Design of MoFe/Beta@CeO2 catalysts with a core−shell structure and their catalytic performances for the selective catalytic reduction of NO with NH3

- MoFe/Beta@CeO2 core-shell catalyst has been controllably synthesized by a self-assembly method.
- MoFe/Beta@CeO2 shows a remarkable improvement of deNOx activity, excellent SO2 and H2O tolerance and high thermal stability.
- CeO2 sheaths have inhibited the generation of ammonium sulfate and nitrate species from blocking the active sites.
- CeO2 shells have served as an effective barrier to prevent the aggregation of metal oxide NPs.
- The CeO2 shells promote the formation of nitrites species and NO oxidation to NO2.

MoFe/Beta@CeO2 core−shell catalyst was designed with nano-size Beta supporting MoFe bimetallic oxides as the core and CeO2 thin film as the shell. The structure and physico-chemical properties of the coated and uncoated CeO2 catalysts were characterized by TEM, SEM, XRD, N2 adsorption-desorption, XPS, XANES, ICP-AES, NH3-TPD, H2-TPR and in-situ DRIFTS. The catalytic activity tests for NH3-SCR of NO indicated that the catalyst coated by CeO2 shell exhibits a remarkable improvement of deNOx activity, excellent tolerance to SO2 and H2O, as well as high thermal stability. The both chemisorbed oxygen species (O2−, O−) and specific surface area increased for the catalysts after the coating of CeO2 shells. CeO2 shells not only increase the acid amount but also improve its acid strength, which could be beneficial to improving NO oxidation to NO2 during NH3-SCR. Furthermore, there is a strong interaction among the iron oxides, molybdenum oxides and CeO2 shells. CeO2 shells can serve as an effective barrier to inhibit the active metal oxides nanoparticles from aggregating at high temperature. As a result, the coated catalyst with CeO2 thin film shows a better thermal stability than the uncoated one. What's more, CeO2 shells can not only suppress the formation of ammonium nitrate and sulfate species blocking the active iron sites but also restrain the generation of iron sulfate, leading to a higher SO2 and H2O-tolerance. The above results demonstrate that the design of a core−shell structure catalyst is favorable for improving the performance of deNOx catalysts.

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