Role of pore size and surface properties of Ti-MCM-41 catalysts in the hydroxylation of aromatics in the liquid phase

[Si,Ti]-MCM-41 with varying Si/Ti ratios and [Si,Ti,Al]-MCM-41 with varying Si/Al ratios, which possess well-ordered long-range structures and one-dim ensional channels, have been synthesized using a hydrothermal process. From N-2 adsorption data. the pore diameters of the materials were calculated t o be about 3.0 nm and the specific surface areas above 500 m(2)/g. When use d as the catalyst for the hydroxylation of benzene in the liquid phase, [Si ,Ti]MCM-41 is more effective than TS-I due to its larger pore sizes. In add ition, [Si,Ti]-MCM-41 significantly favors the hydroxylation of benzene ove r the hydroxylation of phenol, thereby showing the potential for enhanced c hemical selectivity for the hydroxylation of aromatics. The hydroxylation o f benzene becomes less favorable and the hydroxylation of phenol becomes mo re favorable with increasing Al content, indicating that the chemical selec tivity can potentially be further enhanced by changing the surface properti es of the catalyst. Although the [Si,Ti]-MCM-41 catalyst is deactivated dur ing the hydroxylation reaction, it can be fully regenerated by calcination. (C) 2001 Elsevier Science B.V. All rights reserved.