Ionic liquid-enhanced immobilization of biosynthesized Au nanoparticles on TS-1 toward efficient catalysts for propylene epoxidation

The direct vapor-phase epoxidation of propylene in the presence of hydrogen and oxygen was studied at a space velocity of 7000 mL h(-1) g(cat)(-1), over gold catalysts with varying gold and titanium contents prepared by ionic liquid-enhanced immobilization (ILEI) method in which biosynthesized gold nanoparticles (GNPs) were immobilized onto the titanium silicalite-1 (TS-1) supports through the assistance of a small amount of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]). The results showed that [BMIM]. specially adsorbed onto the support to increase its isoelectric point, leading to the enhanced immobilization. The propylene conversion of 14.6% and PO formation rate of 164.4 g(po) K g(cat)(-1) h(-1) were higher than those in any other reports, probably attributing to enhanced interaction between the GNPs and TS-1. Furthermore, the excellent activity and high selectivity of the Au/TS-1 catalysts at a relatively high reaction temperature might be attributed to the existence of residual biomolecules on the catalysts. (C) 2011 Elsevier Inc. All rights reserved.