Rh-Ni synergy in the catalytic partial oxidation of methane:: surface phenomena and catalyst stability

Ni, Rh and Rh/Ni containing catalysts obtained from hydrotalcite type precursors have been studied in the partial oxidation of methane. The catalysts have been characterised by HRTEM to evaluate the effectiveness of the preparation method in the dispersion of the metal. The tests carried out in the partial oxidation of methane at a residence time of 12 ms did not allow to enlighten significant differences of activity among the catalysts due to the proximity of the results with those obtained at the thermodynamic equilibrium. New tests at very low residence times have allowed the catalyst evaluation in conditions far from the thermodynamic equilibrium and in which oxygen is still present. The catalytic bed length and the amount of catalyst have been chosen after the analysis of the thermal profile with the IR thermography. The IR thermography was used with the different catalysts to measure the maximum surface temperature trend as a function of the residence time. The tests carried out at very short residence times allow to compare the catalysts in conditions where 02 is not totally converted and enlighten the high activity of the Rh/Ni catalysts in which the Ni is maintained in the reduced state by the Rh. The comparison of the catalysts have also been carried out studying the endothermic dry reforming at low residence times. The study of the dry reforming of methane have also been related to the evaluation of the activity of the consecutive reaction of the catalytic partial oxidation process, without the effect of a large heat production. Finally, the dry reforming was also used to measure the coke formation on the most active catalysts. (C) 2002 Elsevier Science B.V. All rights reserved.