Spinel supported copper catalyst, preparation method and application of spinel supported copper catalyst in hydrogen production through methanol steam reforming

Abstract

The invention discloses a spinel supported copper catalyst, a preparation method and application of the spinel supported copper catalyst in hydrogen production by methanol steam reforming, the molecular formula of the spinel supported copper catalyst is Cu / ZnB2O4, and B is Cr, Al and Ga. The preparation method comprises the following steps: preparing a spinel carrier by adopting a coprecipitation method, washing, filtering, drying and roasting by taking a 25wt% ammonia water solution as a precipitator to obtain ZnB2O4 spinel, and loading Cu by adopting an impregnation method to prepare the Cu / ZnB2O4 catalyst. The raw material cost is low, and the equipment requirement is low; the preparation process is simple and feasible, and the reaction process is easy to control; the composite material can be applied to a methanol steam reforming hydrogen production reaction for the first time, shows excellent reaction performance and thermal stability, basically does not generate CO, has the CO concentration far lower than 10ppm, and can be applied to a vehicle-mounted power generation system in which methanol steam reforming hydrogen production and proton exchange membrane fuel cells are combined.

Description

Technical Field

[0001] The invention belongs to the technical field of energy catalysis and relates to a methanol reforming hydrogen production catalyst and a preparation method and application thereof. Background Art

[0002] The power generation system combining on-board methanol steam reforming hydrogen production and proton exchange membrane (PEMFC) fuel cells is an effective way to replace internal combustion engines to provide power for motor vehicles. This technology can be divided into three parts: the first part is the raw material methanol aqueous solution; the second part is the methanol reforming hydrogen production system, which consists of a methanol reforming hydrogen production microreactor and a catalytic purification device; the third part is the fuel cell power generation system, which consists of a hydrogen fuel cell stack and a thermal management system (Chen Minsheng, Liu Jie, Zhu Tao, Research Progress of On-board Methanol Steam Reforming Hydrogen Production Technology, Modern Chemical Industry, 2021, 41, 36-41.). According to current research progress, methanol steam reforming hydrogen production is more suitable for application in on-board online hydrogen production reactors. It produces high H2 content and low CO yield. While efficiently supplying hydrogen, it can effectively avoid electrode poisoning in PEMFC fuel cells.

[0003] Methanol reforming hydrogen production catalysts are mainly divided into copper-based catalysts and precious metal catalysts. Since copper-based catalysts have cheaper raw materials than precious metal catalysts and have low CO selectivity, copper-based catalysts are preferred. In order to find an efficient methanol reforming hydrogen production catalyst, it is crucial to choose a suitable carrier material. Among them, spinel oxide (AB2O4) has attracted attention due to its rich surface active sites, adjustable electron exchange capacity and high stability. Its exposed polar surface can anchor the loaded metal particles, thereby enhancing the interaction between the metal and the carrier, thereby inhibiting the agglomeration of metal species. There are methanol steam reforming spinel catalysts (M. Liao, R. Xiang, X. Zhou, Z. Dai, L. Wang, H. Qin, H.Xiao, Enhancing effect of Mn² + substitution in CuAl2O4 spinel for methanolsteam reforming in a microreactor. Renewable Energy, 230 (2024) 120815). The CO selectivity of the catalyst is between 1.68% and 9.85%, and the methanol conversion rate is close to 100% at a reaction temperature of 300°C. Summary of the invention

[0004] The first purpose of the present invention is to provide a spinel-loaded copper catalyst and a preparation method and application in methanol reforming to produce hydrogen. The catalyst has excellent low-temperature activity and thermal stability. Since the concentration of CO produced is extremely low, it can be used in a power generation system that combines vehicle-mounted methanol steam reforming to produce hydrogen with a proton exchange membrane fuel cell.

[0005] The present invention is achieved through the following technical solutions.

[0006] The spinel-supported copper catalyst described in the present invention is a Cu-based catalyst using spinel as a carrier, and its molecular formula is A / ZnB2O4, wherein A=Cu, B=Cr, Al, Ga, and preferably B=Cr.

[0007] When the metal ion at the B position of the catalyst is Cr, the methanol conversion rate of the catalyst at 280° C. is as high as 91%, and the CO concentration at this time is only 1.5 ppm, which will not cause poisoning to the battery.

[0008] The method for preparing a spinel-supported copper catalyst of the present invention comprises firstly preparing ZnB2O4 (B=Cr, Al, Ga) spinel as a carrier by a coprecipitation method, and then loading the active component Cu by an impregnation method to obtain a Cu / ZnB2O4 catalyst sample. Specifically, the method comprises the following steps.

[0009] (1) Based on the molar ratio of metal ions at the A / B sites of spinel being 1:2, weigh Zn(NO3)2∙6H2O, Cr(NO3)3∙9H2O, Al(NO3)3∙9H2O, and Ga(NO3)3∙xH2O respectively and place them in a beaker. Add an appropriate amount of deionized water and stir at room temperature until dissolved.

[0010] (2) The solution obtained in step (1) was added dropwise with 25 wt.% ammonia water while stirring to adjust the pH value to 9. After precipitation was complete, the solution was stirred for 2 h, allowed to stand for 2 h, and then filtered and washed with deionized water until the TDS of the filtrate was less than 20 ppm.

[0011] (3) Dry the filter cake obtained in step (2) in an oven at 110°C for 12 h, and then grind it.

[0012] (4) The product obtained in step (3) is placed in a muffle furnace and heated at a rate of 2 °C / min, and calcined at 550 °C in an air atmosphere for 4 h to obtain a ZnB2O4 (B = Cr, Al, Ga) spinel carrier.

[0013] (5) Weigh the spinel support and Cu(NO3)2∙3H2O prepared in step (4) into a crucible, add an appropriate amount of deionized water, stir for 2 h, heat and stir in a 90 °C water bath to evaporate to dryness, place in a 110 °C oven until completely dry, and then grind.

[0014] (6) The product obtained in step (5) was placed in a muffle furnace and heated at a rate of 2 °C / min, and calcined at 450 °C in an air atmosphere for 4 h to finally obtain a Cu / ZnB2O4 (B = Cr, Al, Ga) catalyst.

[0015] (7) When the preferred B-site metal ion is Cr, there are more dispersed Cu small particles on the support surface and the catalyst performance is optimal. When the preferred B-site metal ion is Al, the thermal stability of the catalyst is optimal. When the preferred B-site metal ion is Ga, the CO concentration of the catalyst is the lowest.

[0016] The invention discloses an application of a spinel copper supported catalyst in hydrogen production by methanol steam reforming. The method comprises the following steps.

[0017] 100 mg of catalyst of 40-60 mesh was placed in the reactor, and a 10 vol% H2 / Ar mixed gas with a flow rate of 30 mL / min was introduced for reduction for 40 min at 1 atm and 300 °C. The reaction temperature was controlled at 200-360 °C by a thermocouple. A mixture of H2O and CH3OH with a CH3OH / H2O molar ratio of 1 / 1.5 and a flow rate of 0.05 mL / min was injected into the vaporization chamber by a micro pump, and the temperature was controlled at 200 °C to completely evaporate the liquid into gas. The corresponding reaction space velocity (WHSV) was 42000 mL / h˙g cat . Then it was brought into the reactor for reaction by Ar at a flow rate of 30mL / min. According to the results of the catalyst performance test, the Cu / ZnCr2O4 catalyst has the best reaction performance. At a reaction temperature of 280 ℃, the methanol conversion rate reaches 91% and the CO selectivity is 0.5%. In contrast, the CO selectivity of the Cu / ZnGa2O4 catalyst is the lowest, which is 0.2%, but the methanol conversion rate is only 70%. The Cu / ZnAl2O4 catalyst has excellent reaction performance, and the methanol conversion rate can reach 81%.

[0018] In order to obtain an efficient methanol steam reforming hydrogen production catalyst, the present invention prepares three spinel-supported copper catalysts by changing the B-site metal ions of Zn-based spinel. According to the XRD characterization of the catalyst, it can be found that the active component Cu is best dispersed when supported on the ZnCr2O4 spinel carrier, and no characteristic diffraction peak of CuO is found. At the same time, according to the copper dispersion test and H2-TPR characterization, it can be found that the ZnCr2O4 spinel carrier has more highly dispersed copper particles.

[0019] For the first time, the Cu / ZnB2O4 (B=Cr,Al,Ga) catalyst was used in the methanol steam reforming hydrogen production reaction. It has excellent low-temperature activity and thermal stability. Its CO concentration is as low as 0.5-1.3 ppm, which will not be toxic to the battery. It can be fully used in the power generation system that combines on-board methanol steam reforming hydrogen production with proton exchange membrane fuel cells.

[0020] Compared with the prior art, the catalyst prepared by the present invention has the following advantages.

[0021] (1) The raw material cost for preparing the catalyst of the present invention is low and the equipment requirement is low.

[0022] (2) The catalyst prepared by the present invention adopts the co-precipitation method and the impregnation method, the preparation process is simple and easy, and the reaction process is easy to control.

[0023] (3) A spinel copper-loaded catalyst prepared by the present invention is used for the first time in the methanol steam reforming hydrogen production reaction and has high catalytic performance and low CO concentration. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the X-ray diffraction (XRD) crystal phase structure analysis spectrum of the carrier ZnB2O4 (B=Cr, Al, Ga) obtained in Example 1.

[0025] Figure 2 This is the X-ray diffraction (XRD) crystal phase structure analysis spectrum of the catalyst Cu / ZnB2O4 (B=Cr, Al, Ga) obtained in Example 2.

[0026] Figure 3 This is a test diagram of the methanol steam reforming hydrogen production performance of the catalyst sample obtained in implementation case 2.

[0027] Figure 4 This is the CO selectivity and concentration diagram of methanol steam reforming hydrogen production at a reaction temperature of 280°C for the catalyst sample obtained in Example 2.

[0028] Figure 5 This is a thermal stability test chart of the catalyst Cu / ZnCr2O4 obtained in Example 2.

[0029] Figure 6 This is a thermal stability test chart of the catalyst Cu / ZnAl2O4 obtained in Example 2.

[0030] Figure 7 This is a thermal stability test chart of the catalyst Cu / ZnGa2O4 obtained in Example 2.

[0031] Figure 8These are the H2-TPR test diagrams of the carrier and catalyst samples obtained in Example 1 and Implementation Case 2. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the embodiments. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially. Example 1

[0033] Preparation of ZnB2O4 (B=Cr,Al,Ga) support.

[0034] Preparation of 4 g of carrier: According to the molar ratio of metal ion at site A to metal ion at site B of 1:2, weigh Zn(NO3)2∙6H2O, Cr(NO3)3∙9H2O, Al(NO3)3∙9H2O, Ga(NO3)3∙xH2O and put them in a beaker, add appropriate amount of deionized water, stir until dissolved at room temperature, add 25 wt.% ammonia water to adjust the pH value to 9, wait for complete precipitation, stir for 2 h, let stand for 2 h, filter and wash with deionized water until the TDS of the filtrate is less than 20 ppm. Dry the filter cake in an oven at 110 °C for 12 h, take it out and grind it. Put it in a muffle furnace at 2 °C / min -1 The heating rate was increased to 550 ℃ and maintained for 4 h to obtain spinel supports Zn Cr2O4, Zn Al2O4, and Zn Ga2O4. Example 2

[0035] Preparation of Cu / ZnB2O4 (B=Cr,Al,Ga) catalyst.

[0036] 2 g catalyst, weigh 1.86 g of each of the three carriers obtained in Comparative Example 1, and add 0.53 g of Cu(NO3)2∙3H2O in a crucible, add an equal amount of deionized water and stir for 2 h, heat and stir in a 90 °C water bath to evaporate to dryness, and put in a 110 °C oven until completely dried. Put it in a muffle furnace at 2 °C / min -1 The heating rate was increased to 450 ℃ and maintained for 4 h to obtain catalyst samples Cu / Zn Cr2O4, Cu / Zn Al2O4, and Cu / Zn Ga2O4. Example 3

[0037] The reaction performance of the Cu / ZnB2O4 (B=Cr, Al, Ga) catalyst sample obtained in Example 2 was evaluated in a methanol steam reforming hydrogen production system. The specific implementation method is as follows: 100 mg of the catalyst of 40-60 mesh was placed in a fixed bed quartz tube reactor, and a 10 vol% H2 / Ar mixed gas with a flow rate of 30 mL / min was introduced for reduction for 40 minutes under the conditions of 1 atm and 300 °C. The reaction temperature was controlled at 200-280 °C, and the temperature was controlled by a thermocouple. A mixture of H2O and CH3OH with a CH3OH / H2O molar ratio of 1 / 1.5 and a flow rate of 0.05 mL / min was injected into the vaporization chamber by a micro pump, and the temperature was controlled at 200 °C to completely evaporate the liquid into gas. The corresponding reaction space velocity (WHSV) was 42000 mL / h˙g cat . Then, Ar was introduced into the reactor at a flow rate of 30 mL / min for reaction. The gas mixture in the product was first condensed by a cold water trap, and then 99.99% Ar was used as a carrier gas and passed into a GC9310 gas chromatograph equipped with a TDX-01 column and a TCD detector for online analysis. The concentrations of H2, CO2 and CO were monitored, and the reaction conversion rate was calculated using carbon balance. In the catalyst activity test, three measurements were taken at each temperature to take the average value, and the error was controlled within 2.0%. Example 4

[0038] The catalyst sample of Cu / ZnB2O4 (B=Cr, Al, Ga) obtained in Example 2 was subjected to stability test evaluation. The specific implementation method is as follows: 100 mg of catalyst of 40-60 mesh was placed in a fixed bed quartz tube reactor, and a 10 vol% H2 / Ar mixed gas with a flow rate of 30 mL / min was introduced for reduction for 40 min at 1 atm and 300 °C, and then the temperature was raised to 280 °C for 55 h of stability test. The thermal stability of the catalyst sample was determined by online analysis on a GC9310 gas chromatograph and changes in methanol conversion and CO2 selectivity. Example 5

[0039] The Cu / ZnB2O4 (B=Cr, Al, Ga) catalyst sample obtained in Example 2 was characterized by H2-TPR to explore the redox performance of the catalyst. The specific implementation method is as follows: 50 mg of the catalyst was used for H2-TPR testing. After the catalyst was pretreated in Ar gas, the temperature was raised from room temperature to 600 °C in a 10% H2 / Ar mixed gas at a heating rate of 10 °C / min to quantify the H2 consumption.

[0040] The experimental results are as follows Figure 1 As shown, the ZnB2O4 (B = Cr, Al, Ga) spinel carrier was successfully synthesized in Example 1. Figure 2 It can be seen that CuO is successfully loaded on the ZnB2O4 (B = Cr, Al, Ga) spinel carrier. Figure 3 , 4 It can be seen that the Cu / ZnB2O4 (B=Cr, Al, Ga) catalyst obtained in Example 2 has obvious performance differences in the methanol steam reforming hydrogen production reaction in Example 3, but the CO selectivity and concentration are not much different. Among them, the Cu / ZnCr2O4 catalyst has the best reaction activity, and its CO concentration is far below 10 ppm. Figure 5 , 6 7 are the stability evaluation results of the Cu / ZnB2O4 (B = Cr, Al, Ga) catalyst obtained in Example 2 in Example 4. It can be found that the Cu / ZnAl2O4 catalyst has the best thermal stability. After reacting for 55 h at a reaction temperature of 280°C, the methanol conversion rate only decreases by 9%, and no CO is generated during the reaction of the three catalysts, and the CO2 selectivity is 100%. Figure 8 The spinel carrier and catalyst samples obtained in Examples 1 and 2 were prepared in H2 -TPR test results show that there are more dispersed Cu particles on the surface of ZnCr2O4 spinel support, which may be the reason why its catalyst is the best.

Claims

1. A spinel-supported copper catalyst having a characteristic molecular formula It is A / ZnB2O4, where A=Cu, B=Cr, Al, Ga.

2. The method for preparing a spinel-supported copper catalyst according to claim 1, characterized in that The following steps are involved: (1) According to the molar ratio of metal ions at the A / B sites of spinel being 1:2, weigh Zn(NO3)2∙6H2O, Cr(NO3)3∙9H2O, Al(NO3)3∙9H2O, and Ga(NO3)3∙xH2O respectively and put them in a beaker, add an appropriate amount of deionized water, and stir at room temperature until dissolved; (2) Add 25 wt.% ammonia water dropwise to the solution obtained in step (1) while stirring to adjust the pH value to 9. After precipitation is complete, stir for 2 h, let stand for 2 h, filter and wash with deionized water until the TDS of the filtrate is less than 20 ppm; (3) drying the filter cake obtained in step (2) in an oven at 110°C for 12 h, taking it out and grinding it; (4) placing the product obtained in step (3) in a muffle furnace and heating it at a rate of 2 °C / min, and calcining it at 550 °C in an air atmosphere for 4 h to obtain spinel supports ZnCr2O4, ZnAl2O4, and ZnGa2O4, respectively; (5) Weigh the spinel support and Cu(NO3)2∙3H2O prepared in step (4) into a crucible, add an appropriate amount of deionized water, stir for 2 h, heat and stir in a 90 °C water bath to evaporate to dryness, place in a 110 °C oven until completely dry, and then grind; (6) The product obtained in step (5) was placed in a muffle furnace and heated at a rate of 2 °C / min, and calcined at 450 °C in an air atmosphere for 4 h to obtain spinel-supported copper catalysts Cu / ZnB2O4, Cu / ZnB2O4, and Cu / ZnB2O4, respectively.

3. Use of the spinel-supported copper catalyst according to claim 1 in hydrogen production by methanol steam reforming.

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