Titania–silica epoxidation catalysts modified by mono- and bidentate organic functional groups

Amorphous, mesoporous titania–silica mixed oxides with covalently bound mono- and bidentate acetoxyalkyl and aminoalkyl functional groups were prepared using the solution sol–gel process and ensuing low temperature supercritical extraction with CO₂. Titanbisacetylace-tonatediisopropoxide, tetramethoxysilane and amino- or acetoxyalkyl-trimethoxysilane precursors were used for the syntheses of hybrid aerogels with a constant Ti:Si atomic ratio of 1:12. The mixed oxides were characterized by thermal analysis, N₂physisorption, ¹³C- and ²⁹Si-CP-MAS NMR spectroscopy, and electron microscopy. The amorphous mesoporous structure of the aerogels depended markedly on the nature of the modifier. Organic modification enhanced remarkably the rate of epoxidation of cyclohexene and cyclohexenol. The highest selectivity in the more demanding epoxidation of cyclohexenol, 91% at 80% TBHP conversion, was achieved with a bidentate (diaminoalkyl)-modified aerogel.     

STM and TEM investigation of a technical platinum/graphite catalyst

A technical, powder, platinum-on-graphite catalyst has been investigated up to atomic scale by transmission electron microscopy (OAI) and scanning tunneling microscopy (STM). The catalyst had been prepared from a colloidal platinum sol. STM confirms, in addition to spherical particles, the presence of raft structures on the support surface, which had been suggested by the TEM images. The height of these raft structures varies from one to ten atomic layers.