Compared properties of Pd on thermo-conductor supports (SiC, Si3N4) and Pd on oxide supports (Al2O3, SiO2) for the 1,3-butadiene hydrogenation reaction

Palladium catalysts were prepared by impregnation with Pd(II)-bis-acetylacetonate dissolved in toluene on various nonporous supports having very different thermal properties, SiO2, Al2O3, Si3N4, and SiC, and their catalytic properties were tested for the gas-phase 1,3-butadiene hydrogenation reaction. The mean metal particle size of 0.5 Pd wt% loaded catalysts was similar (4 nm) for all supports. However, Pd particles have different Pd3d5/2 XPS-binding energies, a sign of different electronic properties through their metal-support interactions. All catalysts show a decrease of their activity versus time at the beginning of a reaction run. However, the effect is more or less pronounced on the different catalysts. The activity of the Pd/SiO2 and Pd/Si3N4 catalysts decreased rather rapidly until a stable situation was reached. This is not the case for Pd/Al2O3 and Pd/SiC catalysts whose activity decreased continuously with time even after 20-h working. No direct relationship can be drawn between the thermal conductivity of the support and the deactivation process. The deactivation via thermal effects induced on the metal particles by the hydrogenation reaction (exothermic and working with a very high TOF) is consequently not the predominant one. The evolution observed is in fact the consequence of the stabilization of the catalyst, probably via the formation of carbonaceous residues, which actually depend on the intrinsic properties of the metal/support couple.