Transformation of methanol in the presence of steam and oxygen over ZnO-supported transition metal catalysts under stream reforming conditions

Steam reforming of methanol (CH3OH + H2O → 3H2 + CO2) has been investigated with various ZnO-supported group 8-10 metal catalysts in the presence of oxygen. The catalysts may be classified into two groups according to their catalytic actions and properties. One group includes Pd/ZnO and Pt/ZnO catalysts, which are active for the steam reforming in the absence of oxygen. In the presence of oxygen, however, partial oxidation of methanol (CH3OH + (1/2)O2 → 2H2 + CO2) rapidly proceeds and the conversion of methanol into hydrogen is drastically enhanced. These catalysts are composed of PdZn and PtZn alloys, which catalyze the steam reforming and the partial oxidation of methanol in the absence and presence of oxygen, respectively. In addition, for Pd/ZnO catalysts, high Pd loading favors the partial oxidation, whereas lower Pd loading is beneficial to the oxidation of methanol similar to the second group of catalysts. The second group includes other group 8-10 metal catalysts such as Fe, Co, Ni, Ru and Ir, which have no alloy components, in contrast to the first group. The decomposition of methanol (CH3OH → 2H2 + CO) occurs with these catalysts in the absence of oxygen in preference to the steam reforming. In the presence of oxygen, the oxidation of methanol (CH3OH + (3/2)O2 → 2H2O + CO2) occurs predominantly and the production of hydrogen is not so improved, although the total conversion of methanol is increased.