Multi-scale phenomena in heterogeneous catalytic processes - impact of chemical phenomena under the micro-scale level on catalyst

Catalyst design requires consideration of all the different dimensional scales involved in heterogeneous catalysis. Identifying phenomena at every scale and defining all the dominant mechanisms are of significance to the multi-scale analysis. Rather than systematically summarizing all the principles of catalyst design encountered at every dimensional scale, the impact of chemical phenomena under the levels of nano-scale and subnano-scale (micro-scale) on catalyst design is illustrated in this paper with two examples in detail. The demonstrations are based on the recent advances of the surface structure and reaction performance of a commercially important PtSn/Al2O3 catalyst for reforming and dehydrogenation of hydrocarbons, and the dehydro-aromatization of methane in the absence of oxygen over a recently explored Mo/HZSM-5 catalyst. The studies of these two cases include the interaction among active components and the synergy between active sites on the catalyst surface. Emphasis is given to the realization and understanding of solid catalyst structure and catalytic performance under the micro-scale level through the use of advanced analytical techniques. (C) 2004 Elsevier Ltd. All rights reserved