A rare earth metal doped nickel-based carbon-supported catalyst, a preparation method thereof and application thereof in a pressurized DRM reaction

Abstract

The application relates to a rare earth metal doped nickel-based carbon carrier catalyst, a preparation method thereof and application of the catalyst in a pressurized DRM reaction. The catalyst comprises modified lignite as a carrier, metal nickel as an active component accounting for 10% of the carrier by weight, and metal samarium as an additive accounting for 3%-5% of the carrier by weight. The lignite is first subjected to acid pickling and ash removal treatment, and the number of oxygen-containing functional groups is increased through oxidation; the modified lignite is subjected to sufficient ion exchange with an active metal salt solution to promote high dispersion of metal ions on the surface of the carbon carrier; the rare earth metal samarium is loaded on the surface of the carbon carrier by using a wet impregnation method; and the Ni-Sm / C catalyst is prepared through heat reduction in an inert gas atmosphere by using a tube furnace. The preparation process is simple, the raw material cost is low, the obtained catalyst has good metal dispersity, the oxygen vacancy concentration is significantly increased, the catalyst has good stability when applied in the pressurized DRM reaction, and the catalytic performance of the DRM reaction can be improved through a sectional pressurization method.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation technology, specifically to a rare earth metal-doped nickel-based carbon-supported catalyst, its preparation method, and its application in pressurized DRM reaction. Background Technology

[0002] With the massive emission of greenhouse gases leading to rising global temperatures, exacerbating climate change, and impacting human survival, CO2 capture and efficient resource utilization of greenhouse gases have become hot research topics. Among them, methane carbon dioxide reforming technology (DRM) can use a heterogeneous catalytic process to convert two greenhouse gases, CO2 and CH4, into CO and H2 (syngas) for use as sustainable alternative fuels. At the same time, it can also serve as an important chemical feedstock for carbonylation, formylation, and Fischer-Tropsch synthesis processes to produce chemical products such as alcohols, gasoline, aromatics, and olefins.

[0003] my country has abundant coal resources, with low-rank coal, represented by lignite, accounting for a large proportion. However, its utilization efficiency is low, and the clean, efficient, and high-value-added utilization of low-rank lignite has gradually attracted widespread attention. Using low-rank lignite as a precursor to prepare carbon-supported catalysts can effectively reduce economic costs. Lignite modified through acid washing and oxidation processes has richer oxygen-containing functional groups and stronger ion exchange capacity, which is beneficial for the adsorption of active metals.

[0004] Currently, laboratory-level catalyst evaluations for basic research purposes are typically conducted only at atmospheric pressure, and research on pressurized DRM reaction processes is relatively limited. However, considering the practical needs of industrial applications, pressurized DRM reactions can reduce reactor volume and downstream process gas compression costs, making it a highly attractive and promising industrial technology. However, because the gas molecule volume increases during the forward reaction, increasing the system pressure leads to a decrease in reaction conversion. Simultaneously, the high-pressure environment promotes carbon deposition, and carbon species adhering to the reactor walls can clog the reactor, affecting the stable operation of the DRM process. Since the sources and types of carbon deposits differ under pressurized conditions, and methods for removing carbon deposits at atmospheric pressure are not entirely applicable to pressurized conditions, DRM catalysts stable at atmospheric pressure may not be suitable for pressurized reactions. Therefore, further research and development of catalysts for pressurized DRM are needed. Summary of the Invention

[0005] The purpose of this invention is to provide a rare earth metal-doped nickel-based carbon-supported catalyst, which has good metal dispersion, significantly increased oxygen vacancy concentration, and good stability when applied to pressurized DRM reaction; the catalytic performance of methane-carbon dioxide reforming reaction can be improved by staged pressurization.

[0006] The second objective of this invention is to provide a method for preparing the above-mentioned rare earth metal-doped nickel-based carbon-supported catalyst, which has a simple preparation process and low raw material cost.

[0007] A third objective of this invention is to provide the application of the above-mentioned rare earth metal-doped nickel-based carbon-supported catalyst in pressurized methane-carbon dioxide reforming reaction.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] In a first aspect, the present invention provides a rare earth metal-doped nickel-based carbon-supported catalyst, comprising lignite as a support, metallic nickel comprising 10 wt% of the support as an active component, and metallic samarium comprising 3 wt%-5 wt% of the support as an additive; wherein the lignite is modified lignite after acid washing and oxidation treatment.

[0010] Furthermore, the acid washing and oxidation treatment steps for lignite are as follows:

[0011] (1) Grind lignite to a particle size of 380-1000 μm;

[0012] (2) Weigh the lignite ground in step (1) and immerse it in hydrochloric acid solution. Heat and stir in a water bath, filter while hot, and wash until Cl is undetectable in the waste liquid. - After the filter cake is dried, acid-washed lignite is obtained.

[0013] (3) Weigh the acid-washed lignite obtained in step (2) and immerse it in hydrogen peroxide solution. Heat and stir in a water bath, filter, wash and dry to obtain acid-washed oxidized lignite, i.e. modified lignite.

[0014] Preferably, in steps (2) and (3), the filter cake is dried at 100°C for 12 hours; in step (2), the concentration of hydrochloric acid solution is 5 mol / L; the water bath heating temperature is 55°C and the heating time is 2 hours; in step (3), the water bath heating temperature is 50°C and the heating time is 2 hours; and the mass concentration of hydrogen peroxide solution is 30%.

[0015] Secondly, the present invention provides a method for preparing the above-mentioned rare earth metal-doped nickel-based carbon-supported catalyst. This method uses an ion exchange method to load active nickel and a wet impregnation method to load auxiliary metal samarium. The specific steps are as follows:

[0016] S1. Prepare a nickel nitrate hexahydrate solution, add ammonium carbonate to promote complex formation, adjust the pH of the system to 11, add modified lignite as a carrier while stirring, stir at room temperature, filter after stirring, wash the sample with deionized water, adjust the sample to neutral and dry.

[0017] S2. Weigh out samarium nitrate hexahydrate and add it to deionized water. Stir to dissolve and then add the sample dried in step S1. Vacuum impregnate and then dry the solution.

[0018] S3. The sample dried in step S2 is transferred to a tube furnace under an argon atmosphere for carbonization treatment. After cooling to room temperature, the Ni-Sm / C catalyst is obtained.

[0019] Preferably, in step S1, the molar ratio between ammonium carbonate and nickel nitrate hexahydrate is 2:1; the concentration of the nickel nitrate hexahydrate solution is 0.05 mol / L, and the pH of the system is adjusted using ammonia water with an ammonia content >40%; the stirring speed is 210 rpm; the drying temperature is 100℃, and the drying time is 5 h; in step S2, the drying temperature is 100℃, the drying time is 12 h, and vacuum impregnation is performed for 24 h.

[0020] Preferably, in step S3, the carbonization conditions are: temperature of 600℃, heating rate of 10℃ / min, and maintained at 600℃ for 1h, and argon flow rate of 250mL / min.

[0021] The third objective of this invention is to provide the application of the above-mentioned rare earth metal-doped nickel-based carbon-supported metal catalyst in pressurized DRM reaction.

[0022] Further, the specific application process includes the following steps: A certain amount of catalyst is weighed and added to a quartz reactor, and experiments are conducted on a micro fixed bed. The temperature is raised to 800℃ under an argon atmosphere, and the reaction pressure is increased to 0.5 MPa using CH4 / CO2 syngas. The catalyst is activated under a syngas atmosphere for more than 20 hours. After the catalytic effect stabilizes, the reaction pressure is increased to 1.0-1.5 MPa to continue the reaction. The catalyst performance is evaluated by online gas chromatography analysis.

[0023] Preferably, the catalyst dosage is 0.05 g, the heating rate is 20 °C / min, the CH4 / CO2 ratio is 1:1, the syngas flow rate is 25 mL / min, and the gas hourly space velocity is 30000 mL·h. -1 ·g -1 cat .

[0024] Furthermore, after the catalyst was activated at 0.5 MPa, the pressure was increased by 0.5 MPa every 50 hours, so that the final reaction pressure was increased to 1.5 MPa. The catalyst performance was evaluated by online gas chromatography analysis.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. This invention features a simple preparation process and low raw material cost. The prepared catalyst has good metal dispersion and significantly increased oxygen vacancy concentration, exhibiting good stability when applied to pressurized DRM reactions. The catalytic performance of the DRM reaction can be improved through a segmented pressurization method.

[0027] 2. The rare earth metal-doped nickel-based carbon-supported catalyst provided by this invention, when the rare earth metal Sm doping amount is 4%, has a catalyst surface oxygen vacancy concentration (O2). β / (O α +O β +O γ The concentration of oxygen vacancies increased from 65.5% without additives to 88.5%. The presence of oxygen vacancies can serve as active sites for reactants CH4 and CO2, promoting the activation of reactant molecules. At the same time, it can also promote the gasification of carbon species, thereby enhancing the catalyst's resistance to carbon deposition. As a result, Ni-4Sm / C exhibits the best conversion rate and stability within 30 hours and shows good reactivity under pressure.

[0028] In summary, the rare-earth metal-doped nickel-based carbon-supported catalyst prepared in this invention can effectively regulate the structure-activity relationship between catalyst structure and catalytic performance. The active sites formed by oxygen-containing functional groups on the surface of the carbon-based catalyst can accelerate the gasification and elimination of carbon species by CO2. The addition of rare-earth metals creates abundant oxygen vacancies on the lignite surface, promoting the adsorption of reactant molecules and the elimination of carbon deposits, thereby improving the catalyst's reaction performance and catalytic stability under pressurized conditions. Furthermore, by increasing the reaction pressure through staged pressurization, the conversion rate of the catalyst under pressurized conditions is effectively improved, providing an effective approach and feasible route for developing pressurized DRM technology. Attached Figure Description

[0029] Figure 1 The following are activity evaluation graphs of the catalysts prepared in Examples 1-3 and the comparative example of the present invention after 30 h: a is the CH4 conversion curve, and b is the CO2 conversion curve.

[0030] Figure 2 The electron paramagnetic resonance spectra of the catalysts prepared in Example 1 and the comparative example of this invention are shown below.

[0031] Figure 3 XPS O1s spectra and oxygen vacancy concentrations of the catalysts prepared in Examples 1-3 and the comparative examples of this invention, respectively;

[0032] Figure 4 The images show low-magnification TEM images and particle size distribution diagrams of the catalysts prepared in Examples 1-3 of this invention.

[0033] Figure 5 The N2- adsorption-desorption isotherms of the catalysts prepared in Examples 1-3 and the comparative example of this invention are shown below;

[0034] Figure 6The following are stability evaluation diagrams for Example 4 and Example 5, respectively, when the catalyst prepared in Example 1 is applied to the DRM reaction: (a) Stability evaluation diagram for Example 4 when the catalyst prepared in Example 1 is applied to the DRM reaction; (b) Stability evaluation diagram for Example 5 when the catalyst prepared in Example 1 is applied to the DRM reaction. Detailed Implementation

[0035] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0036] Example 1

[0037] A rare earth metal-doped nickel-based carbon-supported catalyst comprises lignite as a support, metallic nickel comprising 10 wt% of the support as an active component, and metallic samarium comprising 4 wt% of the support as an additive; wherein the lignite is modified lignite after acid washing and oxidation treatment.

[0038] The acid washing and oxidation treatment steps for the lignite are as follows:

[0039] (1) Grind lignite to a particle size of 380-1000 μm;

[0040] (2) Weigh 20g of the lignite ground in step (1) and immerse it in a 5mol / L hydrochloric acid solution. Heat the solution in a water bath at 55℃ and stir for 2 hours. Filter while hot and wash until no Cl is detected in the waste liquid. - The filter cake was dried at 100℃ for 12 hours to obtain pickled lignite.

[0041] (3) Weigh 20g of the acid-washed lignite obtained in step (2) and immerse it in a 30% hydrogen peroxide solution. Stir for 2 hours at 50°C in a water bath, filter and wash. Dry the filter cake at 100°C for 12 hours to obtain acid-washed oxidized lignite, i.e. modified lignite.

[0042] The preparation method of the above-mentioned rare earth metal-doped nickel-based carbon-supported catalyst uses an ion exchange method to support active nickel and a wet impregnation method to support auxiliary metal samarium. The specific steps are as follows:

[0043] S1. Weigh 4.362 g of nickel nitrate hexahydrate (AR) and add it to 300 mL of deionized water. Dissolve it completely at room temperature to obtain solution A with a nickel concentration of 0.05 mol / L. Add 2.883 g of ammonium carbonate to promote complex formation (as a complexing agent, the CO32- produced by its decomposition in water reacts with the Ni in the solution). 2+ The combination produces nickel carbonate or basic nickel carbonate precipitate, which decomposes into nickel oxide during carbonation and is eventually reduced to metallic nickel, thus achieving metal loading on the lignite carrier. The pH of the system is adjusted to 11 with 10 mL of ammonia solution (ammonia content >40%). (At high pH values, CO3...) 2-Ni binds to OH- through a competitive precipitation mechanism. 2+ To promote the formation of more uniform and finer particles, thereby improving the dispersibility of nickel particles on the carrier, 5g of modified lignite as a carrier was added while stirring. At room temperature, the H groups in the carboxyl groups of the lignite were removed by mechanical stirring. + and Ni in solution A 2+ Ion exchange is performed to make Ni 2+ The sample was uniformly distributed on the surface of the lignite skeleton and structure. The stirring speed was 210 rpm, and the ion exchange process lasted for 24 hours. After stirring, the sample was filtered, washed with deionized water, and dried at 100℃ for 5 hours after the sample was neutralized. Since the metal loading in the ion exchange method requires a washing step, the amount of metal added was greater than the actual loading amount. The Ni loading of the sample obtained by this step was 10% as determined by ICP analysis.

[0044] S2. Dissolve 0.095g of samarium nitrate hexahydrate in 20mL of deionized water and stir to dissolve to obtain solution B. Then add 0.8g of the sample dried in step S1 and vacuum impregnate for 24 hours. The resulting solution is dried at 100℃ for 12 hours.

[0045] S3. The dried sample from step S2 is transferred to a tube furnace under an argon atmosphere for carbonization treatment, which removes volatiles from lignite and reduces the metal valence state. The carbonization conditions are: temperature 600℃, heating rate 10℃ / min, and held at 600℃ for 1h, argon flow rate 250mL / min. After cooling to room temperature, the Ni-Sm / C catalyst is obtained and named the non-precious metal Ni-4Sm / C catalyst.

[0046] Comparative Example: Preparation of Non-Noble Metal Ni / C Catalysts

[0047] The difference from Example 1 is that step S2 is omitted. Instead, the sample obtained in step S1 is directly placed in a tube furnace under an argon atmosphere for carbonization treatment, and the carbonization conditions are the same as those in step S3 in Example 1.

[0048] Example 2: Preparation of non-noble metal Ni-3Sm / C catalyst

[0049] A rare earth metal-doped nickel-based carbon-supported catalyst comprises lignite as a support, metallic nickel comprising 10 wt% of the support as an active component, and metallic samarium comprising 3 wt% of the support as an additive; wherein the lignite is modified lignite after acid washing and oxidation treatment.

[0050] The preparation method is similar to that in Example 1, except that in step S2, the amount of samarium nitrate hexahydrate added to solution B is 0.071 g.

[0051] Example 3: Preparation of non-noble metal Ni-5Sm / C catalyst

[0052] A rare earth metal-doped nickel-based carbon-supported catalyst comprises lignite as a support, metallic nickel comprising 10 wt% of the support as an active component, and metallic samarium comprising 5 wt% of the support as an additive; wherein the lignite is modified lignite after acid washing and oxidation treatment.

[0053] The preparation method is similar to that in Example 1, except that in step S2, the amount of samarium nitrate hexahydrate added to solution B is 0.118 g.

[0054] from Figure 1 It can be seen that at 0.5 MPa and 30000 mL·h -1 ·g -1 cat Under the set conditions, after 30 hours of reaction, the CH4 and CO2 conversion rates of Ni / C were 54% and 61%, respectively. The CH4 conversion rates of Ni-3Sm / C, ​​Ni-4Sm / C, ​​and Ni-5Sm / C were 61%, 75%, and 71%, respectively, and the CO2 conversion rates were 72%, 85%, and 81%, respectively. This demonstrates that the addition of rare earth metal Sm effectively improved the reaction performance of the Ni / C catalyst. After 30 hours of reaction, the conversion rate of Ni / C showed a decreasing trend, while Ni-Sm / C still maintained good stability, demonstrating that the addition of rare earth metal Sm also had a positive effect on improving the stability of the catalyst.

[0055] from Figure 2 It can be seen that the g factor of 2.0003 proves the existence of oxygen vacancies in the Ni-4Sm / C catalyst.

[0056] from Figure 3 As can be seen from the calculation of the oxygen vacancy concentration of the catalyst using O1s energy dispersive spectroscopy, the oxygen vacancy concentration of Ni-4Sm / C increased from 65.5% in Ni / C to 88.5% after the addition of Sm, which proves the effectiveness of rare earth metals in increasing the oxygen vacancy concentration of the catalyst.

[0057] from Figure 4 As can be seen, the particle sizes of Ni-3Sm / C, ​​Ni-4Sm / C and Ni-5Sm / C were measured to be 4.97 nm, 3.16 nm and 4.16 nm, respectively. The added rare earth metals have strong metal dispersibility, which reduces the diameter of the nanoparticles to 3.16 nm.

[0058] from Figure 5 As can be seen, the N2 adsorption-desorption curves of all samples exhibit type IV isotherms, indicating that all samples exist in the form of microporous structures.

[0059] Example 4: Application of Catalysts

[0060] 0.05 g of the catalyst prepared in Example 1 was weighed and added to a quartz reactor, and the experiment was conducted on a micro-fixed bed. The temperature was raised to 800 °C under an argon atmosphere (argon flow rate of 25 mL / min) at a heating rate of 20 °C / min. The reaction pressure was increased to 0.5 MPa using a syngas mixture of CH4 / CO2 (1:1), and the syngas flow rate was adjusted to 25 mL / min with a gas hourly space velocity (GHSV) of 30,000 mL·h. -1 ·g -1 cat The catalyst was activated under syngas conditions at 0.5 MPa for more than 20 hours to promote the exposure of metal sites and facilitate the catalyst's induction period. After the catalytic effect stabilized, the reaction pressure was increased to 1.0 MPa, and the evaluation time was 100 hours.

[0061] Example 5: Gradually increasing the reaction pressure using a segmented pressurization method.

[0062] The difference from Example 4 is that after activation at 0.5 MPa, the pressure is increased by 0.5 MPa every 50 hours, and the reaction pressure is gradually increased to 1.5 MPa to continue the reaction.

[0063] from Figure 6 As can be seen, the conversion rate of Ni-4Sm / C decreased slowly under a pressure of 1 MPa and remained basically stable after 90 h. The CH4 conversion rate and CO2 conversion rate of Example 4 after stabilization were 55% and 65%, respectively, showing good catalytic activity under pressure. Compared with Example 4, Example 5 showed a trend of first increasing and then slowly decreasing activity within 50 h after staged pressure. At 150 h of reaction, the CH4 conversion rate and CO2 conversion rate of Example 5 were 60% and 70%, respectively, maintaining high catalytic activity for a long time.

[0064] 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 modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. Application of a rare earth metal-doped nickel-based carbon-supported catalyst in pressurized DRM reaction, and specific application process. The process includes the following steps: a certain amount of catalyst is weighed and added to a quartz reactor, and the experiment is conducted on a micro fixed bed. The temperature is raised to 800℃ under an argon atmosphere, and the reactor is pressurized to 0.5 MPa using CH4 / CO2 syngas. The catalyst is activated under a syngas atmosphere for more than 20 h. After the catalytic effect stabilizes, the reaction pressure is increased by 0.5 MPa every 50 h, so that the final reaction pressure is increased to 1.5 MPa. The catalyst performance is evaluated by online gas chromatography analysis. The rare earth metal-doped nickel-based carbon-supported catalyst comprises lignite as a support, metallic nickel comprising 10 wt% of the support as an active component, and metallic samarium comprising 3 wt%-5 wt% of the support as an additive; the lignite is modified lignite after acid washing and oxidation treatment; the acid washing and oxidation treatment steps for the lignite are as follows: (1) Grind the lignite to a particle size of 380-1000 µm; (2) Weigh the lignite ground in step (1) and immerse it in hydrochloric acid solution. Heat and stir in a water bath, filter while hot, and wash until Cl is undetectable in the waste liquid. - After drying the filter cake, acid-washed lignite was obtained; the water bath heating temperature was 55℃, and the heating time was 2 h. (3) Weigh the acid-washed lignite obtained in step (2) and immerse it in hydrogen peroxide solution. Heat and stir in a water bath, filter, wash and dry to obtain acid-washed oxidized lignite, i.e. modified lignite; the water bath heating temperature is 50℃ and the heating time is 2 h; the mass concentration of hydrogen peroxide solution is 30%; Active nickel was loaded using ion exchange, and samarium was loaded using wet impregnation.

2. The application according to claim 1, characterized in that, The catalyst was used in an amount of 0.05 g, the heating rate was 20 °C / min, the CH4 / CO2 volume ratio was 1:1, the syngas flow rate was 25 mL / min, and the gas hourly space velocity was 30,000 mL·h. -1 ·g -1 cat .

3. The application according to claim 1, characterized in that, In steps (2) and (3), the filter cake is dried at 100°C for 12 h; in step (2), the concentration of hydrochloric acid solution is 5 mol / L.

4. The application according to claim 1, characterized in that, The method for preparing the rare earth metal-doped nickel-based carbon-supported catalyst involves loading active nickel using an ion exchange method and loading samarium as an auxiliary agent using a wet impregnation method. The specific steps are as follows: S1. Prepare a nickel nitrate hexahydrate solution, add ammonium carbonate to promote complex formation, adjust the pH of the system to 11, add modified lignite as a carrier while stirring, stir at room temperature, filter after stirring, wash the sample with deionized water, adjust the sample to neutral and dry. S2. Weigh out samarium nitrate hexahydrate and add it to deionized water. Stir to dissolve and then add the sample dried in step S1. Vacuum impregnate and then dry the solution. S3. The sample dried in step S2 is transferred to a tube furnace under an argon atmosphere for carbonization treatment. After cooling to room temperature, the Ni-Sm / C catalyst is obtained.

5. The application according to claim 4, characterized in that, In step S1, the molar ratio between ammonium carbonate and nickel nitrate hexahydrate is 2:1; the concentration of the nickel nitrate hexahydrate solution is 0.05 mol / L, and the pH of the system is adjusted using ammonia water with an ammonia content >40%; the stirring speed is 210 rpm; the drying temperature is 100℃, and the drying time is 5 h; in step S2, the drying temperature is 100℃, the drying time is 12 h, and vacuum impregnation is performed for 24 h.

6. The application according to claim 4, characterized in that, In step S3, the carbonization conditions are as follows: temperature is 600℃, heating rate is 10℃ / min, and the temperature is maintained at 600℃ for 1 h, and argon flow rate is 250 mL / min.

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