A doped catalyst NiC / Ni-CeO2, its preparation method and application

Abstract

This invention provides a doped catalyst NiC / Ni-CeO2, its preparation method, and its application. Currently, the preparation process of catalysts for reverse water-gas shift reactions is complex, and there is a technical problem where activity and CO selectivity cannot be simultaneously achieved. This invention first prepares a uniformly morphological nanorod Ni-Ce(OH)3 / CeO2 precursor via a simple one-step hydrothermal method. Then, selective reconfiguration is performed by calcination in a reducible atmosphere (e.g., a mixture of 75 vol% H2 + 25 vol% CO2), converting Ce(OH)3 into a stable porous CeO2 structure. The Ni atoms doped in Ce(OH)3 precipitate to form Ni clusters and partially carbonize to form NiC, generating the NiC / Ni-CeO2 catalyst.

Description

Technical Field

[0001] This invention belongs to the field of thermocatalysis technology, specifically relating to a doped catalyst NiC / Ni-CeO2, its preparation method, and its application. Background Technology

[0002] In heterogeneous catalytic reactions, the rational design and synthesis of catalysts often play a crucial role in catalytic performance. However, most current in-situ catalyst preparation processes are complex and struggle to achieve both catalyst activity and selectivity.

[0003] Currently, the reverse water-gas shift reaction (RWGS) can utilize carbon dioxide to generate high-value-added CO, and the reaction temperature is relatively high. However, the catalysts used not only have complex preparation processes, but also struggle to achieve both high activity and high selectivity for carbon monoxide. For example, while Ni-SAs / N-CNTs catalysts have achieved CO selectivity in the RWGS, they have failed to solve the problem of low CO2 conversion. Furthermore, the preparation process of this catalyst is complex and its activity is not high, demonstrating that the dilemma of not being able to simultaneously achieve high activity and high CO selectivity remains.

[0004] In view of this, the research team of this invention believes that it is necessary to design a catalyst for the reverse water-gas shift reaction that is simple to prepare and can take into account both high activity and high selectivity for CO. Summary of the Invention

[0005] The purpose of this invention is to solve the technical problems of complex preparation process of current reverse water-gas shift reaction catalysts and the inability to simultaneously achieve high activity and high CO selectivity, and to provide a doped catalyst NiC / Ni-CeO2, its preparation method and application.

[0006] The concept of this invention:

[0007] To address the existing problems with current catalysts for reverse water-gas shift reactions, the research team of this invention considers the following points to be met when designing catalysts for reverse water-gas shift reactions:

[0008] 1) It can effectively activate small molecule CO2, improve CO2 conversion rate, and provide a possibility for further improving the reactivity of RWGS;

[0009] 2) Avoid the generation of CH4 byproduct from the hydrogenation of CO2 to CO, which would reduce the purity of CO and limit its application in Fischer-Tropsch synthesis.

[0010] Therefore, considering the design requirements and current bottlenecks of the reverse water-gas shift reaction catalyst, the research team proposes to utilize a dual-site activation approach. The CeO2 surface possesses unique and abundant oxygen vacancies, which can effectively activate small molecules such as H2, CO2, and H2O. Furthermore, hydrogen is easily activated by Ni; therefore, the research team plans to prepare a doped catalyst, NiC / Ni-CeO2, using the transition metal Ni and the supported CeO2 to simultaneously activate H2 and CO2, achieving the application of a bifunctional catalyst. Although the introduction of Ni solves the activity problem of the RWGS reaction, the strong adsorption of CO on Ni often leads to the formation of the byproduct CH4, which is kinetically unfavorable. To address this, the research team optimized the preparation process of the supported CeO2 catalyst, first preparing the precursor Ni-Ce(OH)3 / CeO2, and then selectively reconstructing the Ni-Ce(OH)3 region to form the doped catalyst NiC / Ni-CeO2 with Ni clusters, thus solving the problems of poor CO2 activity and low CO selectivity in the reverse water-gas shift reaction.

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

[0012] A method for preparing a doped catalyst NiC / Ni-CeO2, characterized by the following steps:

[0013] 1) A solution prepared by Ce salt, Ni salt and ultrapure water was added dropwise to a cooled strong alkaline solution to prepare a nanorod-shaped Ni-Ce(OH)3 / CeO2 precursor by hydrothermal method, and the Ni loading in the precursor was less than 2.5 wt%. In this process, Ni can be uniformly doped into the Ce(OH)3 / CeO2 phases, laying the foundation for the selective regional reconstruction of Ni-Ce(OH)3 in the subsequent calcination.

[0014] 2) The Ni-Ce(OH)3 / CeO2 precursor obtained in step 1) is placed in a mixed atmosphere of H2 and CO2 and calcined at 450-600℃ for 2-4h. After natural cooling, a uniform nanorod-shaped porous nickel carbide-doped cerium oxide catalyst NiC / Ni-CeO2 is obtained. During this process, Ce(OH)3 is converted into CeO2. At the same time, the Ni doped in Ce(OH)3 will precipitate and reconstruct Ni clusters during the in-situ treatment and be partially carbonized into NiC.

[0015] Furthermore, step 1) specifically involves:

[0016] A strong alkali (as a precipitant in the co-precipitation method) is slowly added to a glass bottle containing ultrapure water and stirred until homogeneous to form a strong alkali solution. After the strong alkali solution cools, a solution prepared by Ce(NO3)3·6H2O, Ni(NO3)2·6H2O and ultrapure water is slowly added dropwise (nitrates are used here to reduce the influence of other impurities and avoid the influence caused by the introduction of other anions). After the addition is complete and the solution is stirred evenly at room temperature, it is placed in a glass bottle and reacted at 100-120℃ for 12-24 hours (the reaction temperature should not be too high, otherwise it will affect the content of Ce(OH)3; it is preferred to react at 100℃ for 24 hours). After the reaction is complete, the solution is washed several times alternately with water and alcohol, and then dried at 60-80℃ for 8-12 hours to obtain the Ni-Ce(OH)3 / CeO2 precursor.

[0017] Further, in step 1), the strong base is a strong base such as NaOH or KOH; OH - The molar concentration in the reaction solution is 1-9 mol / L (that is, after adding a strong base solution to a solution prepared from Ce(NO3)3·6H2O, Ni(NO3)2·6H2O and ultrapure water, OH... - The molar concentration is 1-9 mol / L, and the performance is best at a concentration of 6 mol / L.

[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 is above 1M, which is an order of magnitude higher than that of Ce, which is conducive to the formation of Ce(OH)3 and lays the groundwork for subsequent reconstruction.

[0019] Furthermore, step 2) specifically involves:

[0020] The Ni-Ce(OH)3 / CeO2 precursor obtained in step 1) was mixed evenly with quartz sand (the volume ratio of Ni-Ce(OH)3 / CeO2 precursor to quartz sand was 1:3) and placed in a fixed-bed reactor. Under a mixed atmosphere of H2 and CO2, the temperature was raised to 450-600℃ and calcined for 2-4 hours. After natural cooling, a uniformly morphological rod-shaped porous nickel carbide-doped cerium oxide catalyst NiC / Ni-CeO2 was obtained.

[0021] Further, in step 2), the mixed atmosphere of H2 and CO2 is a mixture of 75 vol% H2 and 25 vol% CO2, and the flow rate is 50 mL·min. -1The present invention selects a mixed gas of 75 vol% H2 + 25 vol% CO2 as the calcination atmosphere because it has good reducing properties and the generated CO is easy to carbonize on Ni to form NiC. At the same time, the present invention found in the process of exploration that the transformation temperature of Ce(OH)3 is about 200°C. Temperature affects the structure and morphology of pores, and 600°C is the temperature point that maintains the best performance. Therefore, in step 2), it is preferred to raise the temperature to 600°C at a heating rate of 5°C / min. The morphology of the product can be stabilized after calcination for 2 hours. Finally, natural cooling yields a catalyst NiC / Ni-CeO2 with a regular porous rod-shaped morphology.

[0022] This invention provides a doped catalyst NiC / Ni-CeO2 prepared by the above method, with a Ni loading of no more than 2.5 wt%, and its application as a catalyst in the reverse water-gas shift reaction. This catalyst effectively solves the problems of complex preparation processes and difficulty in achieving both high selectivity and high activity in existing catalysts. It can avoid the formation of methane under high-temperature reaction conditions and achieve the preparation of high-purity carbon monoxide.

[0023] Meanwhile, this invention also provides a method for preparing CO via a reverse water-gas shift reaction, characterized in that a doped catalyst NiC / Ni-CeO2 prepared by the above method is used as the catalyst for this reaction. The specific operation process is as follows:

[0024] The doped catalyst NiC / Ni-CeO2 was placed in a fixed-bed reactor, with a WHSV of 72,000 mL·g. -1 ·h -1 H2:CO 2: The N2 ratio is 3:1:8, the reaction temperature is 200-550℃ (the catalyst performs better at 500-550℃), and the reaction pressure is 0.1 MPa. High-purity carbon monoxide is obtained after the reaction is complete. During the reaction, the tail gas from the fixed-bed reactor is connected to a gas chromatograph. The gas components are analyzed online using TCD and FID gas chromatography to calculate the amounts of CH4 and CO. Using this catalyst, the selectivity for carbon monoxide in the product is >97%.

[0025] The principle of this invention:

[0026] This invention first prepares uniformly morphological nanorod-shaped Ni-Ce(OH)3 / CeO2 precursors using a simple one-step hydrothermal method under a strongly alkaline environment with controlled reaction temperature and time via low-pressure hydrothermal processing. These precursors are then calcined in a mixed atmosphere of H2 and CO2 (e.g., a mixture of 75 vol% H2 and 25 vol% CO2). During this process, Ce(OH)3 is converted into stable CeO2, while Ni precipitates and restructures to form Ni clusters, which are then partially carbonized into NiC. The overall design concept involves designing dual-site activation mechanisms, where CeO2 and NiC activate carbon dioxide and hydrogen at different sites, respectively. Specifically, CeO2 activates CO2, and NiC activates hydrogen.

[0027] During the in-situ synthesis of NiC / Ni-CeO2 catalyst, Ni-Ce(OH)3 is selectively reconstructed, and Ni is precipitated to form Ni clusters, which can catalyze the reverse water-gas shift reaction. The Ni clusters are partially carbonized by CO to form NiC, which reduces the CO adsorption capacity and improves the selectivity of the reverse water-gas shift reaction (timely desorption of CO at the active site can avoid excessive hydrogenation to form CH4, thereby improving CO selectivity).

[0028] To facilitate the precipitation and reconstruction of Ni into Ni clusters, this invention selects strong alkaline solutions such as sodium hydroxide, which are more conducive to the preparation of well-crystallized cerium hydroxide. This strong alkaline condition is essential for the selective reconstruction of Ni-Ce(OH)3. Furthermore, different calcination atmospheres affect the degree of Ce(OH)3 conversion to CeO2, the number of surface oxygen vacancies, and the retention of the microstructure. Using pure H2 as the calcination atmosphere can increase the number of surface oxygen vacancies, but CO selectivity is poor; using pure CO as the calcination atmosphere can increase CO selectivity, but catalyst activity is poor. Therefore, this invention explores and optimizes the Ni-Ce(OH)3 / CeO2 precursor under a mixed atmosphere (75 vol% H2 + 25 vol% CO2) and calcination temperature (450℃-600℃) to prepare a porous rod-shaped doped NiC / Ni-CeO2 catalyst. Transmission electron microscopy and nitrogen adsorption-desorption tests show that calcination at 600℃ maintains the best effect, preserving the uniform porous rod-shaped structure. Finally, performance tests confirmed that the NiC / Ni-CeO2 catalyst does indeed exhibit good catalytic activity in the reverse water-gas shift reaction.

[0029] The advantages of this invention are:

[0030] 1. This invention provides a strategy for preparing a catalyst capable of simultaneously activating CO2 and H2 and effectively avoiding the generation of methane in the reverse water-gas shift reaction. Using nanorod-shaped Ni-Ce(OH)3 / CeO2 as a precursor, Ni is precipitated and reconstructed to form Ni clusters and partially carbonized to form NiC through in-situ calcination, ultimately generating a uniformly sized porous rod-shaped catalyst NiC / Ni-CeO2. The entire operation is simple, requires fewer raw materials, and is highly economical, effectively solving the problems of low CO selectivity and low CO2 conversion rate in the reverse water-gas shift reaction.

[0031] 2. This invention designs a NiC / Ni-CeO2 catalyst by utilizing the design concept of dual active sites, specifically NiC activating H2 and CeO2 activating CO2. The process is simple, yielding a well-morphologically regular precursor Ni-Ce(OH)3 / CeO2. Simultaneously, by controlling the calcination atmosphere and temperature, a catalyst with a high oxygen vacancy rate (CeO2) is prepared. 3+ With a content of over 35%, NiC / Ni-CeO2 exhibits a high number of oxygen vacancies on its surface. During the reaction, these oxygen vacancies are maintained and remain undeactivated. Ni precipitates Ni clusters and partially carbonizes to form NiC, achieving a bifunctional catalytic effect. No additional substances or post-treatment are required during the preparation of the NiC / Ni-CeO2 catalyst. The NiC / Ni-CeO2 catalyst has a regular structure, is nanorod-shaped, and has a porous structure.

[0032] 3. The NiC / Ni-CeO2 catalyst prepared by this invention exhibits a high CO generation rate and a low CH4 concentration (selectivity >97%) within the reaction temperature range of 500-550℃ (the catalyst performs better in the high-temperature range). This means that while accelerating the CO2 conversion rate, it also avoids the generation of the byproduct CH4, effectively solving the problem of CO purity and avoiding the additional steps of subsequent gas purification. Furthermore, it solves the bottleneck problem of applying the reverse water-gas shift reaction products in Fischer-Tropsch synthesis. Attached Figure Description

[0033] Figure 1 The preparation process and morphological characterization of the precursor Ni-Ce(OH)3 / CeO2 are shown in the following figures: a) Flowchart of the experimental preparation; b) X-ray diffraction pattern; c) High-resolution transmission electron microscopy image.

[0034] Figure 2 Morphological characterization of the catalyst NiC / Ni-CeO2: a) X-ray diffraction pattern; b) high-angle annular dark field image; c) high-resolution transmission electron microscopy image; d) partially magnified high-angle annular dark field image.

[0035] Figure 3 Morphological characterization of CeO2: a is a transmission electron microscope (TEM) image; b is a high-resolution TEM image.

[0036] Figure 4 Morphological characterization of Ni-CeO2: a is a transmission electron microscope (TEM) image; b is a high-resolution TEM image.

[0037] Figure 5 The following are comparative graphs of the test performance of Examples 1-3: a) Comparison of CO2 conversion rate and CO selectivity of different catalysts; b) Comparison of CO yield of different catalysts.

[0038] Figure 6 Characterization of in-situ reconstruction of the catalyst: a) XANES spectrum; b) Fourier transform EXAFS spectrum; c) Wavelet transform spectrum; de) SRPES analysis under Ar etching; f) In-situ DRIFTS analysis of the precursor Ni-Ce(OH)3 / CeO2 under different gas calcination.

[0039] Figure 7 Defect characterization for different catalysts: a represents Ce 3d Analysis; b is O 1s analyze;

[0040] Figure 8 For Ni cluster Morphological characterization of / CeO2: a is X-ray diffraction pattern; b is high-angle annular dark-field pattern; c is comparison of CO2 conversion and CO selectivity; d is comparison of CO yield of different catalysts;

[0041] Figure 9 The catalytic performance of the precursor Ni-Ce(OH)3 / CeO2 catalyst under different atmospheres is shown in the following figures: a) Comparison of CO2 conversion and CO selectivity of different catalysts; b) Comparison of CO yield of different catalysts.

[0042] Figure 10 Catalytic performance of Ni-Ce(OH)3 / CeO2 precursors with different Ni contents on reverse water-gas shift reaction after calcination in a mixed atmosphere of 75 vol% H2 + 25 vol% CO2: a) Comparison of CO2 conversion rate; b) Comparison of CO selectivity;

[0043] Figure 11 The following graphs illustrate the catalytic performance of NiC / Ni-CeO2 catalysts in the reverse water-gas shift reaction: a) Comparison of CO2 conversion and CO selectivity for different catalysts; b) Comparison of CO yield for different catalysts; c) Activation energy for different catalysts; d) CO production rate for different catalysts; e) Stability test results for NiC / Ni-CeO2 catalysts. Detailed Implementation

[0044] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0045] This invention discloses a method for preparing a doped catalyst for a reverse water-gas shift reaction. The technical solution of this invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments.

[0046] Example 1

[0047] like Figure 1 As shown in a, the preparation of the precursor Ni-Ce(OH)3 / CeO2 includes the following steps:

[0048] (1) Preparation of Ni-Ce(OH)3 / CeO2 precursor

[0049] First, add 70 mL of ultrapure water to a 100 mL glass bottle and place a magnetic stirrer inside. Then, slowly add 19.2 g of sodium hydroxide to the aforementioned inner liner and stir for 30 minutes. After the NaOH solution cools, slowly add the prepared solution containing Ce. 3+ Ni 2+ The solution (prepared by ultrasonic dispersion of 4 mmol Ce(NO3)3·6H2O and 0.08 mmol Ni(NO3)2·6H2O in 10 mL of ultrapure water) was used. During the dropwise addition, the solution slowly turned milky white. After the addition was complete, the solution was stirred at room temperature for 30 minutes, poured into a glass bottle, and reacted at 100°C in a forced-air drying oven for 24 hours. After the reaction was completed, the solution was washed three times alternately with water and alcohol, and then dried at 60°C in a forced-air drying oven for 8 hours to obtain the Ni-Ce(OH)3 / CeO2 precursor.

[0050] (2) Preparation of NiC / Ni-CeO2-based catalysts

[0051] The Ni-Ce(OH)3 / CeO2 precursor obtained in step 1) was mixed evenly with quartz sand (the volume ratio of Ni-Ce(OH)3 / CeO2 precursor to quartz sand was 1:3). The mixture was placed in a fixed-bed reactor and heated at a rate of 5 °C / min in a mixed atmosphere of 75 vol% H2 + 25 vol% CO2 (the flow rate had no significant effect on the treatment results, generally around 50 mL / min). -1 The sample was calcined at 600℃ for 2 hours and then naturally cooled to obtain the sample, which was named NiC / Ni-CeO2-600 (Ni 0.5wt.%).

[0052] Example 2

[0053] The difference from Example 1 is that in step 2), the sample was calcined at 450°C for 2 hours and then naturally cooled to obtain the sample, which was named NiC / Ni-CeO2-450.

[0054] Example 3

[0055] The difference from Example 1 is that in step 2), the sample was calcined at 525°C for 2 hours and then naturally cooled to obtain the sample, which was named NiC / Ni-CeO2-525.

[0056] Example 4

[0057] The difference from Example 1 is that in step 1), Ce 3+ Ni 2+ The solution (prepared by ultrasonic dispersion of 4 mmol Ce(NO3)3·6H2O and 0.06 mmol Ni(NO3)2·6H2O in 10 mL of ultrapure water) was used to obtain the sample, which was named NiC / Ni-CeO2 (Ni 0.3 wt.%).

[0058] Example 5

[0059] The difference from Example 1 is that in step 1), Ce 3+ Ni 2+ The solution (prepared by ultrasonic dispersion of 4 mmol Ce(NO3)3·6H2O and 0.20 mmol Ni(NO3)2·6H2O in 10 mL of ultrapure water) was used to obtain the sample, named NiC / Ni-CeO2 (Ni 1.5 wt.%).

[0060] Example 6

[0061] The difference from Example 1 is that in step 1), Ce 3+ Ni 2+ The solution (prepared by ultrasonic dispersion of 4 mmol Ce(NO3)3·6H2O and 0.33 mmol Ni(NO3)2·6H2O in 10 mL of ultrapure water) was used to obtain the sample, named NiC / Ni-CeO2 (Ni 2.5 wt.%).

[0062] Comparative Example 1

[0063] The difference from Example 1 is that in step 1), Ni(NO3)2·6H2O solution is not added to obtain the precursor Ce(OH)3 / CeO2.

[0064] Step 2) Place the Ce(OH)3 / CeO2 precursor obtained in Step 1) in a fixed-bed reactor and heat it at a rate of 5 °C / min in a mixed atmosphere of 75 vol% H2 + 25 vol% CO2 (the flow rate has no significant effect on the treatment results, generally around 50 mL / min). -1 The sample was calcined at 600℃ for 2 hours and then naturally cooled to obtain CeO2.

[0065] Comparative Example 2

[0066] The difference from Example 1 is that step 2) uses a high-pressure hydrothermal method for preparation. The specific process is as follows: the Ni-Ce(OH)3 / CeO2 precursor is prepared at 2 mg / ml -1 The sample was ultrasonically dispersed in ultrapure water and added to a 100 mL polytetrafluoroethylene inner liner. The mixture was then placed in a reaction vessel and reacted at 180 °C for 12 h in a forced-air drying oven. After the reaction was completed, the sample was collected by centrifugation and then dried at 60 °C for 8 h in a forced-air drying oven to obtain the sample Ni-CeO2.

[0067] Comparative Example 3

[0068] Ni particles were loaded onto the CeO2 surface using a traditional impregnation method to obtain the Ni sample. cluster The / CeO2 catalyst specifically includes the following steps:

[0069] (1) The precursor Ce(OH)3 / CeO2 was prepared using the same hydrothermal method as in Comparative Example 1.

[0070] (2) CeO2 was prepared using the same calcination method as in Example 1.

[0071] (3) Using the traditional impregnation method, Ni particles are loaded onto the CeO2 surface to obtain a supported catalyst Ni. cluster / CeO2 (Ni loading is 2wt%):

[0072] Weigh 200 mg of the porous rod-shaped CeO2 obtained in step (2), place it in a 50 mL dry pot, add 30 mL of ethanol and ultrasonically disperse it. Add 800 μL (Ni wt%: 5 mg / mL) of nickel nitrate aqueous solution to the solution dropwise. After stirring at room temperature for 2 hours, heat to 90 °C and evaporate completely. Then calcine in a 10% H2 / Ar mixed gas at a rate of 5 °C / min to 450 °C for 2 hours to obtain the supported catalyst Ni. cluster / CeO2.

[0073] Comparative Example 4

[0074] The difference from Example 1 is that in step 2), the calcination atmosphere is hydrogen, and the resulting sample is named Ni / Ni-CeO2-H2.

[0075] Comparative Example 5

[0076] The difference from Example 1 is that in step 2), the calcination atmosphere is CO, and the resulting sample is named Ni / Ni-CeO2-CO.

[0077] Comparative Example 6

[0078] The difference from Example 1 is that in step 2), the calcination atmosphere is CO2, and the resulting sample is named Ni / Ni-CeO2-CO2.

[0079] To verify the effectiveness, the present invention also conducted the following experimental examples:

[0080] I. Morphological and structural characterization of the precursor Ni-Ce(OH)3 / CeO2 prepared in Example 1, and the final samples obtained under different conditions in Examples 1 and Comparative Examples 1-6:

[0081] Figure 1 The preparation process, crystal structure, and morphology of the precursor Ni-Ce(OH)3 / CeO2 in Example 1 are as follows: Figure 1 b shows that the crystal structure of Ni-Ce(OH)3 / CeO2 is a two-phase mixed structure of Ce(OH)3 and CeO2 (the detection limit of XRD is 3%, and the Ni content is not that high, so it is not shown here); Figure 1 The c-shaped structure shows that its main exposed crystal planes are Ce(OH)3 (101) with a crystal plane spacing of 0.30 nm and CeO2 (220) with a crystal plane spacing of 0.190 nm.

[0082] Figure 2 The crystal structure and morphology of NiC / Ni-CeO2 in Example 1 are as follows: Figure 2 As shown in a, the crystal structure of NiC / Ni-CeO2 is the crystalline phase of pure CeO2; from Figure 2 b clearly shows that the nanorod has a porous structure; Figure 2 c shows that its interplanar spacing is 0.190 nm, which belongs to the (220) plane of CeO2; Figure 2 The image d is a magnified scanning transmission electron microscope image, which can accurately and scientifically demonstrate the existence of Ni clusters.

[0083] Figure 3 The crystal structure and morphology of CeO2 in Comparative Example 1 are as follows: Figure 3 Figure a shows that the crystal structure of the prepared CeO2 is the crystalline phase of pure CeO2; from Figure 3 b clearly shows the porous structure on the nanorod; furthermore Figure 3 b shows that its interplanar spacing is 0.190 nm, belonging to the (220) plane of CeO2.

[0084] Figure 4 The morphology spectrum of Ni-CeO2 in Comparative Example 2 is shown below: Figure 4Figure a shows that the Ni-CeO2 generated after the second hydrothermal step is a pure CeO2 crystalline phase. Compared with NiC / Ni-CeO2, no Ni clusters were observed, indicating that Ni atoms are still inside the CeO2 lattice. Figure 4 b shows that its interplanar spacing is 0.190 nm, which is consistent with the prepared CeO2 and belongs to the (220) crystal plane of CeO2.

[0085] Figure 8 For Ni cluster Morphology and elemental distribution spectrum of / CeO2: as follows Figure 8 The figure shows that Ni prepared by the traditional impregnation method cluster / CeO2 is the crystalline phase of pure CeO2, and no Ni phase was found, indicating the high dispersion of Ni clusters; Figure 8 b shows a crystal plane spacing of 0.190 nm, consistent with the prepared CeO2, belonging to the (220) crystal plane of CeO2, and there is a crystal plane of 0.200 nm, belonging to the (111) crystal plane of Ni.

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

[0087] Figure 5 Examples 1, 2, and 3 illustrate the treatment at different temperatures. It can be seen that the NiC / Ni-CeO2 catalyst exhibits the highest CO2 conversion rate and the best CO selectivity at 600℃.

[0088] Figure 6 Synchrotron radiation spectra of different catalysts: such as Figure 6 As shown in Figure a, the electronic structure of the reconstructed NiC / Ni-CeO2 catalyst is very similar to that of the Ni foil, indicating that metallic nickel was formed during the in-situ reconstruction process, and that nickel carbide only accounts for a portion of the total nickel, representing partial carbide formation. Figure 6 b and Figure 6 In c, EXAFS spectroscopy and wavelet transform analysis show that the Ni-Ni bond distance in the reconstructed NiC / Ni-CeO2 catalyst is... The position is consistent with the Ni-Ni peak observed in the Ni foil. Notably, the Ni-O bonds are still clearly present on the reconstructed NiC / Ni-CeO2 catalyst, indicating that the structure of doped Ni in the CeO2 region remains unchanged. Figure 6 d and Figure 6 In the e, the Ni L-edge of the NiC / Ni-CeO2 catalyst shows Ni 0 and Ni 2+The coexistence of species further confirms the formation of Ni clusters. With increasing Ar plasma treatment time, the number of C species displayed at the CK edge gradually decreases, indicating that carbonaceous species are being etched. Furthermore, with the reduction of C species, Ni... 0 The binding energy of the species also decreased significantly, indicating a strong interaction between the C species and the Ni clusters. Therefore, SRPES spectral analysis clearly demonstrates that environmentally induced reconstruction and carbonization produced carburized nickel clusters.

[0089] In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to investigate how NiC is reconstructed during calcination under different atmospheres. For example... Figure 6 In f, the DRIFTS spectrum of the precursor Ni-Ce(OH)3 / CeO2 shows that there is Ni-(CO) on the catalyst surface. 2 / 3 Twin adsorption was observed, indicating that Ni is atomically dispersed. After in-situ treatment of Ni-Ce(OH)3 / CeO2 at 350 °C with a mixed atmosphere (75 vol% H2 + 25 vol% CO2) to simulate a catalytic environment, Ni-(CO) adsorption was observed. 2 / 3 The corresponding peak value decreased significantly. Meanwhile, 1930cm -1 and 1840cm -1 The peaks observed at the given locations are attributed to the bridging adsorption of CO with three nickel atoms (Ni3-CO) and the nickel carbide species (NiC-CO), respectively. Furthermore, characteristic peaks of NiC-CO were also observed on the CO-treated Ni-Ce(OH)3 / CeO2 catalyst. Therefore, these experiments clearly demonstrate that reduced CO plays a crucial role in the formation of NiC.

[0090] Figure 7 Characterization of oxygen vacancies: such as Figure 7 The result shows that by analyzing the various cerium oxides (Ce) 3d Orbit fitting revealed that the NiC / Ni-CeO2 catalyst possesses 35.2% Ce content. 3+ The content is much higher than that of other cerium oxides; such as Figure 7 b shows that the NiC / Ni-CeO2 catalyst has the highest Ce content. 3+ With an O content as high as 53.4%, NiC / Ni-CeO2 has the highest oxygen defect concentration.

[0091] II. Comparison of NiC / Ni-CeO2 prepared in Example 1 and Ni prepared in Comparative Example 3 cluster The catalytic performance of / CeO2 and the Ni / Ni-CeO2-H2, Ni / Ni-CeO2-CO, and Ni / Ni-CeO2-CO2 prepared in Comparative Examples 4-6 were analyzed. The specific procedures are as follows:

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

[0093] (2) Inject 60 mL min -1 The reaction was carried out in a mixed atmosphere with a WHSV of 72,000 mL g. -1 h -1 H2:CO 2: The N2 ratio was 3:1:8, the reaction temperature was 200-550℃, and the reaction pressure was 0.1 MPa. During the reaction, the tail gas from the fixed-bed reactor was connected to a gas chromatograph, and the gas components were analyzed online using TCD and FID gas chromatography, and the amounts of CH4 and CO were calculated. Specific results are shown in [link to results]. Figure 8 , Figure 9 .

[0094] pass Figure 8 The values ​​of c and d reveal the superior catalytic performance of the reconstructed NiC / Ni-CeO2 catalyst. cluster / CeO2 has a low CO2 conversion rate and poor CO selectivity.

[0095] Figure 9 Catalytic performance of the precursor Ni-Ce(OH)3 / CeO2 after reconstruction and calcination under different atmospheres for the reverse water-gas shift reaction: such as Figure 9 Figure a shows that the catalyst performance was significantly improved after calcination in a mixed atmosphere of H2, CO, and 75 vol% H2 + 25 vol% CO2, indicating that the reducing atmosphere is a key factor in the calcination of the precursor. However, only the catalyst calcined in the mixed atmosphere (75 vol% H2 + 25 vol% CO2) exhibited the best CO2 conversion rate and CO selectivity. In the H2 atmosphere, there is no C source, so NiC cannot be formed, resulting in poor selectivity. The catalyst activity was not good in the pure CO atmosphere.

[0096] Figure 10 The catalytic performance of Ni-Ce(OH)3 / CeO2 precursors with different Ni contents on the reverse water-gas shift reaction after calcination in a mixed atmosphere of 75 vol% H2 + 25 vol% CO2 is as follows: Figure 10 Figures a and b show that the CO2 conversion is low in the catalyst without Ni, and increases with increasing Ni content. However, CO selectivity is very poor when the Ni content is 2.5%. Therefore, the optimal Ni doping level should be less than 2.5%.

[0097] III. The catalysts CeO2 and Ni-CeO2 prepared in Comparative Examples 1-2 and the NiC / Ni-CeO2 catalyst prepared in Example 1 were used for the reverse water-gas shift reaction, respectively. The specific operations are as follows:

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

[0099] (2) Inject 60 mL min -1 The reaction was carried out in a mixed atmosphere with a WHSV of 72,000 mL·g. -1 ·h -1 H2:CO 2: The N2 ratio is 3:1:8, the reaction temperature is 200-550℃, and the reaction pressure is 0.1 MPa. During the reaction, the tail gas from the fixed-bed reactor is connected to a gas chromatograph, and the gas components are analyzed online using TCD and FID gas chromatography, and the amounts of CH4 and CO are calculated.

[0100] from Figure 11 As can be seen from a, the NiC / Ni-CeO2 catalyst has a higher CO2 conversion rate and CO selectivity compared with other catalysts; Figure 11 As can be seen from b, the CO yield of NiC / Ni-CeO2 reaches 55.0% at 550℃, which is very close to the theoretical CO equilibrium yield (55.1%) of RWGS under experimental conditions. Figure 11 The value of c represents the activation energy of each catalyst. The NiC / Ni-CeO2 catalyst has a relatively low activation energy (41.4 kJ mol). -1 The result indicates that it has the best catalytic reaction pathway, which also explains the superior performance of the NiC / Ni-CeO2 catalyst. Figure 11 The figure d shows the CO generation rate of the NiC / Ni-CeO2 catalyst. The CO generation rate of the NiC / Ni-CeO2 catalyst is very high, reaching 27.3 mol·g. Ni -1 ·h -1 This is at least an order of magnitude higher than previously reported Ni-based catalysts, and it also exhibits higher 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-CeO2 catalysts. Figure 11 The graph (e) represents the stability test results. Even at a high temperature of 550°C, the NiC / Ni-CeO2 catalyst exhibits excellent stability against RWGS. Over at least 1000 hours of reaction, the CO yield remains almost constant and approaches the thermodynamic equilibrium yield. Furthermore, each Ni site achieves a very high conversion frequency, exceeding 4,500,000 cycles, demonstrating the structural stability of the NiC / Ni-CeO2 catalyst and its potential for commercialization.

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

[0102] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the scope of the technology disclosed in the present invention, and such modifications or substitutions should all be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a doped catalyst NiC / Ni-CeO2, characterized in that, Includes the following steps: 1) A solution prepared by Ce salt, Ni salt and ultrapure water was added dropwise to a cooled strong alkaline solution to prepare Ni-Ce(OH)3 / CeO2 precursor by hydrothermal method, and the Ni loading in the precursor was less than 2.5 wt%. 2) The Ni-Ce(OH)3 / CeO2 precursor obtained in step 1) was calcined in a mixed atmosphere of H2 and CO2 at 450-600℃ 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) specifically involves: A strong base was slowly added to a glass bottle containing ultrapure water and stirred until homogeneous to form a strong base solution. After the strong base solution cooled, a solution prepared by Ce(NO3)3·6H2O, Ni(NO3)2·6H2O and ultrapure water was slowly added dropwise. After the addition was complete, the solution was stirred until homogeneous at room temperature and placed in a glass bottle. The reaction was carried out at 100-120℃ for 12-24 hours. After the reaction was completed, the solution was washed several times with water and alcohol alternately, and then dried at 60-80℃ for 8-12 hours to obtain the 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℃ and the reaction time was 24h.

5. The method for preparing the doped catalyst NiC / Ni-CeO2 according to any one of claims 1-4, characterized in that, Step 2) specifically involves: The Ni-Ce(OH)3 / CeO2 precursor obtained in step 1) was mixed evenly with quartz sand and placed in a fixed-bed reactor. Under a mixed atmosphere of H2 and CO2, the temperature was raised to 450-600℃ and calcined for 2-4 hours. After natural cooling, a uniform rod-shaped porous nickel carbide-doped cerium oxide catalyst NiC / Ni-CeO2 was obtained.

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 mixture of 75 vol% H2 and 25 vol% CO2, and the flow rate is 50 mL / min. -1 ; The temperature was increased to 600℃ at a rate of 5℃ / min, and calcined for 2 hours.

7. A doped catalyst NiC / Ni-CeO2, characterized in that: It is prepared by any of the preparation methods described in claims 1-6.

8. The application of the doped catalyst NiC / Ni-CeO2 prepared by any of the preparation methods described in claims 1-6 as a catalyst in the reverse water-gas shift reaction.

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

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