Characterization of Synthetic Iron Oxides and their Performance as Support for Au Catalysts

Gold(0) catalysts supported on ferric oxide are effective catalysts, and so far, the only heterogeneous ones known for the regioselective hydrogenation of alpha,beta-unsaturated ketones to the corresponding alpha,beta-unsaturated secondary alcohols. A set of ferric oxide samples, synthesized under strictly controlled conditions and thoroughly characterized (X-ray powder diffraction, Mossbauer spectroscopy, micro-Raman spectroscopy, transmission electron microscopy, temperature-programmed reduction), were employed as supports of gold(0) catalysts for this reaction. The activity and selectivity of the catalysts changed in the same direction from one catalyst to another; increasing fractions of nanostructured ferric oxide phases in the support (with nanoparticles size lower than 10 nm) increased both. With a 4% gold catalyst supported on the ferric oxide sample containing the highest proportion of nanostructured matter, we achieved a selectivity of 66% towards the unsaturated alcohol at more than 90% conversion in the hydrogenation of benzalacetone (ethanol, 60°C, 103 kPa), which is one of the best performances ever reported for this reaction.