CN105964261A - A kind of preparation method of anti-coking anti-sintering methane dry reforming Ni-based catalyst - Google Patents

Abstract

The invention discloses a preparation method of an anti-carbon-deposition and anti-sintering methane dry reforming Ni-based catalyst. The methane dry reforming catalyst takes one of mesoporous silica-based materials such as silica sol, SBA-15, KIT-6, HMS and the like as a carrier, and an alkaline complexing agent is added to enable a nickel complex and silicon hydroxyl on the surface of the silica-based material to form a stable nickel-phyllosilicate layer under a hydrothermal condition, so that the Ni particles are limited, and the catalyst with strong metal carrier effect and high dispersion of the Ni particles is obtained after high-temperature reduction.

Description

An anti-carbon deposition anti-sintering methane dry reforming Ni base catalyst preparation method

technical field

The invention belongs to the technical field of catalyst preparation and environmental protection, and in particular relates to a preparation method of an anti-carbon deposition and anti-sintering methane dry reforming Ni-based catalyst.

Background technique

Methane widely exists in natural gas, coalbed methane, oilfield gas and refinery gas, and its activation and further chemical utilization is one of the research hotspots in the field of heterogeneous catalysis. There are two ways to convert and utilize methane, direct method and indirect method. The direct method is to convert methane directly into chemical products such as methanol, ethylene or aromatics. The indirect method is to convert methane into synthesis gas first, and then use the synthesis gas as raw material to produce downstream chemical products, such as methanol, ammonia, dimethyl ether, low-carbon Important basic chemical raw materials such as olefins or synthetic liquid fuels, among which synthetic ammonia, synthetic methanol and synthetic liquid fuels have been industrialized. The direct method has disadvantages such as difficulty in controlling the degree of reaction and low yield, and there is still a distance from large-scale industrialization, and technological breakthroughs are still needed. In the indirect route, the cost of making synthesis gas from methane accounts for about 50-75% of the whole process. Therefore, reducing the cost of making synthesis gas from methane and improving the efficiency of making synthesis gas from methane are the key to improving the economic benefits of subsequent processing and the indirect utilization of natural gas. key to rate. The synthesis gas preparation processes that have been industrialized and are currently being developed mainly include: methane steam reforming, methane dry reforming, methane partial oxidation, and coupled reforming technologies. Among them, methane dry reforming makes full use of methane and carbon dioxide, which are the main components of greenhouse gases, and simultaneously converts two difficult-to-activate small molecules, which has multiple research significances such as economics, environmental protection, and science.

Metal catalysts capable of catalyzing the methane dry reforming reaction include Rh, Ru, Ir, Pt and Ni. Most of the research work has focused on Ni-based catalysts, because the catalytic activity of Ni metal is comparable to that of noble metal catalysts, and because of its price advantage, Ni catalysts are the most likely to realize the industrialization of methane dry reforming reaction. catalyst. However, the two major problems that come with it are that the carbon on the surface of the catalyst and the thermal sintering of the metal active center will cause the catalyst to deactivate rapidly during the reaction process. Therefore, while ensuring the catalytic activity of Ni-based catalysts, it is also very important to improve their anti-coking and anti-sintering capabilities.

Methane dry reforming catalysts are mainly supported catalysts, and the reforming reaction is carried out under high temperature conditions. So to solve the problem of carbon deposition and sintering in methane dry reforming, three aspects can be considered: the size and distribution of metal particles, the nature of the support, and the interaction between the metal and the support. Therefore, reducing the size of Ni particles, improving their dispersion, selecting a carrier with better stability, and forming a very stable structure between Ni and the carrier by enhancing the interaction between the metal and the carrier will help to achieve the anti-oxidation effect. The purpose of carbon deposition and anti-sintering. Many preparation methods have been used to prepare catalysts with high dispersion and small Ni particle size. Although their initial activity is high, they are prone to lead to Sintering caused by carbon deposition and migration, aggregation and growth of metal particles.

Contents of the invention

The purpose of the present invention is to provide a method for preparing an anti-coking and anti-sintering methane dry reforming Ni-based catalyst to obtain a Ni-based catalyst with excellent anti-coking and anti-sintering performances in methane dry reforming reaction.

A kind of anti-coking anti-sintering methane dry reforming Ni-based catalyst preparation method of the present invention, carry out according to the following steps:

a. Catalyst preparation: Weigh the nickel precursor salt and dissolve it in deionized water, and add a basic complexing agent to the nickel precursor salt solution at a molar ratio of 1:2 to 1:10 between Ni and the basic complexing agent. Stir at room temperature for 10-15 minutes; add mesoporous silicon-based material as a carrier with a nickel loading of 2-10wt%, and stir for 4-6 hours at room temperature; put the evenly stirred mixture in a water bath at 60-80°C until the pH is 7-8, Keep the pH and temperature and continue the water bath for 1h; put it into the reactor and heat it at 180~220°C for 10~14h; filter, wash with deionized water for 3~5 times, dry at 80~120°C for 10~12h, then dry at 400~600°C Calcination for 4~5h;

b. Reduction and activation of the catalyst: the catalyst prepared in step A is loaded into the reaction tube, and the hydrogen gas is used for temperature-programmed reduction, and the hydrogen flow rate of 15 mL/min is reduced in situ at 700 ° C for 1 hour to obtain the anti-carbon deposition and anti-sintering Methane dry reforming Ni-based catalyst.

The nickel precursor salt is nickel nitrate.

The basic complexing agent is one of ammonia, ethylenediamine, and triethanolamine; the basic complexing agent can isolate Ni ions, increase steric hindrance, avoid the agglomeration of metal particles, and be beneficial to obtain smaller, A more dispersed catalyst.

The mesoporous silicon-based material is one of silica sol, SBA-15, KIT-6, and HMS; wherein SBA-15, KIT-6, and HMS are synthesized by conventional hydrothermal methods (refer to methods in the literature: 1, SBA-15 Preparation of: Zhao D, Feng J, Huo Q, et al. Triblock copolymer Syntheses of mesoporous silica with periodic 50 to 300 angstrom pores[J]. Science, 1998, 279(5350):548-52.; 2. Preparation of KIT-6: Kleitz F, Choi S H, Ryoo R. Cubic Ia3d large mesoporous silica: synthesis and replication to platinum nanowires, carbon nanorods and carbon nanotubes.[J]. Chemical Communications, 2003, 17(17):2136- 2137.; 3. Preparation of HMS: Tanev P T, Pinnavaia T J. A neutral templating route to mesoporous molecular sieves.[J]. Science, 1995, 267(5199): págs. 865-867.), the process of removing the template agent is roasting, and the roasting temperature should not exceed 350°C to ensure that the carrier has abundant surface silicon Hydroxyl; the specific surface area of the mesoporous silicon-based material is larger, making it easier for Ni to disperse, with better stability, thicker pore walls, and less likely to collapse the structure, which can improve the confinement effect on Ni nanoparticles.

The nickel loading is 2-10wt%. If the loading is too high, the Ni particle size may be too large and easy to deposit carbon. If the loading is too small, the number of active sites may be insufficient and the catalytic activity may be affected.

The purpose of the water bath process is to drive Ni particles slowly into the inside of the channel.

In the hydrothermal treatment process, the temperature is 180-220° C., and the time is 10-14 hours. If the temperature is too low or the time is too short, a stable nickel-phyllosilicate layer with confined Ni particles may not be formed, while the temperature is too high or the time is too short. If the time is too long, the catalyst structure will be easily damaged.

In the calcination process, the heating rate is 2° C./min.

The anti-coking and anti-sintering methane dry reforming Ni-based catalyst prepared by the preparation method has a nickel particle size of 2-7 nm.

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

1, the catalyst nickel particle size that makes by the method for the present invention is smaller, dispersion degree is better;

2. Under hydrothermal conditions, the nickel complex forms a nickel-phyllosilicate stable layer with the silicon hydroxyl group on the surface of the silicon-based material, confines the Ni particles, enhances the interaction between the metal and the carrier, and inhibits the metal The migration and growth of particles under high temperature reaction conditions improves the stability of the catalyst;

3. The preparation process is simple, the cost is low, the environment is not polluted, and the activity and stability of the prepared catalyst are better.

Description of drawings

Fig. 1 is the change of the conversion rate of methane and carbon dioxide with temperature in the methane dry reforming reaction of the catalyst obtained in Example 1.

Fig. 2 is a transmission electron microscope (TEM) image of the nickel particle distribution of the reduced methane dry reforming catalyst Ni/SBA-15 obtained in Example 2.

Fig. 3 is the life diagram of Ni/SBA-15, the methane dry reforming catalyst obtained in Example 2.

Fig. 4 is a transmission electron microscope (TEM) image of the nickel particle distribution of the methane dry reforming catalyst Ni/SBA-15 obtained in Example 2 after a 100 h stability test.

detailed description

The present invention will be further described below in conjunction with specific embodiments and accompanying drawings. The present invention is not limited by the following embodiments, and specific implementation methods can be determined according to the technical solutions and actual conditions of the present invention.

Example 1

Weigh 0.515g of nickel nitrate (Ni(NO ₃ ) ₂ 6H ₂ O), dissolve it in 30mL of deionized water, and then add 2.5mL of ammonia water (25wt%, the commercially available product is used for the test here, using other concentrations of ammonia water will not affect The effect of the present invention, the same below), the molar ratio of Ni and ammonia water is 1:9, stir for 10min, then add 3.25mL silica sol (30wt%, use commercially available products to test here, adopt other content of silica sol does not affect the present invention effect), the nickel loading was 8wt%, stirred for 4h. The above processes were all carried out at room temperature. The uniformly stirred mixture was placed in a water bath at 70° C. until the pH dropped to 8, and the water bath was continued for 1 h while maintaining the pH and temperature. Put it into the reaction kettle for hydrothermal treatment at 180°C for 14h, filter, wash with deionized water three times, dry at 80°C for 11h, and then program the temperature from room temperature to 600°C for 4h in a muffle furnace at a rate of 2°C/min. Fill in a reaction tube, and reduce in situ at 700° C. for 1 h at a hydrogen flow rate of 15 mL/min to obtain the final product.

Catalytic activity test: Weigh 0.08g (40-60 mesh) of the above catalyst and put it into a fixed-bed quartz tube reactor for catalytic performance test. The injection volume of CH ₄ and CO ₂ is 1:1 (both flows are 15mL/min), the activity test is from 600°C to 800°C, the activity is the highest at 800°C, and the conversion rates of CH ₄ and CO ₂ are 93.2% and 94.9% respectively ; Keep at 800°C for 3 hours, and then cool down from 800°C to 600°C, the conversion rate of CH ₄ and CO ₂ has no obvious drop compared with the corresponding temperature before, as shown in Figure 1. The catalyst stability test was carried out at 700°C. After 100 hours of reaction, the catalyst still maintained good activity without obvious deactivation.

Example 2

Weigh 0.566g nickel nitrate (Ni(NO ₃ ) ₂ 6H ₂ O), dissolve it in 44mL deionized water, then add 3mL ammonia water (25wt%), the molar ratio of Ni to ammonia water is 1:10, stir for 12min, then add 2g of SBA-15, with a nickel loading of 6wt%, was stirred for 6h. The above processes were all carried out at room temperature. The uniformly stirred mixture was placed in a water bath at 80° C. until the pH dropped to 7, and the water bath was continued for 1 h while maintaining the pH and temperature. Put it into the reaction kettle for hydrothermal treatment at 200°C for 12h. After filtering, washing with deionized water for 5 times, drying at 100°C for 10h, the temperature was programmed to rise from room temperature to 550°C for 4h in a muffle furnace at a rate of 2°C/min. Fill it into a reaction tube, and reduce it in situ at 700 °C for 1 h at a hydrogen flow rate of 15 mL/min to obtain the final product. The transmission electron microscope image of the nickel particle distribution is shown in Figure 2.

The catalytic activity test conditions are the same as in Example 1. The activity test ranged from 600°C to 800°C, and the activity was the highest at 800°C, and the conversion rates of CH ₄ and CO ₂ were 94.5% and 95.7%, respectively. The catalyst stability test was carried out at 700°C, as shown in Figure 3, after 100 hours of reaction, the conversion rates of _CH4 and _CO2 remained at 75% and 80%, respectively, and the catalyst still maintained good activity without obvious deactivation . Figure 4 illustrates that only slight filamentous carbon is formed, and the Ni particles are still highly dispersed and small in size.

Example 3

Weigh 0.664g of nickel nitrate (Ni(NO ₃ ) ₂ 6H ₂ O), dissolve it in 50mL of deionized water, then add 2.8mL of ammonia water (25wt%), the molar ratio of Ni to ammonia water is 1:8, stir for 15min, and then Add 1.5g KIT-6, the nickel loading is 8wt%, and stir for 5h. The above processes were all carried out at room temperature. The uniformly stirred mixture was placed in a water bath at 80° C. until the pH dropped to 7, and the water bath was continued for 1 h while maintaining the pH and temperature. Put it into the reactor for hydrothermal treatment at 220°C for 10h, filter, wash with deionized water three times, dry at 110°C for 10h, and then program the temperature from room temperature to 400°C for 5h in a muffle furnace at a rate of 2°C/min. Fill in a reaction tube, and reduce in situ at 700° C. for 1 h at a hydrogen flow rate of 15 mL/min to obtain the final product.

The catalytic activity test conditions are the same as in Example 1. The activity test ranged from 600°C to 800°C, and the activity was the highest at 800°C, and the conversion rates of CH ₄ and CO ₂ were 90.9% and 92.6%, respectively. After keeping at 800°C for 3h, and then cooling down from 800°C to 600°C, the conversion rate of CH ₄ and CO ₂ did not decrease significantly compared with the corresponding temperature before, and no obvious carbon deposition and sintering phenomena were observed.

Example 4

Weigh 0.304g of nickel nitrate (Ni(NO ₃ ) ₂ 6H ₂ O), dissolve it in 20mL of deionized water, then add 1.3mL of ammonia water (25wt%), the molar ratio of Ni to ammonia water is 1:8, stir for 10min, and then Add 3g of HMS, the nickel loading is 2wt%, and stir for 6h. The above processes were all carried out at room temperature. The evenly stirred mixture was placed in a water bath at 60° C. until the pH dropped to 7.5, and the water bath was continued for 1 h while maintaining the pH and temperature. Put it into the reactor for hydrothermal treatment at 200°C for 12h, filter, wash with deionized water 4 times, dry at 80°C for 12h, and then program the temperature from room temperature to 600°C for 4h in a muffle furnace at a rate of 2°C/min. Fill in a reaction tube, and reduce in situ at 700° C. for 1 h at a hydrogen flow rate of 15 mL/min to obtain the final product.

The catalytic activity test conditions are the same as in Example 1. The activity test ranged from 600°C to 800°C, and the activity was the highest at 800°C, and the conversion rates of CH ₄ and CO ₂ were 91.4% and 92.9%, respectively. After keeping at 800°C for 3h, and then cooling down from 800°C to 600°C, the conversion rate of CH ₄ and CO ₂ did not decrease significantly compared with the corresponding temperature before, and no obvious carbon deposition and sintering phenomena were observed.

Example 5

Weigh 0.862g nickel nitrate (Ni(NO ₃ ) ₂ 6H ₂ O), dissolve it in 45mL deionized water, then add 0.85mL ethylenediamine, the molar ratio of Ni to ethylenediamine is 1:4, stir for 10min, then Add 2g of SBA-15, the nickel loading is 8wt%, and stir for 6h. The above processes were all carried out at room temperature. The uniformly stirred mixture was placed in a water bath at 80° C. until the pH dropped to 8, and the water bath was continued for 1 h while maintaining the pH and temperature. Put it into the reactor for hydrothermal treatment at 200°C for 12h, filter, wash with deionized water three times, dry at 120°C for 10h, and then program the temperature from room temperature to 500°C for 4h in a muffle furnace at a rate of 2°C/min. Fill in a reaction tube, and reduce in situ at 700° C. for 1 h at a hydrogen flow rate of 15 mL/min to obtain the final product.

The catalytic activity test conditions are the same as in Example 1. The activity test ranged from 600°C to 800°C, and the activity was the highest at 800°C, and the conversion rates of CH ₄ and CO ₂ were 92.5% and 93.7%, respectively. After keeping at 800°C for 3h, and then cooling down from 800°C to 600°C, the conversion rate of CH ₄ and CO ₂ did not decrease significantly compared with the corresponding temperature before, and no obvious carbon deposition and sintering phenomena were observed.

Example 6

Weigh 0.551g nickel nitrate (Ni(NO ₃ ) ₂ 6H ₂ O), dissolve it in 45mL deionized water, then add 0.55mL triethanolamine, the molar ratio of Ni to triethanolamine is 1:2, stir for 10min, then add 1g SBA-15, with a nickel loading of 10wt%, stirred for 6h. The above processes were all carried out at room temperature. The uniformly stirred mixture was placed in a water bath at 80° C. until the pH dropped to 7, and the water bath was continued for 1 h while maintaining the pH and temperature. Put it into the reaction kettle for hydrothermal treatment at 200°C for 12h, filter, wash with deionized water three times, dry at 80°C for 12h, and then program the temperature from room temperature to 600°C for 4h in a muffle furnace at a rate of 2°C/min. Fill in a reaction tube, and reduce in situ at 700° C. for 1 h at a hydrogen flow rate of 15 mL/min to obtain the final product.

The catalytic activity test conditions are the same as in Example 1. The activity test ranged from 600°C to 800°C, and the activity was the highest at 800°C, and the conversion rates of CH ₄ and CO ₂ were 90.8% and 92.3%, respectively. After keeping at 800°C for 3h, and then cooling down from 800°C to 600°C, the conversion rate of CH ₄ and CO ₂ did not decrease significantly compared with the corresponding temperature before, and no obvious carbon deposition and sintering phenomena were observed.

Claims (7)

1. a preparation method of an anti-coking anti-sintering methane dry reforming Ni-based catalyst is characterized in that it is carried out in the following steps: A. Catalyst preparation: Weigh the nickel precursor salt and dissolve it in deionized water, and add alkaline complexing agent After stirring for 10~15min at room temperature; adding mesoporous silicon-based material as a carrier, the nickel loading is 2~10wt%, stirring at room temperature for 4~6h; Continue the water bath for 1 hour; put it into the reactor for hydrothermal treatment at 180~220°C for 10~14 hours; filter, wash with deionized water for 3~5 times, dry at 80~120°C for 10~12 hours, and then calcinate at 400~600°C for 4~5 hours; B. Reduction and activation of the catalyst: the catalyst prepared in step A is reduced by hydrogen temperature programming, and the hydrogen flow rate of 15mL/min is reduced in situ at 700°C for 1h, and the dry weight of the anti-coking and anti-sintering methane is obtained Whole Ni-based catalyst. 2. The preparation method according to claim 1, characterized in that the nickel precursor salt is nickel nitrate. 3. preparation method according to claim 1 is characterized in that described alkaline complexing agent is the one in ammoniacal liquor, ethylenediamine, triethanolamine. 4. The preparation method according to claim 1, characterized in that the mesoporous silicon-based material is one of silica sol, SBA-15, KIT-6, and HMS. 5. The preparation method according to claim 4, characterized in that SBA-15, KIT-6, and HMS in the mesoporous silicon-based material are prepared by hydrothermal synthesis, and the process of removing the template agent is roasting, and the roasting temperature does not exceed 350°C. 6. The preparation method according to claim 1, characterized in that the heating rate of the calcination process is 2° C./min. 7. The anti-carbon deposition and anti-sintering methane dry reforming Ni-based catalyst prepared by the preparation method described in any one of claims 1 to 6, characterized in that the nickel particle size is 2 to 7 nm.