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.