화학공학소재연구정보센터
Journal of Catalysis, Vol.161, No.1, 31-42, 1996
Transient Kinetic-Study of the Oxidation and Hydrogenation of Carbon Species Formed During CH4/He, CO2/He, and CH4/CO2 Reactions over Rh/Al2O3 Catalyst
The dissociation of CH4 and CO2 on 0.5 wt% Rh/Al2O3 catalyst has been investigated at 650 degrees C using transient techniques with on-line mass spectrometry. The dissociation of CH4 results in the formation of large amounts of gaseous H-2 and carbonaceous species (CxHy, y congruent to 0) on the surface after 10 min of reaction. Oxidation of these carbon species to CO2 proceeds with an intrinsic activation energy of 63 kJ mol(-1), while hydrogenation to CH4 with an intrinsic activation energy of the order of 240 kJ mol(-1). On the other hand, dissociation of CO2 results in the formation of much lower quantities of carbon species under the same reaction conditions. In this case, two kinds of carbon species were identified. Hydrogenation of the main carbon species proceeds with an activation energy of 96 kJ mol(-1), while its oxidation proceeds with significantly different kinetics than the carbon derived from CH4 dissociation. Characterization of carbon accumulated on the catalyst surface during reforming reaction of CH4 with CO2 has also been performed. It was found that this carbon mostly originates from the CO2 molecule and it is significantly more reactive than the carbon derived from CH4 decomposition, but of similar reactivity as the carbon derived from CO2 dissociation. Temperature-programmed hydrogenation (TPH) experiments of the carbonaceous species formed during reforming reaction at 650 degrees C revealed three different kinds of carbon species. The carbon species with the largest quantity hydrogenated to CH4, according to the TPH response, is found to be associated with an intrinsic activation energy of 125 kJ mol(-)1 for its hydrogenation process.