Titanosilicate analogues

Microporous titanosilicate compounds have received significant consideration as ion exchangers ever since the introduction of ETS-4 and ETS-10 materials in 1989 [91,97-100], Some of these titanosilicates have proven to be good ion exchangers in neutral and alkaline solutions. For example, a potassium titanosilicate analogue of the mineral pharmacosiderite has been evaluated for the removal of cesium and strontium from various aqueous waste streams [91,101,102],... 

In the case of titanosilicate analogues to zeolites, the titanium has been nnequivocally shown to adopt tetrahedral coordination upon dehydration of the as-synthesised material. Upon adsorption of aqueous solutions of hydro-... 

In contrast to their vanadosilicate analogues, the titanosilicate molecular sieves do not hydroxylate the terminal primary carbon in n-alkanes. Ramaswamy et al. (218,219) found that when n-hexane was hydroxylated under identical conditions in the presence of TS-2 or VS-2 (VS-2 is a vanadium analogue of TS-2), the distribution of products was as follows ... 

All mesoporous titanosilicates obtained by the Ti-isopropoxide grafting exhibit the same XRD patterns and the intensity remained almost constant as those for their pure silica analogues as shown in Figure 1. These confirm that structural integrity of the mesoporous materials remained intact after TIPOT grafting treatment. 

The first materials discovered which belong to this novel group of titanosilicates, having numerous sixfold-coordinated Ti sites in a microporous crystalline array, was ETS-4, which is an analogue of the mineral zorite while the other, ETS-10, is topologically comparable to zeolite (1 [96],... 

In addition to the aluminosilicates, some obvious synthetic analogues, such as borosilicates, gallosilicates and ferrisilicates, have also been explored. The boro-silicates are more difficult to prepare, probably because the much smaller boron, with its tendency towards planar, three-fold coordination, is not an obvious substitute for the role of aluminum. Gallium and iron(III) materials, though, are well known and usually have properties similar to those of the aluminosilicates. There is evidence, however, for some unique behavior with gallosilicates, as in their ability to catalyze cyclization reactions and activate methane [30]. Other silicate-based systems include the titanosilicates, mentioned earlier, and some recently discovered vanadium silicates that show excellent thermal stability and can potentially be activated for catalysis [31]. 

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