Transforming Chlorobenzene with Stepwise Calcinated CrOx Catalysts

Scientists have discovered that the process used to make CrOx catalysts from MIL-101(Cr) greatly influences their ability to oxidize chlorobenzene (CB). Calcinating in an argon atmosphere keeps the organic parts intact and prevents the CrOx clusters from clumping together. This results in many exposed Cr3+ sites and oxygen vacancies. When treated with a mix of oxygen and argon, these Cr3+ sites turn into active Cr6+ sites surrounded by acid sites that help in CB adsorption and intermediate oxidation.The oxygen vacancies allow surface lattice oxygen to move and replenish the consumed oxygen around Cr6+. The best catalyst, MIL-101(Cr)-Ar-T, made by stepwise calcination and treatment, had the highest CB oxidation activity, with a T90 at 233°C. It also showed great selectivity for COx and HCl at 240°C and proved stable over five days.