Vapour phase formic acid decomposition over PdAu/γ-Al2O3 catalysts: Effect of composition of metallic particles

Abstract: A series of 1.8wt.% PdAu/γ-Al2O3 catalysts with a mean metal particle size of more than 10nm and different Pd/Au ratios were prepared by impregnation followed by hydrazine reduction and tested in the decomposition of vapour phase formic acid (2.2vol.%, 1bar) with and without added CO to the gas mixture. The catalytic activity was correlated with the bulk (AAS, XRD, EDS/TEM) and surface (XPS) composition of PdAu particles. A novel result was obtained that the surface composition of the particles did not change despite a considerable variation of the Au atomic fraction and it was found to be close to that of the Pd2Au alloy. The activity of the Au/Al2O3 catalyst was negligible compared with that of the Pd/Al2O3 catalyst being a factor of 65 lower per gram of metal at 403K. The surface electronic properties (XPS) and the catalytic activity of the Pd2Au layer calculated per one surface Pd atom (TOF) did not depend on the bulk composition of the metal particles. A lower activity of the Pd2Au layer as compared with the pure Pd layer (2–3 times) was observed, but the activation energies for the Pd and PdAu catalysts were similar (40kJmol−1) and were lower than that for the Au/Al2O3 catalyst (62kJmol−1). Addition of CO led to a considerable inhibition of the reaction for all PdAu catalysts, this being accompanied by an increase in the activation energy to 69kJmol−1. [Copyright &y& Elsevier]