Ni-based perovskite type catalyst with high specific surface area, preparation method of Ni-based perovskite type catalyst and application of Ni-based perovskite type catalyst in methane dry reforming

Abstract

The invention discloses a Ni-based perovskite type catalyst with a high specific surface area, a preparation method of the Ni-based perovskite type catalyst and application of the Ni-based perovskite type catalyst in methane dry reforming, the catalyst with the composition of Ni / CeAlO3-CeO2 is obtained through two steps of a citrate combustion method and a conventional impregnation method, and Al is introduced into commercial CeO2 with the high specific surface area; ceAlO3 perovskite grown in a calcination reduction process is used for enhancing the stability of a carrier structure and generating interaction with an active component Ni to limit the growth of particles at high temperature, so that the catalyst is obtained, and the specific surface area of the catalyst is 4 times that of a traditional perovskite type catalyst; the dispersion degree of the active component reaches 1.5 times that of a conventional impregnation method supported catalyst, the catalyst keeps the conversion rate of 90% or above at a high space velocity, the reversible transformation step of the perovskite structure enhances oxygen transfer, the purpose of inhibiting reaction carbon deposition is achieved, and only a small amount of carbon deposition exists within 200 hours of a stability test. The preparation method is simple, easy to implement, economical and environmentally friendly, and the prepared catalyst is high in activity, good in stability and suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of methane dry reforming, and in particular to a high specific surface area Ni-based perovskite catalyst used in methane dry reforming, and a preparation method and application thereof. Background Art

[0002] Over the past half-century, surging global energy demand has led to overexploitation of fossil fuels, whose combustion releases large amounts of greenhouse gases such as CH4 and CO2. These gases not only contribute to environmental problems such as global warming, sandstorms, and acid rain, but also have profound impacts on human production and daily life. However, as energy demand continues to rise, greenhouse gas emissions continue to increase annually. In this context, the development of economical and environmentally friendly renewable energy has become a major global challenge. Natural gas, as a low-carbon fossil energy source, has recently attracted considerable attention for its potential to alleviate energy shortages and environmental pollution. It holds an irreplaceable position in the global energy supply system and is projected to surpass coal to become the world's second-largest energy source by 2040. Natural gas is primarily composed of methane (over 90%). While methane is a greenhouse gas, it can be converted into clean hydrogen fuel through reforming reactions. Methane reforming to syngas (CO + H2) has become a research hotspot in the energy conversion field. Current mainstream reforming processes include methane partial oxidation, steam reforming, and dry reforming. The resulting syngas can be further converted into liquid fuels (such as diesel) or high-value-added chemicals (ammonia, methanol, dimethyl ether, etc.) through Fischer-Tropsch synthesis. How to efficiently utilize methane and convert it into high-value-added chemicals has always been a core topic in the energy and chemistry fields.

[0003] At present, the catalysts used for methane dry reforming can be roughly divided into precious metal and non-precious metal catalysts. Although precious metal catalysts (Pt, Ru, etc.) have excellent catalytic activity and resistance to carbon deposition, they are expensive and not suitable for industrial production. Non-precious metal catalysts based on Ni and Co have catalytic activity comparable to precious metal catalysts at high temperatures, but due to their strong catalytic ability for CH bonds, they often lead to excessive cracking of CH4 and carbon deposition problems; at the same time, due to the endothermic nature of methane dry reforming itself, the reaction is usually carried out at high temperatures, which can easily lead to Ni and Co metal migration and agglomeration, resulting in sintering problems. An effective strategy is to disperse Ni on a carrier with a high specific surface area, such as γ-Al2O3, SiO2, and CeO2; among them, the CeO2 carrier relies on Ce 4+ / Ce 3+ The variable valence ability can realize the continuous conversion between CeO2 and Ce2O3, thereby improving the catalyst's ability to store and release oxygen, promoting the transfer of oxygen in the system, and effectively inhibiting the formation of carbon deposits in the reaction. In addition, CeO2 can effectively decompose CH4 to generate hydrocarbons CH xIt is oxidized to CO and reduced to Ce2O3, leaving oxygen vacancies on the support surface. CO2 can then oxidize Ce2O3 again and fill the oxygen vacancies, enhancing catalytic activity. However, CeO2 itself is not stable at high temperatures, and the interaction between Ni and CeO2 is weak.

[0004] Patent application number 201710835034.6 discloses a method for preparing and applying a cerium-modified lanthanum oxide catalyst: the method first prepares a La2C2O3 carrier, then introduces Ce for modification, and finally impregnates and loads Ni as an active component. The catalyst is Ni-Ce / La=x. Although the complex synthesis method achieves the purpose of stabilizing Ni particles and enhancing the metal-carrier interaction, the catalyst has a low GHSV of 60,000 mL / (h·g cat ) has an activity of only 60% at low space velocities. Patent application number 202111231386.3 discloses a method for plasma-assisted catalytic dry reforming of methane using a nickel-based boron nitride catalyst under low temperature conditions. The catalyst uses the discharge frequency of the plasma to provide reaction energy at room temperature. Although the reaction temperature is greatly reduced, the maximum conversion rate is only 61%, and the plasma discharge increases the complexity of the operation, making it unsuitable for large-scale industrial production. It can be seen that it is very necessary to develop a highly active and stable catalyst that does not require complex operation and can adapt to high space velocities and industrial applications. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the existing technology. In order to solve the problem that the catalyst conversion rate decreases or even becomes inactivated due to carbon deposition and sintering problems during high-temperature reaction in the existing methane dry reforming technology, a high specific surface area Ni-based perovskite catalyst, a preparation method thereof, and its application in methane dry reforming are provided.

[0006] In the technical solution of the present invention, Al is introduced into commercial CeO2 with a high specific surface area, so that CeAlO3 perovskite grows during its calcination and reduction process to enhance the stability of the support structure and produce a strong interaction with the active component Ni, limiting the growth of particles at high temperatures. At the same time, the reversible transformation of the perovskite structure can further enhance oxygen transfer. The catalyst exhibits excellent thermal stability during high-temperature reactions, and the resulting perovskite effectively anchors the Ni component and enhances its adsorption and activation capacity for CO2. Its simple synthesis method, low cost, and controllable preparation conditions offer promising applications.

[0007] The technical purpose of the present invention is achieved through the following technical solutions.

[0008] A high-specific-surface-area Ni-based perovskite catalyst comprises Ni / CeAlO3-CeO2, wherein Ni nanoparticles are separated by CeAlO3 and uniformly dispersed on the surface of a CeO2 carrier. Strong interaction occurs between Ni and CeAlO3, the elemental nickel loading is 8-12 wt%, and the molar ratio of elemental aluminum to the raw material CeO2 is (0.1-0.5):1.

[0009] In the above technical solution, the molar ratio of elemental aluminum to raw material CeO2 is (0.1-0.3):1.

[0010] In the above technical solution, the loading amount of elemental nickel is 10-12 wt %, and the size of the nanoparticles is 10-20 nm.

[0011] In the above technical solution, the specific surface area of CeO2 carrier can reach 120m 2 / g or more, preferably 125-128m 2 / g, especially the specific surface area after high temperature calcination.

[0012] The preparation method of the above catalyst is carried out according to the following steps:

[0013] Step 1: Disperse aluminum nitrate and citric acid evenly in deionized water to fully complex aluminum ions and citric acid, adjust the pH to 8-10 with ammonia water, add CeO2 carrier and continue stirring, remove most of the water by heating and evaporation to obtain complex wet gel, and continue to keep warm to form dry gel; then calcine the dry gel at high temperature to completely decompose citric acid and nitrate to obtain a composite metal oxide carrier, wherein the molar ratio of aluminum ions to citric acid is 1: (1-2), the calcination atmosphere is air, and the temperature is raised from room temperature 20-30 degrees Celsius to 200-400°C, and the heat preservation time is 1

[0014] —5 hours;

[0015] In step 1, the molar ratio of aluminum ion to citric acid is 1:(1-1.5).

[0016] In step 1, aluminum nitrate and citric acid are evenly dispersed in deionized water, and stirred with a magnetic stirrer at a speed of 300-400 r / min for 1-3 hours to make Al 3+ Fully complexed with CA.

[0017] In step 1, a muffle furnace is selected for high-temperature calcination.

[0018] In step 1, 28 wt.% ammonia water was used to adjust the pH value.

[0019] In step 1, after adding the CeO2 carrier, transfer the whole to a water bath for heating, maintain a stirring speed of 300-400 rpm, keep the water bath heating until a dry gel is formed, raise the temperature from room temperature 20-30 degrees Celsius to 70-80°C and keep it warm for 3-5 hours to form a wet gel, and then keep it warm for 2-4 hours to form a dry gel, with a heating rate of 3-5°C / min.

[0020] In step 1, calcination is performed at 200-400° C. for 3-5 hours.

[0021] Step 2: uniformly dispersing nickel nitrate and citric acid in deionized water to fully complex the nickel ions and the citric acid, grinding the composite metal oxide support obtained in step 1 and adding it thereto, continuously stirring and impregnating, drying the impregnated suspension, and then calcining the dried solid at high temperature to ensure complete decomposition of the citric acid and nitrate to obtain a catalyst precursor, wherein the molar ratio of nickel ions to citric acid is 1:(1-2), the calcination atmosphere is air, and the temperature is raised from room temperature of 20-30 degrees Celsius to 400-700 degrees Celsius, and the calcination time is 4-6 hours;

[0022] In step 2, nickel nitrate and citric acid are uniformly dispersed in deionized water, stirred at a speed of 300-400 r / min, and stirred for 1-3 hours to form a uniformly dispersed Ni-CA complex.

[0023] In step 2, a muffle furnace is selected for high-temperature calcination.

[0024] In step 2, the molar ratio of nickel ions to citric acid is 1:(1-1.1).

[0025] In step 2, after adding the composite metal oxide support obtained in step 1, the mixture is stirred and impregnated for 10-12 hours, and the impregnated suspension is placed in an oven at 80-120° C. and dried for 8-12 hours.

[0026] In step 2, the catalyst is calcined at 500-600° C. for 4-6 hours to form a Ni-Al-Ce-O catalyst precursor through a high-temperature solid-phase reaction.

[0027] Step 3: The catalyst precursor obtained in step 2 is subjected to hydrogen reduction at a reduction temperature of 700-900 degrees Celsius in a reducing atmosphere of a combination of hydrogen and inert gas, with a hydrogen volume percentage of 10-15%, and a reduction time of 1-5 hours to obtain a high specific surface area Ni-based perovskite catalyst having a composition of Ni / CeAlO3-CeO2.

[0028] In step 3, the catalyst precursor (in the form of powder) obtained in step 2 is pressed into 40-60 mesh size tablets, mixed with quartz sand, and loaded into a fixed bed reactor for hydrogen reduction.

[0029] In step 3, the mass ratio of quartz sand to catalyst is (5-10):1, preferably (5-7):1.

[0030] In step 3, the inert gas is argon, helium or nitrogen.

[0031] In step 3, the temperature is raised from room temperature (20-30 degrees Celsius) to the reduction temperature at a heating rate of 8-10 degrees Celsius / min, the reduction temperature is 800-900 degrees Celsius, and the reduction temperature is 2-4 hours.

[0032] After the reduction is completed, Ar is passed through for 10 minutes to purge the residual H2 and the temperature is lowered to the reaction temperature for testing. The purge gas Ar flow rate is 50-100 ml / min and the purge time is 5-15 minutes to remove the residual hydrogen on the surface.

[0033] The catalyst of the present invention is used in methane dry reforming to prepare synthesis gas containing carbon monoxide and hydrogen using methane and carbon dioxide as raw materials, especially at high space velocity, such as 100000-120000 mL / (h·g cat ), and can reduce the reaction carbon deposition rate to 0.5-1.2mg C / (g cat ·h).

[0034] Compared with the prior art, the beneficial effects of the invention are:

[0035] (1) The present invention discloses a high specific surface area Ni-based perovskite catalyst and a preparation method thereof. With the help of a commercial CeO2 carrier with a high specific surface area, the specific surface area of the catalyst and the dispersion of the active components can be increased, thereby showing high activity even at high space velocities. At the same time, the formation of in-situ grown CeAlO3 is itself restricted by CeO2, and the two can produce a strong interaction with Ni metal during the reduction process, thereby limiting the growth and aggregation of Ni particles during the high-temperature reaction and suppressing sintering problems. In addition, the perovskite structure grown in situ on the commercial carrier can give full play to the porosity of the carrier and the restrictive effect of the perovskite. This strategy provides ideas for designing catalysts.

[0036] (2) The present invention studies the effect of the CeAlO3 formation ratio on the commercial cerium oxide support on the final catalytic performance. It is found that the addition of a small amount of Al can significantly improve the catalytic activity, but when the ratio exceeds 0.3, the catalytic activity decreases due to the decrease in specific surface area and Ni dispersion. The data of the catalyst stability over 200 hours show that the formation of CeAlO3 can enhance the ability to eliminate carbon deposits, and the carbon deposition rate is reduced to 1 / 4 of that of directly loaded Ni / CeO2, greatly reducing the carbon deposition problem.

[0037] (3) The present invention provides new insights into Ni-Ce-Al interactions. The formation of CeAlO3 can improve the structural stability of the support and regulate the formation of surface oxygen vacancies. Characterization revealed that CeAlO3 can both reduce Ni particle size to prevent excessive cracking of CH4 and enhance the adsorption of CO2. The catalyst of the present invention can be used in the dry reforming of methane to produce synthesis gas, activating CO2 and promptly eliminating carbon deposits. It has excellent catalytic performance and thermal stability, and a long service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a graph showing the CH4, CO2 conversion rate and H2 / CO curve of methane dry reforming of Ni / CeAlO3-CeO2 (Al:CeO2=0.1, 0.3, 0.5) and Ni / CeO2, Ni / CeAlO3 catalysts of the present invention.

[0039] Figure 2 It is a 200-hour stability curve of methane dry reforming of Ni / CeAlO3-CeO2 (Al:CeO2=0.1, 0.3) and Ni / CeO2 catalysts of the present invention.

[0040] Figure 3 The thermogravimetric curves of the Ni / CeAlO3-CeO2 (Al:CeO2=0.1, 0.3) and Ni / CeO2 catalysts of the present invention after 200 hours of stability.

[0041] Figure 4 This is an XRD spectrum diagram of the high specific surface area Ni-based perovskite catalyst prepared by the present invention.

[0042] Figure 5 It is a TPR curve diagram of the high specific surface area Ni-based perovskite catalyst prepared by the present invention.

[0043] Figure 6 It is a graph of H2-TPD and CO2-TPD of the high specific surface area Ni-based perovskite catalyst prepared by the present invention.

[0044] Figure 7 These are TEM, HRTEM, and STEM-mapping photos of the high specific surface area Ni-based perovskite catalyst prepared in the present invention. DETAILED DESCRIPTION

[0045] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0046] Example 1

[0047] Step 1, taking Al:CeO2=0.1 (molar ratio) as an example. Take 0.7503g aluminum nitrate nonahydrate (Al(NO3)3·9H2O) and completely dissolve it in deionized water. Then add 0.6304g citric acid monohydrate (CA) (C6H 10 O8) was stirred at 350 r / min for 1 hour (Al 3+ : CA = 1:1.5, molar ratio); adding ammonia water to adjust the pH to 10, and then adding 3.4422g of commercial CeO2 (S BET =128m 2 / g). The whole is transferred to an 80 ° C water bath and stirred at a speed of 350 r / min until a complex wet gel is formed. Continue to keep warm to form a dry gel, then transfer it to a hot plate and pre-burn at about 250 ° C to remove organic matter until a black fluffy solid is formed. Cool down and turn off the heating in time. The solid is then ground and heated in a muffle furnace in an air atmosphere from room temperature 20-30 degrees Celsius to 400 ° C at a heating rate of 5 degrees Celsius per minute and kept warm for calcination for 3 hours. Cool with the furnace to form an Al-modified CeO2 carrier, which is dried and stored. Step 2, with a Ni loading of 10wt% (nickel element mass / overall catalyst mass, the overall catalyst is Ni / CeAlO3-CeO2 catalyst after reduction of Ni-Al-Ce-O composite oxide), 1.1011g of nickel nitrate hexahydrate (Ni(NO3)2·6H2O) is completely dissolved in deionized water, and then 0.8752g of citric acid monohydrate (C6H2O) is added under stirring. 10 O8) was stirred vigorously at 400 r / min for 1 h (Ni 2+ :CA=1:1.1, molar ratio) to form a Ni-CA complex; adding 2g of the modified support obtained in step 1 to the above dispersion, stirring at room temperature and 300r / min for 12 hours to promote sufficient contact between Ni-CA and the support to achieve a good impregnation effect, and then drying in a 110°C oven for 10 hours; grinding the solid obtained after drying in a mortar and placing it in a muffle furnace, in an air atmosphere, heating from room temperature 20-30 degrees Celsius at a heating rate of 5 degrees Celsius per minute to 500°C and calcining for 5 hours at this temperature, cooling with the furnace to fully remove organic matter and nitrate ions and form a Ni-Al-Ce-O composite oxide through a high-temperature solid-phase reaction.

[0048] Step 3: Take the composite oxide powder from step 2, compress it under a pressure of 3 MPa for 2 minutes, then crush it into granules, pass it through a 40-60 sieve, and screen it to obtain catalyst precursor particles with a certain strength. Take 0.05g of the prepared precursor particles, mix it with 0.35g of quartz sand, and then load it into a micro-tubular fixed-bed reactor. Reduce it at 900°C for 4 hours in a 10.0 vol.% H2 / Ar atmosphere (i.e., the volume percentage of hydrogen is 10%, the ratio of the volume of hydrogen to the volume of hydrogen and argon) at a gas rate of 100 mL / min to obtain a catalyst with a final composition of Ni / CeAlO3-CeO2. Subsequently, Ar is passed through for 10 minutes to purge residual H2 and the temperature is lowered to the reaction temperature (700-900°C, such as 750°C) for testing. The reaction gas composition and flow rate are CH4:CO2:Ar=25:25:50 mL / min. Every 50°C is a test point, and each temperature is tested twice. The pressure is normal pressure. The CH4 and CO2 conversions of methane dry reforming were analyzed by gas chromatography.

[0049] Example 2

[0050] The molar ratio of Al:CeO2 was adjusted to 0.3, and Ni / CeAlO3-CeO2 was prepared in the same manner as in Example 1.

[0051] Example 3

[0052] The molar ratio of Al:CeO2 was adjusted to 0.5, and Ni / CeAlO3-CeO2 was prepared in the same manner as in Example 1.

[0053] Comparative Example 1

[0054] In order to verify the effect of Al addition on Ni / CeO2, a conventional supported Ni / CeO2 catalyst was prepared according to the same calcination and reduction conditions as in steps 2 and 3 of Example 1.

[0055] Comparative Example 2

[0056] In order to verify the effect of high specific surface area commercial CeO2 support, a traditional perovskite Ni / CeAlO3 catalyst was prepared as a comparison. The specific steps were as follows: 3.488g of aluminum nitrate nine hydrate (Al(NO3)3·9H2O) and 4.038g of cerium nitrate hexahydrate (Ce(NO3)3·6H2O) were completely dissolved in deionized water, and then 5.863g of citric acid monohydrate (C6H2O) was added under stirring. 10 O8), stirred at 350 r / min for 1 hour ((Ce 3+ +Al 3+):CA=1:1.5 molar ratio); add ammonia water to adjust the pH to 10. Transfer the whole to an 80℃ water bath, continue stirring at a speed of 350r / min until a complex wet gel is formed, and continue to keep warm until a dry gel is formed; then transfer it to a heating plate at about 250℃ to pre-burn to remove organic matter until a black fluffy solid is formed, cool it down in time and turn off the heating. The obtained solid is ground and heated to 400℃ in an air atmosphere in a muffle furnace at a heating rate of 5℃ / min, kept warm for 3 hours to form a Ce-Al-O carrier, and dried for storage. Subsequently, the same impregnation method, calcination and reduction conditions as in steps 2 and 3 of Example 1 were used to obtain a catalyst with a final composition of Ni / CeAlO3, and the methane dry reforming performance test was carried out.

[0057] Using GHSV = 120000 mL / (h·g cat ) The activity test was carried out at high space velocity, the reaction temperature was 700-900℃, and the activity curve is shown in the attached figure. Figure 1 As shown, the curve shows that the addition of a small amount of Al can increase the catalytic activity by about 10% compared to conventional impregnation Ni / CeO2 (Comparative Example 1), but when Al:CeO2=0.5 (Example 3), the low-temperature activity decreases instead. This may be related to the excessive addition of Al, which leads to the destruction of the carrier structure, resulting in the inability of Ni to fully contact the reaction gas at low temperatures. Under high temperature conditions, CeAlO3 can form more O vacancies than a simple CeO2 carrier, thereby enhancing the adsorption capacity for CO2, resulting in increased activity. At the same time, the use of high-specific-surface-area commercial CeO2 as a carrier also improves the performance of the perovskite catalyst Ni / CeAlO3 (Comparative Example 2) obtained by direct high-temperature calcination by about 20%. This shows that the invention is effective in addressing the problem of decreased catalytic activity caused by the decrease in specific surface area of perovskite calcined at high temperature, and the use of high-specific-surface-area commercial carrier modification is effective.

[0058] At GHSV = 120000 mL / (h·g cat ) The long-term stability of the catalyst was investigated under the reaction temperature of 750℃. Figure 2As shown, curves 1, 2, and 7 correspond to the changes in CH4, CO2 conversion rates and H2 / CO ratios within 200 hours when methane dry reforming is carried out using the catalyst prepared under the conditions of Al:CeO2=0.1; curves 3, 4, and 8 correspond to the changes in CH4, CO2 conversion rates and H2 / CO ratios within 200 hours when methane dry reforming is carried out using the catalyst prepared under the conditions of Al:CeO2=0.3; curves 5, 6, and 9 correspond to the changes in CH4, CO2 conversion rates and H2 / CO ratios over time when methane dry reforming is carried out using the comparative example Ni / CeO2. Due to severe carbon deposition during the reaction, in order to prevent explosion caused by blockage of the reaction tube, the stability test was only carried out for 90 hours. Al:CeO2 = 0.1 and 0.3 (Examples 1 and 2) showed only a 3% decrease in activity over the 200-hour reaction period, maintaining a high H2 / CO ratio. Ni / CeO2, on the other hand, exhibited significant CO2 fluctuations and a slight increase during the reaction. This is due to the fact that more CeO2 lattice oxygen is reduced by the reaction products in the reaction atmosphere, and the exposed oxygen vacancies enhance CO2 adsorption. However, the overall conversion rate still did not reach that of the case with Al addition. In summary, the addition of Al can simultaneously improve the activity of the catalyst and maintain high activity in long-term stability tests. Compared with the existing technology, the conversion rates of CH4 and CO2 at 800℃ with Al:CeO2=0.1 reached 94% and 90%, respectively, and the H2 / CO ratio was maintained at 0.91. This is comparable to the activity of noble metal catalysts or modified Ni metal catalysts reported in the literature, for example, the Pt–CeO2 noble metal catalyst reported in (Langmuir, 2024, 40, 26) showed a GHSV of 36000 mL / (h·g at 800℃). cat ) has only an 80% conversion rate; the PtCo / CeO2 noble metal catalyst reported in (Applied Catalysis B: Environmental, 2018, 236, 15) has a GHSV of 24000 mL / (h·g) at 800°C. cat ) has a conversion rate of only 83%; the Ni / CeZr non-precious metal catalyst reported in (International Journal of Hydrogen Energy, 2018, 43, 41) has a GHSV of 120000 mL / (h·g) at 800℃. cat ) with a conversion rate of only 15%.

[0059] Table 1 Summary of catalyst activity and stability data

[0060]

[0061] a) Catalytic activity at GHSV = 120000 mL / (h·g cat), CH4, CO2 conversion and H2 / CO were tested at 700-900℃, and the activity data at 800℃ are summarized in the table for comparison.

[0062] b) Catalytic stability at GHSV = 120000 mL / (h·g cat ) conditions for 200 hours, and Al / CeO2=0.1, 0.3 and Ni / CeO2 were selected as the conditions that easily generate carbon deposits at 750℃. The table summarizes the data on stability changes for comparison.

[0063] Figure 3 The carbon deposit amount and type of the catalyst after 200 hours of reaction are shown. From the figure, it can be seen that the thermal gravimetric temperature (DTG) of the catalyst after the reaction of Al:CeO2=0.1 is concentrated at 610℃, indicating that graphite carbon is accumulated during the reaction. The carbon deposit amount is calculated by mass change (TG) to be 5.39mg, and the corresponding carbon deposition rate is only 0.54mg C / (g cat ·h); In contrast, the carbon deposition of Ni / CeO2 catalyst reached 18.47 mg within 100 h, with a carbon deposition rate of 3.69 mg C / (g cat ·h); while the carbon deposition amount of Al:CeO2=0.3 is 11.19mg, and the carbon deposition rate is 1.12mg C / (g cat ·h); This shows that the addition of a small amount of Al can effectively inhibit carbon deposition. This is consistent with the carbon deposition inhibition ability of modified Ni metal catalysts or noble metal catalysts reported in the literature, for example: (Applied Catalysis B: Environmental, 2014, 63, 37) reported that Ni-Mg-Al at 700 ° C, GHSV = 18000 mL / (h·g cat ) within 100 hours, the carbon deposition rate is 1.19 mg C / (g cat ·h); (Chemical Engineering Journal, 2023, 446, 15) reported that the MOF-modified 20wt.% Ni / CeO2 catalyst at 700℃, GHSV = 30000mL / (h·g cat ) within 10 hours, the carbon deposition rate is 0.875 mg C / (g cat ·h) and (Applied Catalysis A: General, 517, 5) reported that the perovskite-type noble metal catalysts BaZrRhO3, BaZrRuO3, and BaZPtO3 have a GHSV of 353000 mL / (h·g at 750℃). cat ) within 65 hours, the carbon deposition rate reached 1.9 mg C / (g cat ·h)、2.7mg C / (gcat ·h)、9.4mg C / (g cat ·h).

[0064] As attached Figure 4 As shown in the XRD of Al:CeO2=0.1, a small amount of CeAlO3, Ni peak and main CeO2 peak were detected, which shows that the CeAlO3 perovskite synthesized according to the embodiment and the active component Ni are highly dispersed on the surface of the CeO2 support; with the increase of Al content, the CeAlO3 peak is enhanced, the CeO2 peak is weakened, and the degree of CeO2 peak shift is weakened. According to literature reports, this may be because Ce is formed during the calcination process. 1-x Ni x O 2-y Composite oxides, Ce appears during the reduction process 4+ To Ce 3+ The transformation of Ni / CeO2 into Ni / CeO2 will lead to lattice expansion. At the same time, the Ni reduced in the pores will also lead to lattice expansion of CeO2. The two together cause the CeO2 peak to move to a lower angle. However, the Ni that penetrates into the CeO2 pores has very few exposed crystal faces, and the chance of contact with the reaction gas becomes smaller, so the Ni / CeO2 activity is poor. The grain size of Ni calculated by the Scherrer formula is shown in Table 1. The calculated grain size of Al:CeO2=0.1 is only 19.1nm, and compared with the directly supported structure Ni / CeO2 (26.3nm) and the traditional perovskite structure Ni / CeAlO3 (30.9nm), the grain size is greatly reduced. This is because the high specific surface area supported perovskite catalyst prevents local Ni aggregation during the synthesis process by virtue of the dispersibility of the high specific surface area commercial CeO2 carrier, and the in situ grown CeAlO3 perovskite inhibits the aggregation of Ni particles during the high temperature reduction process. The resulting small-sized Ni particles can reduce the generation of carbon deposits during the reaction process. Table 1 shows the specific surface area of the catalysts tested by low temperature N2 adsorption and desorption experiments. BET =72m 2 / g is 4 times that of the perovskite formed by direct calcination, indicating that the application of high specific surface area commercial CeO2 carrier can increase the specific surface area of perovskite catalyst. Figure 6 From the H2-TPD curve and the dispersion data in Table 2 obtained based on the curve, it is found that the maximum Ni H2 chemical adsorption peak appears between 300-600 °C for Al:CeO2=0.1, which is converted to a dispersion of 36%. This also shows that relying on high specific surface area supports and in-situ grown CeAlO3 perovskite, a significant improvement in the dispersion of the active component Ni can be achieved, which is 1.5 times and 3 times that of direct impregnation and traditional perovskite catalysts, respectively.

[0065] Table 2

[0066]

[0067] a) Calculated by Scherrer formula, where the grain size d = (0.9λ / βCosθ), λ is the wavelength of the Cukα X-ray, which is taken as the value according to the instrument 2θ is the strongest crystal plane (1 1 1) of Ni in XRD, and β corresponding to it is the half-maximum width of the diffraction peak.

[0068] b) Obtained by calculating the average size of more than 50 particles in the TEM image.

[0069] As attached Figure 5 As shown in the figure, the interaction between the component reduction temperature and the Ni metal-support was analyzed by TPR. The reduction of CeAlO3 starts at 400℃. The peak between 400-600℃ is usually attributed to the surface CeO2+H2→Ce2O3+H2O. In this process, oxygen vacancies are formed along with the reduction of oxygen on the CeO2 surface. The generated oxygen vacancies will promote the Al 3+ Diffusion into the CeO2 lattice and the occurrence of Ce2O3+Al2O3→CeAlO3, the peak between 600-800℃ is attributed to the reduction of subsurface CeO2, they occur after the surface reduction, so the reduction peak is wide and high, the peak after 800℃ is the CeAlO3 formed by the reduction of bulk CeO2; after adding Ni, due to hydrogen overflow, the H species adsorbed and dissociated by Ni at low temperature will promote the reduction of CeO2 and the formation of CeAlO3. On the one hand, the reduction peak temperature of oxygen on the CeO2 surface is reduced to about 250℃, which makes Al 3+ It is easier to diffuse into the CeO2 lattice, and on the other hand, it causes the reduction temperature of CeO2→Ce2O3 to drop. The two together promote the formation of CeAlO3. The reduced CeAlO3 itself will interact with NiO, increasing the reduction temperature of NiO, which is manifested in the peak of strong interaction between NiO and CeAlO3 at around 550℃. At the same time, at high temperatures, the lattice oxygen of bulk CeO2 may be reduced to form CeAlO3 or defective CeO 2-x Based on the above analysis, it was found that the addition of Al to the commercial CeO2 carrier would promote the reduction of surface oxygen (O surPeak enhancement), which can produce a large number of oxygen vacancies at low temperatures and enhance the adsorption of CO2; at the same time, the addition of Al will shift the peak of NiO-CeO2 interaction to a temperature above 400°C. This is because Al improves the surface defects of CeO2 and enhances the interaction of Ni-CeO2. However, since Al and Ni are Ce-Al-O-Ni composite oxides formed by penetrating into the pores of CeO2, it is more difficult to reduce them due to the confinement effect of CeO2 compared to the case without a carrier (Ni / CeAlO3). Therefore, the reduction peak will move to a higher temperature as a whole, and the resulting Ni / CeAlO3-Al2O3 interaction is stronger, which can effectively inhibit the sintering problem of the active component Ni during the high temperature process.

[0070] As attached Figure 6 As shown, (a) and (b) correspond to the H2-TPD curve and CO2-TPD curve of the high specific surface area Ni-based perovskite catalyst prepared by the present invention, respectively. The adsorption of CO2 by the catalyst was analyzed by CO2-TPD. The sample roughly showed three adsorption peaks. The α peak at low temperature below 100°C is the weak adsorption of CO2 by surface hydroxyl groups or hydrogen bonds; the β peak between 100-200°C is due to the adsorption of CO2 by oxygen vacancies generated by the surface oxygen reduction of CeO2; these two peaks are related to the surface oxygen vacancies during the catalyst reduction process. When the specific surface area of the catalyst is larger and the surface oxygen vacancies are more, the chances of contact with CO2 are more, and the peak area is also larger. This part of the adsorbed CO2 is easy to escape and diffuse, which is conducive to the increase in activity. The higher temperature γ peak is attributed to the adsorption between the lattice oxygen of CeO2 or CeAlO3 and CO2. This part of the adsorbed CO2 will produce CO3 with the lattice oxygen. 2- , although it is beneficial to remove the C * However, strong adsorption will lead to untimely removal of CO2 and thus decreased activity. As can be seen from the curve, the addition of Al will cause a decrease in the overall adsorption amount on the one hand, which is attributed to the decrease in the specific surface area of the catalyst and the reduction of oxygen vacancies exposed on the surface; on the other hand, it will cause the high-temperature peak to move to a higher temperature and increase its proportion. Combined with the previous analysis, the formation of a small amount of CeAlO3 is conducive to the formation of surface oxygen vacancies, thereby enhancing the weak adsorption of CO2 and enhancing the catalytic activity; at the same time, the strong adsorption of CO2 by CeAlO3 lattice oxygen is conducive to the timely removal of carbon deposits generated on the surface, thereby enhancing the reaction stability, but the formation of too much CeAlO3 will lead to excessive CO2 adsorption, resulting in a decrease in catalytic activity.

[0071] As attached Figure 7As shown in the figure, the micromorphology of the catalyst was analyzed by transmission electron microscopy (TEM-F200). The Ni / CeO2 obtained by conventional impregnation showed the characteristics of porous and flaky uniform dispersion (a1) and (a2), and inherited the porosity of CeO2 as a whole. In HRTEM (a3), Ni and CeO2 were in close contact. This part of Ni was embedded in the lattice of CeO2, but due to the weak interaction force, the average particle size reached 29nm; when Al:CeO2=0.1, the CeAlO3 perovskite grown from CeO2 would partially destroy the porous structure of the support (b1), but STEM-Mapping (b2) showed that Ni was uniformly distributed, and because Ni was subject to the common interaction of CeAlO3 and CeO2 (b3), the average particle size was 17nm. At the same time, the close spatial proximity of CeAlO3 and Ni can ensure that the C produced by excessive cracking of CH4 in the reaction * It can be removed promptly by CO2 adsorbed on the surface of CeAlO3; when Al:CeO2=0.3, although Ni is still dispersed in clusters (c1), the catalyst agglomerates due to excessive formation of CeAlO3; at the same time, the formation of more CeAlO3 limits the size of Ni particles to a smaller size, with an average particle size of only 14nm (c2) and (c3). This small size of Ni is due to CH x * It is not easy to accumulate and thus has the ability to inhibit carbon deposition. At the same time, the adsorption of CO2 by CeAlO3 around Ni can also timely eliminate the C generated by excessive cracking of CH4. * Therefore, Al:CeO2=0.3 shows a low carbon deposition rate and good stability, but the diffusion of the reaction gas is hindered due to catalyst agglomeration, and the activity is relatively low.

[0072] Adjustments to the preparation process according to the present invention can achieve the preparation of the catalyst and exhibit performance substantially consistent with the present invention. The above description of the present invention is illustrative, and it should be noted that any simple variation, modification, or equivalent substitution that can be made by a person skilled in the art without inventive effort without departing from the core of the present invention falls within the scope of protection of the present invention.

Claims

1. A high specific surface area Ni-based perovskite catalyst, characterized in that: The composition is Ni / CeAlO3-CeO2, Ni nanoparticles are separated by CeAlO3 and uniformly dispersed on the surface of the CeO2 carrier, strong interaction is generated between Ni and CeAlO3, the loading amount of elemental nickel is 8-12wt%, and the molar ratio of elemental aluminum and raw material CeO2 is (0.1-0.5):

1.

2. A high specific surface area Ni-based perovskite catalyst according to claim 1, characterized in that: The molar ratio of elemental aluminum to raw material CeO2 is (0.1-0.3):

1.

3. A high specific surface area Ni-based perovskite catalyst according to claim 1, characterized in that: The loading amount of elemental nickel is 10-12 wt %, and the size of the nanoparticles is 10-20 nm.

4. A high specific surface area Ni-based perovskite catalyst according to claim 1, characterized in that: The specific surface area of CeO2 carrier can reach 120m 2 / g or more, preferably 125-128m 2 / g.

5. The method for preparing a high specific surface area Ni-based perovskite catalyst according to any one of claims 1 to 4, characterized in that: Follow the steps below: Step 1: Disperse aluminum nitrate and citric acid evenly in deionized water to fully complex aluminum ions and citric acid, adjust the pH to 8-10 with ammonia water, add a CeO2 carrier and continue stirring, remove most of the water by heating and evaporation to obtain a complex wet gel, and continue to keep warm to form a dry gel; then calcine the dry gel at a high temperature to completely decompose the citric acid and nitrate to obtain a composite metal oxide carrier, wherein the molar ratio of aluminum ions to citric acid is 1:(1-2), the calcination atmosphere is air, and the temperature is raised from room temperature of 20-30 degrees Celsius to 200-400°C, and the calcination time is 1-5 hours; Step 2: uniformly disperse nickel nitrate and citric acid in deionized water to allow nickel ions and citric acid to fully complex, then grind the composite metal oxide support obtained in step 1 and add it thereto. The impregnation is continued with stirring, and the impregnated suspension is dried. The dried solid is then calcined at high temperature to ensure that the citric acid and nitrate are completely decomposed to obtain a catalyst precursor, wherein the molar ratio of nickel ions to citric acid is 1:(1-2), the calcination atmosphere is air, and the temperature is raised from room temperature of 20-30 degrees Celsius to 400-700 degrees Celsius, and the calcination time is kept at this temperature for 4-6 hours; Step 3: The catalyst precursor obtained in step 2 is subjected to hydrogen reduction at a reduction temperature of 700-900 degrees Celsius in a reducing atmosphere of a combination of hydrogen and inert gas, with a hydrogen volume percentage of 10-15%, and a reduction time of 1-5 hours to obtain a high specific surface area Ni-based perovskite catalyst having a composition of Ni / CeAlO3-CeO2.

6. The method for preparing a high specific surface area Ni-based perovskite catalyst according to claim 5, characterized in that: In step 1, the molar ratio of aluminum ion to citric acid is 1: (1-1.5); aluminum nitrate and citric acid are evenly dispersed in deionized water, stirred with a magnetic stirrer at a speed of 300-400 r / min for 1-3 hours to make Al 3+ After fully complexing with CA, add CeO2 carrier and continue stirring; calcine at 200-400℃ for 3-5 hours.

7. The method for preparing a high specific surface area Ni-based perovskite catalyst according to claim 5, characterized in that: In step 2, nickel nitrate and citric acid are uniformly dispersed in deionized water, stirred at a speed of 300-400 r / min, and stirred for 1-3 hours to form a uniformly dispersed Ni-CA complex; the molar ratio of nickel ions to citric acid is 1:(1-1.1); and calcined at 500-600° C. for 4-6 hours to form a Ni-Al-Ce-O catalyst precursor through a high-temperature solid-phase reaction.

8. The method for preparing a high specific surface area Ni-based perovskite catalyst according to claim 5, characterized in that: In step 3, the catalyst precursor (in the form of powder) obtained in step 2 is pressed into 40-60 mesh, mixed with quartz sand, and loaded into a fixed bed reactor for hydrogen reduction; the quartz sand and catalyst loading mass ratio is (5-10):1, preferably (5-7):1; the inert gas is argon, helium or nitrogen; the temperature is raised from room temperature of 20-30 degrees Celsius to the reduction temperature at a heating rate of 8-10°C / min, the reduction temperature is 800-900 degrees Celsius, and the reduction temperature is reduced for 2-4 hours.

9. Use of a high specific surface area Ni-based perovskite catalyst in methane dry reforming according to any one of claims 1 to 4, characterized in that: Synthesis gas containing carbon monoxide and hydrogen is produced from methane and carbon dioxide.

10. The use according to claim 9, characterized in that Preparation of synthesis gas at high space velocity, such as 100000-120000 mL / (h·g cat ), and can reduce the reaction carbon deposition rate to 0.5-1.2mg C / (g cat ·h).

Images