A series of Cd-doped NiO catalysts were prepared and tested in the N 2 O catalytic decomposition reaction. In comparison with NiO, it was found that the Cd 0.04 Ni catalyst showed higher N 2 O decomposition activity in the temperature range of 300–450 °C with or without O 2 , and lower activation energy (77.8 kJ mol −1 ). The incorporation of Cd into the NiO lattice was verified by X-ray diffraction (XRD) patterns and Raman spectra. This led to the distortion of the original NiO structure and weakened the Ni-O bond. X-ray photoelectron spectroscopy (XPS) results showed that compared with NiO and CdO, Cd 0.04 Ni possessed higher Ni 2+ and Cd (n+1)+ contents, which might have been induced by the electron transfer behavior between CdO and NiO. A possible mechanism for active site regeneration and O 2 desorption over Cd 0.04 Ni was proposed. The Cd 0.04 Ni catalyst also exhibited good resistance to NO and O 2 .
Jiangyao Chen,Jiajing Yi,Weikun Zhu,Weina Zhang,Taicheng An
O2 and H2O influence the photocatalytic oxidation mechanism of gaseous monoaromatics, but still in an unclear manner, due to the lack of direct evidence. Tracing an oxygen atom from 16O2 and H218O to intermediates can clarify their roles. The low H218O content suppressed the formation of benzenedicarboxaldehydes during the oxidation of xylenes and 16O2 greatly affected the yield of total intermediates, while neither of them altered the percentage order of the products. Methylbenzaldehydes, methylbenzyl alcohols, and benzenedicarboxaldehydes possessed greater 16O percentage (≥69.49%), while higher 18O distribution was observed in methylbenzoic acids and phthalide (≥59.51%). Together with the interconversion results of the products revealed, 16O2 determined the transformation of xylenes initially to methylbenzaldehydes and then to methylbenzyl alcohols or benzenedicarboxaldehydes, while H218O mainly contributed to conversion of methylbenzaldehydes to methylbenzoic acids or phthalide. Further interaction sites of xylene and its products with H2O and O2 were confirmed by molecular dynamics calculations. The same roles of 16O2 and H218O in the degradation of toluene, ethylbenzene, 1,2,4-trimethylbenzene, and 1,3,5-trimethylbenzene were also verified. This is the first report that provides direct evidence for the roles of O2 and H2O in the photocatalytic oxidation mechanism of gaseous monoaromatics. These findings are helpful to achieve controllable product formation from the oxidation of monoaromatics and predict their migration process in the atmospheric environment.
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