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Alkali-Resistant Mechanism of a Hollandite DeNOx Catalyst
- Hu, Pingping, Huang, Zhiwei, Gu, Xiao, Xu, Fei, Gao, Jiayi, Wang, Yue, Chen, Yaxin, Tang, Xingfu
- Environmental Science & Technology 2015 v.49 no.11 pp. 7042-7047
- X-radiation, X-ray absorption spectroscopy, X-ray diffraction, adsorption, alkalis, ammonia, catalysts, energy conservation, ion exchange, manganese oxides, metal ions, models, protons
- A thorough understanding of the deactivation mechanism by alkalis is of great importance for rationally designing improved alkali-resistant deNOₓ catalysts, but a traditional ion-exchange mechanism cannot often accurately describe the nature of the deactivation, thus hampering the development of superior catalysts. Here, we establish a new exchange-coordination mechanism on the basis of the exhaustive study on the strong alkali resistance of a hollandite manganese oxide (HMO) catalyst. A combination of isothermal adsorption measurements of ammonia with X-ray absorption near-edge structure spectra and X-ray photoelectron spectra reveals that alkali metal ions first react with protons from Brønsted acid sites of HMO via the ion exchange. Synchrotron X-ray diffraction patterns and extended X-ray absorption fine structure spectra coupled with theoretical calculations demonstrate that the exchanged alkali metal ions are subsequently stabilized at size-suitable cavities in the HMO pores via a coordination model with an energy savings. This exchange-coordination mechanism not only gives a wholly convincing explanation for the intrinsic nature of the deactivation of the reported catalysts by alkalis but also provides a strategy for rationally designing improved alkali-resistant deNOₓ catalysts in general.