO 2 : a is the transmission electron microscopy image; b is the high-resolution transmission electron microscopy image;

[0036] Figure 4 For Ni-CeO 2 Morphology characterization diagram: a is a transmission electron microscopy image; b is a high-resolution transmission electron microscopy image;

[0037] Figure 5 Test performance comparison diagram for Examples 1 - 3: a is a comparison diagram of CO 2 conversion rate and CO selectivity of different catalysts; b is a comparison diagram of CO yield of different catalysts;

[0038] Figure 6 Characterization of in-situ reconstruction of catalyst: a is XANES spectrum; b is Fourier transform EXAFS spectrum; c is wavelet transform spectrum; d - e are SRPES analyses under Ar etching; f is in-situ DRIFTS analysis of the precursor Ni-Ce(OH) 3 / CeO 2 ;

[0039] Figure 7 Defect characterization of different catalysts: a is Ce 3d analysis; b is O 1s analysis;

[0040] Figure 8 For Ni cluster / CeO 2 Morphology characterization diagram: a is an X-ray diffraction pattern; b is a high-angle annular dark field image; c is a comparison diagram of CO 2 conversion rate and CO selectivity; d is a comparison of CO yield of different catalysts;

[0041] Figure 9 Catalytic performance diagram of the precursor Ni-Ce(OH) 3 / CeO 2 catalyst treated under different atmospheres: a is a comparison diagram of CO 2 conversion rate and CO selectivity of different catalysts; b is a comparison of CO yield of different catalysts;

[0042] Figure 10 For Ni-Ce(OH) with different Ni contents 3 / CeO 2 Precursor in 75 vol% H 2 + 25 vol% CO 2 mixed atmosphere after calcination for the catalytic performance of the reverse water gas shift reaction: a is a comparison diagram of CO 2 conversion rate; b is a comparison diagram of CO selectivity;

[0043] Figure 11 For NiC / Ni-CeO 2Catalytic performance diagram of the catalyst for reverse water gas shift reaction: a shows the comparison diagram of CO 2 conversion rate and CO selectivity of different catalysts; b shows the comparison of CO yields of different catalysts; c shows the activation energy diagram of different catalysts; d shows the CO production rate diagram of different catalysts; e shows the stability test diagram of the NiC / Ni-CeO 2 catalyst. Specific implementation mode

[0044] The following further describes the content of the present invention in detail in conjunction with the accompanying drawings and specific embodiments:

[0045] The present invention discloses a preparation method of a doped catalyst for reverse water gas shift reaction. The technical solutions in the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments.

[0046] Example 1

[0047] As Figure 1 shown in a of, prepare the precursor Ni-Ce(OH) 3 / CeO 2 , including the following steps:

[0048] (1) Prepare the Ni-Ce(OH) 3 / CeO 2 precursor

[0049] First, add 70 mL of ultrapure water into a 100 mL glass bottle and place a magnetic stirrer. Then, slowly add 19.2 g of sodium hydroxide to the inner container and stir for 30 minutes. After the NaOH solution cools down, slowly dropwise add the prepared solution containing Ce 3+ , Ni 2+ (prepared by ultrasonic dispersion of 4 mmol Ce(NO 3 ) 3 ·6H 2 O and 0.08 mmol Ni(NO 3 ) 2 ·6H 2 O into 10 mL of ultrapure water). During the dropping process, the solution will slowly turn milky white. After the dropping is complete, stir at room temperature for 30 minutes, put it into a glass bottle, react at 100 °C in a blast drying oven for 24 h. After the reaction is completed, wash it three times alternately with water and alcohol, and then dry it at 60 °C in a blast drying oven for 8 h to obtain the Ni-Ce(OH) 3 / CeO 2 precursor.

[0050] (2) Prepare the NiC / Ni-CeO 2 based catalyst

[0051] Mix the Ni-Ce(OH) 3 / CeO 2 precursor obtained in step 1) with quartz sand evenly (wherein, the volume ratio of Ni-Ce(OH) 3 / CeO 2 precursor to quartz sand is 1:3), place it in a fixed-bed reactor, and at a heating rate of 5 °C / min, in 75 vol% H 2 + 25 vol% CO 2 mixed atmosphere (the flow rate has no obvious influence on the treatment result, generally at 50 mL·min -1 ), calcine at 600 °C for 2 hours, and cool naturally to obtain a sample, named NiC / Ni-CeO 2 -600 (Ni 0.5 wt.%).

[0052] Example 2

[0053] The difference from Example 1 is that in step 2), calcine at 450 °C for 2 hours, and cool naturally to obtain a sample, named NiC / Ni-CeO 2 -450.

[0054] Example 3

[0055] The difference from Example 1 is that in step 2), calcine at 525 °C for 2 hours, and cool naturally to obtain a sample, named NiC / Ni-CeO 2 -525.

[0056] Example 4

[0057] The difference from Example 1 is that in step 1), a solution of Ce 3+ , Ni 2+ (prepared by adding 4 mmol Ce(NO 3 ) 3 ·6H 2 O and 0.06 mmol Ni(NO 3 ) 2 ·6H 2 O to 10 mL of ultrapure water and ultrasonic dispersion), to obtain a sample, named NiC / Ni-CeO 2 (Ni 0.3 wt.%).

[0058] Example 5

[0059] The difference from Example 1 is that in step 1), a solution of Ce 3+ , Ni 2+ (prepared by adding 4 mmol Ce(NO 3 ) 3 ·6H 2O and 0.20 mmol Ni(NO 3 ) 2 ·6H 2 O was added to 10 mL of ultrapure water and ultrasonically dispersed to prepare), and a sample was obtained, named NiC / Ni-CeO 2 (Ni 1.5 wt.%).

[0060] Example 6

[0061] The difference from Example 1 is that in step 1), Ce 3+ , Ni 2+ solution (prepared by adding 4 mmol Ce(NO 3 ) 3 ·6H 2 O and 0.33 mmol Ni(NO 3 ) 2 ·6H 2 O was added to 10 mL of ultrapure water and ultrasonically dispersed to prepare), and a sample was obtained, named NiC / Ni-CeO 2 (Ni 2.5 wt.%).

[0062] Comparative Example 1

[0063] The difference from Example 1 is that in step 1), Ni(NO 3 ) 2 ·6H 2 O solution was not added to obtain the precursor Ce(OH) 3 / CeO 2 .

[0064] Step 2) The Ce(OH) 3 / CeO 2 precursor obtained in step 1) was placed in a fixed-bed reactor and calcined at 600 °C for 2 hours at a heating rate of 5 °C / min in a mixed atmosphere of 75 vol% H 2 + 25 vol% CO 2 (the flow rate has no obvious effect on the treatment result, generally at 50 mL·min -1 ), and then cooled naturally to obtain a sample, named CeO 2 .

[0065] Comparative Example 2

[0066] The difference from Example 1 is that in step 2), it was prepared by the hydrothermal method under high pressure. The specific process is as follows: Ni-Ce(OH) 3 / CeO 2 precursor at 2 mg ml -1Ultrasonic dispersion was added to a 100 mL polytetrafluoroethylene liner, placed in a reactor, and reacted at 180 ° C in a blast drying oven for 12 h. After the reaction was completed, the sample was collected by centrifugation and then placed in a blast drying oven at 60 ° C for 8 h to obtain a sample Ni-CeO 2 .

[0067] Comparative Example 3

[0068] Ni particles were loaded onto CeO using conventional impregnation method. 2 Surface, get sample Ni cluster / CeO 2 The catalyst specifically comprises the following steps:

[0069] (1) The precursor Ce(OH) was prepared by the same hydrothermal method as in Comparative Example 1. 3 / CeO 2

[0070] (2) CeO was prepared by the same calcination method as in Example 1. 2

[0071] (3) Using the traditional impregnation method to load Ni particles onto CeO 2 surface, and obtain the supported catalyst Ni cluster / CeO 2 (Ni loading is 2wt%):

[0072] Weigh 200 mg of the porous rod-shaped CeO prepared in step (2) 2 , put it in a 50mL dry pot, add 30mL ethanol and ultrasonically disperse it, take 800uL (Ni wt%: 5mg / mL) of nickel nitrate aqueous solution and drop it into the solution, stir at room temperature for 2 hours, heat at 90℃ to completely evaporate, and then heat at 10% H 2 / Ar mixed gas was heated to 450℃ at a rate of 5℃ / min and calcined for 2 hours to obtain the supported catalyst Ni cluster / CeO 2 .

[0073] Comparative Example 4

[0074] The difference from Example 1 is that in step 2), the calcination atmosphere is hydrogen, and the obtained sample is named Ni / Ni-CeO 2 -H 2 .

[0075] Comparative Example 5

[0076] The difference from Example 1 is that in step 2), the calcination atmosphere is CO, and the obtained sample is named Ni / Ni-CeO 2 -CO.

[0077] Comparative Example 6

[0078] The difference from Example 1 is that in step 2), the calcination atmosphere is CO 2 , obtaining a sample named Ni / Ni-CeO 2 -CO 2 .

[0079] To verify the effect, the following test examples were also carried out in the present invention:

[0080] I. Morphological structure characterization of the precursor Ni-Ce(OH) 3 / CeO 2 obtained during the preparation process of Example 1, and the final samples obtained under different conditions in Example 1 and Comparative Examples 1-6:

[0081] Figure 1 For the preparation process, crystal structure and morphology of the precursor Ni-Ce(OH) 3 / CeO 2 in Example 1: As shown in b of Figure 1 , the crystal structure of Ni-Ce(OH) 3 / CeO 2 is a two-phase mixed structure of Ce(OH) 3 and CeO 2 (the detection limit of XRD is 3%, and the content of Ni is not that high, so it is not presented here); Figure 1 c of 3 shows that its main exposed crystal planes are Ce(OH) 2 (101) with an interplanar spacing of 0.30 nm and CeO

[0082] Figure 2 For the crystal structure and morphology of NiC / Ni-CeO 2 in Example 1: As shown in a of Figure 2 , the crystal structure of NiC / Ni-CeO 2 is the crystalline phase of pure CeO 2 ; It can be clearly seen from b of Figure 2 that the nanorods belong to a porous structure; Figure 2 c of 2 shows that its interplanar spacing is 0.190 nm, attributed to the (220) crystal plane of CeO Figure 2 d of

[0083] Figure 3 For the crystal structure and morphology of CeO 2 in Comparative Example 1: As shown in Figure 3The a of CeO prepared 2 has a crystal structure of pure CeO 2 as the crystalline phase; From Figure 3 the b of it, it can be clearly seen that there is a porous structure on the nanorod; In addition Figure 3 the b of it shows that its interplanar spacing is 0.190 nm, which belongs to the (220) crystal plane of CeO 2 .

[0084] Figure 4 For the Ni-CeO in Comparative Example 2 2 morphology spectrum: As Figure 4 the a of it shows that the Ni-CeO generated by the second-step hydrothermal method 2 is a pure CeO 2 crystalline phase. Compared with NiC / Ni-CeO 2 , the appearance of Ni clusters is not observed, indicating that Ni atoms are still inside the CeO 2 lattice; Figure 4 the b of it shows that its interplanar spacing is 0.190 nm, which is consistent with the prepared CeO 2 and belongs to the (220) crystal plane of CeO 2 .

[0085] Figure 8 For the morphology and element distribution spectrum of Ni cluster / CeO 2 : As Figure 8 the a of it shows that the Ni cluster / CeO 2 prepared by the traditional impregnation method is a pure CeO 2 crystalline phase, and no Ni phase is found, indicating the high dispersion of Ni clusters; Figure 8 the b of it shows that its interplanar spacing is 0.190 nm, which is consistent with the prepared CeO 2 and belongs to the (220) crystal plane of CeO 2 , and there is an interplanar spacing of 0.200 nm, which belongs to the (111) crystal plane of Ni.

[0086] 2. Structural characterization of cerium oxide calcined under different atmospheres

[0087] Figure 5 For Examples 1, 2 and 3, the treatment conditions at different temperatures. It can be seen that the CO 2 conversion rate of the NiC / Ni-CeO 2 catalyst is the highest at 600 °C, and the CO selectivity is the best.

[0088] Figure 6 For the synchrotron radiation spectra of different catalysts: As Figure 6 the a of it shows that the reconstructed NiC / Ni-CeO2 The electronic structure of the catalyst is very similar to that of Ni foil, indicating that metallic nickel is formed during in-situ reconstruction, and nickel carbide only accounts for a part of the total nickel, being partially carbonized. As Figure 6 in b of Figure 6 and c of 2 , EXAFS spectra and wavelet transform analysis show that in the reconstructed NiC / Ni-CeO catalyst, the Ni-Ni bond distance is 2 consistent with the position of the Ni-Ni peak observed in Ni foil. It is worth noting that on the reconstructed NiC / Ni-CeO 2 catalyst, the presence of the Ni-O bond is still obvious, indicating that the structure of doped Ni in the CeO Figure 6 region has not changed. As Figure 6 in d of 2 and e of 0 , the Ni L-edge of the NiC / Ni-CeO 2+ catalyst shows the coexistence of Ni 0 and Ni

[0089] species, once again confirming the formation of Ni clusters. With the continuous extension of the Ar plasma treatment time, the C species shown by the C K-edge gradually decrease, indicating that the carbonaceous species are etched. In addition, with the decrease of the C species, the binding energy of the Ni Figure 6 species also becomes significantly lower, indicating a strong interaction between the C species and the Ni clusters. Therefore, SRPES spectral analysis clearly proves that environmentally induced reconstruction and carbonization produce carburized nickel clusters. 3 / CeO 2 shows the twin adsorption of Ni-(CO) 2 / 3 on the catalyst surface, indicating the atomic dispersion of Ni. After in-situ treatment of Ni-Ce(OH) 2 +25vol% CO 2 ) at 350 °C with a mixed atmosphere (75vol% H 3 / CeO 2 to simulate the catalytic environment, it is observed that the peak corresponding to Ni-(CO) 2 / 3 decreases significantly. At the same time, the peaks appearing at 1930 cm -1 and 1840 cm -1 are respectively attributed to the bridged adsorption of CO with three nickel atoms (Ni 3-CO) and nickel carbide species (NiC-CO). In addition, the characteristic peak of NiC-CO was also observed on the Ni-Ce(OH) 3 / CeO 2 catalyst treated with CO. Therefore, these experiments clearly demonstrated that the reducing CO plays a crucial role in the formation of NiC.

[0090] Figure 7 For oxygen vacancy characterization: As Figure 7 shown in a of, by fitting the Ce 3d orbital, it was found that the NiC / Ni-CeO 2 catalyst had a Ce 3+ content of 35.2%, much higher than that of other cerium oxides; as Figure 7 shown in b of, the highest Ce 2 -O content of the NiC / Ni-CeO 3+ catalyst was as high as 53.4%. Therefore, NiC / Ni-CeO 2 had the highest oxygen defect concentration.

[0091] II. Perform catalytic performance analysis on the NiC / Ni-CeO 2 prepared in Example 1, the Ni cluster / CeO 2 prepared in Comparative Example 3, and the Ni / Ni-CeO 2 -H 2 prepared in Comparative Examples 4-6, Ni / Ni-CeO 2 -CO, Ni / Ni-CeO 2 -CO 2 as follows:

[0092] (1) Mix 50 mg of the catalyst evenly with 150 mg of quartz sand and fill it in a fixed-bed reactor;

[0093] (2) Pass a mixed atmosphere of 60 mL min -1 for reaction, with a WHSV of 72,000 mL g -1 h -1 , H 2 :CO 2: N 2 = 3:1:8, the reaction temperature is 200 - 550 °C, and the reaction pressure is 0.1 Mpa. During the reaction, connect the tail gas of the fixed-bed reactor to a gas chromatograph, and online analyze the gas components through the gas chromatograph TCD and FID, and calculate the amounts of substances of CH 4 and CO. The specific results are shown in Figure 8 , Figure 9 .

[0094] ThroughFigure 8 For c and d, it can be found that the NiC / Ni-CeO formed by comparative reconstruction 2 The excellent catalytic performance of the catalyst, Ni cluster / CeO 2 of CO 2 has a low conversion rate and poor CO selectivity.

[0095] Figure 9 Using Ni-Ce(OH) as the precursor 3 / CeO 2 Catalytic performance for the reverse water-gas shift reaction after reconstruction and calcination in different atmospheres: As Figure 9 As shown in a of, H 2 , CO, mixed atmosphere (75 vol% H 2 + 25 vol% CO 2 ), after calcination in the atmosphere, the performance of the catalyst has been significantly improved, indicating that the reducing atmosphere is the key factor for calcining the precursor; but only in the mixed atmosphere (75 vol% H 2 + 25 vol% CO 2 ) the catalyst after calcination in the atmosphere shows the best CO 2 conversion rate and CO selectivity; there is no C source in the H 2 atmosphere, and NiC cannot be formed, so the selectivity is very poor; while the activity of the catalyst in the pure CO atmosphere is not good.

[0096] Figure 10 Using Ni-Ce(OH) with different Ni contents 3 / CeO 2 Precursor in 75 vol% H 2 + 25 vol% CO 2 Catalytic performance for the reverse water-gas shift reaction after calcination in the mixed atmosphere: As Figure 10 As shown in a and b of, in the catalyst without Ni, the CO 2 conversion rate is low. As the Ni content increases, the CO 2 conversion rate increases. When the Ni content is equal to 2.5%, the CO selectivity is very poor. Therefore, the optimal doping amount of Ni should be less than 2.5%.

[0097] III. Respectively, the catalysts CeO 2 , Ni-CeO 2 prepared in Comparative Examples 1-2 and the NiC / Ni-CeO 2 catalyst prepared in Example 1 are used for the reverse water-gas shift reaction, and the specific operation is as follows:

[0098] (1) Mix 50 mg of the catalyst evenly with 150 mg of quartz sand and fill it in a fixed-bed reactor;

[0099] (2) 60 mL min -1 The reaction was carried out in a mixed atmosphere with a WHSV of 72,000 mL g -1 ·h -1 , H 2 :CO 2: N 2 =3:1:8, reaction temperature 200-550°C, reaction pressure 0.1Mpa. During the reaction, the tail gas of the fixed bed reactor was connected to the gas chromatograph, and the gas components were analyzed online by gas chromatograph TCD and FID, and CH 4 and the amount of substance of CO.

[0100] from Figure 11 It can be seen from a that NiC / Ni-CeO 2 The catalyst has higher CO 2 Conversion and CO selectivity; Figure 11 As can be seen from b, NiC / Ni-CeO 2 The CO yield of RWGS reaches 55.0% at 550 °C, which is very close to the theoretical CO equilibrium yield (55.1%) of RWGS under experimental conditions. Figure 11 c shows the activation energy of each catalyst, NiC / Ni-CeO 2 The catalyst has a low activation energy (41.4 kJ mol -1 ), indicating that it has the best catalytic reaction pathway, which also well explains the NiC / Ni-CeO 2 The reasons for the superior performance of the catalyst. Figure 11 d shows the NiC / Ni-CeO 2 CO generation rate of catalyst, NiC / Ni-CeO 2 The CO generation rate of the catalyst was very high, reaching 27.3 mol·g Ni -1 ·h -1 , which is at least one order of magnitude higher than the previously reported Ni-based catalysts and has a high CO selectivity. Although some catalysts in the literature show similar activity in terms of CO generation rate, their CO selectivity is significantly lower than that of NiC / Ni-CeO 2 catalyst. Figure 11 Figure e is a stability test diagram. Even at a high temperature of 550°C, NiC / Ni-CeO 2 The stability of the catalyst to RWGS is also excellent. The CO yield remains almost unchanged and close to the thermodynamic equilibrium yield for at least 1000 hours of reaction. In addition, each Ni site achieves a high conversion frequency of more than 4,500,000 times, proving that NiC / Ni-CeO 2The catalyst has a stable structure and the potential for commercialization.

[0101] In summary, the catalyst prepared by the present invention can solve the technical problems of the complex preparation process of the current reverse water gas shift reaction catalyst and the low CO selectivity.

[0102] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a doped catalyst NiC / Ni-CeO2, characterized in that: The following steps are involved: 1) In the cooled strong alkaline solution, a solution prepared by Ce salt, Ni salt and ultrapure water is added dropwise to prepare a Ni-Ce(OH)3 / CeO2 precursor by a hydrothermal method, wherein the Ni loading in the precursor is less than 2.5wt%; 2) The Ni-Ce(OH)3 / CeO2 precursor obtained in step 1) is placed in a mixed atmosphere of H2 and CO2 at 450-600°C for 2-4 hours, and then naturally cooled to obtain a porous nickel carbide doped cerium oxide catalyst NiC / Ni-CeO2.

2. The method for preparing the doped catalyst NiC / Ni-CeO2 according to claim 1, characterized in that: Step 1) is specifically as follows: Slowly add a strong base into a glass bottle filled with ultrapure water and stir evenly to form a strong base solution. After the strong base solution is cooled, slowly add a solution prepared by Ce(NO3)3·6H2O, Ni(NO3)2·6H2O and ultrapure water. After the addition is completed, stir evenly at room temperature and place in a glass bottle. React at 100-120℃ for 12-24h. After the reaction is completed, wash alternately with water and alcohol several times, and then dry at 60-80℃ for 8-12h to obtain Ni-Ce(OH)3 / CeO2 precursor.

3. The method for preparing the doped catalyst NiC / Ni-CeO2 according to claim 2, characterized in that: In step 1), the strong base is NaOH or KOH; OH - The molar concentration in the reaction solution is 1-9 mol / L; The molar ratio of Ni to Ce is 1:10-70, and the molar concentration of Ce in the reaction solution is 40-60 mmol / L.

4. The method for preparing the doped catalyst NiC / Ni-CeO2 according to claim 3, characterized in that: In step 1), OH - The concentration in the reaction solution is 6 mol / L; The molar ratio of Ni to Ce is 1:50; The reaction temperature was 100°C and the reaction time was 24h.

5. The method for preparing the doped catalyst NiC / Ni-CeO2 according to any one of claims 1 to 4, characterized in that: Step 2) is specifically as follows: The Ni-Ce(OH)3 / CeO2 precursor obtained in step 1) is evenly mixed with quartz sand and placed in a fixed bed reactor. In a mixed atmosphere of H2 and CO2, the temperature is raised to 450-600°C, calcined for 2-4 hours, and naturally cooled to obtain a rod-shaped porous nickel carbide-doped cerium oxide catalyst NiC / Ni-CeO2 with uniform morphology.

6. The method for preparing the doped catalyst NiC / Ni-CeO2 according to claim 5, characterized in that: In step 2), the mixed atmosphere of H2 and CO2 is a mixed gas of 75 vol% H2 and 25 vol% CO2, and the flow rate is 50 mL min -1 ; The temperature was raised to 600 °C at a heating rate of 5 °C / min and calcined for 2 h.

7. A doped catalyst NiC / Ni-CeO2, characterized in that: The product is prepared by the preparation method described in any one of claims 1 to 6.

8. Use of the doped catalyst NiC / Ni-CeO2 prepared by the preparation method according to any one of claims 1 to 6 as a catalyst in the reverse water gas shift reaction.

9. A method for preparing CO by reverse water-gas shift reaction, characterized in that: The doped catalyst NiC / Ni-CeO2 prepared by any preparation method described in claims 1-6 is used as the catalyst for the reaction.

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