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NEW POROUS SOLIDS ORGANIC INORGANIC PILLARED COMPOSITES

Objective

The primary objective of the project is to assess the capabilities of the techniques of pillaring layered phosphates to 'fine tune' the cavity dimensions in porous solids. Cavity manipulation will be extended to the synthesis of phosphates with channels and three-dimensional structures. The thermally stable solids obtained using these techniques and having rationally-induced cavity dimensions will be tested to assess their capabilities as catalysts, gas absorbents, ionic conductors and inorganic organic composites. Pillaring is currently one of the most widely used techniques in molecular engineering for fabricating useful porous solids. However, it has not been successful to date in producing a material capable of competing with the zeolite family of materials. The present study intends to rectify this situation by improving the thermal stability of pillared materials for application as sieves and catalysts using layered phosphates.
Series of porous solids have been prepared with alumina and chromiapillars between phosphate layers, the cavities of which can be manipulated by suitable choice of reaction conditions. Surface areas of 18-400 m{z}g{-1} have been obtained to date, in materials which can be modulated so as to be either crystalline or amorphous (whilst still being in many cases monopore). Thus, alumina pillared series contain both wide pore radius distributions (11-50 angstroms) and others narrow ones (10-25 angstroms).
Furthermore, series of materials can be manipulated to give free heights (as assessed by X-ray diffraction) which can be rationally varied, between 5.5 and greater than 25 angstroms. New methods have also been found for preparing starting Keggin ion (and non Keggin ion) clusters which can be generalised to smectite clays.

The materials selectively exchange transition metal ions, and absorb large organic molecules both in bulk and as adherent thermally stable films on metallic and vitreous surfaces. They also allow polymerisation of conducting organic molecular wires and supporting semiconductor clusters to give quantum well devices.

Colloidal methods are successful for obtaining new porous oxide pillared layered phophates with tunable pore sizes. For alumina pillared alpha tin phosphates, surface areas of 190 to 228 m{2} g{-1} have been attained with differing lateral pillar density depending on the intercalate precursor used (commercial chlorhydrol or in situ prepared A 113 containing Keggin cation). A new method for preparing Keggin ion precursors has also given almost monopore alumina pillared materials with the same phosphates. Forced surface polymerization of a simple acetate ion on such colloids can give entire series of chromia pillared layer phosphates (after calcination) with both alpha tin phosphate and alpha zirconium phosphate. They have surface areas in the range 200 to 340 m{2} g{-1} and narrow pore size distributions. It has been found possible to perform pore chemistry analagous to that in zeolites.
Colloidal manipulation methods have provided a large selection of porous oxide pillared materials to be obtained from layered phosphates. The success in preparing entire series of thermally stable pillared phosphates is being followed by the extension of the colloid methods to other layered phosphates and to preparation of silicon dioxide and titanium dioxide pillars.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Consiglio Nazionale delle Ricerche (CNR)
Address
Via Salaria Km 29.300
00016 Montelibretti Roma
Italy

Participants (1)

UNIVERSIDAD DE MALAGA
Spain