CN110893346A - Bimetallic low-temperature methanation catalyst and preparation method and application thereof - Google Patents
Bimetallic low-temperature methanation catalyst and preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses a bimetallic low-temperature methanation catalyst, which takes mesoporous molecular sieve SBA-15 as a carrier, metal Ni as a main active component and at least one of transition metal or rare earth metal as an auxiliary metal; wherein, the content of metal Ni is 5 wt% -20 wt%, the content of auxiliary metal is 0.5 wt% -2 wt%, and the rest is mesoporous molecular sieve SBA-15. The active metal and the assistant metal exist in the prepared catalyst in the form of alloy, and electron transfer exists between the assistant metal and the active metal, so that the low-temperature catalytic performance of the catalyst is obviously improved, and meanwhile, the enhancement of the interaction force and the limitation of the carrier pore channel inhibit the high-temperature sintering agglomeration of the active component, so that the catalyst has the advantages of high catalytic activity, good methane selectivity, good thermal stability, long service life of the catalyst and the like; the prepared catalyst can reach the CO conversion rate of 100 percent and the methane selectivity of 96 percent at the low temperature of 250 ℃, and has great industrial prospect.
Description
Technical Field
The invention belongs to the technical field of catalytic chemistry, and particularly relates to a high-dispersion limited-range bimetallic low-temperature methanation catalyst, a preparation method thereof and application thereof in preparation of methane from synthesis gas.
Background
The resource structure of China is characterized in that coal is rich, oil is deficient, and gas is low, about 80% of coal consumption is directly converted through combustion, the gradient utilization of resources cannot be realized, not only is the waste of coal resources caused, but also the heat energy utilization rate is low, and a large amount of pollutants are discharged. And natural gas has incomparable economic and environmental protection benefits as clean and efficient energy. At present, the contradiction between supply and demand of natural gas in China is increasingly prominent, and the external dependence degree shows a rapidly rising trend. The statistical natural gas consumption in 2014 is 1870 billion cubic meters, the increase is 12 percent on the same scale, and the external dependence reaches 32 percent; it is expected that gas consumption will likely reach 4850 billion cubic meters in 2020 and that the external dependence will likely reach 37%. Therefore, the relatively rich coal resources (particularly lignite) in China are optimally utilized to prepare Synthetic Natural Gas (SNG), the supply of the SNG with high energy utilization rate can be increased, the emission of greenhouse gases can be greatly reduced, the win-win effect of energy and environment is achieved, and the economic value and the social significance are great.
For coal-based natural gas, the key is synthesis gas methanation technology, and the development of excellent and efficient methanation catalyst has become one of the important points of methanation technology research. The requirements on the coal SNG industrial methanation catalyst are mainly as follows: low temperature, high efficiency (i.e. low reaction temperature, wide range of hydrogen-carbon ratio of raw material gas, high conversion rate of CO and CH)4High selectivity, good stability (i.e. wear resistance, high temperature resistance, sintering resistance and poisoning resistance), long service life and low cost. Because a large amount of heat is generated in the methanation process of the synthesis gas, the lower the reaction temperature is, the more favorable the methanation reaction is according to thermodynamic equilibrium calculation, and simultaneously, the requirements on the heat resistance of the catalyst and the reactor are also reduced. When the metal Ru is used as an active component, the catalyst still has good activity at the reaction temperature of 200 ℃, but the Ru is expensive, so that the cost of the catalyst is obviously increased, and the development of the low-temperature high-efficiency nickel-based catalyst is necessary. The operation temperature of the current industrial methanation reaction is generally above 400 ℃.
The activity of the catalyst mainly comes from active reaction centers provided by active components, and the distribution and structural properties of the active components Ni on the surface of the carrier directly determine the number of effective active reaction centers, so that the activity, selectivity and stability of the catalyst are influenced finally. From the current research reports, the size of metal particles, the loading amount of active components and metal-carrier interaction are main factors influencing the distribution of Ni on the surface of the carrier, and the structural properties of the active components are closely related to the Ni species type on the surface of the carrier, the atomic arrangement on the surface of the metal particles and the electronic state. The auxiliary agents of the methanation catalyst are mainly divided into two categories: (1) electron assistant: changing the electron transfer property of the catalyst; (2) structural auxiliary agents: the dispersity and thermal stability of metals in the catalyst are improved by changing the chemical composition, crystal structure, pore structure, dispersion state of active components and mechanical strength of the catalyst. In addition, some oxide assistants have both of these functions.
The carrier plays an important role in heterogeneous catalysts in gas-solid reactions, and generally influences the interaction force between metal and the carrier and the dispersion degree of the metal, thereby further influencing the activity, selectivity and stability of the catalyst. So far, metal oxides (Al)2O3、SiO2、ZrO2、TiO2、CeO2Etc.), composite supports (hexaaluminate, solid clay, perovskite) and SiC supports may all be used as supports for methanation catalysts. Among these supports, alumina Al2O3Is the most typical and widely studied one, but it readily forms NiAl with Ni at high temperatures2O4Spinel, which at the same time sinters under the effect of water vapor and leads to rapid deactivation of the catalyst. Amorphous SiO2Are also frequently used as supports for catalysts. SiO relative to other supports2There is a major advantage in that the pore size, specific surface area and pore volume are easily adjustable and controllable. But increase SiO as well as alumina support2The hydrothermal stability of the support also requires further investigation. Compared with common silicon dioxide and aluminum oxide, the mesoporous molecular sieve SBA-15 has obvious advantages as a catalyst carrier, and has excellent physicochemical properties, larger specific surface area and ordered pore structure, so that the dispersion of metal can be effectively improved, and the catalytic performance of the mesoporous molecular sieve SBA-15 is improved. In addition, the nonionic surfactant is adopted as the template agent in the preparation process, so that the acting force between the formed micelle and the silicon precursor is reduced, a thicker pore wall can be formed, and the structure of the SBA-15 is further enabled to be realizedThe stability is improved, and the thermal and hydrothermal stability of the catalyst is further improved.
At present, methanation catalysts are mostly prepared by coprecipitation or common impregnation methods, and the uniform distribution of active components can not be basically realized. Patent CN105709741A discloses a preparation method capable of distributing active components in an eggshell, and the CO conversion rate of the prepared catalyst can only reach 23.4% at 250 ℃. Patent CN104815662A provides a nano composite methanation catalyst and a preparation method thereof, which uses nano TiO2With Al2O3The composite material is used as a carrier, the nickel-iron alloy is used as an active component, and the catalyst is complex in preparation process, high in cost and not suitable for large-scale production.
Disclosure of Invention
The invention aims to provide a high-dispersion limited-range bimetallic low-temperature methanation catalyst.
The invention also aims to provide a preparation method of the high-dispersion limited-range bimetallic low-temperature methanation catalyst.
The invention further aims to provide application of the high-dispersion limited-range bimetallic low-temperature methanation catalyst in preparation of methane from synthesis gas.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
the invention provides a high-dispersion limited-range bimetallic low-temperature methanation catalyst, which takes mesoporous molecular sieve SBA-15 as a carrier, metal Ni as a main active component and at least one of transition metal or rare earth metal as an auxiliary metal; wherein, the content of metal Ni is 5 wt% -20 wt%, the content of auxiliary metal is 0.5 wt% -2 wt%, the rest is mesoporous molecular sieve SBA-15, and the active component nickel and the auxiliary metal exist in the catalyst in the form of alloy.
The mesoporous molecular sieve SBA-15 has stable chemical property, good heat conduction performance and large specific surface area of 600-1000 m2A micropore surface area of 100 to 200m2The pore size is adjustable within 4.6-30 nm, the pore wall is thicker (3-9 nm), and the pore volume can reach 0.8-1.3 cm3Per g, micropore volume of 0.02E0.04cm3(ii) in terms of/g. The mesoporous molecular sieve carrier SBA-15 is a molecular sieve material with a larger pore diameter at present, and the SBA-15 has a larger pore diameter size, a thicker pore wall structure and better hydrothermal stability than the traditional MCM-41 while keeping a highly ordered two-dimensional hexagonal structure, so that the mesoporous molecular sieve carrier has wide potential application prospects in the fields of adsorption, catalysis, biomedicine, new material processing and the like.
The transition metal is selected from at least one of Fe, Mo and Co.
The rare earth metal is selected from at least one of La and Ce.
The specific surface area of the high-dispersion limited-range bimetallic low-temperature methanation catalyst is 600-660 m2Per g, the surface area of the micropores is 60-75 m2The pore volume is 0.85-1 cm3The volume of the micropores is 0.01-0.03 cm3(ii)/g, the pore diameter is 5.5 to 5.7 nm.
The second aspect of the invention also provides a preparation method of the high-dispersion limited-range bimetallic low-temperature methanation catalyst, which comprises the following steps:
dissolving nickel salt, a metal precursor and an additive in deionized water, wherein the mass ratio of the nickel salt to the metal precursor to the additive to the deionized water is (1-100): 1: (0.1-15): (10-1000), soaking the mesoporous molecular sieve SBA-15 in the mixed solution at room temperature for 2-12 hours, wherein the mesoporous molecular sieve SBA-15 accounts for 1-90% of deionized water by mass percent, vacuum drying is carried out at the temperature of 30-80 ℃ for 5-12 hours, roasting is carried out at the temperature of 400-800 ℃ for 1-10 hours, and cooling and grinding are carried out to obtain the bimetallic low-temperature methanation catalyst.
The nickel salt is at least one of nickel chloride, nickel sulfate, nickel acetate, nickel oxalate and nickel nitrate.
The metal precursor is a compound containing at least one of the following metals: fe. Mo, Co, La, Ce; specifically, at least one selected from ammonium molybdate, lanthanum nitrate and ferric nitrate.
The additive is at least one of citric acid, Cetyl Trimethyl Ammonium Bromide (CTAB), ethylene glycol, glucose, sorbitol or sodium dodecyl sulfate.
The invention provides application of the high-dispersion limited-range bimetallic low-temperature methanation catalyst in preparation of methane from synthesis gas.
The conditions for preparing methane from the synthesis gas are as follows: the volume space velocity of the synthesis gas is 3000-30000 mL/g.h, the pressure is from normal pressure to 3.0Mpa, the temperature is 200-500 ℃, and H in the synthesis gas2The ratio of/CO is 2-4.
Due to the adoption of the technical scheme, the invention has the following advantages and beneficial effects:
the high-dispersion limited-range bimetallic low-temperature methanation catalyst provided by the invention shows excellent activity and methane selectivity in the reaction of preparing methane from synthesis gas, the catalyst has activity in a temperature range of 200-500 ℃, the CO conversion rate can reach more than 98% at a low temperature of 250 ℃, and the methane selectivity can reach more than 92%.
The active metal and the assistant metal exist in the form of alloy in the high-dispersion limited-range bimetal low-temperature methanation catalyst provided by the invention, and electron transfer exists between the assistant metal and the active metal, so that the low-temperature catalytic performance of the catalyst is obviously improved, and meanwhile, the high-temperature sintering agglomeration of active components is inhibited by the enhancement of interaction force and the limited-range action of carrier pore channels, so that the catalyst has the advantages of high catalytic activity, good methane selectivity, good thermal stability, long service life of the catalyst and the like; the prepared catalyst can reach the CO conversion rate of 100 percent and the methane selectivity of 96 percent at the low temperature of 250 ℃, and has great industrial prospect.
According to the high-dispersion limited-range bimetallic low-temperature methanation catalyst provided by the invention, in the preparation process of the catalyst, the additive is added, so that the size of active component particles can be reduced, the active component particles are uniformly dispersed in pore channels of a carrier, and the limitation effect can prevent the active component particles from sintering, so that the dispersion of the active component particles is improved, and the activity and the stability of the catalyst are finally improved; the catalyst has the advantages of simple and easy preparation method, higher performance and larger advantage in cost performance, and is suitable for industrial large-scale production.
The high-dispersion limited-range bimetallic low-temperature methanation catalyst provided by the invention improves the utilization rate of active components, so that the catalyst has good catalytic performance at low temperature, and meanwhile, the prepared catalyst has excellent high-temperature resistance and long-term stability, is simple in preparation process, and is suitable for industrial large-scale production.
Drawings
FIG. 1 is a HRTEM-EDS spectrum of a bimetallic low-temperature methanation catalyst Mo-Ni/S15-CA prepared in example 1 of the invention, wherein the left-hand side shows the structure of the catalyst and the distribution of active metals, black particles are active metals, and the right-hand side shows the energy spectrum diagram which shows the elements present in the left-hand side.
FIG. 2 is a HRTEM-EDS spectrum of La-Ni/S15-EG prepared by the bimetallic low-temperature methanation catalyst of example 2 of the present invention, wherein the left graph shows the structure of the catalyst and the distribution of active metals, black particles are active metals, and the right graph is a spectrum graph showing elements present in the left graph.
FIG. 3 is an HRTEM-EDS spectrum of a bimetallic low-temperature methanation catalyst Fe-Ni/S15-CTAB prepared in example 3 of the present invention, wherein the left-hand side shows the structure of the catalyst and the distribution of active metals, the black particles are active metals, and the right-hand side shows the energy spectrum diagram, which shows the elements present in the left-hand side.
FIG. 4 is a comparative schematic of the low temperature methanation performance of the catalysts prepared in examples 1-3 and comparative example 1 of this invention in example 4.
FIG. 5 is an HRTEM spectrum of the bimetallic low-temperature methanation catalyst in example 5 of the invention after the bimetallic low-temperature methanation catalyst Mo-Ni/S15-CA prepared in example 1 is tested for high temperature resistance in the reaction of preparing methane from synthesis gas.
FIG. 6 is an HRTEM spectrum of the bimetallic low-temperature methanation catalyst in example 5 of the invention after the bimetallic low-temperature methanation catalyst La-Ni/S15-EG prepared in example 2 is used for testing high-temperature resistance in a reaction for preparing methane from synthesis gas.
FIG. 7 is an HRTEM spectrum of the bimetallic low-temperature methanation catalyst after the bimetallic low-temperature methanation catalyst Fe-Ni/S15-CTAB prepared in example 5 is used for testing high-temperature resistance in a reaction for preparing methane from synthesis gas.
Detailed Description
In order to more clearly illustrate the invention, the invention is further described below in connection with preferred embodiments. It is to be understood by persons skilled in the art that the following detailed description is illustrative and not restrictive, and is not to be taken as limiting the scope of the invention.
The experimental procedures, in which specific conditions are not noted in the following examples, are generally carried out under conventional conditions or conditions recommended by the manufacturers.
Details of the reagents used in the examples are shown in the following table:
TABLE 1
Name (R) | Specification of | Manufacturer of the product |
Nickel nitrate | Analytical purity | Shanghai Lingfeng Chemicals Co., Ltd |
Nickel acetate tetrahydrate | Analytical purity | Shanghai Lingfeng Chemicals Co., Ltd |
Lanthanum nitrate | Analytical purity | Shanghai Lingfeng Chemicals Co., Ltd |
Ammonium molybdate | Analytical purity | Shanghai Lingfeng Chemicals Co., Ltd |
Polyethylene oxide-polypropylene oxide-polyethylene oxide | Analytical purity | Sigma-Aldrich |
Tetraethoxysilane | Analytical purity | Shanghai Lingfeng Chemicals Co., Ltd |
Hydrochloric acid | Analytical purity | Shanghai Lingfeng Chemicals Co., Ltd |
Deionized water | - | University of eastern China |
Citric acid monohydrate | Analytical purity | Shanghai Lingfeng Chemicals Co., Ltd |
Ethylene glycol | Analytical purity | Shanghai Lingfeng Chemicals Co., Ltd |
Ferric nitrate | Analytical purity | Shanghai Lingfeng Chemicals Co., Ltd |
Cetyl trimethyl ammonium Bromide | Analytical purity | Shanghai Lingfeng chemical testAgents Ltd |
The vector SBA-15 used in the examples was prepared as follows:
in the experiment, a mesoporous molecular sieve SBA-15 is synthesized by taking a nonionic surfactant P123 as a template agent and Tetraethoxysilane (TEOS) as a silicon source in an acid environment by adopting a hydrothermal crystallization method, wherein the mass ratio of the raw materials is 1 TEOS: x P123, 123: 5.88 HCl: 136H 2O. The specific process is as follows: triblock surfactant P123(EO20PO70EO20, M ═ 5800) was dissolved in 125g of deionized water at a constant temperature of 40 ℃, and then 23.6g of a HCl solution with a mass fraction of 36 to 38% was added. After complete dissolution, 8.5g of tetraethoxysilane is slowly added, and vigorous stirring is maintained for 24 h. And then transferring the mixed solution into a polytetrafluoroethylene bottle, crystallizing, filtering, washing, drying, and finally roasting the dried product at 550 ℃ for 6 hours (the heating rate is 1 ℃/min) to remove the template agent, thus obtaining white powder of the carrier SBA-15 mesoporous molecular sieve.
Example 1
Selecting citric acid monohydrate (CA.H)2O) as an additive, nickel nitrate and ammonium molybdate as nickel salts and promoter metal precursors. 1.0g of SBA-15 white powder (specific surface area 838 m) was weighed out2(ii)/g, micropore surface area 118m2G, pore volume of 1.21cm3Per g, micropore volume of 0.04cm3Per g, pore diameter of 6.2nm and pore wall of 4nm), 0.43g of nickel nitrate, 0.013g of ammonium molybdate and 0.1g of CA.H2Dissolving O in 5g of deionized water, adding 1.0g of SBA-15 white powder into the solution at room temperature, soaking for 12h, vacuum drying for 12h at 50 ℃, roasting for 5h in air at 500 ℃, naturally cooling to room temperature, grinding into fine powder, and filtering by using a 100-mesh sample sieve to prepare a high-dispersion limited-area bimetallic low-temperature methanation catalyst which is marked as Mo-Ni/S15-CA, wherein the loading amounts of Ni and Mo are respectively 10 wt% and 1 wt%; the HRTEM-EDS result is shown in FIG. 1, FIG. 1 is an HRTEM-EDS spectrum of the bimetallic low-temperature methanation catalyst Mo-Ni/S15-CA prepared in example 1 of the invention, in the diagram, the left side shows the structure of the catalyst and the distribution of active metals, wherein black particles are active metals, and the right side showsThe energy spectrum diagram shows the elements present in the left diagram. As is clear from the figure, the active component is uniformly distributed in the carrier pore channels, and the EDS spectrum confirms the presence of Ni and Mo elements. The specific surface area of the catalyst is 659m2Per g, micropore surface area 62m2Per g, pore volume of 0.96cm3Per g, pore volume of the micropores was 0.02cm3(ii)/g, pore diameter is 5.7 nm.
Example 2
The preparation method is the same as that of example 1, except that: 0.56g of nickel acetate tetrahydrate is used for replacing 0.43g of nickel nitrate in example 1, 0.133g of lanthanum nitrate is used for replacing 0.013g of ammonium molybdate, 0.03g of ethylene glycol is used for replacing 0.1g of CA, and the high-dispersion limited-range bimetallic low-temperature methanation catalyst is marked as La-Ni/S15-EG, wherein the loading amounts of Ni and La are 5 wt% and 2 wt% respectively; the HRTEM-EDS is shown in FIG. 2, FIG. 2 is an HRTEM-EDS spectrum of the bimetallic low-temperature methanation catalyst La-Ni/S15-EG prepared in example 2 of the invention, in the graph, the left side shows the structure of the catalyst and the distribution of active metals, wherein black particles are the active metals, and the right side is a spectrum diagram which shows elements existing in the left side. As can be seen from the figure, the black particles are active metals, which are highly dispersed within the carrier pore channels, while the presence of the metals Ni and La is confirmed by EDS. The specific surface area of the catalyst is 626m2(ii)/g, micropore surface area 71m2Per g, pore volume of 0.90cm3Per g, pore volume of the micropores was 0.02cm3Per g, pore size 5.6 nm.
Example 3
The preparation method is the same as that of example 1, except that: replacing 0.013g of ammonium molybdate with 0.028g of ferric nitrate, replacing 0.1g of CA with 0.17g of CTAB, drying in vacuum at 80 ℃ for 5h, then roasting in air at 600 ℃ for 8h, naturally cooling to room temperature to prepare a high-dispersion limited-range bimetal low-temperature methanation catalyst which is recorded as Fe-Ni/S15-CTAB, wherein the loading amounts of Ni and Fe are respectively 10 wt% and 0.5 wt%; HRTEM-EDS As shown in FIG. 3, FIG. 3 is an HRTEM-EDS spectrum of a bimetallic low-temperature methanation catalyst Fe-Ni/S15-CTAB prepared in example 3 of the invention, wherein the left graph shows the structure of the catalyst and the distribution of active metals, black particles are active metals, the right graph is an energy spectrum graph showing the existence of active metals in the left graphThe elements of (a) are (b). The specific surface area of the catalyst is 608m2Per g, micropore surface area of 72m2Per g, pore volume of 0.89cm3Per g, pore volume of the micropores was 0.02cm3Per g, pore size 5.6 nm.
Example 4
The application of the bimetallic low-temperature methanation catalyst prepared in the embodiments 1 to 3 in the reaction of preparing methane from synthesis gas is described.
The bimetallic low-temperature methanation catalysts prepared in the embodiments 1 to 3 are respectively filled in a fixed bed micro-reactor with the inner diameter of 8mm, and N is used before reaction2Blowing air, and introducing pure H at 500 deg.C2The catalyst was reduced for 2 hours. And then catalyzing the methanation reaction of the raw material gas by using the catalyst obtained after reduction. The composition of the feed gas and the catalytic reaction conditions were as follows:
the raw material gas composition is as follows: CO: 20% of H2:60%,N2:20%;
Catalyst loading: 400 mg;
reaction temperature: 250 ℃;
reaction pressure: normal pressure;
the reaction space velocity: 30,000 mL/g.h.
The raw material gas composition and the catalytic reaction conditions applicable to the bimetallic low-temperature methanation catalyst provided by the invention can also be as follows: the volume space velocity of the synthesis gas is 3000-30000 mL/g.h, the pressure is from normal pressure to 3.0Mpa, the temperature is 200-500 ℃, and H in the synthesis gas2The ratio of/CO is 2-4.
CO conversion and CH were determined and calculated as follows4The selectivity results are shown in fig. 4, and fig. 4 is a comparative graph showing the low temperature methanation performance of the catalysts prepared in examples 1-3 and comparative example 1 of the present invention in example 4.
Conversion rate of CO: xCO(1-amount of CO contained in product/amount of CO contained in raw material gas). times.100%
CH4And (3) selectivity: sCH4Is converted to CH4CO amount of (2)/amount of CO conversion) × 100%
Example 5
The method is used for illustrating the high temperature resistance of the bimetallic low-temperature methanation catalyst prepared in the examples 1-3 in the reaction of preparing methane from synthesis gas.
The bimetallic low-temperature methanation catalyst prepared in the embodiment 1-3 is filled in a fixed bed micro-reactor with the inner diameter of 8mm, and N is used before reaction2Purging air, reusing pure H2Reducing catalyst with CO and H as raw material gas2Mixing, filtering, introducing into a reactor, measuring the activity of the catalyst at 350 ℃, calcining the catalyst at 700 ℃ for 2h in the atmosphere of raw material gas, and cooling the reaction temperature to 350 ℃ to examine the activity of the catalyst. The gas obtained by the reaction was analyzed on-line by gas chromatography, and the CO conversion and CH were calculated in the same manner as in example 44The selectivity results are shown in Table 2. The test conditions were: the temperature T is 350 ℃, the pressure is normal pressure, and the feed gas N2:CO:H21:1:3, space velocity 30,000 mL/g.h.
Comparative example 1
This comparative example serves to illustrate the low temperature methanation catalyst for carbon monoxide of the prior art and its use in the synthesis gas to methane reaction.
Respectively using SBA-15, MCM-41 and Al2O3And SiO2As a carrier, obtaining the catalyst which is marked as Ni/SBA-15, Ni/MCM-41 and Ni/Al according to an isometric impregnation method2O3、Ni/SiO2Wherein the Ni loading was 10 wt%, and the catalytic performance was examined by applying the same method as in example 4 to the CO methanation reaction, the results are shown in FIG. 4, and FIG. 4 is a comparative graph showing the low-temperature methanation performance of the catalysts prepared in examples 1-3 and comparative example 1 according to the present invention in example 4.
Comparative example 2
This comparative example serves to illustrate the carbon monoxide methanation catalyst of the prior art and its high temperature resistance in the synthesis gas to methane reaction.
The catalyst obtained in comparative example 1 was examined for its catalytic performance in the methanation reaction of CO in the same manner as in example 5, and the results are shown in Table 2.
TABLE 2
As can be seen from FIG. 4, the high-dispersion limited-range bimetallic low-temperature methanation catalyst prepared by the organic additive assisted impregnation method has the CO conversion rate and CH at the low temperature of 250 DEG C4The selectivity is obviously improved, the CO conversion rate is improved from about 30 percent to more than 98 percent, and the CH content is4The selectivity is improved from less than 80 percent to more than 92 percent. In addition, as can be seen from table 2, after the high-dispersion limited-range bimetallic low-temperature methanation catalyst prepared by the organic additive assisted impregnation method is calcined for 2 hours at 700 ℃ in the atmosphere of raw material gas, the conversion rate of CO is still maintained to be more than 99.5%, and CH is4The yield reduction range is within 2 percent. FIG. 5 is an HRTEM spectrum of the bimetallic low-temperature methanation catalyst in example 5 of the invention after the bimetallic low-temperature methanation catalyst Mo-Ni/S15-CA prepared in example 1 is tested for high temperature resistance in the reaction of preparing methane from synthesis gas. FIG. 6 is an HRTEM spectrum of the bimetallic low-temperature methanation catalyst in example 5 of the invention after the bimetallic low-temperature methanation catalyst La-Ni/S15-EG prepared in example 2 is used for testing high-temperature resistance in a reaction for preparing methane from synthesis gas. FIG. 7 is an HRTEM spectrum of the bimetallic low-temperature methanation catalyst after the bimetallic low-temperature methanation catalyst Fe-Ni/S15-CTAB prepared in example 5 is used for testing high-temperature resistance in a reaction for preparing methane from synthesis gas. It can also be seen from fig. 5 to 7 that the active component in the catalyst after high-temperature calcination still maintains high dispersion. While Ni/SBA-15, Ni/MCM-41, Ni/Al in the comparative examples2O3And Ni/SiO2The CO conversion rates are respectively reduced by 65.8%, 73.4%, 70.0% and 74.3%, which shows that the high-dispersion limited-range bimetallic low-temperature methanation catalyst prepared by adopting an organic additive assisted impregnation method has good low-temperature catalytic activity, good high-temperature resistance and great industrial prospect.
The foregoing shows and describes the general principles, essential features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are given by way of illustration of the principles of the present invention, and that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (10)
1. A bimetallic low-temperature methanation catalyst is characterized in that: taking mesoporous molecular sieve SBA-15 as a carrier, taking metal Ni as a main active component, and taking at least one of transition metal or rare earth metal as an auxiliary metal; wherein, the content of metal Ni is 5 wt% -20 wt%, the content of auxiliary metal is 0.5 wt% -2 wt%, and the rest is mesoporous molecular sieve SBA-15.
2. The bimetallic low-temperature methanation catalyst of claim 1, characterized in that: the specific surface area of the mesoporous molecular sieve SBA-15 is 600-1000 m2A micropore surface area of 100 to 200m2The pore diameter is 4.6-30 nm, the pore wall is 3-9 nm, and the pore volume is 0.8-1.3 cm3The volume of the micropores is 0.02-0.04 cm3/g。
3. The bimetallic low-temperature methanation catalyst of claim 1, characterized in that: the transition metal is selected from at least one of Fe, Mo and Co;
the rare earth metal is selected from at least one of La and Ce.
4. The bimetallic low-temperature methanation catalyst of claim 1, characterized in that: the specific surface area of the bimetallic low-temperature methanation catalyst is 600-660 m2Per g, the surface area of the micropores is 60-75 m2The pore volume is 0.85-1 cm3The volume of the micropores is 0.01-0.03 cm3(ii)/g, the pore diameter is 5.5 to 5.7 nm.
5. A method for preparing the bimetallic low-temperature methanation catalyst as claimed in any one of claims 1 to 4, characterized in that: the method comprises the following steps:
dissolving nickel salt, a metal precursor and an additive in deionized water, wherein the mass ratio of the nickel salt to the metal precursor to the additive to the deionized water is (1-100): 1: (0.1-15): (10-1000), soaking the mesoporous molecular sieve SBA-15 in the mixed solution at room temperature for 2-12 hours, wherein the mesoporous molecular sieve SBA-15 accounts for 1-90% of deionized water by mass percent, vacuum drying is carried out at the temperature of 30-80 ℃ for 5-12 hours, roasting is carried out at the temperature of 400-800 ℃ for 1-10 hours, and cooling and grinding are carried out to obtain the bimetallic low-temperature methanation catalyst.
6. The preparation method of the bimetallic low-temperature methanation catalyst according to claim 5, characterized in that: the nickel salt is at least one of nickel chloride, nickel sulfate, nickel acetate, nickel oxalate and nickel nitrate.
7. The preparation method of the bimetallic low-temperature methanation catalyst according to claim 5, characterized in that: the metal precursor is a compound containing at least one of the following metals: fe. Mo, Co, La, Ce; specifically, at least one selected from ammonium molybdate, lanthanum nitrate and ferric nitrate.
8. The preparation method of the bimetallic low-temperature methanation catalyst according to claim 5, characterized in that: the additive is at least one of citric acid, cetyl trimethyl ammonium bromide, ethylene glycol, glucose, sorbitol or sodium dodecyl sulfate.
9. Use of a bimetallic low temperature methanation catalyst as claimed in any one of claims 1 to 4 in the production of methane from synthesis gas.
10. Use of the bimetallic low temperature methanation catalyst of claim 9 in the production of methane from synthesis gas, characterized in that: the conditions for preparing methane from the synthesis gas are as follows: the volume airspeed of the synthetic gas is 3000-30000 mL/g.h, and the pressure is from normal pressure to normal pressure3.0Mpa at 200-500 deg.C, H in synthetic gas2The ratio of/CO is 2-4.
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