Understanding the effect of postsynthesis ammonium treatment on the catalytic activity of Au/Ti-SBA-15 catalysts for the oxidation of propene

Abstract

Postsynthesis ammonium treatment induces a Substantial increase in the catalytic activity of Au/Ti-SBA-15 catalysts for the direct vapor-phase epoxidation of propylene using hydrogen and oxygen. The PO formation rate of a calcined Au/Ti-SBA-15 catalyst prepared by this method increased from cat at 200 degrees C compared with a catalyst prepared in an identical 4.3 mg(PO) h(-1) g(cat)(-1) to 37.2 mg(PO) h(-1) g(cat)(-1) manner without this treatment. The catalysts were characterized by XRD, N-2-sorption, UV-vis-NIR DRS, Si-29 MAS NMR, FT-IR spectroscopy, and TEM to gain insight into the relationship between ammonia treatment and catalyst activity. 29Si MAS NMR measurements Proved that the ammonium nitrate solution caused hydrolysis of Si-O-Si or Ti-O-Si bonds, resulting in a Ti-SBA-15 Surface with a greater amount of surface hydroxyl groups. FT-IR measurements indicated the presence of amine species that favor the homogeneous deposition of Au nanoparticles. This was confirmed by TEM measurements showing greater metal dispersion for NH4NO3-treated Au/Ti-SBA-15 materials. (c) 2008 Elsevier Inc. All rights reserved.