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

The preparation of four kinds of α-, β-, γ-, and δ-type MnO2 with distinct crystal phases and tunnel structures were achieved and applied for 1,2-dichloroethane (1,2-DCE) catalytic combustion. The redox ability and acidity of MnO2 as well as the corresponding reaction mechanism were studied by means of various surface-sensitive techniques, including TPR, TPD, OIE, XPS, in situ DRIFTS together with DFT calculation. The catalytic activities in 1,2-DCE combustion illustrated that γ-MnO2 displayed the most superior activity with the maximum HCl yield of 95% and CO2 yield of 92%, due to its abundant oxygen vacancies on surface, easy formation of active oxygen species, and strong acidity that readily reacted with the adsorbed reactant to form HCl, which reflects the synergies of redox property and acidity. However, the strong Mn-Cl bonding associated with high valent Mn4+ and scarcity of acidic sites in β- and δ-MnO2 hinder the HCl elimination process, even leading to undesirable chlorine deposition associated with series of the polychlorinated byproducts including 1,1,2-C2H3Cl3 and CCl4 via Cl substitution process. A mechanism for 1,2-DCE combustion involving dehydrochlorination via the C-Cl bonds cleavage at acidic sites as well as excess polychlorination by Cl2 over relatively oxidative sample was accordingly proposed.