Preparation of titania-based catalysts for formaldehyde photocatalytic oxidation from TiCl4 by the sol-gel method

Titania sols were prepared by acid hydrolysis of a TiCl4 precursor instead of titanium alkoxides. The effect of acid concentration on the particle siz e and stability of sol was investigated. Stable titania sols with mean part icle size of 14 nm could be obtained when the H+/Ti molar ratio was 0.5. Th e titania sols were modified with Pt, SiO2, ZrO2, WO3 and MoO3 to prepare a series of modified catalysts, which were used for the photocatalytic oxida tion of formaldehyde at 37 degreesC. They showed different photocatalytic a ctivities due to the influence of the additives. Comparing with pure TiO2, the addition of silica or zirconia increased the photocatalytic activity, w hile the addition of Pt and MoO3 decreased the activity, and the addition O f WO3 had little effect on the activity. It is of great significance that t he conversion of formaldehyde was increased up to 94% over the SiO2-TiO2 ca talyst. The increased activity was partly due to higher surface area and po rosity or smaller crystallite size. A comparison of our catalyst compositio ns with the literature in this field suggested that the difference in activ ity due to the addition of a second metal oxide maybe caused by the surface chemistry of the catalysts, particularly the acidity. (C) 2001 Elsevier Sc ience B.V. All rights reserved.