The role of NO in the mechanism of reduction with ammonia over a BaNa?Y catalyst

Nano Catalysts for Diesel Engine Emission Remediation

“…Thus, it is possible that there is a correlation between high NO x reduction activity and the enhanced of NO + formation at 150°C. Since NO + species is retained even after He purge, it is probably linearly bound to Cu center in a weak mode rather than being present only in the gas phase as suggested by Sachtler et al 42 Thus, our results suggest that NO + plays an important role in fast SCR reaction, and the high catalytic activity of heterobimetallic zeolites at 150°C can be attributed to the high NO + concentration as compared with monometallic zeolites. This is in contrast with earlier postulation 41,42 that attributed NO x reduction under fast SCR conditions to N 2 O 3 , which can form as an intermediate in the gas phase equilibrium of NO + NO 2 , and can react with 2 equivalent of NH 3 to yield ammonium nitrite (NH 4 NO 2 ) that decomposes to N 2 and H 2 O near 100°C.…”

An acid catalyzed step in the catalytic reduction of NO x to N2

“…For these reasons it is mandatory for any vehicular NO x abatement catalyst that nitrate ions on its surface have to be swiftly reduced chemically, preferentially to nitrite ions. Indeed, as we have shown in a recent paper, reduction of nitrates with NO to nitrites is catalyzed by zeolite-based materials, such as BaNa/Y [12].…”

Role of Nitrate Species in the “NO2-SCR” Mechanism over a Commercial Fe-zeolite Catalyst for SCR Mobile Applications

“…However, the low stability of titania at high temperatures, the tightening of the NO x emission limits for both HD and LD vehicles that calls for higher activity at low T, and the issues related to vanadium toxicity have now motivated the introduction of new zeolite-based catalysts promoted by transition metals like Fe, Cu. In the literature the DeNO x activity of Fe-zeolite catalysts is widely addressed, and many papers have recently appeared which analyse the reactivity and the kinetics of the complex NO/NO 2 -NH 3 SCR reacting system over such catalysts [1][2][3][4][5][6][7][8][9][10][11][12].…”

“…Even if the general goal is the promotion of the Fast SCR reaction, for which a 1/1 NO/NO 2 molar ratio is needed [5,7,9,10,13,14], the NO 2 feed contents are not constant and typically depend on the operating conditions of the preox catalyst, such as temperature and space time. So it is important to assess the SCR reaction network in the presence of NO 2 , and the relative importance of the reactions involved upon varying the NO 2 feed content.…”