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Monday, October 15

Is NO Oxidation to NO2 the Rate-Determining
Step of the Standard SCR Reaction?

Enrico Tronconi, Laboratory of Catalysis and Catalytic Processes, Milan, Italy
NTRC Seminar
9:00 AM — 10:00 AM, National Transportation Research Center,
Conference Room D01
Contact: Bill Partridge (partridgewp@ornl.gov ), 865.946.1234

Abstract

In NH3-SCR converters for the abatement of NOx from vehicles the most important reaction is the so called Standard SCR (4NH3 + 4NO + O2 → 4N2 + 6H2O). When NO2 is present in the feed stream, however, the deNOx efficiency is greatly enhanced by the Fast SCR reaction (4NH3 + 2NO+ 2 NO2 → 4N2 + 6H2O). For this reason, NO oxidation to NO2 is a desired reaction and is popularly regarded to be the rate determining step in the mechanism of the Standard SCR reaction itself. This assumption however is not really proven, and appears to be actually in contrast with some experimental evidence reported in the literature.

With the aim of analyzing such an issue, in this talk we will first present data collected over state-of-the-art Fe- and Cu-promoted zeolites: for each catalyst we compare the catalytic activities under NO oxidation and under Standard SCR conditions, using both dry and wet feeds.

A second part of the talk will illustrate an in-situ FTIR investigation of NO oxidation over a Fe-zeolite, focused on the identification of the adsorbed species and of their reactivities.

Finally, we will discuss a tentative reaction mechanism which attempts to reconcile all of the observations.