期刊
APPLIED CATALYSIS B-ENVIRONMENTAL
卷 97, 期 1-2, 页码 98-107出版社
ELSEVIER
DOI: 10.1016/j.apcatb.2010.03.028
关键词
Catalyst deactivation; Fe-beta; FTIR; Metal-exchanged zeolites; NMR; NOx reduction; SCR; Urea
资金
- Columbia University in the City of New York and BASF SE
The selective catalytic reduction (SCR) with urea over metal-exchanged zeolites is one of the most promising contenders for the reduction of NO, emissions in diesel exhaust However, one major concern - a possible deactivation of the catalyst by urea deposits - has not been investigated sufficiently as yet. The formation of urea deposits on the catalyst after long-term operation was simulated by impregnating Fe-beta zeolite powder with 32 5 wt % aqueous urea solution followed by hydrothermal aging at temperatures between 250 and 750 degrees C The SCR activity was measured after each hydrothermal aging step It could be shown that Fe-beta can be reversibly deactivated by urea deposits such as cyanuric acid and ammelide (as identified by ATR-FTIR) if the impregnated catalyst was hydrothermally aged at temperatures not higher than 250 degrees C Upon steaming at 500 degrees C a complete regeneration of the SCR activity as well as a total decomposition of urea deposits left on the catalyst was observed. In addition, MAS (27) AI and Si-29 NMR experiments clearly show that no detrimental changes of the Si/Al zeolite framework were induced by urea-impregnation followed by steaming at 750 degrees C compared to the dealumination observed for hydrothermal aging alone. Thus, the urea-induced deactivation is fully reversible since no permanent structural changes in the zeolite could be identified (C) 2010 Elsevier B.V All rights reserved
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