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 reaction conditions applied Pt/ZrO2 and Rh supported on gamma-Al2O3 and ZrO2 are active and stable catalysts for CO2/CH4 reforming. Using steady state, transient kinetic measurements and physico-chemical characterization techniques have shown that the catalyst activity is determined by the available Pt-ZrO2 perimeter. Methane is decomposed on the metal to CHx (average value of x = 2) and H-2. The main route to CO2 reduction occurs via initial formation of carbonate close to the metal-support boundary. Carbon on the metal reduces that carbonate to formate by forming CO. The formate decomposes rapidly to CO and a surface hydroxyl group. Hydroxyl groups recombine and form water or react further with methane to CO and hydrogen (steam reforming). When the rate of methane decomposition and carbonate reduction are in balance, the catalytic activity remains stable. In contrast, the activity of Rh is mainly determined by the concentration of accessible surface atoms and a concerted metal catalyzed mechanism of methane decomposition and subsequent CO2 reduction dominates. The support plays a minimal role in that chemistry. (C) 1998 Academic Press.