Mesoporous [M]-MSU-x metallo-silicate catalysts by non-ionic polyethylene oxide surfactant templating

Abstract

Solutions of low and high pH have been used to form non-ionically templated mesoporous metallo-silicates [M]-MSU-x materials; where [M]=Al, Ti, V and Zr. Two new assembly routes are proposed which exploit the acid and base catalysed hydrolysis and simultaneous condensation of metal oxo-salts and silicon tetraethoxide. Acid catalysed hydrolysis, labeled N0X−I+ or N+X−I+ (N0=nonyl-phenyl polyethylene oxide, X−=Cl− or SO2−4, I+=protonated tetraethyl orthosilicate), produces well-defined materials with uniform pores in the small mesoporous region and moderate pore volumes, but reduced metal incorporation owing to the high solubilities of metal cations in acidic solutions. Base catalysed hydrolysis, labeled N0M+I− (N0=nonyl-phenyl polyethylene oxide, M+=Na+ or NH+4, I−=hydroxylated tetraethyl orthosilicate), also leads to materials with uniform channels in the small mesoporous region. Pore volumes and metal substitution are higher and framework shrinkage during calcination is reduced as a result of thicker pore walls. These new pathways show distinct similarities to those described by Attard et al. [Nature 378 (1995) 366] and Zhao et al. [Science 279 (1998) 548] for the formation of hexagonally symmetric silica from non-ionic surfactants under acidic conditions and also to mesoporous MCM-41 assembly routes via (S+X−I+) anion mediated acid catalysed assembly. The results demonstrate the feasibility of preparing templated mesoporous metallo-silicates from non-ionic polyethylene oxide surfactants and metal oxy-hydroxy cationic precursors, but indicate that further optimisation of the reaction conditions is required to maximise the potential of this synthesis approach.