Surface Alloy or Metal-Cation Interaction-The State of Zn Promoting the Active Cu Sites in Methanol Synthesis Catalysts

摘要

Model catalysts containing disordered CuO and ZnO species in the pores of SBA-15 were reduced under different conditions (standard: H-2, 513 K; severe: CO/H-2, 673 K), studied by X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) including operando work and used as catalysts for methanol synthesis at pressures up to 8 bar, where they were comparable with a commercial reference in terms of reaction rates related to Cu surface area. Severe reduction caused significant activation of the Cu sites beyond the sizeable level achieved al-ready after standard reduction. In XRD, which failed to detect most of the active components, owing to small particle sizes, weak indications of alloy formation were found after severe reduction. XAFS, which averages over all species present, showed the interaction of Cu with zinc ions to increase by severe reduction, while formation of Zn-0 was below detection limit. On this basis, the promoting interaction of Zn to Cu was ascribed to an interaction of zinc cations with Cu-0.