Study On Preparation And Catalytic Performance Of Ni Based Composite Support Catalysts

Methane reforming with carbon dioxide(dry reforming of methane) can resolve the greenhouse effect and has important significance in the energy gap filled. The yields of dry reforming of methane:syngas(H2、CO) can be further converted into new chemical products, that would reduce the cost and improve the economic benefits. There are various of catalysts in dry reforming of methane. The noble catalysts have high catalytic activity and less carbon deposition, but due to the expensive price and the limited resource, the Ni-based catalysts have been choosen as the catalysts in this thesis. The paper is focused on the selection of supporter, preparation of catalysts and addition of promoter, for improving the performance and stability of Ni-based catalysts.The impregnation method and coprecipitation method were used in the preparation of MgO-ZrO2supporter. After studying on the supporters, the3MgO-ZrO2-C which was prepared by the coprecipitation method is the best choice either from its morphology or the particle size. The preparation conditions are as follows:ZrOCl2·8H2O solution and Mg(NO3)2solution were prepared, and NH3·H2O was diluted taken as precipitation agent. The two solutions were mixed in water bath at373K according to the molar ratio of Mg/Zr=3:1. NH3-H2O was slowly added into the mixed solution under controlled pH of10and constant stirring until white sediments stopped increasing. The filtratated sediments were dried in the oven at383K for12h and calcinated in the Muffle Furnace at873K. for3h. The particle of supporter is regular in shape and the average particle diameter can be achieved33.5nm.In comparison, the10%Ni/1MgO-ZrO2-J catalyst whose supporter was prepared by the impregnation method has the best activity. Also the10%Ni/1MgO-ZrO2-C catalyst whose supporter was prepared by the coprecipitation method has the higest activity. However,10%Ni/1MgO-ZrO2-C catalyst’s activity is more higher than that of the10%Ni/1MgO-ZrO2-J catalyst.It is determined that the optimum Ni content is10%in the modified catalysts, and also the La promoter was added to the catalysts. First impregnated Ni and then La is determined as the better impregnation sequence. Comparatively, the10%Ni-3%La/3MgO-ZrO2-J catalyst’s activity is higher than that of the10%Ni/1MgO-ZrO2-J catalyst. There are reasons as follow: suitable addition of La can improve the metal-support interaction and the amount of active center is increased.The catalysts10%Ni/3MgO-ZrO2-C and10%Ni/1MgO-ZrO2-J were studied by the pulse experimental. The pulses of CH4�'+CO2�'CH4and CO2�'CH4�'CO2can determine that the methane decomposition shows high activity in the pulse experimental, but also the carbon elimination is occurred between CO2and the carbon deposition which increases the generation of CO. Because of10%Ni/3MgO-ZrO2-C catalyst has higher metal-support interaction, its supporter can provide much more oxygen vacancies to produce more H2and CO.