The steam reforming of phenol reaction over supported-Rh catalysts

Abstract

The steam reforming of phenol reaction towards H2 production was studied in the 575-730°C range over Rh supported on CeO2, ZrO2 and SiO2 single metal oxides and various mixed metal oxides such as CeO2-SiO2, ZrO2-SiO2 and CeO2-ZrO2. The effect of synthesis method (wet impregnation versus sol-gel) of the mixed metal oxide used as support of Rh on the activity and selectivity of reaction towards hydrogen formation has also been investigated. It was found that the 1.5wt.% Rh/Ce-Zr-O catalyst, the support of which was prepared by the sol-gel method, exhibits better performance than a commercial Ni-based catalyst both solids examined under the same experimental conditions. The 1.5wt.% Rh/Ce-Zr-O catalyst presented practically constant hydrogen product concentration (~10mol%) in the 575-730°C range and after using a 0.5% C6H5OH/40% H2O/He feed gas mixture at a space velocity of 80.000h-1, to be compared to 8-9.5mol% H2 obtained over the commercial Ni-based catalyst. This particular supported-Rh catalyst showed also no more than 18% drop in activity after 24h of continuous reaction. The effect of Rh loading (0.5 and 1.5wt.%) on catalyst activity towards H2 production was studied over Rh supported on CeO2 and ZrO2. It was found that the steam reforming of phenol reaction is favored over catalysts with small Rh particles. The effect of the partial pressure of water and phenol in the reaction feed stream on catalyst activity towards hydrogen was found to strongly depend on catalyst support chemical composition and reaction temperature. Increasing the water concentration in the 20-40mol% range resulted in a significant increase of H2 product yield. A similar result was also obtained in the case of phenol in the 0.3-0.5mol% range. The accumulation of carbonaceous deposits during reaction conditions was investigated by temperature-programmed oxidation (TPO) and transient isothermal reaction with steam experiments following reaction. More than one kind of carbonaceous species have been identified with varying composition and reactivity towards oxygen and steam.