CHARACTERIZATION OF CARBONACEOUS SPECIES FORMED DURING REFORMING OF CH4 WITH CO2 OVER NI CAO-AL2O3 CATALYSTS STUDIED BY VARIOUS TRANSIENT TECHNIQUES/

Carbon dioxide reforming of methane to synthesis gas at 750 degrees C over 5 wt% Ni/CaO-Al2O3 catalysts has been investigated with respect t o effects of support composition (CaO to Al2O3 ratio) on catalyst stab ility, amount and reactivity of carbon species formed during reaction, and relative proportion of reaction routes that lead to carbon format ion (CH4 vs CO2 molecule). Temperature-programmed oxidation (TPO) and hydrogenation (TPH) experiments, following reforming reaction with 20% CH4/20% CO2/He and 20% (CH4)-C-13/20% CO2/He mixtures, have been cond ucted for the aforementioned carbon characterization studies. Two kind s of carbon species (free of chemically bound hydrogen) were mainly fo und to accumulate on the catalyst surface, where the amount and reacti vity of them are influenced by the CaO/Al2O3 ratio used to deposit the nickel metal. Transient isothermal hydrogenation experiments of the c arbon species formed during reforming reaction resulted in CH4 respons es, where the time of appearance of the CH4 peak maximum in hydrogen s tream as a function of hydrogenation temperature was used to obtain th e intrinsic activation energy of the hydrogenation process. It was fou nd that this activation energy is influenced by the support compositio n. TPO experiments conducted following reforming reaction with (CH4)-C -13/CO2/He mixture have demonstrated that the relative amount of adsor bed carbon species formed via the CH4 and CO2 molecular routes was str ongly dependent on support composition. H-2 temperature-programmed des orption, temperature-programmed reduction, and X-ray photoelectron spe ctroscopic measurements conducted over the present catalysts suggest t hat the nickel particle morphology and its size distribution must be i nfluenced by the support composition, which in turn controls the origi n, the kinetics, and the reactivity of carbon deposition under reformi ng reaction conditions. (C) 1996 Academic Press, Inc.