Re-recognizing W/Mo promoter as a transformer changing inactive V into highly active catalytic species distribution

The promoter is very important for effective catalysts, and the relationship among active species, promoter, and support is a hot topic in the field of catalysis. This work aims to investigate the influence of the promoter on the formation of effective active species. For this purpose, V was leached out from V-loaded TiO 2 (V/Ti) step by step, and the loaded V was classified into different species based on their performances in the catalytic oxidation of chlorobenzene. As a result, when V/Ti was co-doped with Mo or W, the chlorobenzene conversion rate was increased from 48.1% to 54.0% (Mo) or 61.0% (W) at 210 °C. The enhancement was attributed to the redistribution of V species. Specifically, 7.8% of V was “Inactive” V on V/Ti. This “Inactive” V was transformed into an “Active” species. At the same time, “Highly-active V” amounts were increased from 86.0% (V 3.3 /Ti) to 88.1% (WV 3.3 /Ti) and 87.1% (MoV 3.3 /Ti). According to the mechanism investigation, when W and Mo coexisted with V during the synthesis, V 3+ was oxidized into V 5+ , which is easily invaded into the TiO 2 , created more strong acidic sites, and activated more active lattice oxygens. These are all in favor of the effective catalytic oxidation of chlorobenzene. The new understanding of the promoter effect will help to produce a more effective catalyst using the same amount of active species. Graphical abstract