SELECTIVE HYDROGENATION OF ACETYLENE OVER SiO2-MODIFIED TITANATE NANOTUBES SUPPORTED PALLADIUM CATALYSTS

Abstract

Silica-modified titanate nanotubes with various Ti/Si molar ratios of 95:5, 90:10, 80:20 and 50:50 were prepared via the hydrothermal treatment of titanium dioxide powder in an aqueous NaOH solution containing different amounts of tetraethyl orthosilicate at 150 °C. The silica-modified titanate nanotubes were used for preparation of supported Pd catalysts by the incipient wetness impregnation method. The catalysts were tested in the gas-phase selective acetylene hydrogenation and characterized by XRD, SEM, TEM, FTIR, XPS, N2 physisorption, H2 chemisorption and Ethylene TPD. The presence of silica in the titanate nanotubes supports resulted in higher Pd dispersion. In addition, the formation of Ti-O-Si bond could suppress the titanate phase transformation to anatase TiO2. When reduced at 150 °C, the highest ethylene yield was obtained over Pd/T50:S50 catalysts. The modification of silica on titanate nanotubes supports weakened ethylene adsorption on Pd catalyst surface so that the selectivity of ethylene was increased. For high reduction temperature of 500 °C, the 5-20 mol% silica-modified titanate nanotubes supported Pd catalysts exhibited better catalytic performance than the ones reduced at 150 °C. Due probably to the formation of Na2(TiO)(SiO4) complex, sintering of Pd occurred on Pd/T50:S50 under high reduction temperature and poor catalytic performance was obtained instead.