Decomposition of methanol by Pd, Co, and bimetallic Co-Pd catalysts:: A combined study of well-defined systems under ambient and UHV conditions

We investigated the decomposition of methanol over Pd-based catalysts and the influence of Co as a second metal. To obtain mechanistic information on the reaction, we prepared structurally well-defined systems for studies in the ambient pressure regime and systems suitable for UHV studies in a dual approach. For the ambient pressure regime, monometallic and bimetallic Co/Pd nanoparticles supported on MgO were prepared by a wet-chemical method. FTIR spectroscopy was used to analyze the surface species that formed on the catalysts in the interaction with methanol, and the catalytic performance was studied in continuous-flow reactors. We found that methanol is dehydrogenated to CO already at room temperature by the Pd and Pd-Co catalysts, but high steady-state conversion requires temperatures above similar to 150 degrees C. As could be shown by parallel studies of methanol decomposition on model catalysts prepared by physical vapor deposition under UHV conditions, CO desorption is the limiting factor at lower temperature. Pure Pd catalysts were found to be more active for methanol decomposition than the bimetallic Co-Pd catalysts. Although electronic effects in the bimetallic system facilitate desorption of CO at low temperature, this cannot compensate for the lower intrinsic activity of Co sites. We also investigated the influence of small amounts of oxygen on the decomposition of methanol. The activity of the Me/MgO catalysts was found to be higher in the presence of oxygen than in the absence of oxygen. Oxygen facilitates the removal of carbon species resulting from the C-O bond scission reaction channel. (C) 2008 Elsevier Inc. All rights reserved.