Synthesis, characterization, and catalytic properties of micro-mesoporous, amorphous titanosilicate catalysts

Abstract

Titanosilicates, synthesized under ambient conditions in the absence of nitrogenated organic bases, exhibit (i) an amorphous nature (XRD, electron diffraction, TEM); (ii) a bimodal, narrow pore size distribution with pore widths around 0.8 and 3.6 nm, respectively, and surface areas of about 500-700 m2g−1 (BET); (iii) absorption bands at 960 cm−1 (IR) and 220 nm (UV), respectively; (iv) a radial electron density distribution pattern indicating the presence of isolated TiO4 units in a silica matrix; and (v) catalytic activity and selectivity comparable to crystalline TS-1 (MFI) in the oxidation (with aqueous H2O2) of benzene, toluene, and phenol. Unlike other solid catalysts known so far, these amorphous titanosilicates provide a higher yield of catechol than hydroquinone in the oxidation of phenol. In contrast to TS-1 or TS-2 (MEL), the oxyfunctionalization of the side chain in toluene is more predominant than the aromatic ring hydroxylation indicating a radical mechanism of oxidation.