Catalytic activities of MCM41

Abstract

The solid catalysts, used in heterogeneous catalysis, have been conveniently subdivided into microporous (pore diameter lt 2 nm) and mesoporous (2-50 nm) materials. The activity of these materials is manifested in their microstructures, which allow large internal surface cavities for reactant and product molecules for various types of transformations. The molecular sieve zeolites, which are the best-known heterogeneous catalysts, have micropores consisting of regular arrays of uniformly sized channels. Silicas, transitional alumina and pillared clays and silicates have been typically projected as mesoporous materials. The pores of these materials are irregularly spaced and broadly distributed in size and for a long time, attempts to synthesize mesoporous molecular sieves with regular, well-defined channel systems have not been successful. However, in 1992, Kresge et al. of Mobil Research and Development Corporation, U. S. A. have reported for the first time the synthesis of a new family of mesoporous molecular sieves designated as M41S. MCM-41, a member of this family has been shown to have a hexagonal array of uniform mesopores (-1.5 nm to gt10 nm in size). The surface area of these materials is very large, typically of the order ofgt700m2/g and they have hydrocarbon sorption capacity of 0.7 cm3/g and greater. The Mobil group followed up their initial discovery with detailed methods of synthesis using liquid crystal templates. Since then a number of other reports have come up on the synthesis and possible use of this new type of molecular sieves. These works have been mostly confined to synthesis and characterization of MCM-41. Use of MCM-41 as a catalyst for hydrocracking of vacuum gas oil is also recently tested. The use of MCM-41 as a Friedel-Craft catalyst, a basic catalyst for Knoevaenagal condensation and Michael addition, and as acid catalyst for acetalization and aldol condensation has also been reported. The MCM-41 has attracted considerable interest due to its periodic framework of regular mesopores,...