Preparation method and application of pd-ni composite metal oxide methane dry reforming catalyst

Abstract

The application provides a preparation method and application of a Pd-Ni composite metal oxide methane dry reforming catalyst. The application uses a palladium-nickel-based composite metal oxide catalyst with distributed active metals (Ni, Mg, Pd). The application applies the catalyst to a methane dry reforming reaction to prepare synthesis gas. The preparation method is simple. The proportion of each metal in the catalyst is adjustable and controllable, and the active metal nickel is uniformly distributed. Through relevant data processing and catalyst evaluation, it is confirmed that the catalyst has high catalytic activity, and has remarkable anti-coking and anti-sintering abilities. After 600 hours of stability test, the methane and carbon dioxide conversion rates are high and stable, and the H2 / CO ratio of the obtained synthesis gas is close to 1.

Description

Technical Field

[0001] This invention belongs to the field of CH4 and CO2 conversion and utilization materials technology, specifically relating to the preparation and application of a palladium-nickel-based composite metal oxide catalyst, which is used in the dry reforming of methane to produce syngas. Background Technology

[0002] Since the Industrial Revolution, human activities have led to a continuous increase in the concentration of greenhouse gases in the atmosphere, with CO2 and CH4 contributing particularly significantly to the greenhouse effect. Among various CO2 emission reduction technologies, the integrated CO2 capture-methane dry reforming (ICCC-DRM) technology simultaneously converts both CO2 and CH4 into syngas (CO + H2). This technology, through system integration, reduces operating costs and energy consumption while simultaneously achieving the resource utilization of greenhouse gases. The resulting syngas is a fundamental raw material for important chemical processes such as ammonia synthesis, methanol, ethylene glycol, and Fischer-Tropsch synthesis, and market demand continues to grow. Therefore, ICCC-DRM technology not only contributes to low-carbon emission reduction but also provides raw material support for the synthesis of downstream high-value-added products.

[0003] According to the thermodynamic equilibrium of DRM, its reaction conditions are suitable for high temperature and low pressure, under which both the raw materials and products are gases. Fixed-bed reactors are typically used for this type of reaction. Due to the harsh reaction conditions, researchers generally use supported catalysts, which consist of an active metal and a support. Extensive literature indicates that the activation of CH4 mostly occurs on the metal, while carbon dioxide is mostly adsorbed and activated on the support.

[0004] As a high-temperature endothermic reaction, the deactivation of the active metal catalyst under high-temperature conditions is an unavoidable problem in DRM, further limiting its application in large-scale industry. The main causes of catalyst deactivation include carbon deposition and metal sintering.

[0005] For active metals in methane dry reforming catalysts, they can generally be divided into noble metals and non-noble metals. Among non-noble metals, nickel exhibits the best activity, making nickel dispersed on oxides a favorable choice for methane dry reforming processes. Since non-noble metals are more prone to carbon deposition than noble metals, researchers have modified the catalysts using various methods. Currently reported methods in literature and patents include adding promoters, altering the size of active metal particles, and improving the interaction between the active metal and the support. For example, Chinese patent CN105107515A reported a nickel-molybdenum carbide composite catalyst for methane dry reforming to syngas, using a nickel and molybdenum dual-component approach to establish a Mo2C carbonization-oxidation cycle, improving the stability and hydrogen selectivity of the methane dry reforming to syngas process. However, its preparation method is overly complex.

[0006] Among precious metals, rhodium exhibits the best activity. Patent CN201710248150.8 reports a Rh / La2Ti2O7 catalyst in which the mass percentage of the active component Rh is 0.5-7%. Although this catalyst achieves high conversion rates at low temperatures, the high loading of precious metals leads to excessively high catalyst costs.

[0007] Patent CN121797348A reports a NiPt-CaO / MgO bifunctional material for methane dry reforming reaction. The catalyst has a Pt loading of 0.1-1 wt.%, but the conversion rates of methane and carbon dioxide are both below 80%, and the stability has not been verified (20 cycle experiments).

[0008] The cost and stability of dry reforming catalysts are factors that need to be considered for the industrialization of this technology. Therefore, developing methane dry reforming catalysts with low development costs, stable performance, and a wide reaction temperature window is particularly important for the industrial application of this technology. Summary of the Invention

[0009] This invention provides a palladium-nickel-based composite metal oxide catalyst with distributed immobilized active metals (Ni, Mg, Pd), and applies this catalyst to the dry reforming reaction of methane.

[0010] A method for preparing a palladium-nickel based composite metal oxide catalyst is as follows: A certain amount of soluble nickel salt, ammonia, and silica sol were dissolved in a certain amount of deionized water and stirred at 25 °C until fully mixed. The temperature was then increased to evaporate the ammonia. Heating was stopped when the pH of the solution decreased to weakly acidic or neutral. The precipitate was collected by vacuum filtration while hot, washed with deionized water, and the filter cake was dried in an oven for the first time. The dried sample was then crushed and sieved to 20-40 mesh, and then transferred to a muffle furnace for the first high-temperature calcination to obtain Ni / SiO2. A suitable amount of soluble magnesium salt was weighed and dissolved in deionized water, and then a certain amount of dried Ni / SiO2 catalyst was added and impregnated at 25 °C. The catalyst precursor was then heated to dryness in a water bath. The resulting catalyst precursor was dried a second time in an oven. A certain amount of soluble palladium salt solution was then added to the catalyst precursor and impregnated at 25 °C. The resulting catalyst precursor was then dried a third time in an oven, and finally calcined a second time in a muffle furnace to prepare the Pd-Ni / Mg-SiO2 catalyst. Based on the different amounts of Mg and Pd doping, it is named Pd x -Ni / Mg y -SiO2 (x=0.01-0.1; y=1-12).

[0011] The soluble nickel salt is one of Ni(NO3)3·6H2O, NiSO4·6H2O, NiCl2·6H2O, and NiC4H6O4, with Ni(NO3)3·6H2O being the preferred choice. The temperature of ammonia evaporation is controlled at 50-100 ℃, preferably 75-85 ℃, during the heating process. The pH value of the solution is reduced to a weakly acidic or neutral pH value controlled at 5-7, preferably 6-7; The oven temperature for the first heating and drying is controlled at 100-150 ℃, preferably 120-125 ℃, and the heating and drying time is controlled at 6-15 h, preferably 8-12 h. The temperature for the first high-temperature roasting in the muffle furnace is controlled at 700-1000 ℃, preferably 750-850 ℃, and the roasting time is controlled at 6-20 h, preferably 8-16 h. The soluble magnesium salt is one of magnesium nitrate, magnesium chloride, magnesium sulfate, and magnesium gluconate, with magnesium nitrate being preferred; The oven temperature for the second heating and drying process is controlled at 100-180 ℃, preferably 130-155 ℃, and the heating and drying time is controlled at 6-18 h, preferably 8-15 h. The soluble palladium salt is one of palladium nitrate, palladium chloride, tetraamminepalladium salt, and palladium sulfate, with palladium nitrate and palladium chloride being preferred. The temperature of the oven used for the third heating and drying process is controlled at 100-160 ℃, preferably 120-140 ℃, and the heating and drying time is controlled at 6-20 h, preferably 10-15 h. The temperature for the second high-temperature roasting in the muffle furnace is controlled at 700-1000 ℃, preferably 850-950 ℃, and the roasting time is controlled at 6-20 h, preferably 10-16 h. The Pd mentioned x -Ni / Mg y The mass percentage of nickel in SiO2 is 5-15%, preferably 8-10%, the mass percentage of palladium is 0.01-0.1%, preferably 0.05-0.1%, and the mass percentage of magnesium is 1-12%, preferably 5-7%.

[0012] When evaluating catalyst performance, the reaction temperature was 500-900 ℃, the pressure was 0.01-0.5 MPa, and the space velocity was 10000-150000 h⁻¹. -1 The reaction feed gases are CH4, CO2, and He in a ratio of 1:1:5-10. The gas after the reaction is analyzed by an online gas chromatograph.

[0013] The preferred reaction temperature is 700-800 ℃; The preferred reaction pressure is 0.05-0.2 MPa; The preferred airspeed is 60,000-100,000 h. -1 ; The gas chromatograph uses a dual-column system, with PQ and TDX-01 analytical columns used in series; the absolute concentration of each component is calculated using the external standard method.

[0014] The optimal catalyst has a CH4 conversion rate of over 95% and a CO2 conversion rate of over 93%. The main gas components after the reaction are H2 and CO, with a ratio of H2:CO = 0.9-1.0.

[0015] The advantages of the methane dry reforming catalyst provided by the present invention are: (1) The catalyst prepared by the present invention is simple in preparation method, low in cost, and conducive to large-scale production. (2) The proportion of each metal component in the catalyst is adjustable and controllable, the active metal nickel is evenly distributed, it is not easy to deposit carbon, the conversion rate is high, the selectivity is high, the stability is high, and the ratio of H2 and CO in the product is close to 1. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the stability (600 h) of the catalyst used in the dry reforming reaction of methane in Example 2, including the change of carbon dioxide conversion rate over time, the change of methane conversion rate over time, and the product H2 / CO ratio.

[0017] Figure 2 These are X-ray powder diffraction patterns of the fresh catalysts in Examples 1-4.

[0018] Figure 3 and Figure 4 This is a transmission electron microscope (TEM) image of the fresh catalyst from Example 2.

[0019] Figure 5 This is a transmission electron microscope (TEM) image of the catalyst in Example 2 after a 600-h stability study. Detailed Implementation

[0020] The specific embodiments of the present invention will be described in detail below, but the scope of protection of the present invention is not limited thereto.

[0021] Figure 1 The catalyst Pd in ​​Example 2 0.08 Lifetime evaluation of Ni / Mg5-SiO2 in methane dry reforming reaction, due to Pd 0.08 The Ni / Mg5-SiO2 catalyst exhibited good catalytic activity and stability in the reaction, therefore long-term lifetime testing was conducted on Pd. 0.08The Ni / Mg5-SiO2 sample exhibited very stable performance over a reaction time of 600 h, with methane conversion rates consistently above 95% and carbon dioxide conversion rates consistently above 93%, and the H2 / CO ratio of the products approaching 1.

[0022] Figure 2 The images show X-ray powder diffraction patterns of the fresh catalysts prepared in each embodiment, with obvious diffraction peaks of Mg2SiO4 in the catalysts.

[0023] Figure 3 and Figure 4 The catalyst Pd in ​​Example 2 0.08 Transmission electron microscopy image of -Ni / Mg5-SiO2, from Figure 3 As can be seen, the nickel in the catalyst has a uniform size distribution, with an average particle size of 8.78 nm. Figure 4 The interplanar spacing measurement (0.498 nm) revealed obvious MgSiO4(020) species.

[0024] Figure 5 It is the catalyst Pd in ​​Example 2 0.08 Transmission electron microscopy (TEM) image of Ni / Mg5-SiO2 after 600 h of stability study. No carbon deposition is observed in the image.

[0025] Preparation of catalyst precursor Ni / SiO2 5.98 g of Ni(NO3)2·6H2O, 30.00 g of silica sol, and 20 mL of 13 mol / L ammonia were weighed and dissolved in 400 mL of deionized water. The mixture was stirred at 25 °C until fully mixed, and then the temperature was raised to 80 °C and held for 8 h to evaporate the ammonia. Heating was stopped when the pH of the solution dropped to 6.5. The precipitate was collected by vacuum filtration while hot and washed three times with deionized water. The filter cake was then dried in an oven for 12 h at 120 °C. The dried sample was then crushed and sieved to 20-40 mesh and transferred to a muffle furnace for a first high-temperature calcination of 15 h at 850 °C to obtain 9.85 g of catalyst precursor Ni / SiO2. Example 1

[0026] (1) Catalyst preparation 0.19 g of magnesium nitrate was dissolved in 3 mL of deionized water, and 1.00 g of catalyst precursor Ni / SiO2 was added. The mixture was impregnated at 25 °C for 8 h, then heated to dryness in a water bath. The resulting catalyst precursor was then subjected to a second heating and drying in an oven at 140 °C for 10 h to obtain Ni / Mg3-SiO2. 0.0014 g of palladium nitrate was dissolved in 2 mL of 5% dilute nitric acid solution. Ni / Mg3-SiO2 was impregnated in the palladium nitrate solution for 12 h, then subjected to a third heating and drying in an oven at 130 °C for 15 h. Finally, a second high-temperature calcination was performed in a muffle furnace at 900 °C for 12 h to prepare Pd. 0.08 -Ni / Mg3-SiO2.

[0027] (2) Catalyst evaluation First, 0.100 g of the 20-40 mesh sieved catalyst was packed into the middle of a quartz reaction tube with an inner diameter of 6 mm. Activation was performed by reduction at 800 °C for 1 h under atmospheric pressure in an H2 / He atmosphere. After reduction, the temperature was lowered to 550 °C in the He atmosphere, and reactant gases CH4, CO2, and dilution gas He were introduced; the flow rate ratio of He:CH4:CO2 was controlled at 10:1:1; the total space velocity was 72000 h⁻¹. -1 After the mixed gas was introduced into the reaction bed, a dry reforming reaction of methane was initiated at 550 °C. After 2 hours of reaction, the temperature was increased by 50 °C to 600 °C for another 1 hour. Each temperature interval was followed by a 2-hour reaction. Online sampling and analysis of the reaction results were performed at 50, 80, and 110 minutes. The heating rate was 5 °C / min, with a maximum measured temperature of 800 °C. Unless otherwise specified, the reaction pressure was maintained at a gauge pressure of 0.1 MPa.

[0028] The performance test results are shown in Table 1. The catalyst achieved a methane conversion rate of 91% and a carbon dioxide conversion rate of 89% within a 30-hour reaction time. Example 2

[0029] (1) Catalyst preparation The catalyst preparation method is the same as in Example 1 (1), except that the amount of magnesium nitrate used is 0.32 g, and Pd is prepared. 0.08 -Ni / Mg5-SiO2.

[0030] (2) Catalyst evaluation First, 0.100 g of the 20-40 mesh sieved catalyst was packed into the middle of a quartz reaction tube with an inner diameter of 6 mm. Activation was performed by reduction at 800 °C for 1 h under atmospheric pressure in a H2 / He atmosphere. After reduction, the temperature was lowered to 550 °C in the He atmosphere, and reactant gases CH4, CO2, and dilution gas He were introduced; the flow rate ratio of He:CH4:CO2 was controlled at 10:1:1; and the total space velocity was 100,000 h⁻¹. -1 After the mixed gas was introduced into the reaction bed, a dry reforming reaction of methane was initiated at 550 °C. After 2 hours of reaction, the temperature was increased by 50 °C to 600 °C for another 1 hour. Each temperature range was followed by a 2-hour reaction. The reaction results were sampled and analyzed online at 50, 80, and 110 minutes. The heating rate was 5 °C / min, and the highest temperature reached was 800 °C. The reaction was carried out at a pressure of 0.1 MPa.

[0031] The performance test results are shown in Table 1. The catalyst achieved a methane conversion rate of 95% and a carbon dioxide conversion rate of 93% within a 600-h reaction time, with a product H2 / CO ratio close to 1. Catalyst stability testing was conducted at 800 ℃. Figure 1 ). Example 3

[0032] (1) Catalyst preparation The catalyst preparation method is the same as in Example 1 (1), except that the amount of magnesium nitrate used is 0.44 g, and Pd is prepared. 0.08 -Ni / Mg7-SiO2.

[0033] (2) Catalyst evaluation The catalyst was evaluated in the same way as in Example 1. The performance test results are shown in Table 1. The catalyst achieved a methane conversion rate of 93% and a carbon dioxide conversion rate of 90% within a 30-hour reaction time. Example 4

[0034] The catalyst preparation method is the same as in Example 1 (1), except that the amount of magnesium nitrate used is 0.63 g, and Pd is prepared. 0.08 -Ni / Mg 10 -SiO2.

[0035] (2) Catalyst evaluation The catalyst was evaluated in the same way as in Example 1. The performance test results are shown in Table 1. The catalyst achieved a methane conversion rate of 91% and a carbon dioxide conversion rate of 89% within a 30-hour reaction time. Example 5

[0036] (1) Catalyst preparation The catalyst preparation method is the same as in Example 1 (1), except that the amount of palladium nitrate used is 0.0004 g, and Pd is prepared.0.02 -Ni / Mg3-SiO2.

[0037] (2) Catalyst evaluation The catalyst evaluation was the same as in Example 1, except that the total space velocity was 60,000 h⁻¹. -1 The performance test results are shown in Table 1. The catalyst achieved a methane conversion rate of 88% and a carbon dioxide conversion rate of 86% within a 30-hour reaction time. Example 6

[0038] (1) Catalyst preparation The catalyst preparation method is the same as in Example 1 (1), except that the amount of palladium nitrate used is 0.0004 g and the amount of magnesium nitrate used is 0.32 g, thus preparing Pd 0.02 -Ni / Mg5-SiO2.

[0039] (2) Catalyst evaluation The catalyst evaluation was the same as in Example 1, except that the total space velocity was 80,000 h⁻¹. -1 The performance test results are shown in Table 1. The catalyst achieved a methane conversion rate of 94% and a carbon dioxide conversion rate of 93% within a 30-hour reaction time. Example 7

[0040] (1) Catalyst preparation The catalyst preparation method is the same as in Example 1 (1), except that the amount of palladium nitrate used is 0.002 g and the amount of magnesium nitrate used is 0.44 g, thus preparing Pd 0.1 -Ni / Mg7-SiO2.

[0041] (2) Catalyst evaluation The catalyst evaluation was the same as in Example 1, except that the total space velocity was 80,000 h⁻¹. -1 The performance test results are shown in Table 1. The catalyst achieved a methane conversion rate of 96% and a carbon dioxide conversion rate of 93% within a 30-hour reaction time. Example 8

[0042] (1) Catalyst preparation The catalyst preparation method is the same as in Example 1 (1), except that the amount of palladium nitrate used is 0.0002 g and the amount of magnesium nitrate used is 0.63 g, thus preparing Pd 0.01 -Ni / Mg 10 -SiO2.

[0043] (2) Catalyst evaluation The catalyst evaluation was the same as in Example 1, except that the total space velocity was 60,000 h⁻¹. -1The reaction pressure was 0.2 MPa. The performance test results are shown in Table 1. The catalyst achieved a methane conversion rate of 86% and a carbon dioxide conversion rate of 85% within a 30-h reaction time.

[0044] Table 1 Comparison of Catalyst Performance in Examples

Claims

1. A method for preparing a Pd-Ni composite metal oxide methane dry reforming catalyst, characterized in that, The steps are as follows: Soluble nickel salt, ammonia, and silica sol were dissolved in deionized water and stirred at 25 °C until fully mixed. The temperature was then increased to evaporate the ammonia, with the evaporation temperature controlled at 50-100 °C. Heating was stopped when the pH of the solution decreased to weakly acidic or neutral. The precipitate was collected by vacuum filtration while hot, washed with deionized water, and the filter cake was dried in an oven for the first time. The dried sample was then crushed and sieved to 20-40 mesh, and then transferred to a muffle furnace for the first high-temperature calcination, controlled at 700-1000 °C for 6-20 h, to obtain Ni / SiO2. Soluble magnesium salt was weighed and dissolved in deionized water, then the dried Ni / SiO2 catalyst was added and impregnated at 25 °C, followed by evaporation in a water bath. The resulting catalyst precursor was dried a second time in an oven. A soluble palladium salt solution was then added to the catalyst precursor and heated to 25 °C. The catalyst precursor was impregnated at ℃, then dried for the third time in an oven, and finally calcined for the second time in a muffle furnace at a temperature controlled at 700-1000 ℃ for 6-20 h to prepare a Pd-Ni composite metal oxide methane dry reforming catalyst, wherein the mass percentage of nickel was 5-15%, the mass percentage of palladium was 0.01-0.1%, and the mass percentage of magnesium was 1-12%.

2. The catalyst prepared by the method described in claim 1, characterized in that: Named Pd x -Ni / Mg y -SiO2, where x=0.01-0.1; y=1-12.

3. The method according to claim 1, wherein, The soluble nickel salt is one of Ni(NO3)3·6H2O, NiSO4·6H2O, NiCl2·6H2O, and NiC4H6O4; the soluble magnesium salt is one of magnesium nitrate, magnesium chloride, magnesium sulfate, and magnesium gluconate; and the soluble palladium salt is one of palladium nitrate, palladium chloride, tetraamminepalladium salt, and palladium sulfate.

4. The method according to claim 1, wherein, The pH value of the solution is reduced to a weakly acidic or neutral pH value controlled between 5 and 7; the oven temperature for the first heating and drying is controlled at 100-150 ℃, and the heating and drying time is controlled at 6-15 h; the oven temperature for the second heating and drying is controlled at 100-180 ℃, and the heating and drying time is controlled at 6-18 h; the oven temperature for the third heating and drying is controlled at 100-160 ℃, and the heating and drying time is controlled at 6-20 h.

5. The application of the catalyst according to claim 2, wherein, The reaction temperature was 500-900 ℃, the pressure was 0.01-0.5 MPa, and the space velocity was 10,000-150,000 h⁻¹. -1 The reaction feed gases are CH4, CO2, and He in a ratio of 1:1:5-10. The gas after the reaction is analyzed by an online gas chromatograph.

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