Preparation of improved Ag–Pd/TiO2 catalysts using the combined strong electrostatic adsorption and electroless deposition methods for the selective hydrogenation of acetylene

Abstract

TiO₂-supported Ag–Pd catalysts were prepared by strong electrostatic adsorption (SEA) of Pd followed by electroless deposition (ED) of Ag with incremental surface coverages of Ag (θ_Ag) ranging from 0–0.92. Theoretical monolayer (ML) coverage values (θ_Theo), assuming monodisperse deposition of Ag on Pd, were equal to experimental coverage values (θ_Expt) up to approximately θ_Ag = 0.7. Above this value, autocatalytic deposition of Ag on Ag occurred as well as further catalytic deposition of Ag on Pd. The atomic Pd/Ag compositions determined from transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDX) were in very good agreement with the values from atomic absorption spectroscopy (AAS), decreasing from 16.2 to 1.5 as θ_Ag coverages increased from 0.36 to 0.92 ML. The selectivity of acetylene hydrogenation to ethylene and the turnover frequency for acetylene hydrogenation were maximized at the highest θ_Ag in this study. The uniform deposition of Ag on the surfaces of small Pd particles using the combined methods of SEA and ED resulted in significant improvement of the bimetallic Ag–Pd surface for the selective hydrogenation of acetylene.