Selective hydrogenation of butadiene over TiO2supported copper, gold and gold–coppercatalysts prepared by deposition–precipitation

International audienceOxide supported copper and gold catalysts are active for the selective hydrogenation of polyunsaturatedhydrocarbons but their low activity compared to palladium catalysts and the deactivation of copper catalystslimit their use. There are only a very limited number of studies concerned with the use of bimetallic Au–Cucatalysts for selective hydrogenation reactions and the aim of this work was to prepare TiO2-supported monometallicAu and Cu and bimetallic AuCu (Cu/Au atomic ratio of 1 and 3) catalysts and to evaluate their catalyticperformance in the selective hydrogenation of butadiene. Small gold, copper and gold–copper nanoparticles(average particle size o 2 nm) were obtained on TiO2 using the preparation method of deposition–precipitationwith urea followed by reduction under H2 at 300 1C. Very small clusters were observed for Cu/TiO2 (B1 nm)which might result from O2 induced copper redispersion, as also supported by the XPS analyses. The alloying ofcopper with gold was found to inhibit its redispersion and also limits its reoxidation, as attested by XPS. Thebimetallic character of the AuCu nanoparticles was confirmed by XPS and EDX-HAADF. Cu/TiO2 was initiallymore active than Au/TiO2 in the selective hydrogenation of butadiene at 75 1C but it deactivated rapidly duringthe first hours of reaction whereas the gold catalyst was very stable up to 20 hours of reaction. The bimetallicAuCu/TiO2 catalysts displayed an activation period during the first hours of the reaction, which was very pronouncedfor the sample containing a higher Cu/Au atomic ratio. This initial gain in activity was tentativelyassigned to copper segregation at the surface of the bimetallic nanoparticles, induced by the reactants. Whenthe AuCu/TiO2 catalysts were pre-exposed to air at 75 1C before butadiene hydrogenation, surfacecopper segregation occurred, leading to higher initial activity and the suppression of the activation period. Underthe same conditions, Cu/TiO2 totally lost its activity, probably due to irreversible copper oxidation