Tungstated zirconia catalyzed bromination of phenol red under nearly neutral solution

The performance of tungstated zirconia catalysts prepared by co-precipitation (WZ) and impregnation (W/m-ZrO2) techniques in phenol red bromination reaction was tested. Both types of catalysts showed excellent activity in this reaction in aqueous solution. The activity of WZ increases as the W loading decreases and the most active 0.6WZ catalyst contained highly dispersed WOx of low surface density on zirconia. The W/m-ZrO2 catalysts showed even higher activity in this reaction but maximum performance is observed for 1.3W/m-ZrO2 instead. The active site for the redox reaction is probably the monomer or dimer of WOx with a single oxo group whereas low surface density of WOx provides enough space on zirconia for the adsorption of phenol red without blocking the redox sites. (c) 2005 Elsevier B.V. All rights reserved.