Novel methanol steam reforming activity and selectivity of pure In2O3

Electron-microscopy suitable In2O3 thin films prepared by thermal deposition of In2O3 powder in 10−2 Pa O2 at 600 K and, for comparison, a commercial polycrystalline In2O3 powder catalyst were tested in methanol steam reforming and in both routes of the water–gas shift reaction as a function of reaction temperature. The effect of oxidative (1 bar O2, 373–673 K, 1 h) and reductive (1 bar H2, 373–673 K, 1 h) catalyst pre-treatments was assessed. The resulting structural and morphological changes occurring during catalyst activation and catalytic reaction were monitored by (high-resolution) transmission electron microscopy, scanning electron microscopy and surface area measurements by N2 adsorption according to BET. Both the In2O3 thin film and the powder sample were observed to be structurally stable under typical catalyst pre-treatments in oxygen and hydrogen at temperatures T ≤ 673 K and T < 673 K, respectively, as well as under typical methanol steam reforming conditions at temperatures T ≤ 680 K. No pronounced catalyst sintering was observed below 673 K. Both In2O3 samples were found to be highly active and selective toward CO2 in methanol steam reforming over a broad temperature range (450 < T < 673 K). Selectivities of >95% toward CO2 were usually observed, with at maximum 5% or less CO formed. No dependence of selectivity on either reaction temperature or oxidative/reductive pre-treatment was observed. No catalytic activity in both routes of the water–gas shift reaction as tested in the same temperature region where the catalysts exhibit high reforming activity and selectivity, could be observed. Therefore In2O3 based catalysts offer a broad range of temperature not influenced by unwanted CO formation via the inverse water–gas shift process.