H2O2-based selective oxidations over titaniumsilicates of SBA-15 type

Titanium-monosubstituted polyoxometalates: relation between homogeneous and heterogeneous Ti-single-site-based catalysis

“…The oxidation of alkylphenols with H 2 O 2 over Ti,Siand Ti-POM-catalysts has been studied using 2,3,6-trimethylphenol (TMP) as model substrate [73][74][75][76][77]135,136]. For both types of catalysts we found the same products, 2,3,5-trimethyl-1,4-benzoquinone (TMBQ, vitamin E precursor) and 2,2´,3,3´,5,5´-hexamethyl-4,4´-biphenol (BP) (scheme 5).…”

“…To overcome the steric limitation of TS-1, a considerable amount of research was focused on the preparation of titanium-containing materials with lager pores [29][30][31][32][33][34][35][36][37][38][39][40][41]63]. In the late 1990s, we also started our activity in the development of mesoporous Ti,Si-catalysts for selective oxidation of bulky organic substrates with H 2 O 2 [71][72][73][74][75][76][77][78][79]. For successful designing new catalysts and processes, we needed a basic knowledge about the mechanism of the formation of active titanium species and the mechanisms of their interaction with organic substrates.…”

Environmentally Benign Oxidation of Alkylphenols to p-Benzoquinones: A Comparative Study of Various Ti-Containing Catalysts

“…Importantly, no anatase-like species were present in the catalysts evaluated in this work, as confirmed by the absence of the characteristic absorption at 330 nm in DRS UV and the lack of the Raman band at 145 cm -1 , both typical of anatase [22][23][24][25].…”

“…The higher the degree of Ti oligomerization, the more red-shifted is the adsorption [20][21][22]. Isolated Ti centers (DRS UV maximum at 208-220 nm) and anatase microcrystallites (DRS UV 330 nm [23,24] ) favor the formation of a dimeric byproduct in TMP oxidation, 2,2 0 ,3,3 0 ,6,6 0 -hexamethyl-4,4 0 -biphenol (BP) [19,25]. It was suggested that a dinuclear (or clusterized) structure of Ti-O-Ti centers is required to enable fast oxidation of the key intermediates, phenoxyl radicals, thereby preventing their coupling and the formation of aromatic dimeric species [18,19].…”

Synthesis and Characterization of Dendrimer-Templated Mesoporous Oxidation Catalysts

“…In recent years, several heterogeneous and homogeneous catalysts have been shown to be effective in the selective oxidation of alkenes [7][8][9][10][11]. Of the heterogeneous catalysts studied, mesoporous oxide materials have in many cases proven to be ideal because of their high surface areas, large pore diameters, mechanical strength, and controllable surface properties [12][13].…”