Gold Nanoparticles Supported on Fe₂O₃–MO(x) (M = Al, Zr, Zn) Composite Oxides for Partial Oxidation of Methanol.

Selective production of hydrogen by partial oxidation of methanol (POM), using gold supported on composite metal oxides, Fe2O3–MO x (M: Al, Zr, Zn) was investigated. The catalysts were characterized by TGA, XRD, TEM and XPS analyses. TGA and DTGA analysis indicates that minimum decomposition temperature required to obtain α-Fe2O3 in Fe2O3–ZrO2 composite support is 570 K. The catalytic activity and stability of Au/Fe2O3 catalyst is improved by using Al2O3 as an additional support, but there is no improved activity was observed with ZrO2. The uncalcined catalysts shows high activity for selective formation of hydrogen. The presence of Al2O3 in Au/Fe2O3–Al2O3 stabilize the gold particles against sintering during calcination as evidenced from TEM analysis. XPS analysis revealed that in the uncalcined catalysts gold is present as Au2O3 and Auº. The amount of metallic gold (Auº) in the catalyst increases with increase in calcination temperature. The catalytic behavior is related to the presence of highly dispersed Au of partially oxidized state in the catalyst. Under the optimized condition, the most active catalyst Au/Fe2O3–Al2O3 shows 100% conversion and 48% H2 selectivity at 523 K. The catalytic activity of Au/Fe2O3–Al2O3 catalysts in the temperature range 423–548 K showed that methanol conversion increased with rise in temperature and attains 100% at 448 K; Hydrogen selectivity increased with rise in temperature up to 523 K and then decreased at high temperatures. The overall reactions involved are methanol combustion, partial oxidation, steam reforming and decomposition. CO produced by methanol decomposition and/or by reverse water gas shift is subsequently transformed into CO2 and H2 by the water gas shift and/or CO oxidation thereby reduce the CO selectivity. The low hydrogen selectivity at high temperature is due to reverse water gas shift and/or hydrogen combustion.