An intermetallic NiMo alloy catalyst and its preparation method and application

Abstract

The present invention discloses an intermetallic NiMo alloy catalyst and a preparation method and application thereof. The catalyst is prepared by a liquid phase synthesis method: nickel acetylacetonate and molybdenum hexacarbonyl are used as precursors and prepared into a solution with a complexing agent; then reacted to obtain a NiMo alloy with an alloy structure. The alloy is used for partial oxidation of methane to achieve high activity and high selectivity to partially oxidize methane to produce synthesis gas, and has broad application potential in the field of methane reforming to produce hydrogen.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and in particular, relates to an intermetallic NiMo alloy catalyst and a preparation method thereof, and application of the catalyst in partial oxidation of methane to produce synthesis gas and hydrogen. Technical Background

[0002] Natural gas reforming to produce hydrogen is considered to be the most promising large-scale hydrogen production technology for the next generation. In recent years, with the continuous improvement of shale gas and methane hydrate development technology, how to efficiently convert large amounts of methane into energy (hydrogen energy) and chemicals (through synthesis gas conversion) has gradually become a key technical problem that needs to be solved urgently. Hydrogen energy, as a clean and renewable energy carrier that is currently being vigorously promoted, has received great attention from the world, especially the rapid development of hydrogen fuel cell vehicles, which has made distributed hydrogen refueling stations an indispensable condition for promoting the use of hydrogen energy. Methane reforming to produce hydrogen is currently one of the main sources of hydrogen in industry. Methane steam reforming (MSR) is a key link in industrial hydrogen production. In addition to the industrialized methane steam reforming technology, the most studied technology is the partial oxidation of methane (POM) technology. The reaction formula of methane partial oxidation is: CH4+ 1 / 2O2→CO+2H2 (i.e., carbon monoxide and hydrogen are obtained through the oxidation of methane). Compared with steam reforming to produce hydrogen, the methane partial oxidation process is more suitable for distributed hydrogen production. It has the advantages of lower reaction temperature, lower energy consumption, shorter response time, small equipment scale and low equipment cost. It can be carried out with less catalyst loading and higher space velocity, thus potentially replacing the steam reforming reactor with large footprint and high energy consumption, further reducing the footprint of the device and improving the energy efficiency of the system.

[0003] The current bottleneck of hydrogen production by partial oxidation of methane is still the difficulty in obtaining cheap, stable and efficient catalysts. Among the catalysts for hydrogen production by partial oxidation of methane, Ni-based catalysts are considered to have large-scale industrial application prospects due to their high methane catalytic conversion activity and high economy. However, due to the low Tamman temperature of metal Ni (590°C), in the reforming reaction, under high temperature and oxidizing atmosphere, the active component Ni is prone to carbon deposition or sintering and agglomeration, resulting in a sharp decrease in the number of exposed active sites of the catalyst and deactivation. The widely used method of regulating metal-support interaction (MSI) to stabilize metal Ni has been found to be closely related to the size of Ni particles. The construction of a core-shell structure to regulate the size of Ni particles can inhibit sintering and carbon deposition. However, metal Ni is still very easy to aggregate after long-term operation, and the atomic utilization efficiency is low, resulting in limited conversion rate and product selectivity (ChemCatChem, 2013, 5, 3781-3787.). In addition, metal oxides with strong anchoring ability and active oxygen supply capacity (such as perovskite, CeO2, La2O3) can be introduced to anchor Ni atoms and provide active oxygen species to promote methane activation and improve syngas selectivity. However, this strategy is limited by the oxygen supply capacity of the carrier, which limits its potential activity and requires the use of a large amount of rare earth metals. Raw materials and prices limit its large-scale industrial application (Applied Catalysis B: Environmental, 2015, 164, 135-143.; Applied Catalysis B: Environmental, 2017, 202, 473-488.). Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art. In view of the common problems in the existing methane partial oxidation reaction, such as the catalyst is easily deactivated by carbon deposition and sintering, the reaction temperature is high, the syngas selectivity is low, and the hydrogen production efficiency is low, a NiMo intermetallic alloy catalyst and a preparation method thereof are provided, and the application of the catalyst in the methane partial oxidation reaction is provided. The Ni atoms are isolated by the geometric electronic action of Mo to improve the performance of the catalyst - a CH4 conversion rate of 99.97% is achieved at 800°C, and the CO and H2 selectivities are 97.9% and 97%, respectively, which are far superior to other Ni-based catalysts reported so far.

[0005] In order to solve the above technical problems, the present invention is implemented by the following technical solutions:

[0006] An intermetallic NiMo alloy catalyst and a preparation method thereof, wherein Mo is doped into a Ni lattice to form a NiMo ordered intermetallic alloy, and the steps are as follows:

[0007] Step 1, weigh nickel acetylacetonate and molybdenum hexacarbonyl and uniformly disperse them in a solvent to prepare a precursor solution, wherein the molar ratio of the two metals Ni:Mo is (1-5): (1-10)

[0008] In step 1, select 60-70° C. and mechanically stir for 4-6 hours to form a precursor solution at a stirring speed of 100-300 revolutions per minute.

[0009] In step 1, the molar ratio of the two metals Ni:Mo is 1:(1-10).

[0010] In step 1, the solvent is oleylamine, oleic acid or benzyl ether.

[0011] Step 2: Place the precursor solution obtained in step 1 under an inert protective atmosphere, heat it from room temperature 20-25 degrees Celsius to 230-270 degrees Celsius at a rate of 10-20 degrees Celsius / min and keep it warm for 10-40 minutes to carry out alloying reaction, cool it naturally to room temperature 20-25 degrees Celsius, add anhydrous ethanol to precipitate the alloy.

[0012] In step 2, after anhydrous ethanol is added to precipitate the alloy, the alloy is washed with anhydrous ethanol and cyclohexane and centrifuged (such as at a centrifugal rate of 6000-10000 rpm), the lower alloy precipitate is retained, and after ultrasonic washing with cyclohexane, the alloy precipitate is ultrasonically dispersed in cyclohexane.

[0013] In step 2, the inert protective atmosphere is nitrogen, helium or argon.

[0014] In step 2, the temperature is raised to 230-250°C and kept warm for 20-30 minutes.

[0015] Step 3, the alloy obtained in step 2 is loaded on a carrier, and in a mixed atmosphere of hydrogen and inert protective gas, the temperature is raised to 550-600°C at a rate of 10-20°C / min, maintained for 2-4h, and then the temperature is raised to 800-900°C at a rate of 10-20°C / min, roasted and reduced for 6-10h, and naturally cooled to room temperature 20-25°C; in the mixed atmosphere, the volume percentage of hydrogen is 5-50%, and the gas flow rate is 50-500mL·min -1 .

[0016] In step 3, the support is commercial SBA-15 molecular sieve.

[0017] In step 3, the alloy obtained in step 2 is dispersed in cyclohexane by ultrasonication and then loaded on a carrier at a stirring rate of 300-600 rpm and a stirring temperature of 50-80°C.

[0018] In step 3, the inert protective gas is nitrogen, helium or argon.

[0019] In step 3, the volume percentage of hydrogen is 20-30%, and the gas flow rate is 100-300 mL·min -1 .

[0020] The catalyst of the present invention is used in the preparation of synthesis gas by partial oxidation of methane. The catalyst solid powder is pressed into tablets, sieved, and a granular catalyst with a size of 20-40 mesh is taken out and placed in a fixed bed device for partial oxidation of methane. The reaction atmosphere ratio is CH4:Air:N2=10:25:65, and the total flow rate is 100-500mL·min -1 , mass space velocity WHSV is 6000-60000mL CH4 g cat -1 h -1 .

[0021] The technical solution of the present invention introduces oxygen activated central Mo atoms to construct an ordered NiMo intermetallic alloy, stabilizes the active component Ni to prevent sintering deactivation, greatly improves the methane conversion rate and syngas selectivity, and has a large price advantage. It has great industrial application value for the partial oxidation reaction of methane to produce syngas and hydrogen. Specifically, the beneficial effects of the present invention are as follows:

[0022] (i) The NiMo intermetallic alloy catalyst developed by the present invention provides a design method for ordered unit-site Ni catalysts at the nanoscale, which can construct high-density, highly dispersed catalytic active sites. The catalyst has high activity, high product selectivity and high stability at 800°C.

[0023] (ii) The catalyst developed by the present invention is applied to the partial catalytic oxidation reaction of methane at 800°C, and has high activity and high product selectivity, which is much better than the Ni-based catalyst reported previously. It has cost and performance advantages in industrial applications, has the potential for industrial application, and is conducive to industrial promotion and use.

[0024] (III) The intermetallic NiMo alloy catalyst of the present invention has the advantages of high activity, high product selectivity, high stability and strong resistance to carbon deposition in the methane reforming reaction, achieving a CH4 conversion rate of 99.97% at 800°C, and CO and H2 selectivities of 97.9% and 97%, respectively. It has great industrial application prospects and is far superior to other Ni-based catalysts reported so far. See Tables 1 and 2 for details.

[0025] Table 1. Performance comparison of the intermetallic NiMo alloy catalyst of the present invention and reported Ni-based catalysts

[0026]

[0027] NG in the table stands for Not Given, which is not given in the literature.

[0028] Table 2. Performance comparison of the intermetallic NiMo alloy catalyst of the present invention and reported noble metal-based catalysts

[0029]

[0030] NG in the table stands for Not Given, which is not given in the literature. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The figure is a performance comparison chart of conversion rate and selectivity between the catalyst of the present invention and the reported catalysts.

[0032] Figure 2 This is a diagram showing the HRTEM microstructure test results of the intermetallic NiMo alloy catalyst of the present invention.

[0033] Figure 3 XRD spectra of metallic Ni and intermetallic NiMo alloy.

[0034] Figure 4 This is the AC-HAADF-TEM lattice structure magnification of the intermetallic NiMo alloy catalyst and the height distribution map of Ni and Mo atoms.

[0035] Figure 5 Schematic diagram of the structure of the catalyst of the present invention. DETAILED DESCRIPTION

[0036] The present invention is further described in detail below through specific examples. The following examples can enable those skilled in the art to more fully understand the present invention, but do not limit the present invention in any way.

[0037] Embodiment 1:

[0038] Step 1, weighing 1.285 parts by mass (one part by mass is 1 g) of nickel acetylacetonate and 1.32 parts by mass (one part by mass is 1 g) of molybdenum hexacarbonyl, dissolving them in 50 mL of oleylamine to prepare a precursor solution, wherein the molar ratio of the two metals Ni:Mo is ensured to be 1:1, and stirring at 60° C. for 6 hours;

[0039] Step 2, the precursor solution obtained in step 1 is placed in a 250mL three-necked flask, and then heated to 250°C at a rate of 20°C / min under N2 atmosphere, maintained at this temperature for 30min, cooled naturally to room temperature, 100mL of anhydrous ethanol is added to precipitate the alloy, washed with anhydrous ethanol and cyclohexane three times respectively, and then centrifuged at 8000rpm, retaining the lower alloy deposit, ultrasonically washed with cyclohexane three times, and the alloy deposit is ultrasonically dispersed in cyclohexane, loaded on SBA-15 molecular sieve (purchased from Nanjing Jichang Nano Technology Co., Ltd.), the alloy ratio is 5% (that is, the alloy mass is 5% of the mass of SBA-15 molecular sieve), stirred at 60°C for 6h, and after the solvent is evaporated, the powder is placed in a tubular furnace, in a 20% H2 / He atmosphere (that is, the hydrogen volume is 20% of the total volume of helium and hydrogen), and the gas flow rate is 100mL min -1 The temperature was raised to 600°C at a rate of 10°C / min, maintained for 4 h, then raised to 800°C, and calcined for 6 h.

[0040] Step 3: Press the catalyst solid powder into tablets, sieve, and take the granular catalyst with a size of 20-40 mesh and place it in a fixed bed device for methane partial oxidation reaction to test the reaction activity. The reaction atmosphere (volume) ratio is CH4:Air:N2=10:25:65, and the total flow rate is 100mL·min -1 , mass space velocity WHSV is 6000mL CH4 g cat -1 h -1 .

[0041] The methane conversion rate and syngas selectivity are calculated using the following formulas:

[0042] Conversion rate: (F CH4总 -F CH4余 ) / F CH4总

[0043] CO selectivity: F CO / (F CH4总 -F CH4余 )

[0044] H2 selectivity: F H2 / 2*(F CH4总 -F CH4余 )

[0045] At 800°C, the CH4 conversion rate reaches 99.9%, and the CO and H2 selectivities are 97.9% and 97% respectively. That is, the application of the catalyst of the present invention in the partial oxidation reaction of methane can obtain a mixed gas of methane, carbon monoxide and hydrogen. Figure 1It can be seen that the catalyst of the present invention has the highest performance among the current Ni-based catalysts, which is higher than most of the precious metal-based catalysts reported so far.

[0046] The reaction products were analyzed online by GC-2060 gas chromatograph produced by Shanghai Ruimin Instrument Co., Ltd., with a TCD thermal conductivity detector and TDX01 and 5A molecular sieve columns; the characterization instrument used for XRD was a D8 ADVANCE X-ray diffractometer with a Cu target Kα (60 kV, 80 mA, λ=1.5418 angstroms); the characterization instrument used for XPS was a PHI 1600ESCA instrument produced by PE, with an Al target (hν=1486.6 eV) as the X-ray source; the characterization instrument used for O2-TPO was a Micromeritics AutoChemII 2920 chemical adsorption instrument; and the characterization instrument used for TEM was a FEI Tecnai G2 F20. Figure 2 This is an enlarged HRTEM microstructure diagram of the intermetallic NiMo alloy catalyst of the present invention (including the line scan distribution diagram of Ni and Mo elements), showing the formation of the NiMo ordered intermetallic alloy. Figure 3 Figure 2 is the XRD spectrum of metallic Ni and intermetallic NiMo alloy. 2θ=44.5° corresponds to the (111) plane of Ni, and there is an obvious migration to low angles. According to Black's formula, it can be explained that the lattice spacing increases, proving that Mo is successfully incorporated into the Ni lattice, that is, the formation of NiMo ordered intermetallic alloy. Figure 4 This is the AC-HAADF-TEM lattice structure magnification of the intermetallic NiMo alloy catalyst and the Ni, Mo atomic height distribution diagram. It can be seen that the Ni and Mo atoms (bright spots are Mo, dark spots are Ni) are arranged in an orderly manner with a lattice spacing of 0.207nm, which is consistent with Figure 3 The XRD data are consistent with the results calculated according to the Bragg formula 2dsinθ=nλ, proving the formation of NiMo ordered intermetallic alloy.

[0047] Embodiment 2:

[0048] The preparation was carried out by the method of Example 1, the only difference being that the molar ratio of metal Ni:Mo in step (1) was 1:5. At 800°C, the CH4 conversion was 98.9%, and the CO and H2 selectivities were 95.5% and 97%, respectively.

[0049] Embodiment 3:

[0050] The preparation was carried out by the method of Example 1, except that the molar ratio of metal Ni:Mo in step (1) was 1:10. At 800°C, the CH4 conversion rate was 97.9%, and the CO and H2 selectivities were 97% and 97.8%, respectively.

[0051] Embodiment 4:

[0052] The preparation was carried out by the method of Example 1, the only difference being that the molar ratio of metal Ni:Mo in step (1) was 5:1. At 800°C, the CH4 conversion was 99%, and the CO and H2 selectivities were 97.9% and 97%, respectively.

[0053] Embodiment 5:

[0054] The preparation was carried out by the method of Example 1, except that the holding time in step (2) was 20 minutes. At 800°C, the CH4 conversion was 99.9%, and the CO and H2 selectivities were 97.9% and 97%, respectively.

[0055] Embodiment 6:

[0056] The preparation was carried out by the method of Example 1, except that the holding time in step (2) was 40 minutes. At 800°C, the CH4 conversion was 99.9%, and the CO and H2 selectivities were 97.9% and 97%, respectively.

[0057] Embodiment 7:

[0058] The preparation was carried out by the method of Example 1, the only difference being that the reaction temperature in the liquid phase synthesis was 230° C. At 800° C., the CH4 conversion was 99.9%, and the CO and H2 selectivities were 97.9% and 97%, respectively.

[0059] Embodiment 8:

[0060] The preparation was carried out by the method of Example 1, the only difference being that the reaction temperature in the liquid phase synthesis was 240° C. At 800° C., the CH4 conversion was 99.9%, and the CO and H2 selectivities were 97.9% and 97%, respectively.

[0061] Embodiment 9:

[0062] The preparation was carried out by the method of Example 1, the only difference being that the reaction temperature in the liquid phase synthesis was 270° C. At 800° C., the CH4 conversion was 97.9%, and the CO and H2 selectivities were both 97%.

[0063] According to the content of the present invention, the relevant process parameters of the invention technical solution are adjusted to achieve the preparation of the intermetallic NiMo alloy catalyst, and after testing, the performance is basically consistent with the present invention. The above is an exemplary description of the present invention. It should be noted that any simple deformation, modification or equivalent replacement that can be made by other technicians in this field without spending creative labor falls within the protection scope of the present invention without departing from the core of the present invention.

Claims

1. An intermetallic NiMo alloy catalyst, characterized in that: Mo is incorporated into the Ni lattice to form a NiMo ordered intermetallic alloy, following the steps below: Step 1, weighing nickel acetylacetonate and molybdenum hexacarbonyl and uniformly dispersing them in a solvent to prepare a precursor solution, wherein the molar ratio of the two metals Ni:Mo is (1-5):(1-10); Step 2, placing the precursor solution obtained in step 1 under an inert protective atmosphere, heating from room temperature 20-25 degrees Celsius to 230-270 degrees Celsius at a rate of 10-20 degrees Celsius / min and keeping the temperature for 10-40 minutes to perform an alloying reaction, naturally cooling to room temperature 20-25 degrees Celsius, and adding anhydrous ethanol to precipitate the alloy; Step 3, the alloy obtained in step 2 is loaded on a carrier, and in a mixed atmosphere of hydrogen and inert protective gas, the temperature is raised to 550-600°C at a rate of 10-20°C / min, maintained for 2-4h, and then the temperature is raised to 800-900°C at a rate of 10-20°C / min, roasted and reduced for 6-10h, and naturally cooled to room temperature 20-25°C; in the mixed atmosphere, the volume percentage of hydrogen is 5-50%, and the gas flow rate is 50-500mL·min -1 .

2. An intermetallic NiMo alloy catalyst according to claim 1, characterized in that: In step 1, the molar ratio of the two metals Ni:Mo is 1:(1-10); the solvent is oleylamine, oleic acid or dibenzyl ether.

3. An intermetallic NiMo alloy catalyst according to claim 1, characterized in that: In step 2, the inert protective atmosphere is nitrogen, helium or argon; the temperature is raised to 230-250° C. and maintained for 20-30 minutes.

4. The intermetallic NiMo alloy catalyst according to claim 1, characterized in that: In step 3, the inert protective gas is nitrogen, helium or argon; the volume percentage of hydrogen is 20-30%, and the gas flow rate is 100-300 mL·min -1 .

5. A method for preparing an intermetallic NiMo alloy catalyst, characterized in that: Follow these steps: Step 1, weighing nickel acetylacetonate and molybdenum hexacarbonyl and uniformly dispersing them in a solvent to prepare a precursor solution, wherein the molar ratio of the two metals Ni:Mo is (1-5):(1-10); Step 2, placing the precursor solution obtained in step 1 under an inert protective atmosphere, heating from room temperature 20-25 degrees Celsius to 230-270 degrees Celsius at a rate of 10-20 degrees Celsius / min and keeping the temperature for 10-40 minutes to perform an alloying reaction, naturally cooling to room temperature 20-25 degrees Celsius, and adding anhydrous ethanol to precipitate the alloy; Step 3, the alloy obtained in step 2 is loaded on a carrier, and in a mixed atmosphere of hydrogen and inert protective gas, the temperature is raised to 550-600°C at a rate of 10-20°C / min, maintained for 2-4h, and then the temperature is raised to 800-900°C at a rate of 10-20°C / min, roasted and reduced for 6-10h, and naturally cooled to room temperature 20-25°C; in the mixed atmosphere, the volume percentage of hydrogen is 5-50%, and the gas flow rate is 50-500mL·min -1 .

6. The method for preparing an intermetallic NiMo alloy catalyst according to claim 5, characterized in that: In step 1, the molar ratio of the two metals Ni:Mo is 1:(1-10); the solvent is oleylamine, oleic acid or dibenzyl ether.

7. The method for preparing an intermetallic NiMo alloy catalyst according to claim 5, characterized in that: In step 2, the inert protective atmosphere is nitrogen, helium or argon; the temperature is raised to 230-250° C. and maintained for 20-30 minutes.

8. The method for preparing an intermetallic NiMo alloy catalyst according to claim 5, characterized in that: In step 3, the inert protective gas is nitrogen, helium or argon; the volume percentage of hydrogen is 20-30%, and the gas flow rate is 100-300 mL·min -1 .

9. The method for preparing an intermetallic NiMo alloy catalyst according to claim 5, characterized in that: In step 3, the carrier is a commercial SBA-15 molecular sieve; the alloy obtained in step 2 is ultrasonically dispersed in cyclohexane and then loaded on the carrier at a stirring rate of 300 to 600 rpm and a stirring temperature of 50 to 80°C.

10. Use of an intermetallic NiMo alloy catalyst as claimed in any one of claims 1 to 4 in the partial oxidation reaction of methane to produce synthesis gas.

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