Water-containing ethanol reforming hydrogen production catalyst and preparation method thereof

Abstract

The invention discloses a hydrous ethanol reforming hydrogen production catalyst and a preparation method thereof. The preparation method comprises the following steps: (1) carrier pretreatment; (2) preparing a CeO2 / Al2O3 carrier; (3) according to the mass ratio of Ni to Co to Mn to Mg to the gamma-Al2O3 carrier being (8-10): (3-5): (2-2.5): (2-3): 100, dissolving nitrate of each metal in water, adding citric acid to prepare a mixed solution, and then immersing the CeO2 / Al2O3 carrier in the mixed solution for dipping; and (4) drying and roasting. The CeO2 / Al2O3 composite carrier is firstly prepared, so that the oxygen vacancy and the oxygen storage capacity can be enhanced, and the sintering resistance of the catalyst is improved. The raw materials adopted by the prepared catalyst do not contain precious metal, and the cost is low. The catalyst takes Ni and Co as main active components and Ce, Mn and Mg as cocatalysts, and through the synergistic effect of multiple metals and the carrier, the catalyst is good in catalytic activity, high in H2 selectivity, stability, sintering resistance and carbon deposition resistance and good in low-temperature activity; the hydrogen yield can be obviously improved when the catalyst is used for catalyzing hydrous ethanol reforming hydrogen production.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial reforming hydrogen production, and particularly relates to a catalyst for reforming hydrogen production from aqueous ethanol and a preparation method thereof. Background Art

[0002] Hydrogen energy is widely regarded as one of the alternative energies due to its high energy density, high thermal conversion efficiency, non-greenhouse gas combustion products, cleanliness, high efficiency and other characteristics, and is widely used in social life. The development of hydrogen fuel cells has promoted the utilization of hydrogen energy into a brand-new field. Compared with traditional hydrogen production fuels such as natural gas, hydrogen production from biomass ethanol as raw material uses renewable raw materials, does not rely on fossil energy, and has advantages such as high unit energy, high hydrogen content, non-toxicity, easy storage and transportation, etc., and has become a hot spot in recent years.

[0003] Currently, there are mainly three ways to produce hydrogen from biomass ethanol: steam reforming of ethanol (SRE), partial oxidation of ethanol (POX) and autothermal / oxidative reforming of ethanol (ATR). Among them, steam reforming of ethanol stands out among many hydrogen production raw materials due to its high hydrogen content, non-toxicity, easy storage and operational safety. In the hydrogen production reaction, steam reforming of ethanol to produce hydrogen has unique advantages: (1) Ethanol has a wide source, and the raw materials used in the biological fermentation method to produce ethanol can be regenerated; (2) Ethanol is non-toxic, is in a liquid state at normal temperature and pressure, is easy to store, transport and is safe; (3) The energy of ethanol is much higher than that of methanol and hydrogen; (4) Ethanol has thermal diffusivity on the catalyst, and on a highly active catalyst, ethanol reforming can occur in a low temperature range. However, the reaction system is complex and there are many by-products. Therefore, the catalyst used is particularly important.

[0004] The hydrogen production reaction by ethanol steam reforming usually requires the assistance of a catalyst to improve the hydrogen production efficiency. According to the existing literature reports, the current catalysts for ethanol steam reforming to produce hydrogen mainly include nickel-based catalysts, copper-based catalysts, cobalt-based catalysts, and noble metal catalysts, etc. Among them, nickel-based catalysts and cobalt-based catalysts have relatively high catalytic performance, relatively low reaction temperature, and good activity, but they are prone to deactivation phenomena such as sintering and carbon deposition during the reaction. Noble metal catalysts are favored in the ethanol steam reforming reaction due to their excellent catalytic performance and stability. Currently, the mainly reported catalyst systems include Rh, Ru, Pt, and Ir-based catalysts, etc. Rhodium (Rh) is a commonly used active component because of its good ability to break C-C bonds. Compared with Ni and Co-based catalysts, noble metal catalysts show relatively high catalytic activity at low loadings, but there are problems such as high reaction temperatures, about 600 - 800 °C, expensive noble metals, high costs, low reserves, and difficulty in widespread use. For supported catalysts, different carriers also have a great influence on the performance of the catalyst. The carrier helps to improve the dispersion of the active component; through the interaction between the carrier and the active component, sintering during the reaction can be reduced, and the catalytic effect can be improved. Therefore, it is of great significance to study a catalyst for aqueous ethanol reforming to produce hydrogen with high catalytic activity, selectivity, stability, good catalytic effect, and low cost. Summary of the Invention

[0005] The purpose of the present invention is to provide a catalyst for aqueous ethanol reforming to produce hydrogen and its preparation method in view of the deficiencies of the prior art. Through the synergistic effect of multiple metals and the carrier, the present invention improves the H2 selectivity, anti-sintering property, and anti-carbon deposition ability of the prepared catalyst, can significantly improve the hydrogen production rate and stability. The catalyst prepared by the method of the present invention has good catalytic activity, relatively high selectivity, stability, and anti-carbon deposition performance. Moreover, the catalyst does not powder, does not deposit carbon, and has good durability; the raw materials used do not contain noble metals, the preparation method is simple, and the cost is low.

[0006] The technical solution adopted by the present invention is as follows: A preparation method of a catalyst for aqueous ethanol reforming to produce hydrogen, comprising the following steps: (1) Carrier pretreatment: Roast the γ-Al2O3 carrier with a particle size of 1 - 3 mm at 490 - 500 °C for 3 - 4 hours and then cool it to room temperature, which can remove surface impurities and stabilize the crystal phase; (2) Preparation of CeO2 / Al2O3 support: According to the mass ratio of Ce to γ-Al2O3 support being 6.5 - 8:100, take cerium nitrate, dissolve it in deionized water, add the obtained solution to the γ-Al2O3 support for mixing and stirring, then dropwise add ammonia water or Na2CO3 solution until the pH is 9 - 10, age for 2 - 2.5 hours, filter and wash until neutral, dry at 100 - 110 °C for 12 - 13 hours, and calcine at 500 °C for 4 hours to obtain the CeO2 / Al2O3 support; (3) Impregnation: According to the mass ratio of Ni:Co:Mn:Mg:γ-Al2O3 support being 8 - 10:3 - 5:2 - 2.5:2 - 3:100, take nitrates of each metal, dissolve them in deionized water, then add 12 - 16% of citric acid based on the total mass of nitrates, stir evenly to obtain a mixed solution; immerse the CeO2 / Al2O3 support in the mixed solution, stir at room temperature for 2 - 4 hours, and then let it stand for 10 - 12 hours; (4) Drying and calcination: After the impregnation is completed, dry the material, then place it in a muffle furnace and calcine at 500 °C for 4 - 5 hours, and cool to room temperature to obtain the product.

[0007] Further, in the preparation method of the above-mentioned aqueous ethanol reforming hydrogen production catalyst, in step (4), the drying of the material specifically means drying the material at 90 - 110 °C for 12 - 13 hours to remove moisture.

[0008] The present invention also provides a catalyst prepared by using the preparation method of the above-mentioned aqueous ethanol reforming hydrogen production catalyst.

[0009] The application of the catalyst prepared by the present invention in the aqueous ethanol / ethanol steam reforming hydrogen production reaction. Specifically in application, the aqueous ethanol solution can be vaporized in a vaporizer and then introduced into a hydrogen production reactor filled with the catalyst of the present invention, and hydrogen-rich gas is prepared at normal pressure and a temperature of 300 - 500 °C. The catalyst prepared by the present invention is suitable for catalyzing the aqueous ethanol / ethanol steam reforming hydrogen production, and can be applied to in-situ hydrogen production in hydrogen refueling stations and on-vehicle on-line hydrogen production.

[0010] The beneficial effects of the present invention are as follows: 1. In the present invention, γ-Al2O3 is used as the support. γ-Al2O3 has the characteristics of high specific surface area, good mechanical strength and thermal stability, and can provide abundant anchoring sites to ensure the highly dispersed active components; by performing calcination pretreatment on the γ-Al2O3 support, surface impurities can be removed and the crystal phase can be stabilized, and the porosity can be increased.

[0011] 2. In the present invention, cerium (Ce) nitrate is first loaded onto a γ-Al2O3 support to form a CeO2 / Al2O3 composite support, which can enhance oxygen vacancies and oxygen storage capacity, improve the dispersion of Ni, Co, Mn, and Mg, and increase the number of active sites. The oxygen vacancies of CeO2 can promote the water-gas shift reaction, reduce CO by-products, and increase the H2 yield. Moreover, CeO2 can remove surface carbon deposits through oxidation, and the high thermal stability of CeO2 can delay the high-temperature deactivation of the support and metal particles, preventing high-temperature sintering. Preparing the CeO2 / Al2O3 composite support first can improve the anti-sintering and anti-carbon deposition properties of the prepared catalyst; Ce 3+ / Ce 4+ cycle can promote the dynamic reduction of the active metal during the reaction process and maintain the catalytic activity.

[0012] 3. In the preparation method of the present invention, adding citric acid to the nitrate solutions of the prepared metals can promote the dispersion of metal ions and prevent the aggregation of active components.

[0013] 4. The catalyst prepared by the present invention uses nickel (Ni) and cobalt (Co) as the main active components. Ni can improve the C-C bond breaking ability, promote ethanol dehydrogenation and cracking, and Co can enhance the water-gas shift reaction (WGSR), promote the conversion of CO to H2, and reduce CO by-products. Ni has high activity but is prone to carbon deposition. The addition of Co can adjust the electronic structure of Ni, enhance the anti-carbon deposition ability, and improve the low-temperature activity. The Ni-Co bimetal synergistically can effectively promote C-C bond breaking and dehydrogenation, improve H2 selectivity and anti-carbon deposition ability, and increase the hydrogen yield. Moreover, using non-precious metals as the main active components can reduce the production cost.

[0014] 5. In the present invention, manganese (Mn) and magnesium (Mg) are used as co-catalysts and combined with nickel (Ni) and cobalt (Co). Mn can adjust the electronic structure of Ni / Co, enhance the C-C bond breaking ability, weaken the strong adsorption of carbon species, and inhibit carbon deposition. Moreover, CeO2 and Mn, Mn 3+ promote the dehydrogenation of ethanol to acetaldehyde, Ce 4+ / Ce 3+ oxidizes acetaldehyde to CO and H2, and the oxygen vacancies and MnOx composite can promote carbon gasification, thereby playing a synergistic role in carbon elimination. Moreover, by adding manganese elements, the redox performance of the catalyst can be improved (Mn 2+ / Mn 3+The cycle inhibits the sintering of metal particles at high temperatures and maintains dispersibility. The basicity of the MgO introduced in the catalyst of the present invention can neutralize the acidic sites existing on the surface of the Al2O3 support, modulate the acidity and basicity of the catalyst surface, inhibit the dehydration of ethanol to produce ethylene (a precursor of carbon deposition), and reduce carbon deposition. Moreover, Mg can stabilize Ni crystallites and inhibit agglomeration. The oxides of Mn and Mg can enhance the anti-sintering property and the concentration of oxygen vacancies, promote the water-gas shift reaction, enhance the anti-carbon deposition ability of the catalyst, and reduce the reduction temperature through the interaction with Ni / Co, thereby increasing the hydrogen yield and stability.

[0015] 6. The raw materials used for the catalyst for reforming water-containing ethanol to produce hydrogen prepared by the present invention do not contain precious metals, and the preparation method is simple and the cost is low. Through the synergistic effect of multiple metals and the support, the present invention improves the H2 selectivity, anti-sintering property and anti-carbon deposition ability of the prepared catalyst, and can significantly increase the hydrogen yield and stability. The catalyst prepared by the method of the present invention has good catalytic activity, high selectivity, stability, anti-sintering and anti-carbon deposition properties, good low-temperature activity, and the ethanol conversion rate reaches more than 99% at 300 °C; moreover, the catalyst does not powder, does not deposit carbon, and has good durability. Using the catalyst prepared by the present invention for catalytic reforming of water-containing ethanol / ethanol steam to produce hydrogen can significantly increase the hydrogen yield, and the ethanol conversion rate and hydrogen yield are high. Detailed implementation mode Example 1

[0016] A preparation method of a catalyst for reforming water-containing ethanol to produce hydrogen, comprising the following steps: (1) Support pretreatment: The γ-Al2O3 support with a particle size of 1-3 mm is calcined at 490 °C for 4 hours and then cooled to room temperature to remove surface impurities and stabilize the crystal phase; (2) Preparation of CeO2 / Al2O3 support: According to the mass ratio of Ce:γ-Al2O3 support of 6.5:100, cerium nitrate (Ce(NO3)3•6H2O) is taken and dissolved in deionized water. The obtained solution is added to the γ-Al2O3 support, mixed and stirred, and then ammonia water is added dropwise until the pH = 9-10, aged for 2 hours, filtered and washed to neutral, dried at 100 °C for 13 hours, and calcined at 500 °C for 4 hours to obtain the CeO2 / Al2O3 support; (3)Impregnation: According to the mass ratio of Ni∶Co∶Mn∶Mg∶γ-Al2O3 support being 8∶3∶2∶2∶100, take the nitrates of each metal: nickel nitrate (Ni(NO3)2•6H2O), cobalt nitrate (Co(NO3)2•6H2O), manganese nitrate (Mn(NO3)2•4H2O), and magnesium nitrate (Mg(NO3)2•6H2O), dissolve them in deionized water, then add 12% citric acid based on the total mass of the nitrates, stir evenly to obtain a mixed solution; immerse the CeO2 / Al2O3 support in the mixed solution, stir at room temperature for 2 hours, and then let it stand for 12 hours; (4)Drying and calcination: After the impregnation, dry the material at 90 °C for 13 hours to remove moisture; then place it in a muffle furnace and calcine at 500 °C for 4 hours, and cool to room temperature to obtain the product. Example 2

[0017] A preparation method of a catalyst for reforming aqueous ethanol to produce hydrogen includes the following steps: (1)Support pretreatment: Calcinate the γ-Al2O3 support with a particle size of 1 - 3 mm at 500 °C for 3 hours and then cool to room temperature to remove surface impurities and stabilize the crystal phase; (2)Preparation of CeO2 / Al2O3 support: According to the mass ratio of Ce∶γ-Al2O3 support being 7:100, take cerium nitrate (Ce(NO3)3•6H2O), dissolve it in deionized water, add the resulting solution to the γ-Al2O3 support, mix and stir, then dropwise add Na2CO3 solution until the pH is 9 - 10, age for 2.5 hours, filter and wash until neutral, dry at 110 °C for 12 hours, and calcine at 500 °C for 4 hours to obtain the CeO2 / Al2O3 support; (3)Impregnation: According to the mass ratio of Ni∶Co∶Mn∶Mg∶γ-Al2O3 support being 9∶4∶2.5∶2∶100, take the nitrates of each metal: nickel nitrate (Ni(NO3)2•6H2O), cobalt nitrate (Co(NO3)2•6H2O), manganese nitrate (Mn(NO3)2•6H2O), and magnesium nitrate (Mg(NO3)2•6H2O), dissolve them in deionized water, then add 14% citric acid based on the total mass of the nitrates, stir evenly to obtain a mixed solution; immerse the CeO2 / Al2O3 support in the mixed solution, stir at room temperature for 3 hours, and then let it stand for 11 hours; (4)Drying and calcination: After the impregnation, dry the material at 100 °C for 12.5 hours to remove moisture; then place it in a muffle furnace and calcine at 500 °C for 4.5 hours, and cool to room temperature to obtain the product. Example 3

[0018] A preparation method of a catalyst for reforming aqueous ethanol to produce hydrogen includes the following steps: (1) Carrier pretreatment: The γ-Al2O3 carrier with a particle size of 1 - 3 mm is calcined at 500 °C for 3.5 hours and then cooled to room temperature; (2) Preparation of CeO2 / Al2O3 carrier: According to the mass ratio of Ce∶γ-Al2O3 carrier of 8:100, cerium nitrate (Ce(NO3)3•6H2O) is taken and dissolved in deionized water. The obtained solution is added to the γ-Al2O3 carrier, mixed and stirred, then ammonia water is added dropwise until pH = 9 - 10, aged for 2.5 hours, filtered and washed until neutral, dried at 100 °C for 13 hours, and calcined at 500 °C for 4 hours to obtain the CeO2 / Al2O3 carrier; (3) Impregnation: According to the mass ratio of Ni∶Co∶Mn∶Mg∶γ-Al2O3 carrier of 10∶5∶2.5∶3∶100, nitrates of each metal are taken: nickel nitrate (Ni(NO3)2•6H2O), cobalt nitrate (Co(NO3)2•6H2O), manganese nitrate (Mn(NO3)2•4H2O), and magnesium nitrate (Mg(NO3)2•6H2O), dissolved in deionized water, and then 16% of citric acid based on the total mass of nitrates is added and stirred evenly to obtain a mixed solution; The CeO2 / Al2O3 carrier is immersed in the mixed solution, stirred at room temperature for 4 hours, and then left standing for 10 hours; (4) Drying and calcination: After impregnation, the material is dried at 110 °C for 12 hours to remove moisture; then placed in a muffle furnace and calcined at 500 °C for 5 hours, and cooled to room temperature to obtain the product. Example 4

[0019] A preparation method of a hydrogen production catalyst by aqueous ethanol reforming, comprising the following steps: (1) Carrier pretreatment: The γ-Al2O3 carrier with a particle size of 1 - 3 mm is calcined at 490 - 500 °C for 3 hours and then cooled to room temperature; (2) Preparation of CeO2 / Al2O3 carrier: According to the mass ratio of Ce∶γ-Al2O3 carrier of 7.2:100, cerium nitrate (Ce(NO3)3•6H2O) is taken and dissolved in deionized water. The obtained solution is added to the γ-Al2O3 carrier, mixed and stirred, then Na2CO3 solution is added dropwise until pH = 9 - 10, aged for 2.2 hours, filtered and washed until neutral, dried at 100 - 110 °C for 12.5 hours, and calcined at 500 °C for 4 hours to obtain the CeO2 / Al2O3 carrier; (3)Impregnation: According to the mass ratio of Ni∶Co∶Mn∶Mg∶γ-Al2O3 support being 9∶4∶2∶2.5∶100, take the nitrates of each metal: nickel nitrate (Ni(NO3)2•6H2O), cobalt nitrate (Co(NO3)2•6H2O), manganese nitrate (Mn(NO3)2•6H2O), and magnesium nitrate (Mg(NO3)2•6H2O), dissolve them in deionized water, then add citric acid accounting for 13% of the total mass of the nitrates, stir evenly to obtain a mixed solution; immerse the CeO2 / Al2O3 support in the mixed solution, stir at room temperature for 3 hours, and then let it stand for 12 hours; (4)Drying and calcination: After the impregnation, dry the material at 110°C for 12 hours to remove moisture; then place it in a muffle furnace and calcine at 500°C for 4.5 hours, and cool it to room temperature to obtain the product. Example 5

[0020] Catalytic effect experiment Load 0.5 g of the catalyst prepared in Example 2 into a fixed-bed reactor, and then pass an ethanol aqueous solution with an ethanol-to-water molar ratio of 1:6 into the reactor at a rate of 0.2 mL / min, with a liquid hourly space velocity of 5 h -1 , and react at normal pressure and 350°C. Use the condensation method to separate the gas and liquid products, and then detect and analyze the gas and liquid product samples respectively. The ethanol conversion rate is 100%, and the proportion of hydrogen in the gas-phase product is 71.654%.

Claims

1. A preparation method of a catalyst for hydrogen production by aqueous ethanol reforming, characterized in that, It includes the following steps: (1) Carrier pretreatment: The γ-Al2O3 carrier with a particle size of 1-3 mm is calcined at 490-500 °C for 3-4 hours and then cooled to room temperature. (2) Preparation of CeO2 / Al2O3 carrier: According to the mass ratio of Ce:γ-Al2O3 carrier of 6.5-8:100, take cerium nitrate, dissolve it in deionized water, add the obtained solution to the γ-Al2O3 carrier, mix and stir, then dropwise add ammonia water or Na2CO3 solution until the pH = 9-10, age for 2-2.5 hours, filter and wash until neutral, dry at 100-110 °C for 12-13 hours, and calcine at 500 °C for 4 hours to obtain the CeO2 / Al2O3 carrier. (3) Impregnation: According to the mass ratio of Ni:Co:Mn:Mg:γ-Al2O3 carrier of 8-10:3-5:2-2.5:2-3:100, take the nitrates of each metal, dissolve them in deionized water, then add 12-16% of citric acid based on the total mass of the nitrates, stir evenly to obtain a mixed solution; immerse the CeO2 / Al2O3 carrier in the mixed solution, stir at room temperature for 2-4 hours, and then stand for 10-12 hours. (4) Drying and calcination: After the impregnation is completed, the material is dried, and then calcined in a muffle furnace at 500 °C for 4-5 hours and cooled to room temperature to obtain the product.

2. The preparation method of the hydrogen production catalyst by aqueous ethanol reforming according to claim 1, characterized in that, In step (4), the drying of the material is specifically to dry the material at 90-110 °C for 12-13 hours to remove moisture.

3. The catalyst prepared by the preparation method of the hydrogen production catalyst for aqueous ethanol reforming as described in claim 1.

4. The application of the catalyst as described in claim 3 in the reaction of aqueous ethanol / ethanol steam reforming for hydrogen production.