Relationship between catalytic deactivation and physicochemical properties of LaMnO3 perovskite catalyst during catalytic oxidation of vinyl chloride
Résumé
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), N-2 sorption, thermogravimetric and differential thermal analysis
(TGA/DTA), energy disperse spectrocopy (EDS), hydrogen
temperature-programmed reduction (H-2-TPR), oxygen
temperature-programmed desorption (O-2-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. (C) 2016 Published by
Elsevier B.V.