Abstract
Effect of presence of oxygen upon steam reforming of methanol (CH3OH + H2O --6gt; 3H2 + CO2) is investigated with ZnO supported various group 8-10 metal catalysts. In the absence of oxygen, Pd/ZnO and Pt/ZnO catalysts exhibit high activity and selectivity for the steam reforming, while the other group 8-10 metal catalysts such as Fe, Co, Ni, Ru and Ir give poor selectivity and the decomposition of methanol (CH3OH --> 2H2 + CO) occurs in preference to the steam reforming. Effects of the presence of oxygen over Pd/ZnO and Pt/ZnO catalysts are markedly different from those over the other group 8-10 metal catalysts. Over Pd/ZnO and Pt/ZnO catalysts, partial oxidation of methanol (CH3OH + 1/2O2 --> 2H2 + CO2) rapidly occurs with high selectivity and conversion of methanol and rate of hydrogen production are drastically enhanced in the presence of oxygen. By contrast, over the other group 8-10 metal catalysts, oxidation of methanol (CH3OH + 3/2O2 --> 2H2O + CO2) occurs predominantly and the rate of hydrogen production is not so increased, although the conversion of methanol is increased. Characterization studies by means of temperature-programmed reduction and X-ray diffraction reveal that PdZn and PtZn alloys are formed by reduction of Pd/ZnO and Pt/ZnO catalysts at high temperature, whereas for the other group 8-10 metal catalysts, no alloys are formed. The steam reforming and partial oxidation of methanol selectively proceed on such Pd and Pt alloys.
