Chapter 5 - Functionalisation and Structure Characterisation of Porous Silicates and Aluminophosphates

Abstract

This chapter encompasses some recent achievements in preparation and structure characterization of transition metal modified nanoporous silica- and phosphate-based framework materials for catalytic applications. Catalysis by microporous materials covers a broad range of economically important processes related to the upgrading of crude oil and natural gas as well as the profitable production of fine chemicals. The reactions and conversions are based on the acid and redox properties and shape-selective behavior of microporous solids. The most common reactions, where microporous acid catalysts are involved, are fluid catalytic cracking, isomerization, and transformation of aromatics. The expansion of their use in chemistry and pharmacy is mostly limited by the size of the pores and sometimes by their deactivation at operating conditions. Regarding the pore size, the discovery of mesoporous solids 15 years ago was a real breakthrough in this field, but the enthusiasm was slowed down because of the low catalytic activity of these materials, which was attributed to the leaching of metal active sites from the amorphous framework and their agglomeration. The search for microporous zeolitic catalysts with larger pores resulted in a recent remarkable discovery of a new silicogermanate zeolite ITQ-33. However, the surface properties of zeolitic materials significantly change when pores get bigger and become similar to layered aluminosilicates. Better solution toward highly active large pore heterogeneous catalysts seems to be the preparation of metal-modified microporous/mesoporous composite catalysts.