A mechanistic basis for the effects of Mn loading on C2+ oxygenates synthesis directly from syngas over Rh–MnOx/SiO2 catalysts. (2nd October 2015) - Mao, Wei
Abstract: Kinetics of the synthesis of C2+ oxygenates directly from syngas was investigated over a series of Rh–MnO x /SiO2 catalysts (atomic ratio of Mn/Rh=0, 0.5 and 5.0). It was evidenced that the activation energies for C2+ oxygenates changed little when introducing MnO x, while the apparent activation energies for hydrocarbons, especially methane, increased remarkably. Kinetic parameters indicate that the formation of hydrocarbons can be suppressed in the presence of MnO x . In the meantime, the reaction orders with respect to different products were also altered with the variation of MnO x loadings. In accordance with in situ DRIFTS, we found that two new active sites on Rh surfaces resulting from the Rh–MnO x interaction might be responsible for the enhancement of reaction rates and the selectivity to C2+ oxygenates. However, the over-loading of MnO x leads to a decrease in the number of active sites. Graphical abstract: Highlights: The intrinsic kinetics of CO hydrogenation over Rh–MnO x catalysts was established. The E a for CH4 increased rapidly, but changed little for ethanol when adding MnO x . CO dissociation is enhanced by tilted CO adsorption on Rh–MnO x interface. Linearly adsorbed CO on Rh δ + sites promoted CO insertion over Rh–MnO x catalysts.