The Preparation Of Nano-mesoporous ZnO And Composite Oxides And Their Catalytic Performances For The Steam Reform Of Methanol

A interesting catalyst for steam reforming of methanol is Pd/ZnO catalyst possessed highly activity and selectivity due to its high temperature resistance,uneasy aging and steady performance,but lower dispersion of active component Pd for the sake of smaller surface area of ZnO.It is recently shows that mesoporous metal oxides with large surface areas and uniform pore distribution show interesting catalystic properites which are superior to non-porous samples of the same metal oxides.There has been no report on mesoporous ZnO prepared by using hydrothermal method and triblock copolymer Pluronic F-127(F-127) worked as template reagent,Pd-based catalysts synthesized by taking advantage of deposition-precipitation method so far.The addition of Ce,Mg and Zr could not only promote the dispersion of Pd,but also enhance the catalytic activity and stabilities.In comparison to Pd/m-ZnO-MgO and Pd/m-ZnO-ZrO₂ catalysts,Pd/m-ZnO-CeO₂ catalyst has the best catalytic activity,H₂ yield and CO₂ selectivity for steam reforming of methanol.Herein,we first report a novel hydrothermal approach to synthesize mesoporous ZnO(m-ZnO) utilizing triblock copolymer Pluronic F-127,hexadecylamine and SDS as template reagents.In the same time,studying the effects of it's construction and performance by preparation conditions such as the pH value,preparation methods,the ratio of template reagents and Zinc resource and the hydrothermal and calcining temperature.The catalytic performance of Pd-based catalyst was determined by the reaction of steam reforming of methanol.The structural properties of m-ZnO and Pd/m-ZnO were characterised through FT-IR,XRD,BET,H₂-TPR methods and some significant rusults were obtained.1.Using triblock copolymer Pluronic F-127,hexadecylamine and SDS as template reagents,a series of m-ZnO have been synthesized by hydrothermal methods, respectively.In addition,The pH value,preparation methods,the ratio of template reagents and Zinc resource and the hydrothermal and calcining temperature have been studied.The results indicate that the mesoporouse Zine oxide with higher specific area,pore volumes and average pore diameter were synthesised by using F-127 as template reagent,the ratio of F-127 and Zinc resource is 1:500,CO(NH₂)₂ as precipitator and hydrothermal and calcining temperature are 90℃and 400℃, respectivily.2.The preparation methods(hydrothermal and precipitation) have some influence on the performance of mesoporous Zinc oxides.The m-ZnO has large surface area(124.7m²/g) which higher than that of literature value,pore volumes and average pore diameter.The may reason is that precipitator is CO(NH₂)₂ which can hydrolyze over 90℃and OH can be slowly,uniformily produced in the solution.3.Mesoporous and none-mesoporous Zinc oxide have been synthesized under hydrothermal condition.The BET surface area and pore volume of m-ZnO are about 124.7m²/g and 0.31cm³/g,respectively.Compared with the Pd/ZnO catalyst,except for lower stability,Pd/m-ZnO catalyst exhibits a much better catalytic performance in terms of methanol conversion,H₂ yield and CO₂ selectivity caused by higher dispersion of active secondary component Pd.4.A series of m-ZnO-MO_x(M=Ce,Mg and Zr) mesoporous mixed oxides and their Pd-based catalysts have been synthesized.The addition of Ce,Mg and Zr could not only further promote the dispersion of Pd,but also enhance the catalytic activity. In comparison to Pd/m-ZnO-MgO and Pd/m-ZnO-ZrO₂ catalysts,Pd/m-ZnO-CeO₂ catalyst had the best catalytic activity,H₂ yield and CO₂ selectivity for steam reforming of methanol,which can be related to the higher BET surface area,smaller Pd crystal size and stronger interaction between Pd and ZnO-CeO₂.5.Different amounts of Ce in Pd/m-ZnO_1-xCeO_2(x)(x=0.1,0.2,0.3,0.4,0.5,0.8) have different influence on the performance of catalysts,and Pd/m-ZnO_0.7CeO_2(0.3) is the best.It is due to the surface area of the m-ZnO_0.7CeO_2(0.3) is the largest,the interaction of the active species and the support is the strongest,the alkali sites and absorption of methanol of the catalyst is the most,all these are advantageous to the catalytic performance enhancement.