Design of a potassium-promoted Rh/Al2O3 catalyst for synthesis of C 2 oxygenates by pulse surface reaction rate analysis

Abstract

For the synthesis of C 2 oxygenates from carbon monoxide hydrogenation, a promoted Rh/Al 2O 3 catalyst was logically designed on the basis of a working hypothesis that appropriate suppression of both C O bond dissociation and hydrogenation of the resulting surface carbon species leads to an increase in selectivity. The application of pulse surface reaction rate analysis to determine the rate constants for these two steps indicated that among unpromoted catalysts, both rate constants were relatively small on a highly dispersed Rh/Al 2O 3 catalyst. Such a catalyst yielded an IR absorption for adsorbed carbon monoxide that appeared at lower wavenumber owing to the high electron density in the rhodium metal. This led us to except substantial promotion on adding potassium carbonate to the highly dispersed Rh/Al 2O 3 catalyst, because potassium carbonate had been found to increase the electron density in metal catalysts. Good performance of the catalyst was confirmed by continuous flow hydrogenation of carbon monoxide under pressure.