Mixed-bimetal ruthenium carbonyl clusters supported on silica: Activity and selectivity in CO + H 2 conversion

Abstract

The catalytic performance of bimetallic Ru-M (M = Co,Fe, Ni, Mo, Rh, Cr, Mn) catalysts prepared from a series of RuM carbonyl clusters in CO hydrogenation has been investigated. The catalysts derived from Ru-Co, Ru-Fe and Ru-Mo bimetallic carbonyl clusters showed high activity and selectivity for higher oxygenates, compared with the Ru6/ SiO2 catalyst prepared from impregnation of monometallic cluster Ru6C(CO)17. For Ru-Ni and Ru-Rh catalysts, they did not show high promotion for the formation of oxygenates although the selectivity was over 10% at 519 K. The promoters such as Mn and Cr in Ru-Mn and Ru-Cr catalysts intensively led to a decrease of oxygenate amount, in comparison with to Ru6/SiO2catalyst. In situ FT-IR studies revealed that the intensity of band at 1584 cm-1 for Ru-M (M=Co,Fe and Mo) bimetallic cluster-derived catalysts at 453 K under syngas (CO/H2= 0. 5) has a good linear relationship to rates of oxygenate formation, whereas the band at 1584 cm-1 was not observed for Ru-Mn, Ru-Cr, Ru-Rh and Ru-Ni bimetallic and monometallic cluster- derived catalysts showing poor activity for oxygenates. This strongly suggested that the band at 1584 cm-1 is likely related to an intermediate to produce oxygenates in CO hydrogenation. Isotopic adsorption of 13CO and D2as well as chemical trapping of surface intermediate suggested that the band at 1584 cm-1 corresponds to fornyl species.