Shengnan Guan,Qifu Huang,Jianru Ma,Wenzhi Li,Ajibola T. Ogunbiyi,Zean Zhou,Kun Chen,Qi Zhang
The catalytic performance of MnO2(x)–CeO2 (x = Mn/Ce molar ratio) and the synergistic effect have been investigated in formaldehyde removal. The results showed that formaldehyde achieved 100% conversion at 60 °C for MnO2(1.5)–CeO2, with the gas hourly space velocity = 120 000 mL h–1 gcat–1. It was lower than the formaldehyde removal temperature of MnO2 (130 °C) and CeO2 (170 °C). The apparent activation energy for HCHO oxidation with MnO2(1.5)–CeO2 was 34.2 kJ mol–1. The partial mutual replacement of Mnx+ and Cex+ decreases the crystallite size due to the MnO2/CeO2 interaction. The X-ray photoelectron spectroscopy and the Raman analyses show that the Mn3+/Mn and Oads/Olatt ratios and the relative concentrations of oxygen vacancies for MnO2(1)–CeO2 and MnO2(1.5)–CeO2 were higher than those of the rest of the catalysts. Thus, the lattice oxygen (Olatt) from CeO2 readily transfers to the oxygen vacancy, achieving Olatt activation to surface-adsorbed oxygen (Oads).
Cake-like MnO 2 @CeO 2 catalyst with hierarchical nanosheets structure has been successfully constructed by in situ methods. The relationship between structure and activity of the MnO 2 @CeO 2 catalyst was characterized using various analytical techniques. It is identified that rich surface oxygen species and better reducibility were generated due to the strong synergistic effect between MnO 2 and CeO 2 , and hence nearly T 90 toluene conversion can be obtained for the 10%-MnO 2 @CeO 2 catalyst under 240–300 °C. In addition, it is found that after loading MnO 2 on the multi-layer CeO 2 support to form a hierarchical cake-like structure, the oxygen vacancies, Ce 3+ /Ce 4+ and BET surface area of MnO 2 @CeO 2 increased significantly, which is beneficial to toluene adsorption and reaction. Furthermore, the in situ DRIFTS study demonstrated that the lattice oxygen and surface oxygen both participate in the toluene oxidation , whereas surface active oxygens adsorbed on the oxygen vacancies will lead to deep oxidation by forming abundance intermediates.
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