CN111514897A - Application of high-dispersion carbon-doped mesoporous silicon nanotube nickel-based catalyst in carbon dioxide methanation reaction - Google Patents

Abstract

The invention relates to the application of a highly dispersed carbon-doped mesoporous silicon nanotube nickel-based catalyst in carbon dioxide methanation reaction, and belongs to the technical field of catalytic reaction. The catalyst of the present invention forms organosilica nanotubes with mesoporous structure containing ordered amino groups by directional hydrolysis and polycondensation of amino-containing organosilane molecules in the presence of a soft template agent. The above-mentioned amino groups can effectively coordinate and anchor metal ions, so that the active metal nickel can be highly dispersed and firmly supported on the surface of the mesoporous organosilicon. The carbon-doped supports can improve the electron transfer efficiency of active metals in the catalytic process, and then synergistically improve the catalytic activity of the catalysts in carbon dioxide methanation. The highly dispersed carbon-doped mesoporous silicon nanotube nickel-based catalyst prepared by the invention exhibits high catalytic activity and selectivity in the _CO2 methanation reaction, and has a good application prospect.

Description

A highly dispersed carbon-doped mesoporous silicon nanotube nickel-based catalyst in carbon dioxide methane applications in chemical reactions

technical field

The invention relates to the application of a highly dispersed carbon-doped mesoporous silicon nanotube nickel-based catalyst in carbon dioxide methanation reaction, and belongs to the technical field of catalytic reaction.

Background technique

Carbon dioxide methanation is a process in which carbon dioxide and hydrogen react to form methane under the action of a catalyst. It is well known that Ru and Rh have the best carbon dioxide methanation properties, but their reserves are scarce and expensive, making it difficult to achieve large-scale industrial applications. Co- and Fe-based catalysts have better reactivity, but the selectivity of methane is lower and more used as Fischer-Tropsch synthesis catalysts. Nickel-based catalysts not only have good catalytic performance, but also have large reserves and low prices, so they are widely used in carbon dioxide methanation reactions. The activity of nickel-based catalysts is affected by factors such as supports, additives and preparation methods.

_SiO2 as a methanation catalyst carrier has good hydrothermal stability, large specific surface area and developed pore structure, which is conducive to the dispersion of active components on the surface of the carrier, forming small nano-grains, and improving the active specific surface area of active metals . However, the chemical properties of the _SiO2 support are inactive, and it is difficult to play a synergistic catalysis role with the metal active components, and the interaction force and mechanical strength of the metal support are relatively weak; this makes the catalyst unable to volatilize the optimal catalyst during the reaction process. Function. By adjusting and improving the structure and composition of the carrier by changing the preparation method, etc., some deficiencies of the carrier can be effectively compensated.

Periodic Mesoporous Organosilica (PMO) is a new type of organic-inorganic composite mesoporous material. Under the directional action of surfactant, hydrolyzed organosilane molecules undergo polycondensation to form a material with specific microscopic morphology. Due to its regular pore structure, large specific surface area, tunable surface properties, and the characteristics of different bridging functional groups, periodic mesoporous organosilica plays an important role in heterogeneous catalysis, substance adsorption, chromatographic phase, light absorption and emission. It plays an important role in the delivery of drugs and biomolecules. In addition to the above properties, periodic organic silicon oxide nanotubes also have the characteristics of high specific surface area, strong mechanical stability, hollow structure conducive to molecular diffusion and nanotube confinement effect of one-dimensional nanotube-like materials. It can play an important role as a carrier in heterogeneous catalytic reactions. Periodic mesoporous organosilica nanotubes can also coordinate some metal atoms through bridging functional groups to fix the active center on the support.

On the basis of the above-mentioned prior art, the present invention develops a highly dispersed carbon-doped mesoporous silicon nanotube nickel-based catalyst for the first time, and applies it to the carbon dioxide methanation reaction. The catalyst of the present invention forms organosilica nanotubes with mesoporous structure containing ordered amino groups by directional hydrolysis and polycondensation of amino-containing organosilane molecules in the presence of a soft template agent. The above-mentioned amino groups can effectively coordinate and anchor metal ions, so that the active metal nickel can be highly dispersed and firmly supported on the surface of the mesoporous organosilicon. The carbon-doped supports can improve the electron transfer efficiency of active metals in the catalytic process, and then synergistically improve the catalytic activity of the catalysts in carbon dioxide methanation. The highly dispersed carbon-doped mesoporous silicon nanotube nickel-based catalyst prepared by the invention exhibits high catalytic activity and selectivity in the _CO2 methanation reaction, and has a good application prospect.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a kind of application of highly dispersed carbon-doped mesoporous silicon nanotube nickel-based catalyst in carbon dioxide methanation reaction, and the specific application method is:

Put an appropriate amount of catalyst into the fixed bed reactor, feed the raw material gas H ₂ and CO ₂ into the reactor at a molar ratio of 1-10, maintain the feed space velocity of 5000-50000h ^-1 , and keep the total pressure of the reaction system as 0.1MPa, at 100-450 ℃ for _CO2 methanation catalytic reaction; the catalyst uses carbon-doped mesoporous silicon nanotubes as a carrier, and supports active metal nickel, wherein, in terms of metal, the mass fraction of nickel in the catalyst is 2-15wt%.

Further, the molar ratio of the raw material gas is preferably 2-6, more preferably 4; the feed space velocity is preferably 5000-30000 h ^-1 , more preferably 20000 h ^-1 .

Further, in terms of metal, the mass fraction of nickel in the catalyst is 5-10 wt%.

Further, the preparation method of the catalyst comprises the following preparation steps:

(1) Synthesis of PMO- _NH2 :

Dissolve a certain amount of templating agent cetyltrimethylammonium bromide (CTAB) in a mixed solution of water and ethanol, and dissolve with magnetic stirring; add 3-aminopropyltriethoxysilane (APTES) to the above solution. ) and 1,2-bis(trimethoxysilyl)ethane (BTME), the mass ratio of APTES and BTME was 1:1-10, stirring was continued for 1-2h, and the mixture was poured into a polytetrafluoroethylene liner And stand at 60-100°C for 24-48h reaction; centrifuge the reactants, and the obtained product adopts a mixed solution of ethanol and hydrochloric acid to reflux extract the template agent at 40-80°C, centrifuge and wash to obtain an organic bridged PMO containing amino groups ;

(2) Loading of active metal nickel:

Dissolving the soluble nickel salt in the ethanol solution to obtain a 0.01-0.1M nickel salt precursor solution, immersing the PMO-NH ₂ prepared in step (1) as a carrier in the above nickel salt precursor solution, and ultrasonicating for 2-4 h to make the PMO The amino group and the metal nickel ion fully carry out coordination reaction, and the nickel ion is anchored on the surface of the carrier with a coordination bond; after the reaction is completed, the product is centrifuged, fully washed with deionized water and ethanol, and dried at 60-100 °C;

(3) calcination of catalyst:

The product obtained in step (2) is placed in a tube furnace, and under nitrogen protection, the heating rate of 2-5°C/min is raised to 500-900°C for 2-6h and calcined to obtain the carbon-doped mesoporous material of the present invention. Silicon nanotube nickel-based catalysts.

Further, the mass ratio of the template agent and APTES in the step (1) is 1:1-5, and the mass ratio of APTES and BTME is 1:3-8.

Further, the temperature of the standing reaction in the step (1) is preferably 60-90° C., and the time is preferably 24-36 h.

Further, the nickel salt in the step (2) is one or more of nickel nitrate, nickel chloride and nickel sulfate, and the concentration of the nickel salt precursor solution is preferably 0.02-0.05M.

Further, the calcination temperature in the step (3) is preferably 600-800° C., and the time is preferably 3-4 h.

The present invention forms organic silicon oxide nanotubes with mesoporous structure containing ordered amino groups by directional hydrolysis and polycondensation of amino group-containing organosilane molecules in the presence of a soft template agent. The above-mentioned amino groups can effectively coordinate and anchor the metal ions, so that the active metal nickel can be highly dispersed and firmly loaded on the surface of the mesoporous organic silicon oxide, which effectively solves the problem that the active metal is easy to fall off and agglomerate in the prior art. question. Further, due to the existence of organic groups, in the process of oxygen-free calcination, the organic groups can form carbon doping inside the silicon oxide, and at the same time reduce the metallic nickel. The above steps can omit the subsequent reduction step and simplify the preparation process of the catalyst.

The silicon nanotube material in the present invention has a large specific surface area and a hollow structure, which is conducive to the diffusion and mass transfer of reactant molecules, thereby improving the catalytic reaction efficiency. At the same time, the carbon-doped support can promote the electron transfer efficiency of the active metal in the catalytic process, thereby synergistically improving the catalytic activity of the catalyst in carbon dioxide methanation.

The highly dispersed carbon-doped mesoporous silicon nanotube nickel-based catalyst prepared by the present invention exhibits high catalytic activity and selectivity in the _CO2 methanation reaction, and the yield of methane can reach up to 79.6% at 400°C , the catalytic effect is significantly better than the traditional Ni/ _SiO2 catalyst, and has good application value.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Example 1

(1) Synthesis of PMO- _NH2 :

The templating agent CTAB was dissolved in a mixed solution of water and ethanol, and dissolved by magnetic stirring; APTES and BTME were added to the above solution, wherein the mass ratio of CTAB, APTES and BTME was 1:2:8, and the mixture was stirred continuously for 2h. Pour it into a polytetrafluoroethylene liner and let it stand at 80°C for 30h reaction; centrifuge the reactant, and the obtained product is extracted with a mixed solution of ethanol and hydrochloric acid at 60°C to reflux the template agent, centrifuged and washed to obtain an organic bridge containing amino groups. Connected PMO;

(2) Loading of active metal nickel:

Dissolving nickel nitrate in an ethanol solution to obtain a 0.02M nickel salt precursor solution, immersing the PMO-NH ₂ prepared in step (1) as a carrier in the above nickel salt precursor solution, ultrasonicating for 2h, after the reaction is over, centrifuging the product , fully washed with deionized water and ethanol, and dried at 80 °C;

(3) calcination of catalyst:

The product obtained in step (2) was placed in a tube furnace, and under nitrogen protection, the heating rate of 5°C/min was raised to 800°C and calcined for 3 hours to obtain the carbon-doped mesoporous silicon nanotube nickel base of this embodiment. The catalyst is designated as No. S-1; wherein, in terms of metal, the mass fraction of nickel in the catalyst is 7 wt %.

Example 2

(1) Synthesis of PMO- _NH2 :

The templating agent CTAB was dissolved in a mixed solution of water and ethanol, and dissolved by magnetic stirring; APTES and BTME were added to the above solution, wherein the mass ratio of CTAB, APTES and BTME was 1:1:5, and the mixture was stirred continuously for 2h. It was poured into a polytetrafluoroethylene liner and left to react at 100°C for 28 hours; the reactants were centrifuged, and the obtained product was extracted with a mixed solution of ethanol and hydrochloric acid at 80°C to reflux the template agent, centrifuged and washed to obtain an organic bridge containing amino groups. Connected PMO;

(2) Loading of active metal nickel:

Dissolving nickel nitrate in an ethanol solution to obtain a 0.05M nickel salt precursor solution, immersing the PMO-NH ₂ prepared in step (1) as a carrier in the above nickel salt precursor solution, ultrasonicating for 2h, and after the reaction is over, centrifuging the product , fully washed with deionized water and ethanol, and dried at 80 °C;

(3) calcination of catalyst:

The product obtained in step (2) was placed in a tube furnace, and under nitrogen protection, the heating rate of 5°C/min was raised to 800°C and calcined for 3 hours to obtain the carbon-doped mesoporous silicon nanotube nickel base of this embodiment. The catalyst is designated as No. S-2; wherein, in terms of metal, the mass fraction of nickel in the catalyst is 10 wt %.

Example 3

(1) Synthesis of PMO- _NH2 :

The templating agent CTAB was dissolved in a mixed solution of water and ethanol, and dissolved by magnetic stirring; APTES and BTME were added to the above solution, wherein the mass ratio of CTAB, APTES and BTME was 1:2:6, and the mixture was stirred continuously for 2h. Pour it into a polytetrafluoroethylene liner and let it stand at 100 °C for 24 hours; centrifuge the reactant, and the obtained product is extracted with a mixed solution of ethanol and hydrochloric acid at 80 °C to reflux the template agent, centrifuged and washed to obtain an organic bridge containing amino groups. Connected PMO;

(2) Loading of active metal nickel:

Dissolving nickel nitrate in an ethanol solution to obtain a 0.04M nickel salt precursor solution, immersing the PMO-NH ₂ prepared in step (1) as a carrier in the above nickel salt precursor solution, ultrasonicating for 2h, and after the reaction is over, centrifuging the product , fully washed with deionized water and ethanol, and dried at 80 °C;

(3) calcination of catalyst:

The product obtained in step (2) was placed in a tube furnace, and under nitrogen protection, the heating rate of 5°C/min was raised to 800°C and calcined for 3 hours to obtain the carbon-doped mesoporous silicon nanotube nickel base of this embodiment. Catalyst, denoted as No. S-3; wherein, in terms of metal, the mass fraction of nickel in the catalyst is 5wt%

Example 4

The prepared catalyst was evaluated for _CO2 methanation reaction using a fixed bed reactor. Measure 0.5g of catalyst and put it into the reactor, feed the raw material gas H ₂ /CO ₂ =4 into the reactor, feed space velocity GHSV = 20000h ^-1 , keep the total pressure of the reaction system at 0.1MPa, at 400°C The catalytic reaction of _CO2 methanation is carried out under the After the reaction reaches a steady state, the catalytic reaction result is calculated from the gas chromatographic analysis data of the exhaust gas. The experimental results are shown in Table 1.

For comparison, conventional Ni/SiO ₂ (the mass content of Ni is 7%, denoted as No. D-1) was also subjected to CO ₂ methanation reaction under the same test conditions. The experimental results are listed in Table 1.

Table 1 Catalytic activity data of catalysts in _CO2 methanation reaction

It can be seen from Table 1 that the highly dispersed carbon-doped mesoporous silicon nanotube nickel-based catalyst prepared by the present invention exhibits high catalytic activity and selectivity in the _CO2 methanation reaction. The highest yield can reach 79.6%, and the catalytic effect is significantly better than the traditional Ni/ _SiO2 catalyst. It can be seen that the catalyst of the present invention has excellent catalytic effect of _CO2 methanation, and has a good application prospect.

In addition, it should be understood that although this specification is described in terms of embodiments, not each embodiment only includes an independent technical solution, and this description in the specification is only for the sake of clarity, and those skilled in the art should take the specification as a whole , the technical solutions in each embodiment can also be appropriately combined to form other implementations that can be understood by those skilled in the art.

Claims (8)

1. An application of a high-dispersion carbon-doped mesoporous silicon nanotube nickel-based catalyst in methanation reaction of carbon dioxide is characterized in that the application method comprises the following steps:

charging proper amount of catalyst into fixed bed reactor, and charging raw material gas H₂、CO₂The mixture is introduced into the reactor in a molar ratio of 1-10, and the feeding space velocity is maintained at 5000-^-1Keeping the total pressure of the reaction system at 0.1MPa, and carrying out CO reaction at 100-450 DEG C₂Catalytic methanation reaction(ii) a The catalyst takes a carbon-doped mesoporous silicon nanotube as a carrier and loads active metal nickel, wherein the nickel accounts for 2-15wt% of the catalyst in terms of metal.

2. Use according to claim 1, wherein the molar ratio of the feed gases is preferably 2-6, more preferably 4; the feeding space velocity is preferably 5000-^-1More preferably 20000h^-1。

3. Use according to claim 1, wherein the nickel comprises 5-10 wt.% of the catalyst calculated as metal.

4. The use according to claim 1, wherein the preparation method of the catalyst comprises the following preparation steps:

(1)PMO-NH₂the synthesis of (2):

dissolving a certain amount of template Cetyl Trimethyl Ammonium Bromide (CTAB) in a mixed solution of water and ethanol, and dissolving by magnetic stirring; adding 3-Aminopropyltriethoxysilane (APTES) and 1, 2-bis (trimethoxysilyl) ethane (BTME) into the solution, wherein the mass ratio of the APTES to the BTME is 1:1-10, continuously stirring for 1-2h, pouring the mixture into a polytetrafluoroethylene inner container, and standing at 60-100 ℃ for reaction for 24-48 h; centrifuging the reactant, extracting the template agent by refluxing the obtained product at 40-80 ℃ by using a mixed solution of ethanol and hydrochloric acid, centrifuging and washing to obtain the amino-containing organic bridged PMO;

(2) loading of active metal nickel:

dissolving soluble nickel salt in ethanol solution to obtain 0.01-0.1M nickel salt precursor solution, and preparing PMO-NH from step (1)₂Dipping the carrier serving as the carrier in the nickel salt precursor solution, and carrying out ultrasonic treatment for 2-4h to ensure that amino in PMO and metal nickel ions fully carry out coordination reaction, and anchoring the nickel ions on the surface of the carrier by coordination bonds; after the reaction is finished, centrifugally separating a product, fully washing the product by using deionized water and ethanol, and drying the product at the temperature of 60-100 ℃;

(3) roasting of the catalyst:

and (3) placing the product obtained in the step (2) in a tubular furnace, and roasting for 2-6h at the temperature rising rate of 2-5 ℃/min to 500-900 ℃ under the protection of nitrogen to obtain the carbon-doped mesoporous silicon nanotube nickel-based catalyst.

5. The use according to claim 4, wherein the mass ratio of the template to the APTES in the step (1) is 1:1-5, and the mass ratio of the APTES to the BTME is 1: 3-8.

6. The use according to claim 4, wherein the temperature of the standing reaction in step (1) is preferably 60-90 ℃ and the time is preferably 24-36 h.

7. The use according to claim 4, wherein the nickel salt in step (2) is one or more of nickel nitrate, nickel chloride and nickel sulfate, and the concentration of the nickel salt precursor solution is preferably 0.02-0.05M.

8. The use according to claim 4, wherein the calcination temperature in step (3) is preferably 600 ℃ to 800 ℃ and the time is preferably 3 to 4 hours.