Multi-metal mixed oxide catalyst as well as preparation method and application thereof

Abstract

The invention discloses a multi-metal mixed oxide catalyst as well as a preparation method and application thereof. The catalyst comprises calcium aluminum oxide as a carrier, and nickel and modified transition metal as active components, and the modified transition metal is selected from any one or more of iron, cobalt, ruthenium and zinc. The catalyst disclosed by the invention is applied to a reaction for preparing synthesis gas by catalyzing CH4-CO2 reforming, the adsorption activation capability of the catalyst on CH4 and CO2 molecules can be remarkably enhanced, and the catalyst has high CH4 and CO2 conversion rates and shows a good industrial application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and in particular to a multi-metal mixed oxide catalyst and a preparation method and application thereof. Background Art

[0002] The direct emission of low-concentration coal mine gas (methane concentration below 30%) has led to a large amount of resource waste and serious greenhouse effect. Therefore, in the current global context of environmental pollution and resource scarcity, it is imperative to take effective measures to transform and utilize the emitted methane and other greenhouse gases such as carbon dioxide.

[0003] Dry reforming of methane (DRM) is an efficient conversion method that can not only process two greenhouse gases, carbon dioxide and methane, but also obtain synthesis gas, which can be used as raw materials for a variety of industrial production. It is of great help to environmental protection and resource recycling. Since the reaction is an endothermic reaction, it needs to be carried out at high temperature. In order to reduce the activation energy of the reaction and increase the conversion rate, the role of the catalyst is indispensable. Ni-based catalysts have a strong ability to break hydrogen and can quickly crack methane. The carbon species produced by the reaction can promote the conversion of carbon dioxide into carbon monoxide, forming a perfect closed loop.

[0004] However, with the deepening of research, it was found that Ni-based catalysts have some problems in the DRM reaction process, mainly manifested in poor reaction stability and the inability to carry out a long-term stable reaction process. The main reason is that Ni-based catalysts quickly produce a large amount of carbon deposits due to their excellent hydrogen-breaking ability, which is greater than the conversion rate of carbon dioxide. Excessive carbon deposits cover the surface of the active component Ni, thus leading to the deactivation of the catalyst. Another main reason is that the active component is deactivated by sintering at high temperature. Summary of the invention

[0005] The main purpose of the present invention is to provide a multi-metal mixed oxide catalyst with good catalytic activity and long service life, and a preparation method and application thereof.

[0006] To achieve the above objectives, the present invention provides a multi-metal mixed oxide catalyst, comprising calcium aluminum oxide as a carrier, and nickel and a modified transition metal as active components, wherein the modified transition metal is selected from any one or more of iron, cobalt, ruthenium and zinc.

[0007] Furthermore, the content of nickel is 5-15wt%, the content of modified transition metal is 1-5wt%, the content of calcium oxide is 3-5wt%, and the balance is aluminum oxide.

[0008] The present invention also provides a method for preparing the multi-metal mixed oxide catalyst, comprising the following steps:

[0009] (1) Preparation of multi-metal mixed oxide precursors

[0010] A precursor salt of aluminum, a precursor salt of calcium, a precursor salt of nickel and a precursor salt of a modified metal are added to deionized water, stirred, and then a precipitant is gradually added until the solution suddenly changes into a gel state, and the stirring is continued until a solution state containing flocculent precipitates is formed, and finally heated and stirred, and then solids are collected by filtration, and the solids are dried and ground to obtain a multi-metal mixed oxide precursor;

[0011] (2) Calcination of multi-metal mixed oxide precursors

[0012] The multi-metal mixed oxide precursor is loaded into a plasma reactor, air is introduced, and a calcination treatment is performed under the assistance of the ionization effect of the plasma reactor to obtain the multi-metal mixed oxide catalyst.

[0013] Furthermore, in step (1), the precipitant is prepared by mixing a 2 mol / L sodium hydroxide solution and a 1 mol / L sodium carbonate solution in a volume ratio of 1:1.

[0014] Furthermore, in step (1), the temperature of the heating and stirring treatment is 60 to 80° C., and the time is 24 to 36 hours.

[0015] Furthermore, in step (2), the specific process of the calcination treatment is: heating the temperature to 100-800°C at a heating rate of 4°C / min, and calcining at this temperature for 5 hours.

[0016] Furthermore, in step (2), the discharge power of the plasma reactor is 40-60 W, and the distance between the plates is 4 mm.

[0017] The present invention also provides an application of the above catalyst in catalytic reforming of coal mine gas to produce synthesis gas.

[0018] The present invention also provides a method for catalytic CH4-CO2 reforming to produce synthesis gas, comprising the following steps: reducing the above-mentioned catalyst in a 10 vol% H2 / N2 atmosphere and a temperature of 650-750°C for 2-4 hours, then uniformly mixing with inert silicon carbide in a mass ratio of 1:2-5 through solid phase grinding for 10-20 minutes, and finally catalyzing CH4-CO2 reforming to produce synthesis gas in a vertical micro fixed bed reactor.

[0019] Furthermore, the reaction conditions are: the amount of catalyst is 0.05-0.4 g, the molar ratio of CH4 to CO2 in the reaction feed is 1-1.25, and the gas feed space velocity is 40000-120000 mL·h -1 ·gcat -1, the reaction temperature is 650-850° C. In the process of implementing the present invention, the inventors found that under this reaction condition, the catalyst can still show a high methane / carbon dioxide conversion rate after 700 hours, the carbon dioxide conversion rate exceeds 80%, the methane conversion rate exceeds 90%, and the H2 / CO ratio in the synthesis gas is 0.8-1.2.

[0020] The present invention uses calcium aluminum oxide as a carrier, which brings a large number of basic sites to the catalyst, thereby greatly enhancing the adsorption of carbon dioxide by the catalyst, and can better increase its conversion rate. At the same time, the adsorption of carbon dioxide also further increases the conversion of carbon deposits during the reaction process, effectively enhancing the stability of the catalyst. By adding modified transition metals, the ability of Ni to crack H can be slightly inhibited, and the conversion of carbon deposits by the catalyst is enhanced, which effectively improves the stability of the catalyst and greatly reduces the generation of carbon covering the surface of the active component.

[0021] The present invention can better mix various metals through the co-precipitation method to obtain a highly dispersed catalyst, which is not only beneficial to reducing the particle size of the active components, but also can well solve the sintering problem of the catalyst at high temperature, and effectively solves the sintering problem of the two major problems of carbon deposition and sintering. The plasma-assisted calcination better excites the active components in the catalyst and fixes them well in the catalyst, better anchors the active metals, well solves the catalyst sintering problem, and enhances the stability of the catalyst.

[0022] The beneficial effects of the present invention are embodied in:

[0023] 1. The catalyst of the present invention has the characteristics of green economy and high structural stability. When used in the catalytic CH4-CO2 reforming reaction to produce synthesis gas, it exhibits a high methane / carbon dioxide conversion rate in the 700h catalytic CH4-CO2 reforming reaction to produce synthesis gas, with a carbon dioxide conversion rate exceeding 80%, a methane conversion rate exceeding 90%, and a H2 / CO ratio in the synthesis gas of 0.8 to 1.2.

[0024] 2. The raw materials used in the catalyst of the present invention are all low-cost metals, which effectively reduces the preparation cost of the catalyst while ensuring the performance.

[0025] 3. Compared with other nickel-based catalysts, the catalyst of the present invention enhances the anchoring of active metals through the doping of modified transition metals and the effect of calcium aluminum oxide carriers, and under plasma-assisted calcination, effectively forming a highly dispersed system. Under these favorable conditions, the adsorption and conversion of CO2 is greatly promoted, thereby promoting the removal of carbon deposits, and effectively improving the catalyst's anti-sintering ability, thereby greatly improving the stability of the catalyst, and meeting the requirements for the use of the catalyst from laboratory to industrial application.

[0026] 4. The catalyst of the present invention is used in the catalytic CH4-CO2 reforming reaction to produce synthesis gas, which can significantly enhance the catalytic adsorption and activation ability of CH4 and CO2 molecules, has high CH4 and CO2 conversion rates, and shows good prospects for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The XRD pattern of catalyst No. 1 prepared in Example 1;

[0028] Figure 2 This is the N2 adsorption-desorption isotherm diagram of catalyst No. 1 prepared in Example 1;

[0029] Figure 3 This is the pore size distribution diagram of catalyst No. 1 prepared in Example 1;

[0030] Figure 4 TEM image of catalyst #1 prepared in Example 1;

[0031] Figure 5 This is a lattice fringe spacing analysis diagram of catalyst No. 1 prepared in Example 1;

[0032] Figure 6 This is a CO2 programmed temperature desorption diagram of catalyst No. 1 prepared in Example 1. DETAILED DESCRIPTION

[0033] In order to make the technical scheme of the present invention more clearly understood by those skilled in the art, the following embodiments are listed for illustration. It should be noted that the following embodiments do not limit the protection scope of the present invention.

[0034] Unless otherwise specified, the raw materials, reagents or devices used in the following examples can be obtained from conventional commercial sources or by existing known methods; unless otherwise specified, the methods used in the examples of the present invention are methods known to those skilled in the art. Among them:

[0035] The outer electrode of the plasma reactor is a quartz tube (outer diameter Φ25mm, inner diameter Φ12mm), the inner electrode is stainless steel 316 (diameter Φ8mm), the single-sided discharge gap is 4mm, the effective discharge width is 201mm, and the discharge power is 20~100W.

[0036] Inert silicon carbide was purchased from Shanghai MacLean Biochemical Technology Co., Ltd. with a particle size of 200 mesh.

[0037] Example 1

[0038] Preparation of multi-metal mixed oxide catalysts

[0039] The multi-metal mixed oxide catalyst prepared in this embodiment has a nickel content of 12wt%, an iron content of 2.5wt%, a calcium oxide content of 5wt%, and the balance is aluminum oxide. The preparation method is as follows:

[0040] (1) Add 50 ml of deionized water into a beaker, weigh 0.6352 g of nickel nitrate hexahydrate, 0.1808 g of ferric nitrate hexahydrate, 11.1927 g of aluminum nitrate nonahydrate, and 0.2946 g of calcium nitrate tetrahydrate as precursors and pour them into the beaker, and stir at 40°C for 3 h; then mix 20 ml of a 2 mol / L sodium hydroxide solution and an equal volume of a 1 mol / L sodium carbonate solution as a precipitant, and gradually drip them into the beaker until the solution in the beaker suddenly changes into a gel state, stop dripping the precipitant, continue stirring until it becomes a solution state containing flocculent precipitates, finally raise the temperature to 60°C and continue stirring for 36 h, then vacuum filter and collect the solid, dry the solid in an oven at 105°C for 12 h, and grind to obtain a multi-metal mixed oxide precursor.

[0041] (2) 1 g of the multi-metal mixed oxide precursor was loaded into a quartz tube of a plasma reactor, air was introduced, the ion reactor was started, the discharge power was adjusted to 50 W, the temperature was raised from room temperature to 400 ° C at a heating rate of 4 ° C per minute, and the mixture was calcined at a constant temperature for 5 h, and then naturally cooled to room temperature to obtain the multi-metal mixed oxide catalyst, catalyst number #1.

[0042] Example 2

[0043] Preparation of multi-metal mixed oxide catalysts

[0044] The multi-metal mixed oxide catalyst prepared in this embodiment has a nickel content of 10wt%, a zinc content of 1wt%, a calcium oxide content of 3wt%, and the balance is aluminum oxide. The preparation method is as follows:

[0045] (1) Add 50 ml of deionized water into a beaker, weigh 0.5294 g of nickel nitrate hexahydrate, 0.0488 g of zinc nitrate hexahydrate, 11.9574 g of aluminum nitrate nonahydrate, and 0.1768 g of calcium nitrate tetrahydrate as precursors and pour them into the beaker, and stir at 40° C. for 3 h; then, mix 20 ml of a 2 mol / L sodium hydroxide solution and an equal volume of a 1 mol / L sodium carbonate solution as a precipitant, and gradually drip them into the beaker until the solution in the beaker suddenly forms a gel, stop dripping the precipitant, continue stirring until it becomes a solution containing flocculent precipitates, finally raise the temperature to 70° C. and continue stirring for 30 h, then vacuum filter and collect the solid, dry the solid in an oven at 105° C. for 12 h, and grind to obtain a multi-metal mixed oxide precursor.

[0046] (2) 1 g of the multi-metal mixed oxide precursor was loaded into a quartz tube of a plasma reactor, air was introduced, the ion reactor was started, the discharge power was adjusted to 40 W, the temperature was raised from room temperature to 500 ° C at a heating rate of 4 ° C per minute, and the mixture was calcined at a constant temperature for 5 h, and then naturally cooled to room temperature to obtain the multi-metal mixed oxide catalyst, catalyst number #2.

[0047] Example 3

[0048] Preparation of multi-metal mixed oxide catalysts

[0049] The multi-metal mixed oxide catalyst prepared in this embodiment has a nickel content of 15wt%, a cobalt content of 5wt%, a calcium oxide content of 5wt%, and the balance is aluminum oxide. The preparation method is as follows:

[0050] (1) Add 50 ml of deionized water into a beaker, weigh 0.7941 g of nickel nitrate hexahydrate, 0.2471 g of cobalt nitrate hexahydrate, 10.428 g of aluminum nitrate nonahydrate, and 0.2946 g of calcium nitrate tetrahydrate as precursors and pour them into the beaker, and stir at 40°C for 3 h; then mix 20 ml of a 2 mol / L sodium hydroxide solution and an equal volume of a 1 mol / L sodium carbonate solution as a precipitant, and gradually drip them into the beaker until the solution in the beaker suddenly changes into a gel state, stop dripping the precipitant, continue stirring until it becomes a solution state containing flocculent precipitates, finally raise the temperature to 80°C and continue stirring for 24 h, then vacuum filter and collect the solid, dry the solid in an oven at 105°C for 12 h, and grind to obtain a multi-metal mixed oxide precursor.

[0051] (2) 1 g of the multi-metal mixed oxide precursor was loaded into a quartz tube of a plasma reactor, air was introduced, the ion reactor was started, the discharge power was adjusted to 60 W, the temperature was raised from room temperature to 600 ° C at a heating rate of 4 ° C per minute, and the mixture was calcined at a constant temperature for 5 h, and then naturally cooled to room temperature to obtain the multi-metal mixed oxide catalyst, catalyst number #3.

[0052] Example 4

[0053] Preparation of multi-metal mixed oxide catalysts

[0054] The multi-metal mixed oxide catalyst prepared in this embodiment has a nickel content of 5wt%, a cobalt content of 1.5wt%, a ruthenium content of 1.5wt%, a calcium oxide content of 5wt%, and the balance is aluminum oxide. The preparation method is as follows:

[0055] (1) Add 50 ml of deionized water into a beaker, weigh 0.2647 g of nickel nitrate hexahydrate, 0.0741 g of cobalt nitrate hexahydrate, 0.0471 g of trinitronitrosyl ruthenium, 12.0965 g of aluminum nitrate nonahydrate, and 0.2946 g of calcium nitrate tetrahydrate as precursors and pour them into the beaker, and stir at 40° C. for 3 h; then, mix 20 ml of 2 mol / L sodium hydroxide and an equal volume of 1 mol / L sodium carbonate solution as a precipitant, and gradually drip them into the beaker until the solution in the beaker suddenly forms a gel, stop dripping the precipitant, continue stirring until it becomes a solution containing flocculent precipitates, finally raise the temperature to 60° C. and continue stirring for 32 h, then vacuum filter and collect the solid, dry the solid in an oven at 105° C. for 12 h, and grind to obtain a multi-metal mixed oxide precursor.

[0056] (2) 1 g of the multi-metal mixed oxide precursor was loaded into a quartz tube of a plasma reactor, air was introduced, the ion reactor was started, the discharge power was adjusted to 50 W, the temperature was raised from room temperature to 700 ° C at a heating rate of 4 ° C per minute, and the mixture was calcined at a constant temperature for 5 h, and then naturally cooled to room temperature to obtain the multi-metal mixed oxide catalyst, catalyst number #4.

[0057] Comparative Example 1

[0058] Preparation of comparative catalysts

[0059] The catalyst in this comparative example is prepared according to the method of Example 1, with the only difference being that the precursor raw materials are replaced with: 0.6352g of nickel nitrate hexahydrate, 11.5403g of aluminum nitrate nonahydrate, and 0.2946g of calcium nitrate tetrahydrate, and the final catalyst having a nickel content of 12wt%, a calcium oxide content of 5wt%, and the balance of aluminum oxide, is obtained, catalyst number #5.

[0060] Comparative Example 2

[0061] Preparation of comparative catalysts

[0062] The catalyst in this comparative example is prepared according to the method of Example 1, with the only difference being that the precursor raw materials are replaced with: 0.6352g nickel nitrate hexahydrate, 0.1808g ferric nitrate hexahydrate, and 11.8879g aluminum nitrate nonahydrate, and the final catalyst having a nickel content of 12wt%, an iron content of 2.5wt%, and the balance aluminum oxide, is obtained, catalyst number #6.

[0063] Comparative Example 3

[0064] Preparation of comparative catalysts

[0065] In this comparative example, the catalyst was prepared in the same manner as in Example 1, with the only difference being that the ionization of the ion reactor was turned off during the calcination process in step (2). The catalyst finally obtained was catalyst number #7.

[0066] Experimental Example 1

[0067] Structure Determination of Multi-metal Mixed Oxide Catalysts

[0068] The structure of catalyst No. 1 obtained in Example 1 was analyzed. Figures 1 to 6 shown.

[0069] See also Figure 1 , XRD spectrum of catalyst 1# Figure 2 Characteristic diffraction peaks corresponding to Al2O3 were detected at θ=37.8°, 42.2°, and 62.9°, and no obvious diffraction peaks of other metals appeared, indicating that the dispersion of other metals was good and there was no obvious crystallization phenomenon. In theory, calcium would decompose into CaO after forming calcium carbonate precipitation and then being calcined, but due to the low content of calcium oxide, poor crystallinity, good dispersion, and being in an amorphous state, there was no obvious characteristic peak of CaO in XRD.

[0070] See also Figure 2 According to the IUPAC classification, catalyst 1# exhibits a type IV isotherm accompanied by an H3 type hysteresis loop, which indicates that the catalyst has an obvious mesoporous channel structure.

[0071] See also Figure 3 The pore size distribution of catalyst #1 concentrated at 10 nm further proves the existence of mesoporous channel structure, which can better promote the dispersion of active metals and enhance mass transfer during the reaction.

[0072] See also Figure 4 , Figure 5 From the TEM image and lattice fringe spacing analysis diagram of catalyst No. 1 shown, it can be observed that the active metal is evenly dispersed on the calcium aluminum oxide carrier, which is conducive to exposing more active centers, promoting the reaction performance of the catalyst, accelerating the adsorption of methane during methane dry reforming and subsequent activation and cracking. At the same time, it can be seen from the lattice fringes that Ni is successfully loaded on the calcium aluminum oxide carrier. At the same time, it can also be seen that some active components are not entirely on the surface of the carrier, and some enter the interior of the carrier to better anchor the metal and enhance the interaction between the metal and the carrier, thereby improving the catalyst's anti-sintering ability.

[0073] See also Figure 6 As shown in the figure, during the CO2 programmed temperature desorption process, catalyst 1# showed two obvious desorption peaks at 126°C and 314°C, respectively, which indicated the presence of a large number of weak alkaline sites and medium alkaline sites. In the methane dry reforming reaction, weak alkaline sites and medium alkaline sites have better ability to adsorb carbon dioxide, thereby further promoting the activation of carbon dioxide, accelerating the consumption of carbon species, and improving the stability of the catalyst.

[0074] Experimental Example 2

[0075] Performance test of CH4-CO2 reforming to synthesis gas over multi-metal mixed oxide catalysts

[0076] Test method: 0.05-0.3g of catalyst was ground with inert silicon carbide solid phase at a mass ratio of 1:4 for 15min, then loaded into a vertical micro fixed bed reactor and subjected to reduction treatment at 650-750℃ for 2-4h in a 100mL / min 10vol% H2 / N2 flow for catalytic reaction. The molar ratio of methane to carbon dioxide in the feed was 1 and the gas feed space velocity was 40000mL·h -1 ·g cat -1 , the reaction temperature is 650-850° C. The specific reaction conditions and results are shown in Table 1.

[0077] Table 1

[0078]

[0079] Note: The deactivation time is the time point when the methane conversion rate of the catalyst decreases by 30%.

[0080] From the above results, it can be seen that the catalyst obtained by the preparation method of the present invention has strong performance for CH4-CO2 reforming to produce synthesis gas, the conversion rate of methane and carbon dioxide is above 80%, the H2 / CO ratio in the product is between 0.8 and 1.1, which is close to the ideal product, and can maintain a service life of more than 700 hours.

[0081] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A multi-metal mixed oxide catalyst, characterized in that: The invention comprises calcium aluminum oxide as a carrier, nickel and a modified transition metal as active components, wherein the modified transition metal is selected from any one or more of iron, cobalt, ruthenium and zinc.

2. The multi-metal mixed oxide catalyst according to claim 1, characterized in that: The content of nickel is 5-15wt%, the content of modified transition metal is 1-5wt%, the content of calcium oxide is 3-5wt%, and the balance is aluminum oxide.

3. The method for preparing a multi-metal mixed oxide catalyst according to claim 1 or 2, characterized in that: The following steps are involved: (1) Preparation of multi-metal mixed oxide precursors A precursor salt of aluminum, a precursor salt of calcium, a precursor salt of nickel and a precursor salt of a modified metal are added to deionized water, stirred, and then a precipitant is gradually added until the solution suddenly changes into a gel state, and the stirring is continued until a solution state containing flocculent precipitates is formed, and finally heated and stirred, and then solids are collected by filtration, and the solids are dried and ground to obtain a multi-metal mixed oxide precursor; (2) Calcination of multi-metal mixed oxide precursors The multi-metal mixed oxide precursor is loaded into a plasma reactor, air is introduced, and a calcination treatment is performed under the assistance of the ionization effect of the plasma reactor to obtain the multi-metal mixed oxide catalyst.

4. The method for preparing a multi-metal mixed oxide catalyst according to claim 3, characterized in that: In step (1), the precipitant is prepared by mixing a 2 mol / L sodium hydroxide solution and a 1 mol / L sodium carbonate solution in a volume ratio of 1:

1.

5. The method for preparing a multi-metal mixed oxide catalyst according to claim 3, characterized in that: In step (1), the temperature of the heating and stirring treatment is 60 to 80° C., and the time is 24 to 36 hours.

6. The method for preparing a multi-metal mixed oxide catalyst according to claim 3, characterized in that: In step (2), the specific process of the calcination treatment is: heating the temperature to 400-800°C at a heating rate of 4°C / min, and calcining at this temperature for 5 hours.

7. The method for preparing a multi-metal mixed oxide catalyst according to claim 3, characterized in that: In step (2), the discharge power of the plasma reactor is 40-60W, and the distance between the plates is 4mm.

8. Use of the multi-metal mixed oxide catalyst as claimed in claim 1 or 2 in catalytic reforming of coal mine gas to produce synthesis gas.

9. A method for preparing synthesis gas by catalytic CH4-CO2 reforming, characterized in that: The following steps are involved: The catalyst as claimed in claim 1 or 2 is reduced in a 10 vol% H2 / N2 atmosphere at a temperature of 650-750°C for 2-4 hours, then evenly mixed with inert silicon carbide at a mass ratio of 1:2-5 by solid phase grinding for 10-20 minutes, and finally catalyzed in a vertical micro fixed bed reactor for CH4-CO2 reforming to produce synthesis gas.

10. The method for preparing synthesis gas by catalytic CH4-CO2 reforming as claimed in claim 9, characterized in that: The reaction conditions are: the amount of catalyst is 0.05-0.4 g, the molar ratio of CH4 to CO2 in the reaction feed is 1-1.25, and the gas feed space velocity is 40000-120000 mL·h -1 ·gcat -1 , the reaction temperature is 650~850℃.

Images