Silicalites and aluminophosphates

Since the synthesis of aluminophosphate (AIPO4) molecular sieves (Wilson et al 1982), other novel catalyst materials have been developed by the 

The incorporation of silicon leads to a new class of compounds termed S APOs. These exhibit catalytic properties intermediately between those of zeolite 

Substituting divalent or trivalent elements for the A1 in the framework has been successfully carried out by several groups yielding novel heterogeneous catalysts (metal-substituted ALPOS, MALPOs Thomas et al 2001) for hydrocarbon oxidation and liquid phase oxidation. MALPO catalysts can be complementary to metal-doped silicalite catalysts. Particularly interesting compounds are MALPOs in which a divalent metal (Me) substitutes for the framework Al +, for example MALPO-36 (where M = Mg, Mn, Zn, Co) and MALPO-34 (M = Mg, Mn, Co etc). 

3 Determining three-dimensional structures by ED and HRTEM MALPO solid acid catalysts 

The application of HRTEM and ED can be difficult, however, because of the tendency of the catalysts to become amorphous under the beam. Use of higher accelerating voltages (to minimize the production of inelastic collisions which are primarily responsible for the structural disintegration of the sample), better vacuum in the sample chamber and, when possible, dealumination of the aluminosilicate (by replacing AP+ with in the framework) without losing structural integrity avoids these problems. These studies have indicated that Al-O bonds are more susceptible to rupture under electron-beam irradiation than Si-O bonds. 

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