Barium, calcium and magnesium doped mesoporous ceria supported gold nanoparticle for benzyl alcoholoxidation using molecular O2

Abstract

In the era of sustainable energy, catalysis using gold nanoparticles has drawn considerable attention from world researchers. Oxidation of benzyl alcohol by molecular O₂ is an atom efficient path to synthesize benzaldehyde. Nanocrystalline ceria has been proven as a useful support to disperse gold nanoparticles since last few years, however there are a few reports on mesoporous ceria supported gold nanoparticles. In this work a systematic investigation was carried out to improve the activity of Au/CeO₂ catalyst by incorporating Ba^2+, Ca²⁺ and Mg²⁺ cations into the ceria lattice through a sol–gel procedure. Both the doped ceria and ceria supported gold nanoparticles are characterized by BET S.A, XRD, TEM, SAXS, XPS, TPR, CO₂-TPD techniques. BET S.A measurements show the mesoporous oxides where H3 hysteresis loops are found. The decrease in the crystallite size of ceria after doping by metal cations is observed in the XRD measurement. The TEM and HRTEM characterization shows the nanocrystalline particle size around 30–50 nm and gold nanoparticles around 10–15 nm in size. Distribution in the particle size for doped ceria have been obtained using SAXS measurements where narrow distributions of ceria particles are found in the 10–20 nm range. The existence of oxide vacancies and the mixture of Ce³⁺/Ce⁴⁺ oxidation states are observed for doped ceria materials in the XPS investigation. The strong gold-support interaction was also evidenced by XPS characterization where oxidic gold was found on the doped ceria surface. Lowering of the reduction peak in ceria after gold nanoparticle deposition was observed from TPR investigation whereas the change in basic site distribution is observed from CO₂ TPD experiment, instigating new insights into the surface properties of the catalysts. The catalytic activities of the catalysts were determined for benzyl alcohol oxidation reactions using molecular O₂. The catalytic activity was in the order of Au/Ba–CeO₂ > Au/Ca–CeO₂ > Au/Mg–CeO₂ > Au/CeO₂. The synergistic effect of gold nanoparticles and dopant cations to the ceria was explained in this work.