Influence of the Catalyst Preparation Method, Surfactant Amount, and Steam on CO_2 Reforming of CH_4 over 5Ni/Ce_(0.6)Zr_(0.4)O_2 Catalysts

摘要

A series of ceria-zirconia mixed oxide supports with nominal composition "CeoZr0402B were synthesized by two different routes, namely, a surfactant-assisted route and a coprecipitation route. Among the supports obtained by the surfactant-assisted route, different surfactant/metal molar ratios (namely, 1.25, 0.8, and 0.5) were employed to study the influence of the surfactant amount on the catalyst performance. A nominal S wt % Ni was impregnated on the supports by a wet impregnation method. These catalysts were evaluated for CO_2 reforming of CH4 in both the presence and absence of steam. The textural, structural, and physicochemical characteristics of the catalysts were thoroughly investigated with the help of various bulk and surface characterization techniques. The activity results indicate the superior nature of the catalysts obtained by the surfactant-assisted route over the one obtained by coprecipitation. Also, within the limits of the surfactant ratios used, the amount of surfactant employed during the course of support preparation seems to affect the activity, with catalysts prepared with the higher surfactant/metal molar ratio exhibiting better activity and enhanced stability. Structure "activity relationships (SARs) were formulated for some of the characteristics in order to explain the marked difference in activity between the catalysts obtained by the surfactant-assisted and coprecipitation methods and between the catalysts prepared by the surfactant-assisted route but with different surfactant/metal molar ratios. The SARs helped to identify that high oxygen storage capacity, high surface area, high reducibility, higher nickel surface area, better nickel dispersion, and higher surface nickel content are necessary for good performance in the CO_2 reforming of CH4. On the whole, catalysts obtained by the surfactant-assisted route exhibit a reasonably good performance in the CO_2 reforming reaction but were prone to deactivarion in the presence of steam. The inherent hydrophUic nature of the ceria-zirconia support is the main cause for the apparent deactivation in the presence of steam.