Carbon monoxide hydrogenation over alkali-promoted Ru/Al₂O₃⁺

An experimental study is carried out to investigate alkali promotion effect on Ru/Al₂O₃ catalysts by using temperature-programmed desorption (TPD), ESCA, and CO-hydrogenation reaction. The study was carried out in a differential reactor. TPD studies of hydrogen suggest that a major portion of the alkali species is located on the alumina support rather than on the metal. ESCA results indicate a significant electronic effect of the alkali-metal interaction. The turnover frequencies of alkali-promoted Ru/Al₂O₃ catalysts decrease according to the following order: Unpromoted>Li->Na->K->Rb->Cs-promoted catalysts. The addition of alkali species tends to increase olefin selectivities. There exist oxygen-containing products, primary formaldehyde, which increase with increasing electropositivity. The results seem to support the electron transfer from promoter to Ru metal, leading to a higher electron density in the transitionmetal, a favorable state for the activation of CO-hydrogenation.