Studies of adsorption of α,β-unsaturated carbonyl compounds on heterogeneous Au/CeO2, Au/TiO2 and Au/SiO2 catalysts during reduction by hydrogen

Our research focuses on phenomena accompanying adsorption of mesityl oxide (4-methylpent-3-en-2-one) on the surface of heterogeneous supported gold catalysts: Au/CeO2, Au/TiO2 and Au/SiO2. We have studied reduction in the gas phase of (volatile) alpha,beta-unsaturated carbonyl compounds (R-(V)ABUCC) which mesityl oxide is a basic model of. In situ infrared (IR) spectroscopy was employed to establish that the most active catalysts allow adsorption of conjugated ketones or aldehydes in the enolate (i.e. bridge-like adsorption through the oxygen from the carbonyl group and the beta-carbon) and carboxylic form or with the C-alpha=C-beta double bond on a Lewis acidic site. Reductive properties of the catalysts and pure supports were studied by temperature-programmed reduction (TPR). We show that cerium(iv) oxide (CeO2, ceria) and titanium(iv) oxide (TiO2, titania) when decorated with gold nanoparticles (AuNP) can interact with hydrogen at temperatures approx. 150 degrees C lower than typical for pure oxides what includes even cyclic adsorption and instant release of H-2 below 100 degrees C in the case of gold-ceria system. Morphology and structure characterisation by transmission electron microscopy (TEM) and powder X-ray diffraction (PXRD) confirms that, with the obtained Au loadings, we achieved excellent dispersion of AuNPs while maintaining their small size, preferably below 5 nm, even though the Au/CeO2 catalyst contained broad distribution of AuNPs sizes.

Automated summary

Our research focuses on the phenomena accompanying the adsorption of mesityl oxide on the surfaces of supported gold catalysts. By using in situ infrared spectroscopy, we found that the most active catalysts can adsorb conjugated ketones or aldehydes in the enolate form or with the C-alpha=C-beta double bond. The reductive properties of the catalysts and supports were studied using temperature-programmed reduction. We also observed that ceria and titania, when decorated with gold nanoparticles, can interact with hydrogen at lower temperatures than typical for pure oxides. Transmission electron microscopy and powder X-ray diffraction were used to characterize the morphology and structure of the catalysts.