Catalytic Oxidation of Chlorinated Organics over Lanthanide Perovskites: Effects of Phosphoric Acid Etching and Water Vapor on Chlorine Desorption Behavior

Abstract

In this article, the underlying eff ect of phosphoric acid etching and additional water vapor on chlorine desorption behavior over a model catalyst La3Mn2O7 was explored. Acid treatment led to the formation of LaPO4 and enhanced the mobility of lattice oxygen of La3Mn2O7 evidenced by a range of characterization (i.e., X-ray diff raction, temperature-programmed analyses, NH3−IR, etc.). The former introduced thermally stable Bronsted acidic sites that enhanced dichloromethane (DCM) hydrolysis while the latter facilitated desorption of accumulated chlorine at elevated temperatures. The acid-modified catalyst displayed a superior catalytic activity in DCM oxidation compared to the untreated sample, which was ascribed to the abundance of proton donors and Mn(IV) species. The addition of water vapor to the reaction favored the formation and desorption of HCl and avoided surface chlorination at low temperatures. This resulted in a further reduction in reaction temperature under humid conditions (T90 of 380 °C for the modified catalyst). These results provide an in-depth interpretation of chlorine desorption behavior for DCM oxidation, which should aid the future design of industrial catalysts for the durable catalytic combustion of chlorinated organics.

A Brief Review on Key Role of Perovskite Oxides as Catalyst

“…[49] Wu et al has demonstrated manganite layered perovskite i.e La 3 Mn 2 O 7 + δ as a model catalyst in the oxidation of chlorinated organic due to its high thermal stability and enriched oxygen species. [65,66] Tanaka et al has described the role of Pt-free Sr 3 Fe 2 O 7-δ (Ruddlesden-Popper oxide) as catalyst in NO x oxidation and storage reactions. [66]…”

Facet control of manganese oxides with diverse redox abilities and acidities for catalytically removing hazardous 1,2-dichloroethane

“…explored the influence of phosphoric acid etching and water steam on dichloromethane elimination over La 3 Mn 2 O 7 and found that the former enhanced dichloromethane hydrolysis and the latter promoted desorption of accumulative chlorine with elevated temperatures. 27 However, the study on CVOCs combustion over MnO 2 with different crystal planes is rare reported. What's more, how to improve the anti-poisoning ability of catalyst as well as avoid deactivation and producing more harmful by-products is still a challenge in industrial application.…”

Improved Activity and Stability of Chlorobenzene Oxidation Over Transition Metal-Substituted Spinel-Type Catalysts Supported on Cordierite

“…In these transition metal oxides, ceria-based oxides, like CeO2-TiO2 [6] , CeO2-FeOx [5] , CeO2-CrOx [33,36] , CeO2-VOx [28,37] , CeO2-WOx [3] , and CeO2-MnOx [14,26,38] , have attracted more attention due to the high oxygen storage capacity, Ce 4+ /Ce 3+ redox properties of cerium oxide, and the strong interplay between MOx and CeO2. Recently, composite oxides as perovskitetype and spinel-type were also identified as feasible catalysts to complete catalytic oxidation of CVOCs ascribed to good thermal stability, good tolerance to chlorine poisoning, high oxygen mobility and relatively higher activities [39] . The perovskitetype oxides, such as LaCoO3 [4] and LaMnO3 [40] , are the commonest compounds for CVOCs oxidation.…”