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

The kinetics of CO2 reforming of methane was investigated experimentally ov er a Ni/CaO-Al2O3 catalyst at temperatures of 500 and 650 degreesC, total p ressures of 0.1 and 0.5 MPa and a CO2/CH4 ratio of 1. The kinetic data incl uding carbon formation and deactivation were measured simultaneously by an oscillating microbalance reactor. A microkinetic model was developed to ana lyze the kinetic data and extended with reactions for the carbon formation (encapsulating and filamentous) and deactivation. The deactivation was desc ribed at a microkinetic level, and the changes in activity and selectivity were related to the changes in the surface site coverage of different speci es caused by an increase in the surface site coverage of encapsulating carb on 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 encaps ulating carbon forming reactions, respectively. The carbon formation deacti vated faster than the dry reforming as a result of the larger ensemble size required for the carbon formation. Higher pressure and lower space velocit y increased the carbon formation. The cyclical treatment of carbon formatio n and gasification reduced the carbon formation rate. (C) 2001 Elsevier Sci ence Ltd. All rights reserved.