CN105170156A - Preparation method of nickel-base methane dry-reforming catalyst of aerogel-like structure - Google Patents

Abstract

The invention discloses a preparation method of a nickel-based methane dry reforming catalyst with an airgel-like structure. The methane dry reforming catalyst disperses nickel metal and additives in the mesopore diameter of the airgel-like structure, and is a mesopore-confined methane dry reforming catalyst. The preparation method of the methane dry reforming catalyst is stirring and reacting at low temperature, and then drying under low vacuum, calcining at high temperature, and reducing with H ₂ -TPR to obtain a high-activity and high-stability methane dry reforming catalyst with good anti-coking and anti-sintering properties. 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 nickel-based methane dry reforming catalyst with airgel-like structure

technical field

The invention relates to a method for preparing a nickel-based methane dry reforming catalyst with an airgel-like structure, and belongs to the technical fields of nano-catalyst preparation technology and environmental protection.

Background technique

In recent years, due to the consumption of non-renewable energy and the deteriorating environment, the development and utilization of natural gas have received more and more attention. There are two main approaches to the development and utilization of natural gas, namely the direct method and the indirect method. The direct method is to pyrolyze or partially oxidize natural gas to produce organic substances such as methanol and formaldehyde. However, this method has certain complexity in the treatment of tail gas and the use of pure oxygen, which limits its industrial application. The indirect method refers to converting natural gas into synthesis gas ( _H2 and CO), and then using synthesis gas as raw material to synthesize some chemical products or liquid fuels, such as methanol, ethanol, dimethyl ether, or methanol to olefins, gasoline and acetic acid, etc. . Because the indirect method is easy to implement, it has received widespread attention. It mainly includes the following three approaches: partial oxidation of methane, steam reforming of methane and dry reforming of methane. Among the three pathways, the H ₂ /CO produced by the first two reactions is greater than 1, which is not conducive to the subsequent Fischer-Tropsch synthesis to produce organic products such as hydrocarbons and methanol. The H ₂ /CO obtained from methane dry reforming is 1, which can be directly supplied to Fischer-Tropsch synthesis and carbonylation reactions, so it has attracted much attention. At present, the carbon deposition and deactivation of the catalyst in the dry reforming of methane greatly limit the value of its industrial application. How to effectively suppress catalyst carbon deposition and active component sintering is the top priority in the research of methane dry reforming catalysts.

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 necessary to increase the research on non-noble metal catalysts. Nickel-based catalysts in non-noble metals have higher activity than other non-noble metal catalysts, so we mainly study nickel-based catalysts for methane reforming reaction. However, nickel-based catalysts have fatal disadvantages. Under long-term high-temperature reactions, nickel-based catalysts are prone to carbon deposition and metal nickel sintering, thereby deactivating the catalyst. 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. At the same time, the addition of additives is also beneficial to the nickel-based catalyst to eliminate carbon deposits, so as to achieve the purpose of maintaining the stability of the catalyst for a long time.

Numerous researchers have loaded nickel onto the carrier to make it better dispersed and prevent the agglomeration of nickel through strong metal-carrier interaction. Considering that the dry reforming of methane needs to be carried out at a relatively high temperature, the selected carrier must have good thermal stability, such as Al ₂ O ₃ , SiO ₂ , MgO, MgO-Al ₂ O ₃ , La ₂ O ₃ -ZrO ₂ , CeO ₂ -ZrO ₂ , molecular sieves, foam ceramics, etc. However, only relying on the strong interaction between nickel and the metal support cannot effectively guarantee the good dispersion of active components under high temperature reaction conditions. Researchers have also studied the influence of additives on catalysts. Generally, metal elements that have oxygen storage capacity or can provide alkali sites, such as Ce, Ca, Mg, Sc, etc., are added in the process of making catalysts. The addition of additives can strengthen the bonding strength between the metal nickel nanoparticles and the carrier, and enhance the elimination of carbon deposits, but the agglomeration and sintering of the metal nickel nanoparticles cannot be avoided. None of the above studies can effectively solve the problems of easy sintering and carbon deposition in nickel-based catalysts. In this method, nickel metal, additives and carrier are combined together through gel at the beginning of synthesis. Compared with the traditional loading method, the particles of nickel metal are smaller, the dispersion of nickel metal is better, and the interaction between nickel metal and carrier The action force is stronger, and the addition of additives strengthens the elimination of carbon deposits, and can form an airgel-like structure. The airgel-like structure has a high specific surface area and a mesoporous structure. This special structure can not only expose more The active component improves the activity of the catalyst and can better limit the activity range of the nickel metal and prevent the sintering of the nickel metal.

Contents of the invention

The invention relates to a method for preparing a nickel-based methane dry reforming catalyst similar to an airgel method, and belongs to the technical fields of nano-catalyst preparation technology and environmental protection. Small nickel nanoparticles in the nickel-based catalyst obtained by the preparation method are dispersed in the mesoporous channels of the airgel-like structure formed by the high-temperature-resistant oxide, and the channel walls can play a role of confinement, while the addition of additives It makes the interaction between nickel metal and metal carrier and strengthens the elimination of carbon deposition, so it can well inhibit the growth of metal nickel nanoparticles and greatly reduce the degree of carbon deposition. It is a kind of catalytic performance in methane reforming. And the preparation process is simple nanometer catalyst.

Catalyst preparation method of the present invention is characterized in that comprising the following steps:

Weigh an appropriate amount of nickel precursor salt, aluminum precursor salt and auxiliary agent precursor salt and dissolve in a mixed solution of deionized water and ethanol (the ratio of hydrated ethanol is 1:1~3:1, nickel precursor salt, aluminum Precursor salt and auxiliary agent The mass ratio of the precursor to the solvent is 3:20~5:20) Magnetic stirring until clarification, add propylene oxide (the mass ratio of propylene oxide to the precursor salt is 2:1~3:1 ), continue to stir for 3~10min, then let it stand for 12~24h to form a hydrogel, add the prepared mixed solution of tert-butanol and ethanol (volume ratio 2:5~3:5), seal it, put it in 40~60 ℃ oven for 12~24 hours, then take it out, pour out the solution, then add the prepared mixed solution of tert-butanol and ethanol (volume ratio 7:10~9:10), airtightly put it in an oven at 40~60℃ 12~24 hours, take it out, pour out the solution, then add the prepared mixed solution of tert-butanol and ethanol (volume ratio 1:1~1.1:1), pour out the solution, and bake at 40~60°C under low vacuum Dry, the heating rate is 1~2℃/min in air atmosphere, and calcined at 700~800℃ for 4~6h. Then it is reduced again, using H ₂ -TPR, first pretreatment with N ₂ at 300°C for 30 minutes, and after cooling to room temperature, use H ₂ /N ₂ (volume ratio 1:9) mixed gas (30mL/min) 850 ℃~950℃ for 1 hour to obtain a nickel-methyl methane dry reforming catalyst with an airgel-like structure.

The present invention is characterized in that after forming the hydrogel, a volatile solvent is used to exchange water and ethanol in the hydrogel, and this solvent can be tert-butanol or ethanedinitrile, so that the formed hydrogel does not undergo Complicated freeze-drying and extreme carbon dioxide drying can get aerogels.

The present invention is characterized in that the carrier metal of the prepared nickel-based methane dry reforming catalyst with an airgel-like structure can be Al ₂ O ₃ or SiO ₂ , and this type of metal oxide has high thermal stability. And it is easier to form an airgel-like structure and form a higher specific surface area.

The invention is characterized in that the carrier precursor salt, the auxiliary agent precursor salt and the nickel precursor salt are added into the solution at the same time, so that the auxiliary element and nickel metal have good dispersibility in the catalyst, and the catalytic activity of the catalyst is improved.

The content of nickel in the present invention is 8wt%~12wt%. If the content is too small, the catalytic activity will not be high, and if the content is too large, the formation of larger nickel particles will easily result in the formation of larger nickel particles, which is not conducive to methane dry reforming.

The present invention is characterized in that the additive element can be one of Sc, Ce, Ca, Mg, Zr, these elements provide alkali sites or have good oxygen storage capacity in the methane dry reforming catalyst, effectively Improve catalyst stability and anti-coking ability.

In the calcination process involved in the present invention, the heating rate is 1~2°C/min, the calcination temperature is 700~800°C, and the air atmosphere calcination time is 4~6h. If the heating rate is too fast and the calcination time is too long, the catalyst structure will collapse. If the time is too short, the decomposition of the precursor salt may not be complete, and if the calcination temperature is too high, the structure of the catalyst will be destroyed.

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) Compared with the catalyst obtained by the traditional impregnation method, the method of the present invention can form an airgel-like structure. This special mesoporous structure not only has a strong ability to resist metal agglomeration, but also has a good Anti-coking ability, improve the activity of the catalyst.

(3) The method of the present invention is to form an airgel-like structure together with the nickel precursor, the auxiliary agent precursor and the carrier precursor, so that the obtained catalyst has a higher specific surface area, stronger interaction, and higher nickel metal dispersion Spend.

(4) The nickel nanocrystals of the catalyst obtained in the present invention are small in size, coupled with the confinement effect of mesoporous pores, can well inhibit the formation of carbon deposits in methane dry reforming.

(5) In the present invention, additive elements are added to the catalyst. These additive elements provide alkali sites or good oxygen storage capacity in the methane dry reforming catalyst, and effectively improve the stability and carbon deposition resistance of the catalyst.

Description of drawings

Figure 1 is a transmission electron microscope (TEM) image of the methane dry reforming catalyst aerogelNiScAl 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 AlCl ₃ 6H ₂ O (2.96g), Sc(NO ₃ ) ₂ 6H ₂ O (0.098g), Ni(NO ₃ ) ₂ 6H ₂ O (0.36g) and dissolve them in deionized water and ethanol ( water and alcohol (10ml each), stir magnetically until the solution is transparent, add 7.86g of propylene oxide, stir magnetically for 10min, then let it stand for 24h to form a hydrogel, and prepare a mixed solution of ethanol and tert-butanol 10ml ( The volume ratio of ethanol to tert-butanol is 2:1) into the gel, airtight, put in an oven at 50°C for 24 hours, take out and pour out the supernatant, and prepare 10ml of a mixed solution of ethanol and tert-butanol (ethanol and tert-butanol The volume ratio of butanol is 4:5) into the gel, airtight, put in an oven at 50°C for 24 hours, take out and pour out the supernatant, and prepare 10ml of a mixed solution of ethanol and tert-butanol (the mixture of ethanol and tert-butanol Volume ratio 1:1) was added to the gel, and then dried in a low vacuum environment of 50°C, the heating rate was 1°C/min under the air atmosphere, and calcined at 800°C for 4h. Then it is reduced again, using H ₂ -TPR, first pretreatment with N ₂ at 300°C for 30 minutes, after cooling to room temperature, use H ₂ /N ₂ (volume ratio 1:9) mixed gas (30mL/min) 950 °C for 1 h to obtain a nickel-based methane dry reforming catalyst with an aerogel-like structure, as shown in Figure 1 .

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 CH4 and CO2 is 1:1 (the flow rate is 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 CH4 and CO2 can reach about 96% and 100%, respectively. The catalyst stability test was carried out at 750°C. After 30 hours of reaction, the conversion rates of CH4 and CO2 remained at about 94% and 99%, respectively. The catalyst still maintained good activity and no deactivation occurred.

Example 2

Weigh AlCl ₃ 6H ₂ O (2.96g), Ce(NO ₃ ) ₂ 6H ₂ O (0.054g), Ni(NO ₃ ) ₂ 6H ₂ O (0.36g) and dissolve them in deionized water and ethanol ( 10ml each of water and alcohol), stir magnetically until the solution is transparent, add 7.86g of propylene oxide, stir magnetically for 10min, then let it stand for 24h to form a hydrogel, and configure 10ml of mixed solution of ethanol and tert-butanol ( The volume ratio of ethanol to tert-butanol is 2:1) into the gel, airtight, put in an oven at 50°C for 24 hours, take out and pour out the supernatant, and prepare 10ml of a mixed solution of ethanol and tert-butanol (ethanol and tert-butanol The volume ratio of butanol is 4:5) into the gel, airtight, put in an oven at 50°C for 24 hours, take out and pour out the supernatant, and prepare 10ml of a mixed solution of ethanol and tert-butanol (the mixture of ethanol and tert-butanol volume ratio 1:1) was added to the gel, and then dried in a low vacuum environment at 50°C, and then calcined at 800°C for 4 hours at a heating rate of 1°C/min under the air atmosphere. Then reduce it again, using H ₂ -TPR, first pass N ₂ to pretreat at 300°C for 30 minutes, cool to room temperature and use H ₂ /N ₂ (volume ratio 1:9) mixed gas (30mL/min) 950 Reduction at ℃ for 1 h to obtain a nickel-methyl methane dry reforming catalyst with an airgel-like structure.

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. /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 CH4 and CO2 can reach about 95% and 99%, respectively. The catalyst stability test was carried out at 750°C. After 30 hours of reaction, the conversion rates of CH4 and CO2 remained at about 86% and 94%, respectively. The catalyst still maintained good activity and no deactivation occurred.

Example 3

Weigh tetraethyl orthosilicate (2.39g), Sc(NO ₃ ) ₂ 6H ₂ O (0.098g), Ni(NO ₃ ) ₂ 6H ₂ O (0.36g) were dissolved in deionized water and ethanol ( 10ml each of water and alcohol), stir magnetically until the solution is transparent, add 7.86g of propylene oxide, stir magnetically for 10min, then let it stand for 24h to form a hydrogel, and configure 10ml of mixed solution of ethanol and tert-butanol ( The volume ratio of ethanol to tert-butanol is 2:1) into the gel, airtight, put in an oven at 50°C for 24 hours, take out and pour out the supernatant, and prepare 10ml of a mixed solution of ethanol and tert-butanol (ethanol and tert-butanol The volume ratio of butanol is 4:5) into the gel, airtight, put in an oven at 50°C for 24 hours, take out and pour out the supernatant, and prepare 10ml of a mixed solution of ethanol and tert-butanol (the mixture of ethanol and tert-butanol volume ratio 1:1) was added to the gel, and then dried in a low vacuum environment at 50°C, and then calcined at 800°C for 4 hours at a heating rate of 1°C/min under the air atmosphere. Then reduce it again, using H ₂ -TPR, first pass N ₂ to pretreat at 300°C for 30 minutes, cool to room temperature and use H ₂ /N ₂ (volume ratio 1:9) mixed gas (30mL/min) 950 Reduction at ℃ for 1 h to obtain a nickel-methyl methane dry reforming catalyst with an airgel-like structure.

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 testing. 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 95% and 99%, respectively. The catalyst stability test was carried out at 750°C. After 30 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.

Claims (6)

1. a preparation method for the dry reforming catalyst of Ni-based methane of aerogel-like structure, is characterized in that having following processing step:

A. the preparation of catalyst: take appropriate nickel precursor salt, aluminium precursor salt and auxiliary agent precursor salt are dissolved in deionized water and alcohol mixed solution, deionized water: the ratio of ethanol is 1:1 ~ 3:1, nickel precursor salt, the mass ratio of aluminium precursor salt and auxiliary agent presoma and solvent is 3:20 ~ 5:20, magnetic agitation is to clarification, add expoxy propane, the mass ratio of expoxy propane and precursor salt is 2:1 ~ 3:1, continue stirring 3 ~ 10min, then 12 ~ 24h is left standstill, form hydrogel, then solution exchange is carried out, add the mixed solution of the tert-butyl alcohol and the ethanol configured, volume ratio 2:5 ~ the 3:5 of the tert-butyl alcohol and ethanol, airtight, put into the baking oven 12 ~ 24 hours of 40 ~ 60 DEG C, then take out, pour out solution, add the mixed solution of the tert-butyl alcohol and the ethanol configured again, volume ratio 7:10 ~ the 9:10 of the tert-butyl alcohol and ethanol, the airtight baking oven 12 ~ 24 hours putting into 40 ~ 60 DEG C, take out, pour out solution, add the mixed solution of the tert-butyl alcohol and the ethanol configured again, volume ratio 1:1 ~ the 1.1:1 of the tert-butyl alcohol and ethanol, pour out solution, 40 ~ 60 DEG C of oven dry under the condition of low vacuum, under air atmosphere, heating rate is 1 ~ 2 DEG C/min, 700 ~ 800 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 ₂volume ratio 1:9 gaseous mixture flow velocity is 30mL/min, and the 1h that reduces at 750 ~ 800 DEG C obtains the dry reforming catalyst of Ni-based methane of aerogel-like structure.

2. according to the preparation method of the dry reforming catalyst of Ni-based methane of the aerogel-like structure described in claims 1, it is characterized in that, the method having used solvent to replace when hydrogel is dry, the solvent of displacement is the solvent that volatility is higher, is the one in the tert-butyl alcohol, adiponitrile.

3., according to the preparation method of the dry reforming catalyst of Ni-based methane of the aerogel-like structure described in claims 1, it is characterized in that the one in described nickel precursor salt nickel nitrate, nickel chloride, nickel acetylacetonate.

4., according to the preparation method of the dry reforming catalyst of Ni-based methane of the aerogel-like structure belonging in claims 1, it is characterized in that nickel presoma, auxiliary agent presoma forms gel together with support precursor.

5., according to the dry reforming catalyst of Ni-based methane of the aerogel-like structure described in claims 1, it is characterized in that described auxiliary agent is the one in Sc, Mg, Ce, Ca, Zr.

6., according to the dry reforming catalyst of Ni-based methane of the aerogel-like structure described in claims 1, it is characterized in that described catalyst carrier is Al ₂o ₃, SiO ₂in one.