Abstract

A mesoporous form of titanium phosphate has been prepared by reaction between phosphoric acid solution and either titanium propoxide or titanium chloride in the presence of trimethylammonium surfactants. The surfactant can be almost completely removed by extraction using acidified ethanol. The surface area of the extracted samples depends closely on the pH of the reaction medium, and the reaction temperature, and the highest surface areas, around 740 m² g⁻¹ were obtained for materials prepared at pH 3. This surface area is partially lost when the extracted titanium phosphate is calcined, although the mesoporous character is retained. ³¹P NMR spectroscopy shows the ethanol-extracted sample to be rich in hydrogen phosphate (HPO₄²⁻ and H₂PO₄⁻) groups, which undergo partial condensation after calcination. These hydrogen phosphate groups are responsible for the high surface acidity determined, and for its evolution after calcination: the total numbers of surface acidic sites of ethanol-extracted titanium phosphate and calcined titanium phosphate, evaluated using two-cycle adsorption of ammonia from the gas phase at 80 °C, are 900 and 340 µmol g⁻¹ respectively.