Influence of the Re introduction method onto Pd/TiO2 catalysts for the selective hydrogenation of succinic acid in aqueous-phase

Bimetallic Re-Pd catalysts were prepared by addition of Re onto a Pd/TiO2 monometallic catalyst, either by a catalytic reduction method or by successive impregnation. The physical and chemical properties of the bimetallic catalysts were evaluated by several characterization techniques, including analysis by transmission electronic microscopy, hydrogen chemisorption, temperature programmed reduction and X-ray photoelectron spectroscopy to explain their different catalytic performances in the selective hydrogenation of succinic acid to 1,4-butanediol in aqueous solution. The localization of the Re deposit on the parent Pd catalyst surface varied according to the Re introduction mode. The catalytic reduction method induced a selective Re deposit at the Pd-TiO2 interface compared to a random distribution obtained by successive impregnation. The oxidation state of the Re species (Re3+, Re-0) on the reduced bimetallic samples was also linked to their preparation mode. (C) 2014 Elsevier B.V. All rights reserved.