CO2 reforming of CH4 over Rh-containing catalysts

Two series Rh catalysts were prepared depending on the kind of the support: (i) Rh supported on zeolite and (ii) on oxide carriers. Rh/NaY zeolite catalysts were prepared by ion-exchange from an aqueous solution of [Rh(NH3)(5)]Cl-3. Rh catalysts supported on gamma-Al2O3, Nb2O5 and TiO2 were prepared by incipient wetness impregnation method of the carrier with an aqueous solution of RhCl3.2H(2)O. The catalysts were characterized by X-ray diffraction (XRD) spectroscopy, nuclear magnetic resonance (NMR), temperature-programmed desorption of hydrogen (TPD-H-2). Test reaction for Rh catalysts was CO, reforming of methane at different reaction temperatures. TPD data showed that the dispersion of metal particles depends on the pretreatment activation procedures highest dispersion was observed for samples previously calcined and then activated in H. Catalysts activated directly in H-2, steam or submitted directly to the reaction conditions showed large metal particles. The effect of the protons on the destabilization of the zeolite framework during reaction was revealed by the higher Si/Al ratios, due to a dealumination of the zeolite. Neutralization of protons with solution of NaOH leaded to a stabilization of the dispersion and zeolite structure. Correlation between the dispersion and specific activity in CO2 reforming was found for zeolite-supported Rh catalysts. When the activities are compared by turnover frequencies, oxide-supported Rh catalysts are significantly more active compared to zeolite-supported ones due to a higher degree of participation of the reverse Water-gas shift reaction (WGSR). The difference in activity and thermal stability was related to the nature of the support. (C) 2002 Elsevier Science B.V All rights reserved.