Selective hydrogenation of butadiene over TiO2 supported copper, gold and gold-copper catalysts prepared by deposition-precipitation

• Published in: Physical chemistry chemical physics : PCCP 2014-12, Vol.16 (48), p.26514-26527
• Main Authors: Delannoy, Laurent, Thrimurthulu, Gode, Reddy, Padigapati S, Méthivier, Christophe, Nelayah, Jaysen, Reddy, Benjaram M, Ricolleau, Christian, Louis, Catherine
• Format: Article
• Language: English
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c4cp02141j

Oxide supported copper and gold catalysts are active for the selective hydrogenation of polyunsaturated hydrocarbons but their low activity compared to palladium catalysts and the deactivation of copper catalysts limit their use. There are only a very limited number of studies concerned with the use of bimetallic Au-Cu catalysts for selective hydrogenation reactions and the aim of this work was to prepare TiO 2 -supported monometallic Au and Cu and bimetallic AuCu (Cu/Au atomic ratio of 1 and 3) catalysts and to evaluate their catalytic performance in the selective hydrogenation of butadiene. Small gold, copper and gold-copper nanoparticles (average particle size < 2 nm) were obtained on TiO 2 using the preparation method of deposition-precipitation with urea followed by reduction under H 2 at 300 °C. Very small clusters were observed for Cu/TiO 2 (∼1 nm) which might result from O 2 induced copper redispersion, as also supported by the XPS analyses. The alloying of copper with gold was found to inhibit its redispersion and also limits its reoxidation, as attested by XPS. The bimetallic character of the AuCu nanoparticles was confirmed by XPS and EDX-HAADF. Cu/TiO 2 was initially more active than Au/TiO 2 in the selective hydrogenation of butadiene at 75 °C but it deactivated rapidly during the first hours of reaction whereas the gold catalyst was very stable up to 20 hours of reaction. The bimetallic AuCu/TiO 2 catalysts displayed an activation period during the first hours of the reaction, which was very pronounced for the sample containing a higher Cu/Au atomic ratio. This initial gain in activity was tentatively assigned to copper segregation at the surface of the bimetallic nanoparticles, induced by the reactants. When the AuCu/TiO 2 catalysts were pre-exposed to air at 75 °C before butadiene hydrogenation, surface copper segregation occurred, leading to higher initial activity and the suppression of the activation period. Under the same conditions, Cu/TiO 2 totally lost its activity, probably due to irreversible copper oxidation. The Au 1 Cu 3 /TiO 2 catalyst shows an increase in butadiene selective hydrogenation conversion, assigned to copper segregation at the surface of bimetallic particles.