Mesoporous H-GaMCM-48: A remarkable solid acid catalyst for tertiary butylation of phenol

A mesoporous gallosificate (GaMCM-48) molecular sieve having a silicon-to-gallium (molar) ratio of 60 was synthesized hydrothermally, and the structure, coordination geometry of gallium, acidic properties, and catalytic activity were investigated systematically employing various analytical and spectroscopic techniques. XRD, TEM, and N-2 sorption investigations show a MCM-48 structure with highly ordered (meso)porosity. Ga-71 MAS-NMR studies reveal that gallium substitutes isomorphously in the mesoporous silicate framework of MCM-48. Further, NH3-TPD profiles suggest the presence of a high concentration of moderate-to-strong Bronsted acid sites in H-GaMCM-48. The catalytic performance of this protonated catalyst was evaluated for the t-butylation of phenol reaction. The results indicate that the H-GaMCM-48 catalyst is highly active for the chosen reaction and shows a much higher substrate conversion than many other catalyst systems. However, compared to the analogous H-GaMCM-41. the H-GaMCM-48 shows only a slight decrease in p-t-butyl phenol selectivity owing to the formation of 2,4-di-t-butyl phenol. On the other hand, the deactivation is very minimal on account of the three-dimensional pore system of MCM-48 structure compared to the one-dimensional pore opening of the MCM-41 structure. (C) 2004 Elsevier Inc. All rights reserved.