Preparation of porous MTiO (M = Cr, Mo, or W) composite oxides from a mesostructured material of titanium oxysulfate and surfactant micelles based on a wall ion exchange–calcination method

Abstract

Wall ion exchange (WIE) and subsequent calcination were applied to prepare porous TiO 2-based composite oxides using a composite of TiOSO 4 •xH 2 SO 4 •xH 2 O and cetyltrimethylammonium bromide (TS). Chromium oxyanion HCrO 4 in an aqueous solution was ion-exchanged stoichiometrically with HSO 4 in TS at pH values in the range of 2.2 to 5.5. Calcination of the HCrO 4-introduced TS (Cr-TS) at 673 K for 2 h in air produced Cr-Ti oxide with surface areas of 296-430 m 2 g-1 , pore diameters of 1.7-2.5 nm, and a wormhole-like pore structure. These high surface areas could be achieved at ratios of Cr and Ti in the Cr-Ti oxide of 0.30-0.39 or above. XAFS, FT-IR, and UV-vis diffuse reflectance spectra indicated the occurrence of dimerization of HCrO 4 to Cr 2 O 7 2during drying of the Cr-TS. The Cr 2 O 7 2species was then reduced to Cr(III) species upon calcination at 473-573 K. The Cr(III) species located on the