MONO AND BIFUNCTIONAL PATHWAYS OF CO2 CH4 REFORMING OVER PT AND RH BASED CATALYSTS/

Despite the high thermodynamic driving force to form coke under the re action conditions applied Pt/ZrO2 and Rh supported on gamma-Al2O3 and ZrO2 are active and stable catalysts for CO2/CH4 reforming. Using stea dy state, transient kinetic measurements and physico-chemical characte rization techniques have shown that the catalyst activity is determine d by the available Pt-ZrO2 perimeter. Methane is decomposed on the met al to CHx (average value of x = 2) and H-2. The main route to CO2 redu ction occurs via initial formation of carbonate close to the metal-sup port boundary. Carbon on the metal reduces that carbonate to formate b y forming CO. The formate decomposes rapidly to CO and a surface hydro xyl group. Hydroxyl groups recombine and form water or react further w ith methane to CO and hydrogen (steam reforming). When the rate of met hane decomposition and carbonate reduction are in balance, the catalyt ic activity remains stable. In contrast, the activity of Rh is mainly determined by the concentration of accessible surface atoms and a conc erted metal catalyzed mechanism of methane decomposition and subsequen t CO2 reduction dominates. The support plays a minimal role in that ch emistry. (C) 1998 Academic Press.