Effect of reducing agent on the structure and activity of manganese oxide octahedral molecular sieve (OMS-2) in catalytic combustion of o-xylene

Abstract

Manganese oxide octahedral molecular sieve (OMS-2) with different microstructures were synthesized via simple wet chemical methods of KMnO4/benzyl alcohol and KMnO4/Mn(NO3)2 at room-temperature (the products were denoted as B-OMS-2 and N-OMS-2, respectively). The physicochemical properties of the materials were characterized using numerous analytical techniques. The catalytic activities of the catalysts were evaluated for the complete catalytic oxidation of a typical volatile organic compound (VOCs), o-xylene. It was found that B-OMS-2 presented a loose structure, and contained almost 100% Mn4+, while N-OMS-2 possessed a mixture of Mn4+ and Mn3+. H2-TPR and O2-TPO analyses showed that B-OMS-2 exhibited good low-temperature reducibility and high oxygen exchange ability with gas phase oxygen. The microstructure difference was caused by different reducing reagents used in the synthesis. Benzyl alcohol might adsorb on the surface of MnO2 nuclei acting as a ligand and/or structure-directing agent, and the desorption of the organic compound led to the formation of bulk oxygen vacancy in B-OMS-2. B-OMS-2 could convert 100% o-xylene into CO2 at 190°C at a space velocity of 8000h−1, 50°C lower than N-OMS-2. The excellent catalytic performance of B-OMS-2 might be caused by its bulk oxygen vacancy, potent reducibility and high re-oxidation ability. It is believed that B-OMS-2 is a promising catalyst for the elimination of VOCs from air.