Visible Light-Induced Partial Oxidation of Olefins on Cr-Containing Silica with Molecular Oxygen

Abstract

Photocatalytic oxidation of olefins on Cr-containing silica with molecular oxygen by visible light irradiation (lambda > 400 nm) has been investigated. Cr-SiO(2) catalyst prepared by a conventional sol-gel method, containing highly dispersed chromate species, catalyzes efficient olefin oxidation with very high selectivity for partially oxidized products (>90%), whereas semiconductor TiO(2) promotes complete decomposition (CO(2) production). The Cr-SiO(2) catalyst shows much higher activity than Cr/SiO(2) prepared by an impregnation method or Cr proportional variant MCM-41 prepared by a templating method. ESR analysis reveals that photoirradiation of the chromate species with a tetrahedral coordination (T(d)(6+)) on Cr/SiO(2) and Cr proportional variant MCM-41 catalysts leads to the formation of excited state T(d)(5+) species (T(d)(5+*)), while irradiation to T(d)(6+) on Cr-SiO(2) produces T(d)(4+*) species. This can be explained by a homogeneous T(d)(6+) arrangement with Si species on the Cr-SiO(2) catalyst. On the strongly reduced T(d)(4+*), olefins are strongly attracted by an electron and/or proton donation, resulting in high oxidation activity. The Cr-SiO(2) catalyst is applicable to partial oxidation of various aliphatic and aromatic olefins with very high selectivity, and does not promote undesirable dimerization. The obtained findings suggest a potential use of Cr-SiO(2) as an efficient and recyclable heterogeneous photocatalyst for partial oxidation of olefins.

Preparation of Cr–Ti Binary Oxide Anchored Mesoporous Silica by CVD Method and Their Photocatalytic Activities

“…In the photocatalytic reaction systems, Cr 6? -oxide containing catalyst have also attracted much attention due to their visible light sensitivity and fascinating catalytic activities [9][10][11][12]. Our group has also demonstrated that transition metal oxides containing silica-based materials, which were called single-site photocatalyts, can be used not only to promote the photocatalytic reactions but also to form nanosized metals and alloys [1,13,14].…”

Recent Progress in Semiconductor Photocatalysis for Organic Fine Chemical Synthesis

“…Gradual deactivation was observed for CrO 3 /SiO 2 with the course of the photoreaction, although the initial activity was almost same as that of TiO 2 /SiO 2 . Shiraishi et al [45] prepared Cr-SiO 2 catalyst containing highly dispersed chromate species by a sol-gel method and when subjected to photocatalytic oxidation reaction under visible light irradiation (λ > 400 nm) showed very high selectivity (>90%), which is higher than Cr/SiO 2 catalysts prepared by an impregnation method or Cr/MCM-41 prepared by a templating method. The yield and selectivity to propylene oxide were improved significantly by modification of silica with 1 wt% magnesium oxide loading [46].…”

Low temperature synthesis of polyaniline–crystalline TiO2–halloysite composite nanotubes with enhanced visible light photocatalytic activity

“…Various kinds of supports, such as carbon nanotube [2][3][4][5], silicon nitride composites [6], silica composites [7,8], zeolites composites [9], and clay minerals [10][11][12][13][14][15], have been developed. In particular, tubular halloysite clay (aluminosilicate, Al 2 Si 2 O 5 (OH) 4 .2H 2 O) has garnered particular interests in material science due to its versatile features of large surface area, high porosity, and tunable surface chemistry, which enabled this nanomaterial to be utilized as an attractive support for the assembly of small-size metals and metaloxide aggregates (clusters and nanoparticles) [16][17][18][19][20].…”