Variability of particle configurations achievable by 2-nozzle flame syntheses of the Au-Pd-TiO2 system and their catalytic behaviors in the selective hydrogenation of acetylene

Catalysts with Au and Pd supported on TiO2 (Au:Pd 1:1 wt/wt%) were prepared by 1- and 2-nozzle flame spray pyrolysis (FSP). The 2-nozzle configuration allowed to synthesize various particle configurations by separate or co-feeding of the metal precursor solutions to the two nozzles. For the Au-Pd/TiO2 system, four different catalyst particle configurations were investigated: TiO2 + AuPd, Pd/TiO2 +Au, Au/TiO2 + Pd, and Pd/TiO2 + Au/TiO2, where + separates the corresponding precursor solutions fed to the two nozzles. There were no significant differences in the specific surface areas and the average TiO2 crystallite sizes of the catalysts (100 m(2)/g and 16-17 nm, respectively) with the exception of Pd/TiO2 +Au/TiO2, which exhibited larger surface area and smaller crystallite size (152 m(2)/g, 12 nm) due to halving of the Ti precursor concentration in each nozzle. As revealed by CO chemisorption, XPS, and STEM-EDX results, the catalyst properties varied largely in terms of bimetallic AuPd particle compositions, the interaction between metal metal and metal-support, and the location of Pd (or AuPd) on the TiO2. Among the catalysts studied, TiO2 + AuPd prepared with the 2-nozzle system exhibited the highest conversion of acetylene (similar to 50%) at 40 degrees C with high selectivity to ethylene ( > 95%). Co-feeding the noble metal precursors together with the Ti precursor afforded less active catalysts due to the formation of Ti-O species partially covering the most active bimetallic AuPd particles. Compared to the commercially available acetylene hydrogenation catalyst and the AuPd/TiO2 prepared by conventional co-impregnation and deposition-precipitation, all the FSP-AuPd/TiO2 catalysts showed superior performances under the reaction conditions used.