Higher alcohols synthesis from syngas over CoCu/SiO2 catalysts: Dynamic structure and the role of Cu

A comparative study of higher alcohols synthesis directly from syngas has been performed over monometallic Co and bimetallic CoCu/SiO2 catalysts. Particularly, the role of Cu on the origin of active sites and reaction mechanism were investigated thoroughly using multiple techniques such as ex situ X-rays diffraction (XRD), X-ray absorption spectroscopy (XAS) and Raman spectroscopy. Reduction process of CoCu/SiO2 catalysts was also determined using in situ XRD and in situ Raman spectroscopy while the surface structure of reduced catalysts was detected by CO-DRIFTS. CoCu bimetallic particles covered by Cu atoms are responsible for alcohols synthesis. The intrinsic kinetics was performed over both catalysts under realistic reaction conditions. By comparing the kinetic parameters, including apparent activation energies and reaction orders, the promotional effects of Cu have been identified as: (1) weakening the CO/HCO dissociation and reducing the formation of CHx species; (2) controlling surface Co ensemble size and inhibiting CHx insertion.