Thermostable Rh Catalysts Supported on Metal Phosphates: Effect of Aging on Catalytic Activity for NO–CO–C3H6–O2 Reactions

Abstract

Abstract The catalytic activity and thermostability of Rh catalysts (0.4% loading) have been studied using various metal phosphates (B, Al, Ga, Y, La, Pr, Zr, and Ce) as support materials. Temperature-programmed reactions of mixtures of NO, CO, C3H6, and O2 with the stoichiometric A/F ratio (14.6) exhibited a steep rise in conversion efficiency as a common feature of Rh supported on metal phosphates. The activity of Rh/AlPO4 was found to be the highest even after aging at 900 °C for 25 h in a stream of 10% H2O/air. Among four types of AlPO4 polymorphs having different BET surface area, i.e, berlinite (5 m2 g−1), cristobalite (1 m2 g−1), tridymite (82 m2 g−1), and microporous AlPO4-5 (330 m2 g−1), tridymite AlPO4 achieved the lowest light-off temperature. The slow grain growth of tridymite AlPO4 at ≤1000 °C is a possible reason for the stability against sintering, whereas one-dimensional micropores of AlPO4-5 are unstable in the high-temperature steam.