Relationship between catalytic deactivation and physicochemical properties of LaMnO3 perovskite catalyst during catalytic oxidation of vinyl chloride

Abstract

A LaMnO3 perovskite oxide catalyst prepared by co-precipitation was evaluated for vinyl chloride (VC) oxidation over consecutive catalytic cycles and in steady-state conditions. The LaMnO3 catalyst exhibited relatively poor catalytic stability and durability, with the amount of chlorinated organic species increasing as catalytic activity decreased. Physicochemical properties were characterized by X-ray diffraction (XRD), N2 sorption, thermogravimetric and differential thermal analysis (TGA/DTA), energy disperse spectrocopy (EDS), hydrogen temperature-programmed reduction (H2-TPR), oxygen temperature-programmed desorption (O2-TPD) and X-ray photoelectron spectroscopy (XPS). Fresh and used catalysts presented a typical perovskite structure. No coke and only traces of residual chlorine species were detected on the used catalyst, indicating that coke formation and attack by chlorine were not the causes for deactivation. The used catalyst, however, presented lower specific surface area, low-temperature reducibility and surface oxygen mobility than the fresh one, suggesting that physicochemical and redox properties strongly influenced catalytic deactivation. Finally, a deactivation mechanism was proposed based on the Mn4+/Mn3+ redox cycle, and the formation of chlorinated by-products was inferred to be closely related to the presence of Cl species and catalyst deactivation.