Abstract
New gold catalysts supported on CeO2, ZrO2 and TiO2 were synthesized by two different techniques: deposition-precipitation and colloidal method. The role of the surfactant (PVA, PVP, THPC) was also investigated. The catalysts were tested in the oxidation of glucose to gluconic acid, in aqueous environment and under mild conditions (60 °C and atmospheric pressure). TEM and SEM analyses have shown that the small size of gold nanoparticles is a necessary condition, but not sufficient for a good conversion. In fact, for an active sample, we have verified that the excess of surfactant must be removed because it would coat the surface of the catalyst. The surfactant, however, should not be completely eliminated, since it has the fundamental role of stabilizing the sample preventing nanoparticles from aggregation. It was evidenced that both the synthetic approach and the kind of support affect the catalysts’ activity. In fact, by focusing on the three different supports, with all the preparation methods, the ceria has proved to be the best support. This is due to its ability to obtain small gold nanoparticles and to its ability to accumulate oxygen. The most appropriate synthesis methodology proved to be the colloidal method with PVA. Recyclability issue was investigated too.
Highlights
The catalytic activity of a gold-based heterogeneous catalyst depends on the nature of the support and in particular on the size of the gold nanoparticles deposited on it, which in turn depends on the synthetic methodology
The aim of the work is the synthesis of new gold catalysts active in oxidation reactions
Focusing on the transformation of platform molecules through oxidation oxidation the reactions, the use of nanostructured catalysts based on gold to be the mostalternative
Summary
The catalytic activity of a gold-based heterogeneous catalyst depends on the nature of the support and in particular on the size of the gold nanoparticles deposited on it, which in turn depends on the synthetic methodology. The procedure involves filling the pores of the support by adding an aqueous HAuCl4 solution to form a wet paste, which is dried and calcined. This technique does not allow obtaining high gold dispersion. It leads to nanoparticles of size above 30 nm, due to sintering during the heat treatment, promoted by the Clions still present on the sample [2]. An alternative synthetic approach for Au loading has been recently reported [4,5], namely a liquid phase reductive deposition (LPRD)
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