CO2 reforming of propane over supported Rh

Abstract

The adsorption, decomposition, and reaction of propane with CO2 have been investigated on Rh catalysts, deposited on various supports. The strong interaction of propane with Rh was noticed above 273 K. By means of Fourier transform infrared spectroscopy, π-bonded propylene, di-σ-bonded propylene, and propylidyne have been identified. Propane underwent dehydrogenation and cracking on supported Rh at 824–923 K. Propylene formed with a selectivity of 50–60%. The other major products were ethylene and methane. The deposition of carbonaceous species was also observed, the hydrogenation of which occurred only above 700–750 K, with a peak temperature of 900–950 K. The amount of carbon was more than one order of magnitude higher than that of surface Rh atoms, suggesting its diffusion from the Rh onto the support. The presence of CO2 basically altered the reaction pathway of propane, and the formation of H2 and CO with a ratio of 0.42–0.59 came into prominence. Propylene was detected only in traces. This led to the assumption that propylene reacted quickly with CO2 over Rh after its formation. This idea was confirmed by separate study of the reaction of propylene with CO2. Taking into account the rates of decomposition of propane and CO2 on Rh catalysts, as well as the reaction orders, we came to the conclusion that the CO2 is involved in the rate-determining step of the dry reforming of propane. The highest specific rates for the production of H2 and CO were measured for Rh/TiO2; this was explained by the extended dissociation of CO2 due to the electronic interaction between Rh and TiO2.