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The influence of the combustion products of different lubrication oil additives and impurities in fuel or urea solution on the activity and selectivity of V 2 O 5 /WO 3 -TiO 2 catalysts in the selective catalytic reduction (SCR) of nitrogen oxides by ammonia was investigated. Focusing on the deactivation by calcium, phosphate, and potassium, the DeNO x activity followed the order K)Ca>PO 4 . This trend was investigated on the structural level of the catalyst by means of temperature programmed desorption of ammonia (NH 3 -TPD) and a DRIFT characterization of the adsorbed ammonia species. The results suggest that the studied elements strongly reduce the acidity of the SCR catalyst in the order K ) Ca>PO 4 by mainly affecting the Brønsted acidity of the surface.

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At 150°C, HNCO adsorbs dissociatively on Fe-ZSM5 producing principally isocyanate species (-NCO) adsorbed on Al and Fe sites. In the presence of water the hydrolysis of the -NCO groups to NH 3 was observed. Comparison of the DRIFT results with measurements of the catalytic activity of coated cordierite monoliths suggests that -NCO groups are likely intermediate species in the hydrolysis of HNCO over Fe-ZSM5.

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