Bimetallic ruthenium-gold-on-magnesia catalysts: Chemicophysical properties and catalytic activity

Abstract

Bimetallic Ru-Au catalysts supported on MgO were prepared, their atomic composition varying from 100% Ru to 100% Au. Samples were characterized after impregnation and drying at 110 [deg]C and after further reduction by hydrogen at 400 [deg]C. X-Ray line broadening analysis, small-angle X-ray scattering, transmission electron microscopy, gas chemisorption, diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), and extended X-ray absorption fine structure (EXAFS) analysis were used. Catalytic activity was measured for the oxygen transfer between CO and CO2. The Ru and Au precursor compounds appear to be modified, and have probably interacted in the bimetallic samples, already after impregnation and drying. Relevant amounts of metal oxides are found in some "reduced" catalysts; a metal-support interaction is proposed for Au/MgO. The amounts of the Ru and Au oxidized species found by EXAFS in the examined bimetallic sample are significantly different from those found in Ru/MgO and Au/MgO, respectively. The DR spectra of the bimetallic samples are not a simple combination of those of the monometallic catalysts. The Ru/Au atomic ratios measured by XPS are higher than the analytical ones. The fraction of surface Ru atoms, measured by hydrogen chemisorption, increases on decreasing the bulk Ru/Au atomic ratio. The Au/MgO sample has an activity which is two orders of magnitude higher than that of the remaining samples. All of this suggests the existence of a Ru surface enrichment and also an Ru-Au chemical interaction. These conclusions are also supported by an ir study of CO chemisorbed on the same samples.