期刊
CATALYSTS
卷 8, 期 1, 页码 -出版社
MDPI
DOI: 10.3390/catal8010038
关键词
lean NOx reduction; silver-alumina; indium-alumina; ammonia-SCR; hydrogen effect
资金
- Swedish Research Council
- Swedish Energy Agency
- AB Volvo
- ECAPS AB
- Haldor Topsoe A/S
- Scania CV AB
- Volvo Car Corporation AB
- Wartsila Finland Oy
Alumina-supported silver and indium catalysts are investigated for the hydrogen-assisted selective catalytic reduction (SCR) of NOx with ammonia. Particularly, we focus on the active phase of the catalyst and the formation of surface species, as a function of the gas environment. Diffuse reflectance ultraviolet-visible (UV-vis) spectroscopy was used to follow the oxidation state of the silver and indium phases, and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to elucidate the formation of surface species during SCR conditions. In addition, the NOx reduction efficiency of the materials was evaluated using H-2-assisted NH3-SCR. The DRIFTS results show that the Ag/Al2O3 sample forms NO-containing surface species during SCR conditions to a higher extent compared to the In/Al2O3 sample. The silver sample also appears to be more reduced by H-2 than the indium sample, as revealed by UV-vis spectroscopic experiments. Addition of H-2, however, may promote the formation of highly dispersed In2O3 clusters, which previously have been suggested to be important for the SCR reaction. The affinity to adsorb NH3 is confirmed by both temperature programmed desorption (NH3-TPD) and in situ DRIFTS to be higher for the In/Al2O3 sample compared to Ag/Al2O3. The strong adsorption of NH3 may inhibit (self-poison) the NH3 activation, thereby hindering further reaction over this catalyst, which is also shown by the lower SCR activity compared to Ag/Al2O3.
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