Methanol-steam reforming on Cu/ZnO/Al2O3 catalysts. Part 2. A comprehensive kinetic model

Surface mechanisms for methanol-steam reforming on Cu/ZnO/Al2O3 catalysts a re developed which account for all three of the possible overall reactions: methanol and steam reacting directly to form H-2 and CO2, methanol decompo sition to H-2 and CO and the water-gas shift reaction. The elementary surfa ce reactions used in developing the mechanisms were chosen based on a revie w of the extensive literature concerning methanol synthesis on Cu/ZnO/Al2O3 catalysts and the more limited literature specifically dealing with methan ol-steam reforming. The key features of the mechanism are: (i) that hydroge n adsorption does not compete for the active sites which the oxygen-contain ing species adsorb on, (ii) there are separate active sites for the decompo sition reaction distinct from the active sites for the methanol-steam react ion and the water-gas shift reaction, (iii) the rate-determining step (RDS) for both the methanol-steam reaction and the methanol decomposition reacti on is the dehydrogenation of adsorbed methoxy groups and (iv) the RDS for t he water-gas shift reaction is the formation of an intermediate formate spe cies. A kinetic model was developed based on an analysis of the surface mec hanism. Rate data were collected for a large range of conditions using a fi xed-bed differential reactor. Parameter estimates for the kinetic model wer e obtained using multi-response least squares non-linear regression. The re sultant model was able to accurately predict both the rates of production o f hydrogen, carbon dioxide and of carbon monoxide for a wide range of opera ting conditions including pressures as high as 33 bar. (C) 1999 Elsevier Sc ience B.V. All rights reserved.