Study On Preparation And Catalytic Performance Of Catalysts For Carbon Dioxide Reforming Of Methane

The catalytic reforming of CH₄ with CO₂ is industrially attractive not only because it yields syngas with H_2/CO ratio (＜1) desirable for Fischer-tropsch synthesis, but also because it can be used in some plant favorable circumstances to transform effluent containing CO₂ into valuable feedstock, which is of great importance to control increasing environmental pollution. Catalyst deactivation which is caused by coke deposition and/or sintering at high temperature in high C/H ratio feed is the biggest problem of CH₄/CO₂ reforming reaction. Preparation of catalyst with high activity and stability is the key of CH₄/CO₂ reforming reaction.A serial of works about CH₄/CO₂ reforming catalysts are conducted in this dissertation. First, bimodal supports are obtained by incipient-wetness impregnation of commercial available silica gel Q-50 with SiO₂, ZrO₂ and A1₂O₃ sol, respectively. The surface area, pore size distribution and pore volume of catalysts are investigated by N₂ physical absorption. Experiment results prove that the obtained bimodal support shows a large and a small pore at the same time and increased BET surface area, compared to Q-50. Platinum-supported catalysts with 3wt% metal loading are prepared by incipient-wetness impregnation of different supports, including bimodal ones, and then, their characterization and the effect on the reaction of CO₂ reforming CH₄ are investigated by activity assay, Chemisorption, XRD and TGA-DTA, besides, the effect of W/F and chemical effect of precursor sols are also investigated. Experiment results reveal that Platinum-supported bimodal catalysts show higher Pt metal dispersion, better diffusion of reactant and resultant and higher catalytic activity. 3wt%Pt/Al₂O₃ bimodal catalyst show highest catalytic activity under W/F=1g.h/mol reaction condition and the initial conversion of CO₂ arrive at 84%. The deactivations of Pt-supported bimodal catalysts are caused by sintering rather than by coke deposition.Subsequently, CexZr_1-xO₂ solid solution support is prepared by co- precipitation method. Nickel-supported catalysts are obtained by impregnation of Ce_xZr_1-xO₂ supports with nickel precursor. To investigate the effect of preparation method on catalytic performance of catalyst, Ni_xCe_yZr_1-yO₂ solid solution catalyst is prepared by co-precipitation method, directly. The characterization and catalytic performance of nickel-supported catalyst is investigated by activity assay, XRD and TGA-DTA, besides, the effect of Ce/Zr ratio and W/F on catalytic activity is also investigated. Experiment results show that co-precipitation method prepared catalyst show better activity, compared with the catalyst prepared by impregnation method. The activity of catalyst is increased at bigger W/F and nickel-supported catalyst show highest activity at Ce/Zr=1. The initial conversion of CO₂ over NiCZ50 catalyst reaches 83.9% at W/F=0.5g. h/mol. The coke generation rate of nickel-supported catalyst prepared by co-precipitation method is quicker than nickel-supported catalyst prepared by impregnation method. There are two kinds of coke deposited on nickel-supported catalyst surface:α-C andβ-C, of which,β-C is responsible for catalyst deactivation.