Inorganic oxides, pillaring with

Layered metal oxides(e.g. layered titanates, titanoniobates and niobates) intercalated with organic compounds have been extensively studied because of their potential applications in sorption, catalysis and conduction[1-3]. However, there are few studies on the preparation of inorganic oxide-pillared layered metal oxides, which have higher thermal stability than those layered metal oxides prepared by the intercalation of organic compounds[4-6]. He have reported that layered niobate and titanoniobate can react with NH2(CH2)3Si(OC2H3) 3 (abbreviated hereafter as APS) aqueous solution to obtain porous, thermostable silica-pillared layered metal oxides[7,8]. APS is a trialkoxysilane compound, its trialkoxy groups quickly undergo... 

These clays have been hybridized with diverse structural types of components such as nanoparticles, clusters, complex compounds, polymers, molecules, and ions. Their potential apphcations are found in many fields as inorganic catalysts, adsorbents, ceramics, coatings, and even drug delivery carriers. Various preparation methods have been developed such as pillaring, intercalation, and delamination techniques. The representative examples include organic-clay hybrids," metal oxide-pillared clays, " and bioclay hybrids. ... 

Pillaring would be expected to inqrrove the Bronsted and Lewis acidity of the materials due to increasing the access to these sites within the layers. Pillaring with inorganic oxides has been examined. Alumina and chromium(III) oxide, for example, can be used as suitable props resulting in materials with good surfiice area, porosity and thermal stability 123-126 stability to 400°C have been reported. ... 

Cations based on substituted silsesquioxanes have also been intercalated [7]. On heating the ion-exchanged clay minerals water is evolved, but oxycation or oxide pillars keep the siliceous layers apart. These materials have enhanced thermal stability compared with clay minerals expanded with organic cations. Expanded clay minerals cover at least as wide a range of accessibilities to the interlamellar micropore spaces as the zeolites, but the pore characteristics of clay minerals with inorganic pillars need more detailed investigation. 

In a very interesting connection between modified oxides and phosphates, it is possible to modify lamellar phosphates with inorganic oxides, a process called pillaring [3]. This last example shows how rich is the chemistry of modified oxides and phosphates. 

The diversity of the inclusion of molecules of any type into host lattices which are distinctly inorganic is now becoming apparent [31], Apart from the oxidic zeolites, aluminosilicates and derivatives with other tetrahedral sites, there are the layered silicates and minerals, pillared clays and numerous other intercalation and inclusion systems, including graphite, metal sulfides and metal cyanides [23, 32, 33]. 

More suitable pillars could be inorganic ions or oxides, with which it should be possible to prepare modulated pillared structures with these layered phosphates. 

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