Deactivation during carbon dioxide reforming of methane over Ni catalyst:: microkinetic analysis

The kinetics of CO(2) reforming of methane was investigated experimentally over a Ni/CaO-Al(2)O(3) catalyst at temperatures of 500 and 650 degreesC, total pressures of 0.1 and 0.5 MPa and a CO(2)/CH(4) ratio of 1. The kinetic data including carbon formation and deactivation were measured simultaneously by an oscillating microbalance reactor. A microkinetic model was developed to analyze the kinetic data and extended with reactions for the carbon formation (encapsulating and filamentous) and deactivation. The deactivation was described at a microkinetic level, and the changes in activity and selectivity were related to the changes in the surface site coverage of different species caused by an increase in the surface site coverage of encapsulating carbon with time on stream. The deactivation rate depends significantly on the ensemble size required for each reaction. Ensemble sizes of 3, 4 and 6 were determined for the reforming reaction, water-gas shift reaction and encapsulating carbon forming reactions, respectively. The carbon formation deactivated faster than the dry reforming as a result of the larger ensemble size required for the carbon formation. Higher pressure and lower space velocity increased the carbon formation. The cyclical treatment of carbon formation and gasification reduced the carbon formation rate. (C) 2001 Elsevier Science Ltd. All rights reserved.