CN114308043A - Preparation method of acidified two-dimensional layered vermiculite-supported nickel-based catalyst - Google Patents

Abstract

The present invention is a preparation method of acidified two-dimensional layered vermiculite-supported nickel-based catalyst. The method uses expanded vermiculite as a carrier, and is treated in an acid solution, washed and dried to obtain a vermiculite structure with a large specific surface area layered molecular sieve removed, wherein, the acidified two-dimensional layer is prepared by a slight excess liquid phase high temperature roasting method. vermiculite-supported nickel-based catalysts. The invention has the advantages of simple catalyst composition, simple and easy preparation process, low production cost, and the like, and the catalyst can be prepared without subsequent addition of auxiliary agents, and the catalyst has uniform dispersion of metal particles, small average particle size, and anti-sintering and anti-carbon deposits at high temperature. It has the advantages of high strength and other advantages, and has good industrial prospects in the production of synthesis gas by the reforming of methane and carbon dioxide.

Description

Preparation method of acidified two-dimensional layered vermiculite-supported nickel-based catalyst

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 acidified two-dimensional layered vermiculite-supported nickel-based catalyst.

Background technique

With the intensification of the greenhouse effect, overcoming the possible impact of global warming has become a common global goal and challenge. Methane and carbon dioxide are two major greenhouse gases, and their comprehensive transformation and utilization are of great significance to alleviate the greenhouse effect. The methane and carbon dioxide reforming reaction (DRM) can utilize these two gases and convert them to syngas with an equimolar ratio of _H2 /CO. Syngas produced by DRM can be used to produce high value-added chemicals by Fischer-Tropsch synthesis. According to thermodynamic analysis, DRM is a high-temperature endothermic reversible reaction that requires a higher reaction temperature. Therefore, catalysts used under such conditions may be deactivated by sintering of active metals. In addition, in the process of DRM reaction, there are also side reactions that lead to carbon deposition, namely methane cracking reaction and carbon monoxide disproportionation reaction. Therefore, a great deal of research has been devoted to addressing these two problems, mainly through the use of noble metal-supported catalysts. However, considering the cost of these noble metal catalysts, their industrial application is limited. Therefore, nickel-based catalysts have become one of the most popular alternatives to noble metal catalysts due to their abundant nickel reserves, low price, and high catalytic activity comparable to noble metal catalysts. However, Ni-based catalysts are more prone to deactivation during high-temperature reactions due to sintering and carbon deposition. The sintering of the active components of the nickel-based catalyst reduces the active center of the catalyst and reduces the reaction activity; in addition, the carbon deposition generated by the catalyst during the reaction not only covers the active site of the catalyst, but also blocks its pores, affecting the reactants and product molecules. diffusion. Therefore, it is very important to improve the ability of the catalyst to resist sintering and carbon deposition.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for preparing an acidified two-dimensional layered vermiculite-supported nickel-based catalyst for the deficiencies in the current technology. This method provides a top-down preparation idea. Using expanded vermiculite as a carrier, a vermiculite structure with a large specific surface area layered molecular sieve is obtained through treatment in an acid solution, washing and drying. Preparation of acidified two-dimensional layered vermiculite-supported nickel-based catalysts by high-temperature calcination. The invention has the advantages of simple catalyst composition, simple and easy preparation process, low production cost, and the like, and the catalyst can be prepared without subsequent addition of auxiliary agents, and the catalyst has uniform dispersion of metal particles, small average particle size, and anti-sintering and anti-carbon deposits at high temperature. It has the advantages of high strength and other advantages, and has good industrial prospects in the production of synthesis gas by the reforming of methane and carbon dioxide.

For realizing the preparation of above-mentioned catalyst, technical scheme of the present invention is:

A method for preparing an acidified two-dimensional layered vermiculite-supported nickel-based catalyst, the method comprising the following steps:

(1) Under stirring conditions, immerse the expanded vermiculite in hydrochloric acid solution, vigorously stir and reflux for 4-6 hours at 60-90 °C; the obtained bright yellow precipitate is washed with deionized water, suction-filtered, and dried. The acid-treated vermiculite powder carrier is obtained; wherein, the concentration of the hydrochloric acid solution is 1-3 mol/L; preferably 5-15 g of expanded vermiculite is added to every 200 milliliters of the hydrochloric acid solution; the rotational speed of the vigorous stirring is 700-900 rpm;

(2) adding the Ni(NO ₃ ) ₂ solution dropwise to the acid-treated vermiculite powder carrier after vacuum drying, drying in the air, and drying at 100-120° C. for 6-10 hours to obtain dry powder;

Wherein, every 1 mL of Ni(NO ₃ ) ₂ solution contains 0.06-0.17 g Ni(NO ₃ ) ₂ ·6H ₂ O; every 1 g of acid-treated vermiculite carrier is added dropwise with 0.5-3 mL of mixed solution;

Described vacuum drying temperature is 60～90 ℃, time is 3～5 hours;

(3) heating the dried powder to 500-600°C at a speed of 1-3°C/min in an air atmosphere, and calcining for 3-5h to obtain a catalyst for acidifying two-dimensional layered vermiculite confined nickel nanoparticles;

The method further includes step (4), and then the acidified two-dimensional layered vermiculite-supported nickel-based catalyst is heated to 450-550° C. in a nitrogen atmosphere, and then the gas is switched to a pure hydrogen atmosphere, and reduced for 1-3 hours;

In the catalyst, the loading of nickel is 2.5-7.5wt%;

The hydrochloric acid treatment concentration of the acidified two-dimensional layered porous vermiculite is 2.5 mol/L.

The water absorption per 1 g of the acid-treated vermiculite carrier before the impregnation was 2.3 mL, and the vacuum drying temperature was 80°C.

In the roasting process, the heating rate is 2°C/min, the roasting temperature is 550°C, and the roasting time in an air atmosphere is 4h.

In the reduction process, the reduction temperature is 500°C, and the reduction time in pure hydrogen atmosphere is 2h.

Preferably, in the above-mentioned preparation method of acidified two-dimensional layered vermiculite-supported nickel-based catalyst, the two-dimensional layered porous catalyst prepared by a slight excess impregnation method, the nickel loading is 5wt%, and the nickel is relatively low in the amount of nickel. Under the premise of the loading amount, the catalyst still showed good catalytic activity and stability, and the nickel particle size was only 3-5 nm, indicating that it had good nickel dispersibility.

The application of the method for preparing the acidified two-dimensional layered vermiculite-supported nickel-based catalyst prepared by the method is used for catalyzing the synthesis of carbon monoxide and hydrogen by using carbon dioxide and methane as raw materials.

It specifically includes the following steps: mixing the catalyst with quartz sand and putting it into a fixed-bed reactor, and feeding methane, carbon dioxide and nitrogen into a fixed-bed reactor at a reaction temperature of 700-800°C and a space velocity of 90,000-100,000 mL h ^-1 g _cat ^-1 to obtain carbon monoxide. and hydrogen;

Wherein, the raw material ratio is methane:carbon dioxide:nitrogen=1:1:2.

The essential features of the present invention are:

At present, improving the anti-sintering and anti-coking properties of nickel-based catalysts has become a key scientific and technical issue in the methane dry reforming reaction.

Regarding the problem of catalyst sintering, according to the method for preparing a nickel-based methane dry reforming catalyst described in the patent of the present invention, small nickel nanoparticles in the obtained nickel-based catalyst are dispersed in a two-dimensional layered vermiculite porous structure with good thermal stability. In 2D, the support is rich in silanol structure, which plays an anchoring role for nickel metal particles, and the strong metal-support interaction of two-dimensional layered nickel silicate is used to improve the anti-sintering performance of nickel-based catalysts. Regarding the problem of anti-carbon deposition, about 2-5wt% Fe ₂ O ₃ is left in the acidified porous vermiculite prepared by the patent of the present invention, which can be used as a natural additive to accelerate the gasification of the deposited carbon species, thereby significantly improving the catalyst. stability and anti-carbon deposition properties.

The beneficial effects of the present invention are:

1. Compared with the traditional silica-supported nickel-based catalyst, the present invention can form a two-dimensional layered porous vermiculite structure. Even if the catalyst is prepared by the traditional impregnation method, good metal dispersion and small particle size can be achieved due to the confinement effect of the modified support. This confinement effect inhibits the sintering of metal nanoparticles under high temperature reaction. At the same time, because the carbon deposition reaction is a structure-sensitive reaction, it has a strong anti-metal agglomeration ability and also has a good anti-carbon deposition performance, which significantly improves the stability of the catalyst.

2. The present invention uses a hydrochloric acid acidifying agent to prepare an acidified two-dimensional layered vermiculite-supported nickel-based catalyst, and optimizes the acidification concentration. The vermiculite can be acidified with 2.5 mol/L hydrochloric acid to obtain the most silanol content , which can anchor more nickel metal particles to make it more accessible to the surface of the carrier with silica as the main matrix, and form a strong interaction with the carrier during the high-temperature calcination process to improve the stability of the catalyst.

3. The acidified two-dimensional layered vermiculite-supported nickel-based catalyst used in the present invention still maintains the layered porous structure of the catalyst after 24 hours of high temperature reaction. This is because the high temperature stability of vermiculite makes its structure under high temperature conditions. remained unchanged, so that the size of the supported nickel metal particles hardly grew, indicating the high-temperature stability of the two-dimensional porous vermiculite-supported nickel-based catalyst after acidification.

4. The catalyst prepared by the present invention has no obvious deactivation phenomenon when reacted at a high temperature of 750°C and a high space velocity of 96000mL h ^-1 g-cat ^-1 for 24 hours, and the thermogravimetric characterization shows that no obvious carbon deposition occurs. , which proved that the catalyst prepared by this method has good stability and anti-carbon performance.

Description of drawings

FIG. 1 is a SEM image of the two-dimensional layered porous vermiculite obtained in Example 1 of the present invention after being treated with 2.5 mol/L hydrochloric acid.

Figure 2 is a TEM image of the reduced acidified two-dimensional layered porous vermiculite-supported nickel-based catalyst.

3 is a graph showing the particle size statistics of nickel metal particles of the reduced acidified two-dimensional layered porous vermiculite-supported nickel-based catalyst.

Figure 4 is the TEM image of the acidified two-dimensional layered porous vermiculite-supported nickel-based catalyst after the reaction for 24 h.

Figure 5 is a graph showing the particle size statistics of nickel metal particles of the acidified two-dimensional layered porous vermiculite-supported nickel-based catalyst after the reaction for 24 h.

6 is a TG diagram of the nickel-based catalyst for dry reforming of methane after the reaction obtained in Example 1 of the present invention for 24 h.

Detailed ways

In order to further illustrate the present invention, the present invention will now be described in detail through specific embodiments.

Example 1

Preparation of acidified two-dimensional layered porous vermiculite: Mix 10 g of ball-milled commercial expanded vermiculite (100 mesh) with 200 mL of 2.5 mol/L hydrochloric acid solution to prepare a suspension with a solid-liquid ratio of 1:20, 2.5 mol/L L hydrochloric acid is prepared by dissolving 50 mL of 36-38% concentrated hydrochloric acid in 200 mL of deionized water. The suspension was vigorously stirred and refluxed at 800 rpm for 4 h at 80 °C; the obtained bright yellow precipitate was washed with deionized water by suction filtration until the filtrate became neutral, and the obtained solid was dried at 100 °C overnight to obtain Vermiculite powder carrier treated with 2.5mol/L hydrochloric acid.

Preparation of acidified two-dimensional layered porous vermiculite-supported nickel-based catalyst: 1 g of the acid-treated vermiculite powder carrier prepared above was taken, and the water vapor in the pores was removed by vacuum drying at 80°C, and the water absorption was tested. The specific steps are as follows: in the case of stirring, add deionized water dropwise to the dried vermiculite powder dropwise, until the powder becomes a batter, and the dropwise addition is stopped when the water is just about to seep out slightly. Then continue stirring for 30 min at 25°C until the water evaporates to dryness, and then put it into a vacuum drying oven at 80°C to dry overnight. The water absorption of acidified vermiculite was measured to be 2.3 mL/g.

0.25 g of Ni(NO ₃ ) ₂ ·6H ₂ O solid was dissolved in 2.3 mL of deionized water, and the prepared solution was added dropwise to the above dried 1 g of acidified vermiculite. The above steps were repeated, and the naturally air-dried powder was dried at 100° C. overnight to obtain a nickelate-loaded precursor. After drying, the samples were ground to powder, and then calcined at 550 °C for 4 h, and the temperature was programmed to increase by ₂ °C every minute. The nickel loading of the prepared catalyst was 4.51 wt%.

Test the catalytic activity of the above-mentioned catalyst: take by weighing 25mg (40-60 mesh) of the prepared catalyst and put it into a fixed-bed quartz tube reactor (50cm in length, 10mm in outer diameter, 6mm in inner diameter, the same in the following examples) to carry out the catalyst Performance Testing. Before the test, the catalyst was reduced in situ at 500 °C for 2 h in a pure hydrogen atmosphere. Then change to the raw material atmosphere, the injection volume of methane, carbon dioxide and nitrogen is 1:1:2 (flow rate is 10mL, 10mL and 20mL), 750℃, space velocity 96000mL h ^-1 g _cat ^-1 for activity test, catalyst methane and The carbon dioxide conversion rate was maintained at about 90% in the 24h activity evaluation, and the catalyst after the reaction had almost no carbon deposition.

Example 2

Preparation of acidified two-dimensional layered porous vermiculite: 10 g of ball-milled commercial expanded vermiculite (100 mesh) was mixed with 200 mL of 3mol/L hydrochloric acid solution to prepare a suspension with a solid-liquid ratio of 1:20, and 3mol/L hydrochloric acid was 50mL of 36-38% concentrated hydrochloric acid was dissolved in 150mL of deionized water. The suspension was vigorously stirred and refluxed at 80 °C for 4 h; the obtained bright yellow precipitate was washed with deionized water by suction filtration until the filtrate was neutral, and the obtained solid was dried at 100 °C overnight to obtain a 3mol/ L hydrochloric acid treated vermiculite powder carrier.

Preparation of acidified two-dimensional layered porous vermiculite-supported nickel-based catalyst: 1 g of the acid-treated vermiculite powder carrier prepared above was taken, and the water vapor in the pores was removed by vacuum drying at 80°C, and the water absorption was tested. The specific steps are as follows: in the case of stirring, add deionized water dropwise to the dried vermiculite powder dropwise, until the powder becomes a batter, and the dropwise addition is stopped when the water is just about to seep out slightly. Then continue stirring for 30 min at 25°C until the water evaporates to dryness, and then put it into a vacuum drying oven at 80°C to dry overnight. The water absorption of acidified vermiculite was measured to be 2.8 mL/g.

0.25 g of Ni(NO ₃ ) ₂ ·6H ₂ O solid was dissolved in 2.8 mL of deionized water, and the prepared solution was added dropwise to the dry acidified vermiculite. The above steps were repeated, and the naturally air-dried powder was dried at 100° C. overnight to obtain a nickelate-loaded precursor. After drying, the samples were ground to powder, and then calcined at 550 °C for 4 h, and the temperature was programmed to increase by ₂ °C every minute. The nickel loading of the prepared catalyst was 4.51 wt%.

Test the catalytic activity of the above catalyst: weigh 25 mg (40-60 mesh) of the prepared catalyst and put it into a fixed-bed quartz tube reactor to test the performance of the catalyst. Before the test, the catalyst was reduced in situ at 500 °C for 2 h in a pure hydrogen atmosphere. Then change to the raw material atmosphere, the injection volume of methane, carbon dioxide and nitrogen is 1:1:2 (flow rate is 10mL, 10mL and 20mL), 750℃, space velocity 96000mL h ^-1 g _cat ^-1 for activity test, catalyst methane and The carbon dioxide conversion rates dropped to around 67% and 70%, respectively. The activity has dropped significantly, and obvious sintering phenomenon is observed. The reaction activity is not as good as that of Example 1, which may be because the high concentration of hydrochloric acid causes part of the porous structure of the vermiculite to be destroyed, and the confinement effect of the pore collapse on the nickel metal particles is weakened, which makes the activity poor.

Example 3

Other steps are the same as in Example 1, except that the calcination temperature is changed to 450°C. The catalyst activity test conditions were the same as those in Example 1, and the conversion rates of methane and carbon dioxide were 64% and 68%, respectively. Rapid inactivation at 750 °C may be due to the fact that the calcination temperature is too low, and the active center does not form a strong interaction with the carrier.

Example 4

Other steps were the same as in Example 1, except that the reduction temperature of the catalyst was changed to 750°C. The catalyst activity test conditions were the same as those in Example 1, and the conversion rates of methane and carbon dioxide were 67% and 70%, respectively. And it is rapidly deactivated at a temperature of 750 °C. The reason for the deactivation may be that the reduction temperature is too high, which makes the metal particles sinter quickly.

Example 5

Other steps are the same as in Example 1, except that the preparation method of the catalyst is changed to the excess impregnation method. The specific steps of impregnation are as follows: dissolve 0.25g of Ni(NO ₃ ) ₂ ·6H ₂ O solid in deionized water to prepare a 20 mL aqueous solution, add 1 g of acidified vermiculite carrier to this solution, stir at room temperature for 3 hours, and spin the solution. Evaporate to dry overnight to obtain the nickel-loaded precursor. The catalyst activity test conditions were the same as those in Example 1, and the conversion rates of methane and carbon dioxide were 50% and 53%, respectively. And it is rapidly deactivated at a temperature of 750 °C. The reason for the deactivation may be that the catalyst metal particles prepared by the excessive impregnation method are large and non-uniform, so that the metal active specific surface area is exposed very little, so that the metal particles cannot fully function.

It can be seen from the above examples that the hydrochloric acid concentration of the acidified two-dimensional layered porous vermiculite-supported nickel-based catalyst in Example 1 is 2.5 mol/L, and the hydrochloric acid concentration of the two-dimensional layered porous vermiculite-supported nickel-based catalyst acidified in Example 2 It is 3mol/L, the materials and other operations of the two are exactly the same, the catalyst acidified with 2.5mol/L hydrochloric acid shows excellent catalytic performance of methane dry reforming, as well as enhanced anti-sintering and anti-carbon properties, while for 3mol/L For the catalyst acidified with L hydrochloric acid, the acidification concentration is too high, which causes the pore structure of porous vermiculite to partially collapse, and loses part of the confinement effect on the nickel metal particles, which leads to the decline of the catalytic stability of the catalyst and the problem of metal sintering during the reaction; Next, on the basis of treating the porous vermiculite-supported nickel-based catalyst with 2.5 mol/L hydrochloric acid, Example 3 and Example 4 decreased and increased the calcination and reduction temperature of the catalyst, respectively, which both showed poor methane dry reforming The performance of the catalyst shows that the appropriate calcination temperature can maximize the interaction between the metal supports, and the appropriate reduction temperature can completely reduce the nickel particles on the basis of reducing the sintering of the catalyst. Stability and anti-coking properties are significantly improved. The confinement effect of acidified 2D porous vermiculite coating and the anchoring effect of silanols on metal particles are demonstrated to improve the anti-sintering performance of nickel-based catalysts. For the problem of anti-carbon deposition, using an appropriate amount of hydrochloric acid modification can obtain an appropriate amount of Fe ₂ O ₃ as an auxiliary agent to accelerate the gasification of the deposited carbon, thereby significantly improving the anti-coking performance of the catalyst.

The above are only the preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, without departing from the principles of the present invention, several improvements and modifications can be made. It should be regarded as the protection scope of the present invention.

Matters not addressed in the present invention are known in the art.

Claims (9)

1. A preparation method of an acidified two-dimensional layered vermiculite supported nickel-based catalyst is characterized by comprising the following steps:

(1) immersing expanded vermiculite into a hydrochloric acid solution under the condition of stirring, and violently stirring and refluxing for 4-6 hours at the temperature of 60-90 ℃; washing the obtained bright yellow precipitate with deionized water, filtering, and drying to obtain acid-treated vermiculite powder carrier;

wherein the concentration of the hydrochloric acid solution is 1-3 mol/L;

(2) mixing Ni (NO)₃)₂Dropping the solution into the vacuumDrying the air-dried vermiculite powder carrier on an acid-treated vermiculite powder carrier at 100-120 ℃ for 6-10 hours to obtain dry powder;

wherein, Ni (NO) is added per 1mL₃)₂The solution contains 0.06-0.17 g of Ni (NO)₃)₂·6H₂O; dripping 0.5-3 mL of mixed solution into every 1g of acid-treated vermiculite carrier;

(3) and heating the dried powder to 500-600 ℃ in an air atmosphere, and roasting for 3-5 h to obtain the catalyst of the acidified two-dimensional layered vermiculite confined nickel nanoparticles.

2. The preparation method of the acidified two-dimensional layered vermiculite supported nickel-based catalyst according to claim 1, characterized in that the method further comprises the step (4), the acidified two-dimensional layered vermiculite supported nickel-based catalyst is heated to 450-550 ℃ in a nitrogen atmosphere, and then the gas is switched to a pure hydrogen atmosphere to be reduced for 1-3 hours.

3. The method for preparing the acidified two-dimensional layered vermiculite supported nickel-based catalyst according to claim 1, wherein the supported amount of nickel in the catalyst is 2.5-7.5 wt%.

4. The method for preparing the acidified two-dimensional exfoliated vermiculite-supported nickel-based catalyst according to claim 1, wherein in the step (1), preferably 5 to 15g of expanded vermiculite is added to every 200ml of hydrochloric acid solution; the rotation number of the violent stirring is 700-900 rpm; the vacuum drying temperature in the step (2) is 60-90 ℃, and the time is 3-5 hours; the heating rate in the step (3) is 1-3 ℃/min.

5. The method for preparing the acidified two-dimensional exfoliated vermiculite-supported nickel-based catalyst according to claim 1, wherein the hydrochloric acid treatment concentration of the acidified two-dimensional exfoliated porous vermiculite in the step (1) is 2.5 mol/L;

before impregnation, the water absorption capacity of each 1g of acid-treated vermiculite carrier is 2.3mL, and the vacuum drying temperature is 80 ℃;

in the roasting process, the heating rate is 2 ℃/min, the roasting temperature is 550 ℃, and the roasting time in the air atmosphere is 4 h;

in the reduction process, the reduction temperature is 500 ℃, and the reduction time in a pure hydrogen atmosphere is 2 h.

6. The method of claim 1, wherein the catalyst is prepared by a slight excess impregnation method.

7. The method for preparing the acidified two-dimensional layered vermiculite supported nickel-based catalyst according to claim 1, wherein the loading amount of nickel is 5 wt%, and the particle size of nickel is 3-5 nm.

8. The application of the preparation method of the acidified two-dimensional layered vermiculite supported nickel-based catalyst prepared by the method of claim 1 is characterized in that the catalyst is used for catalytically synthesizing carbon monoxide and hydrogen by using carbon dioxide and methane as raw materials.

9. The application of the preparation method of the acidified two-dimensional layered vermiculite supported nickel-based catalyst prepared by the method according to claim 8 is characterized by comprising the following steps: mixing the catalyst and quartz sand, putting the mixture into a fixed bed reactor, and reacting at the temperature of 700 ℃ plus 800 ℃ and the space velocity of 90000-100000 mL h^-1g_cat ^-1Then introducing methane, carbon dioxide and nitrogen to obtain carbon monoxide and hydrogen;

wherein, the raw material ratio is methane: carbon dioxide: nitrogen is 1:1: 2.

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