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

Abstract

[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-dimensional channels, have been synthesized using a hydrothermal process. From N2 adsorption data, the pore diameters of the materials were calculated to be about 3.0 nm and the specific surface areas above 500 m2/g. When used as the catalyst for the hydroxylation of benzene in the liquid phase, [Si,Ti]-MCM-41 is more effective than TS-1 due to its larger pore sizes. In addition, [Si,Ti]-MCM-41 significantly favors the hydroxylation of benzene over the hydroxylation of phenol, thereby showing the potential for enhanced chemical selectivity for the hydroxylation of aromatics. The hydroxylation of benzene becomes less favorable and the hydroxylation of phenol becomes more favorable with increasing Al content, indicating that the chemical selectivity can potentially be further enhanced by changing the surface properties of the catalyst. Although the [Si,Ti]-MCM-41 catalyst is deactivated during the hydroxylation reaction, it can be fully regenerated by calcination.