Catalytic removal of gaseous unintentional POPs on manganese oxide octahedral molecular sieves

Abstract

Hexachlorobenzene (HCBz), pentachlorobenzene (PeCBz), and polychlorinated biphenyls (PCBs) are persistent organic pollutants emitted unintentionally from combustion and industrial processes. Catalytic removal of gaseous HCBz was achieved using manganese oxide octahedral molecular sieve (OMS) in four crystal structures: α-, β-, γ- and δ-MnO2. All OMS catalysts present high activity at high space velocity (660,000h−1) in comparison to V2O5 based catalyst. The catalytic performance of OMS decreases in the order of δ->α->γ->β-MnO2. It is found that both adsorption and destruction processes influence the removal efficiency (RE). The former is positively correlated with surface area, pore (3.3–6.4nm) volume, and surface acid sites, while the latter is coherent with both catalyst reducibility and the amount of surface labile oxygen. The best-performing δ-MnO2 was further applied for the destruction of gaseous PeCBz, HCBz, and PCB mixture at trace concentration (305μgNm−3). High RE (99.3%) was achieved at 230°C with the space velocity of 132,000h−1.