Liquid-phase alkylation of phenol with t-butanol over various catalysts derived from MWW-type precursors

Three types of MWW-based catalysts (MCM-22, MCM-36 and ITQ-2) were studied in the liquid-phase alkylation of phenol by tert-butanol (TBA). Ammonia adsorption calorimetry was applied to investigate the acid properties of zeolites with different framework topology and crystallinity. It was established that acid properties of MCM-22 family depend mainly of the solid Al-content (the Si/Al ratio varied from 9.1 to 46.0). Delamination of MCM-22 precursor (MCM-22(P)) leading to ITQ-2 results in the decrease of the total acidity and the increase of the intermediate acid sites concentration, while the pillaring process yielding MCM-36 affected mainly the total concentration of acid sites, the acid strength distribution being similar to the corresponding MCM-22 zeolite. The catalytic activity and selectivity of zeolite-based catalysts are discussed. The most active catalyst for the studied reaction was MCM-22 B (Si/Al similar to 15). The results obtained with MCM-22 as catalyst revealed that, despite the expectations due to the presence of 10-MR pores in the structure of this zeolite, no enhanced selectivity top-tert-butyl phenol (p-TBP) is observed. This has been rationalized by the assumption that most of reactions occurring in this system take place on acid sites at or close to the external surface. This assumption is also supported by the similar catalytic selectivity of the MWW-derived structures (viz. MCM-36 and ITQ-2), which expose a higher concentration of external pockets. However, it is noticeable the high catalytic activity of MCM-22 zeolites for the liquid-phase alkylation of phenol by TBA that is comparable to the gas-phase activity of large pore zeolites like as HY or HM. (c) 2005 Academie des sciences. Published by Elsevier SAS. All rights reserved.