THE CHARACTERISTICS AND CATALYTIC PROPERTIES OF TiO2 SUPPORTED Au-Pd CATALYSTS PREPARED BY FLAME SPRAY PYROLYSIS IN SELECTIVE HYDROGENATION REACTIONS

Abstract

The preparation of bimetallic AuPd/TiO2 catalysts by one-step flame spray pyrolysis (FSP) resulted in narrow particle size distribution of small AuPd alloy particles (đp ~5 nm) on the TiO2 support. The conventional methods such as impregnation and deposition-precipitation methods, on the other hand, resulted in wider particle size distribution with some pore blockages and formation of new pore structure of the TiO2. The FSP-made AuPd/TiO2 showed good catalytic performances in the selective hydrogenation of 1-heptyne. More homogeneous composition of the individual AuPd nanoparticles was obtained upon reduction at 500 °C without significant changes of particle size and bulk composition. Nevertheless, the surface atomic Pd/Ti ratio decreased due to the TiOx migration onto the metals (so-called the strong metal-support interaction effect), resulting in lower activity. Reduction at high temperature was found to be unnecessary for the FSP-made AuPd/TiO2 catalysts in the selective hydrogenation of 1-heptyne. The highest yield of 1-heptene was 93% over FSP-AuPd/TiO2 R40 catalyst after 20 min reaction time. The characteristics of FSP-made catalysts were modified by changing the stoichiometric of precursor flow rate (PF) and dispersion O2 gas flow rate (DO). The activity of Pd/TiO2 catalyst prepared at 7PF3DO was improved so that it gave full acetylene elimination at 60 °C similar to the AuPd/TiO2 catalyst. Furthermore, the 2-nozzle FSP was employed for the preparation of AuPd/TiO2 catalysts with various particle configurations by controlling the mixing of the individual components from different flames. The catalyst performances for the selective hydrogenation of acetylene at 40 °C of the AuPd/TiO2 catalysts could be enhanced by separation of the TiO2 precursor from the mixed precursor of Pd and Au metals (TiO2 + AuPd).