Insight into the enhanced activity of Ag/NiOx-MnO2 for catalytic oxidation of o-xylene at low temperatures

NiOx-MnO2 was synthesized by redox and deposition-precipitation methods and its catalytic performance for o-xylene oxidation was investigated. It exhibited higher activity than NiOx-MnO2 and OMS-2. The T-20, T(50)( )and T-100 values were 72, 145 and 190 degrees C, respectively (500 ppm o-xylene/humid air, GHSV = 6000 h(-1)). Moreover, it showed excellent water-resistance and stability, demonstrating its potential for practical application. Characterization results revealed that the introduction of Ni and Ag increased the catalyst reducibility, the amount of electrophilic oxygen species, and the ability for oxygen molecules activation, resulting in the superior performance at low temperatures. In situ DRIFT study indicated that aromatic ring could be directly oxidized into maleate by the electrophilic lattice oxygen of Ag/NiOx-MnO2 in the absence of oxygen molecules, and the formed maleate could be oxidized into formate and/or carbonate in the presence of oxygen molecules. Finally, the possible degradation pathway of o-xylene in the presence or absence gaseous oxygen was discussed.