Acidity crystalline titanium silicates

Acidity, 27 284, 285 catalytic performance, 30 121 crystalline titanium silicates, 41 319-320 estimating, 37 166 heteropoly compounds, 41 139-150 ion exchange and, zeolites, 31 5-6 sulfate-supported metal oxides, 37 186-187 surface, monolayer dispersion, 37 34-35 tin-antimony oxide, 30 114-115, 125-1256 Acids, see also specific compounds adsorption of, on oxide surfaces, 25 243-245... 

Acidity in crystalline titanium silicates has been observed only when a titanium-containing zeolite interacts with H2C>2, but this is due to the formation of peroxo compounds, as discussed below. 

The high-temperature synthesis from strongly alkaline suspensions of salts of Tilv and Silv produces crystalline microporous materials in which Tiiv is present in octahedral coordination. These materials do not exhibit the catalytic properties typical of the other titanium silicates in which TiIV is in tetrahedral coordination (Kuznicki, 1989, 1990 Kuznicki et al., 1991a, 1991b, 1991c, 1993 Deeba et at., 1994). The acidic properties of these materials have been discussed (Section II.B). 

A large number of inorganic layer crystals such as micas, sodium silicates, niobate, uranate, vanadate, titanate, zirconium phosphate, graphitic acids, crystalline silicic acids, vanadium oxyhydrate, calcium phosphoric acid esters, and titanium disulfide develop alkyl crystals between their rigid crystal layers by ion exchange with, for example, alkyl ammonium salts and by intercalation inorganic... 

Amorphous Ti/SiCL oxides and crystalline Ti zeolites are two classes of well-studied solid Ti catalysts (11-14). In both classes, a Lewis-acidic Ti atom is anchored to the surrounding siliceous matrix by Si-O-Ti bonds. The oxidant of choice for Ti zeolites such as titanium silicalite 1 (TS-1) and 11-/1 is H2O2, whereas the amorphous, silica-based materials function optimally with organic peroxides such as /-butyl hydroperoxide (/-BuOOH) or ethyl benzene hydroperoxide. However, there are strictly no homogeneous analogues of these materials, and they therefore do not fit within the context of anchoring of homogeneous catalysts. 

A new class of siliceous microporous materials with varying metal contents and high porosities has recently been presented by Maier et al. [105,106]. These materials which are X-ray amorphous and where no crystalline structure can be seen in the transmission electron microscope are synthesized via a sol-gel-route under hydrothermal conditions without the use of template molecules. The simple reaction of silicon alcoholates and titanium alcoholates which are mixed in ethanol and the condensation of which is induced by the addition of hydrochloric acid, produces a gel that becomes solid after a few days. The following careful calcination process under inert atmosphere and milling of the resulting solid gives the porous material. Detailed analysis of the pore structure para-... 

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