CN104841442A - Preparation method of anti-carbon deposition mesoporous confinement methane dry reforming catalyst - Google Patents

Abstract

The invention discloses a preparation method of a highly dispersed nickel-based methane dry reforming catalyst resistant to carbon deposition and mesoporous confinement. The methane dry reforming catalyst is supported by a high-temperature-resistant oxide with ordered mesoporous channels, so that nickel is highly dispersed in the channels. The preparation method of the methane dry reforming catalyst uses mesoporous oxides with high temperature stability as reactants. Under stirring conditions, the precursor salt of nickel is transported into the mesoporous channels by alcohol, and the inner surface of the mesoporous channels passes through The modification of alcoholic hydroxyl groups can make nickel better dispersed, and then through vacuum drying, high-temperature calcination, and H ₂ -TPR (hydrogen temperature-programmed reduction) reduction, high-activity and high-stability methane with good anti-coking and anti-sintering properties can be obtained Dry reforming catalyst. The invention has the advantages of simple preparation process, low cost, no pollution to the environment, high catalytic efficiency and the like.

Description

Preparation method of anti-carbon deposition mesoporous confined methane dry reforming catalyst

technical field

The invention relates to a method for preparing an anti-carbon deposition mesoporous confined methane dry reforming catalyst, which belongs to the technical fields of nano-catalyst preparation technology and environmental protection.

Background technique

With the increasing depletion of petroleum resources and the increasing seriousness of environmental pollution, the development and utilization of clean and cheap fuel resources has attracted widespread attention from all countries. Natural gas is currently the cleanest fuel, it has the characteristics of less pollution, and it is the most ideal chemical industry raw material. There are abundant natural gas resources in nature, and natural gas (methane) is a very rich chemical fuel resource. Judging from the trend of world energy development, the proportion of natural gas in the energy structure will increase steadily. In recent years, the position of natural gas chemical industry in industrial production and national economy is gradually being strengthened. The chemical utilization of natural gas can be divided into two basic ways: direct conversion and indirect conversion. Direct conversion of natural gas includes direct synthesis of methanol and formaldehyde, preparation of HCN, synthesis of aromatics, oxidative coupling of methane, etc. The indirect conversion method is to convert methane into synthesis gas first, then further synthesize ammonia and methanol, or use CO to synthesize a series of fine chemical products, fuels and olefins. This is currently the most widely used technical route in natural gas chemical industry. In the indirect conversion and utilization of natural gas, the conversion of methane into synthesis gas is the basis and leader of the entire natural gas chemical industry. Traditional methane conversion methods include steam reforming, partial oxidation and carbon dioxide reforming.

Catalysts for methane dry reforming are mainly divided into noble metal catalysts (Ru, Pd, Pt, etc.) and non-noble metal catalysts (Fe, Co, Ni, etc.). And the noble metal active components will be sintered and lost under high temperature conditions, so it is very necessary to study non-noble metal catalysts. Nickel has the best catalytic activity among non-noble metals, so we mainly study nickel-based catalysts for methane reforming reaction. However, nickel-based catalysts have a fatal shortcoming. Under long-term high-temperature reaction, nickel-based catalysts are prone to carbon deposition and metal nickel sintering, which will cause catalyst deactivation. Theoretical research proves that only when the size of nickel is small to a certain extent, can the nucleation and growth of carbon fibers be inhibited, so as to achieve the purpose of anti-carbon deposition. The active components are usually loaded on the carrier to strengthen the interaction between metal supports to improve the catalytic stability and anti-carbon deposition and anti-sintering performance of the catalyst. Recently, many studies have used the confinement effect of the carrier channels to immobilize Ni in it to achieve better anti-sintering and anti-carbon deposition effects. However, nickel nanoparticles are difficult to be transported into the mesoporous channels of the carrier, and most of them are still attached to the outer surface of the mesoporous channels, so they cannot play a good role in anti-sintering and anti-carbon deposition.

Contents of the invention

The invention relates to a preparation method of a carbon deposition-resistant mesoporous confined methane dry reforming catalyst, which belongs to the technical fields of nano-catalyst preparation technology and environmental protection. The small and uniform nickel particles in the catalyst are well and evenly dispersed in the mesoporous channels of the high-temperature-resistant oxide carrier, and the channel walls can play a role of confinement, so the growth of metallic nickel nanoparticles can be effectively inhibited . Through the addition of Ce, the degree of carbon deposition is further reduced, and it is a nano-catalyst with good catalytic performance and simple preparation process in methane reforming.

Catalyst preparation method of the present invention, comprises the following steps:

Weigh an appropriate amount of cerium precursor salt and mesoporous oxide and dissolve in deionized water, the loading amount of cerium is 3wt%~5wt%, mix and stir for 7~8h, and dry to obtain the Ce-modified mesoporous oxide support. An appropriate amount of nickelocene and Ce-modified mesoporous oxide was placed on both ends of the quartz tube, and the nickel loading was 8wt%~12wt%. Vacuumize, the heating rate is 1~2°C/min under vacuum condition, calcinate at 110~120°C for 20~24h, cool to room temperature, dissolve the obtained sample in ethanol and stir for 4~5h, centrifuge wash with ethanol for 3~4 times, drying. The heating rate is 1~2℃/min in the air atmosphere, and the calcination is performed at 500~600℃ for 4~6h. Then reduce it again, using H ₂ -TPR (hydrogen temperature programmed reduction), first pass N ₂ at 300 ° C for 30 minutes, cool to room temperature with 10% (volume percentage) H ₂ /N ₂ mixed gas ( 30mL/min) at 750°C~800°C for 1 hour to obtain a methane dry reforming catalyst that resists carbon deposition and mesoporous confinement.

The precursor salt of cerium is one of cerium nitrate, cerium chloride and cerium acetate. Different cerium salts have different modification effects on the carrier. Using the cerium salt mentioned in the present invention to modify the mesoporous oxide can make nickel nanoparticles better dispersed on the mesoporous oxide carrier. The size of the nickel metal particles is 3-4nm.

The mesoporous oxide carrier is one of mesoporous silicon spheres, SBA-15, γ-Al ₂ O ₃ , KIT-6, and MCM-41. These supports have high temperature resistance and are not prone to collapse during the reaction process. . The mesoporous channels they have are relatively orderly and the channel walls are thicker, which can better fix nickel particles in them, thereby improving the anti-sintering performance.

In the present invention, the loading capacity of cerium is 3wt%~5wt%, too little Ce content can not play a good modification effect on the carrier, the nickel particles can not be well dispersed in the mesoporous oxide, and the anti-coking effect of the catalyst Performance is impacted. If the Ce content is too high, the interaction force between the nickel and the support will be reduced, so that the nickel particles are likely to agglomerate and affect the catalytic performance.

The calcination process of loaded nickel involved in the present invention needs to be carried out under vacuum conditions. The heating rate is 1~2°C/min, the calcination temperature is 110~120°C, and the calcination time is 20~24h. Nickelocene can be sublimated into nickelocene vapor to enter the pores of the mesoporous oxide carrier under vacuum conditions. If the temperature rise rate is too fast, the structure of the catalyst will collapse. If the calcination temperature is too low, the nickelocene cannot be sublimated. If the temperature is too high, the mesopore structure will be irregular. If the calcination time is too short, the sublimation of the nickelocene may be incomplete. Agglomerates nickel particles.

Compared with prior art, the catalyst prepared by the present invention has the following advantages:

(1) The preparation process of the present invention is simple, easy to operate, low in requirements for experimental equipment, low in cost, and will not cause secondary pollution to the environment.

(2) The method of the present invention breaks through the traditional aqueous solution wet impregnation method to load nickel on the carrier, and utilizes the characteristics of nickelocene vacuum sublimation to allow the nickelocene vapor to enter the pores of the mesoporous oxide carrier, and the addition of Ce is beneficial to The inner wall of the carrier channel plays a role of modification, which can better disperse the nickel species in the carrier channel, thereby improving the anti-coking and anti-sintering performance of the catalyst.

(3) The nickel nanocrystal size of the catalyst obtained in the present invention is about 3nm, coupled with the confinement effect of the carrier mesoporous channels, it can well inhibit the agglomeration of nickel particles in the dry reforming of methane and reduce the formation of carbon deposits. The addition of Ce also contributes to the elimination of carbon deposits.

Description of drawings

Fig. 1 is a transmission electron microscope (TEM) image of the methane dry reforming catalyst NiCe/mSiO ₂ obtained in Example 1 of the present invention.

Detailed ways

Specific embodiments of the present invention will be described in detail below in conjunction with technical solutions and accompanying drawings.

Example 1

Weigh 0.066g of cerium nitrate and 0.5g of mesoporous silicon spheres and dissolve them in deionized water, the loading amount of cerium is 5wt%, mix and stir for 8h, and dry to obtain Ce-modified mesoporous silicon spheres. Take 1g nickelocene and 0.5g Ce-modified mesoporous silicon spheres and put them on both ends of the quartz tube, and the nickel loading is about 10wt%. Vacuumize, the heating rate is 1°C/min under vacuum, calcined at 110°C for 24h, cooled to room temperature, the obtained sample is dissolved in ethanol and stirred for 5h, centrifuged with ethanol for 3 times, and dried. The heating rate was 1°C/min in the air atmosphere, and calcined at 500°C for 4h. Then reduce it again, using H ₂ -TPR (hydrogen temperature programmed reduction), first pass N ₂ at 300 ° C for 30 minutes, cool to room temperature with 10% (volume percentage) H ₂ /N ₂ mixed gas ( 30mL/min) at 800℃ for 1h to obtain NiCe/mSiO ₂ catalyst.

Test the catalytic activity of the above catalyst: Weigh 0.15g (40-60 mesh) of the prepared catalyst and put it into a fixed bed quartz tube reactor for catalyst performance test. The injection volume of CH ₄ and CO ₂ is 1:1 (flow average 15mL/min), the activity test ranges from 450°C to 800°C, the catalyst has a certain activity at 450°C, the highest activity is at 800°C, and the conversion rates of CH ₄ and CO ₂ can reach about 94% and 100%, respectively. The catalyst stability test was carried out at 750°C. After 20 hours of reaction, the conversion rates of CH ₄ and CO ₂ remained at about 93% and 98%, respectively, and the catalyst still maintained good activity without deactivation.

Example 2

Weigh 0.04g of cerium chloride and 0.5g of SBA-15 and dissolve them in deionized water, the loading amount of cerium is 5wt%, mix and stir for 8h, and dry to obtain Ce-modified SBA-15. Take 1g of nickelocene and 0.5g of Ce-modified SBA-15 placed at both ends of the quartz tube, and the loading of nickel is about 10wt%. Vacuumize, the heating rate is 1°C/min under vacuum, calcined at 120°C for 24h, cooled to room temperature, the obtained sample is dissolved in ethanol and stirred for 4h, centrifuged with ethanol for 3 times, and dried. The heating rate was 1°C/min in air atmosphere, and calcined at 550°C for 4h. Then reduce it again, using H ₂ -TPR, first pass N ₂ at 300°C for 30 minutes, cool to room temperature and then use 10% (volume percentage) H ₂ /N ₂ mixed gas (30mL/min) at 800°C Under reduction for 1h, NiCe/SBA-15 catalyst was obtained.

Test the catalytic activity of the above catalyst: Weigh 0.15g (40-60 mesh) of the prepared catalyst and put it into a fixed bed quartz tube reactor for catalyst performance test. The injection volume of CH ₄ and CO ₂ is 1:1 (flow average 15mL/min), the activity test ranges from 450°C to 800°C, the catalyst has a certain activity at 450°C, the highest activity is at 800°C, and the conversion rates of CH ₄ and CO ₂ can reach about 91% and 98%, respectively. The catalyst stability test was carried out at 750°C. After 20 hours of reaction, the conversion rates of CH ₄ and CO ₂ remained at about 88% and 94%, respectively, and the catalyst still maintained good activity without deactivation.

Example 3

Weigh 0.04g of cerium nitrate and 0.5g of KIT-6 and dissolve them in deionized water, the loading amount of cerium is 4wt%, mix and stir for 8h, and dry to obtain Ce-modified KIT-6. Take 1g of nickelocene and 0.5g of Ce-modified KIT-6 and put them on both ends of the quartz tube, and the loading of nickel is about 10wt%. Vacuumize, the heating rate is 1°C/min under vacuum, calcined at 110°C for 24h, cooled to room temperature, the obtained sample is dissolved in ethanol and stirred for 5h, centrifuged with ethanol for 3 times, and dried. The heating rate was 1°C/min in air atmosphere, and the calcination was carried out at 600°C for 4h. Then reduce it again, using H ₂ -TPR, first pass N ₂ at 300°C for 30 minutes, cool to room temperature and then use 10% (volume percentage) H ₂ /N ₂ mixed gas (30mL/min) at 800°C NiCe/KIT-6 catalyst was obtained by reduction for 1h.

Test the catalytic activity of the above catalyst: Weigh 0.15g (40-60 mesh) of the prepared catalyst and put it into a fixed bed quartz tube reactor for catalyst performance test. The injection volume of CH ₄ and CO ₂ is 1:1 (flow average 15mL/min), the activity test ranges from 450°C to 800°C, the catalyst has a certain activity at 450°C, the highest activity is at 800°C, and the conversion rates of CH ₄ and CO ₂ can reach about 93% and 99%, respectively. The catalyst stability test was carried out at 750°C. After 20 hours of reaction, the conversion rates of CH ₄ and CO ₂ remained at about 91% and 97%, respectively. The catalyst still maintained good activity and no deactivation occurred.

Claims (4)

1. a preparation method for the dry reforming catalyst of methane of the mesoporous confinement of anti-carbon, is characterized in that having following processing step:

A. the preparation of catalyst: take appropriate cerium precursor salt and mesopore oxide is dissolved in deionized water, the load capacity of cerium is 3wt% ~ 5wt%, mix and blend 7 ~ 8h, dries to obtain the mesopore oxide carrier modified of Ce; The mesopore oxide getting appropriate dicyclopentadienyl nickel and Ce modification is placed in the two ends of quartz ampoule, and the load capacity of nickel is 8wt% ~ 12wt%; Vacuumize, under vacuum condition, heating rate is 1 ~ 2 DEG C/min, and 110 ~ 120 DEG C of calcining 20 ~ 24h, are cooled to room temperature, are dissolved in by gained sample in ethanol and stir 4 ~ 5h, with ethanol centrifuge washing 3 ~ 4 times, dry; Under air atmosphere, heating rate is 1 ~ 2 DEG C/min, 500 ~ 600 DEG C of calcining 4 ~ 6h;

B. the reduction of catalyst: utilize H ₂-TPR, first logical N ₂pretreatment 30min at 300 DEG C, is cooled to after room temperature with H ₂/ N ₂percent by volume is the gaseous mixture of 10%, and flow velocity is 30mL/min, and the 1h that reduces at 750 DEG C ~ 800 DEG C obtains the dry reforming catalyst of methane of the mesoporous confinement of anti-carbon.

2., according to the preparation method of the dry reforming catalyst of methane of the mesoporous confinement of anti-carbon described in claims 1, it is characterized in that described cerium precursor salt is the one in cerous nitrate, cerium chloride, cerous acetate.

3., according to the preparation method of the dry reforming catalyst of methane of the mesoporous confinement of anti-carbon described in claims 1, it is characterized in that described mesoporous material is mesoporous silicon sphere, SBA-15, γ-Al ₂o ₃, the one in KIT-6, MCM-41.

4. according to the preparation method of the dry reforming catalyst of methane of the mesoporous confinement of anti-carbon described in claims 1, it is characterized in that the size of described nickel metallic particles is at 3-4nm, utilize dicyclopentadienyl nickel vacuum sublimation to be that nickel steam enters in carrier mesopore orbit.