Mechanistic insights into the role of acidity to activity and anti-poisoning over Nb based catalysts for CVOCs combustion

A series of Nb-based catalysts with different acid types of carriers (TiO2, Beta molecular sieve, and CeO2) were synthesized. In the catalytic oxidation of dichloromethane (DCM), Nb/CeO2 exhibited the best catalytic activity, resistance to chlorine poisoning/carbon deposits, and stability, due to the abundant acid sites and appropriate ratio of Lewis to Bronsted acid sites on the surface. Both Lewis and Bronsted acid sites could participate in the breakdown of C-Cl bonds, whereas the former exerted a greater influence. The Bronsted acid sites participated in the desorption of Cl species, and were prone to the generation of carbon deposits. The chlorine species easily accumulated at the Lewis acid sites of Nb/TiO2(containing predominantly Lewis acid sites), formed metal chlorides, and caused chlorine poisoning. Carbon deposits made it difficult for Nb/Beta (containing predominantly Bronsted acid sites) to maintain long-term activity. Additionally, the acid sites generated by the active component were more important for DCM degradation than those generated by the carrier.