Chemical and geometric effects of Ce and washcoat addition on catalytic partial oxidation of CH4 on Rh probed by spatially resolved measurements

摘要

Using a spatially resolved sampling technique, the catalytic partial oxidation of CH4 to synthesis gas was investigated over 80 ppi alpha-Al2O3 foams coated with three catalytic formulations: 5 wt% Rh, 5 wt% Rh/2 wt% gamma-Al2O3 washcoat and 5 wt% Rh-2 wt% Ce/2 wt% gamma-Al2O3 washcoat. Experiments were performed at atmospheric pressure and similar to 8 millisecond contact time, with 20% v/v CH4 and C/O ratio equal to 1. Data show that the length of the oxidative zone (similar to 2 mm) is unaffected by the composition of the catalyst. The addition of gamma-Al2O3 washcoat to Rh coated monoliths allows the reaction to reach adiabatic equilibrium by increasing the rates of steam reforming and water gas shift. Additionally, both the maximum and the gradients in the temperature profiles decrease significantly with the addition of washcoat. Data collected on Rh-Ce/washcoat show that the adiabatic equilibrium composition is reached through a different kinetic route: the consumption of CH4 becomes slower, the production of CO2 exhibits a maximum, and the production of H2O is drastically moderated, suggesting that Ce has an active role in the CPO reaction kinetics. The features presented could be detected exclusively with spatially resolved measurements. (C) 2008 Elsevier Inc. All rights reserved.