Selective Hydrogenation of Unsaturated Aldehydes into Unsaturated Alcohols: Role of Metal-Support Interactions in Platinum Catalysts

摘要

With the aim of finding an environmentally friendly catalytic process leading to selective hydrogenation of α,β unsaturated aldehydes into unsaturated alcohols, the platinum catalysts supported on TiO_2, SnO_2, CeO_2, ZnO have been compared to unsupported platinum and platinum supported on Al_2O_3 and MgO, in gaseous hydrogenation of crotonaldehyde. The first series of catalysts leads to 60-90% selectivity in the formation of crotyl alcohol while it never exceeds 10% for the second series. Using reducible oxides, large effects on the selectivity are shown depending on the metal precursor and the reduction temperature. It is shown that certain catalytic systems are selective up to high conversion, stable in time and, when tested in gaseous and liquid phase, the same selectivity evolution was found in both reaction environments. The catalysts were characterised by Temperature Programmed Reduction, X-Ray Diffraction, High Resolution Transmission Electronic Microscopy and Photoelectron Spectroscopy. It reveals that the particle size does not affect directly the selectivity while the formation of alloy is always present, PtSn, CePt_5 and PtZn, respectively when the catalysts show the highest selectivity. This phenomenon as well as the migration of reducible oxide species and the detrimental or beneficial effects of chlorine are revealed.