Reforming of methane with carbon dioxide to synthesis gas over supported rhodium catalysts .1. Effects of support and metal crystallite size on reaction activity and deactivation characteristics

The effects of carrier and metal particle size on the catalytic performance (initial intrinsic activity and deactivation characteristics) of Rh in the reaction of reforming of methane with carbon dioxide were investigated. The specific activity of Rh catalysts was found to strongly depend on the carrier employed to disperse the metal, decreasing in the order yttria-stabilized zirconia (YSZ) > Al2O3 > TiO2 > SiO2 > La2O3 > MgO, a result which correlates directly with the acidity characteristics of the carrier. The initial intrinsic activity and rate of deactivation of Rh were also found to be sensitive to the metal particle size, in the range 1 similar to 6 nm. Both activity and rate of deactivation were found to decrease with increasing metal particle size. However, the degree of these dependences was found to be largely affected by the nature of the carrier, suggesting that the dependence of activity and rate of deactivation on metal particle size is likely to be related to metal-support interactions. While relatively high deactivation rates were observed over Rh supported on TiO2 and MgO, lower deactivation rates were observed over Rh supported on YSZ, Al2O3, La2O3, and SiO2. Evidence was found that at least three kinds of factors contribute to catalyst deactivation, namely, carbon deposition, metal sintering, and poisoning of surface Rh sites by species originating from the carrier. The importance of each of these factors was found to be determined by the nature of the carrier. (C) 1996 Academic Press, Inc.