The infrared spectral performance of the N x O y species observed on oxide surfaces [N2O, NO−, NO, (NO)2, N2O3, NO+, NO2 − (different nitro and nitrito anions), NO2, N2O4, N2O5, NO2, and NO3 − (bridged, bidentate, and monodentate nitrates)] is considered. The spectra of related compounds (N2, H-, and C-containing nitrogen oxo species, C─N species, NH x species) are also briefly discussed. Some guidelines for spectral identification of N x O y adspecies are proposed and the transformation of the nitrogen oxo species on catalyst surfaces are regarded.

Identification of Neutral and Charged N x O y Surface Species by IR Spectroscopy

Automotive catalytic converters: current status and some perspectives

Catalytic removal of NO

Over the last several years, nitrogen oxide(s) (NOx) storage/reduction (NSR) catalysts, also referred to as NOx adsorbers or lean NOx traps, have been developed as an aftertreatment technology to reduce NOx emissions from lean‐burn power sources. NSR operation is cyclic: during the lean part of the cycle, NOx are trapped on the catalyst; intermittent rich excursions are used to reduce the NOx to N2 and restore the original catalyst surface; and lean operation then resumes. This review will describe the work carried out in characterizing, developing, and understanding this catalyst technology for application in mobile exhaust‐gas aftertreatment. The discussion will first encompass the reaction process fundamentals, which include five general steps involved in NOx reduction to N2 on NSR catalysts; NO oxidation, NO2 and NO sorption leading to nitrite and nitrate species, reductant evolution, NOx release, and finally NOx reduction to N2. Major unresolved issues and questions are listed at the end of ...

Overview of the Fundamental Reactions and Degradation Mechanisms of NOx Storage/Reduction Catalysts

Research on the selective reduction of NOx with hydrocarbons under lean-burn conditions using non-zeolitic oxides and platinum group metal (PGM) catalysts has been critically reviewed. Alumina and silver-promoted alumina catalysts have been described in detail with particular emphasis on an analysis of the various reaction mechanisms that have been put forward in the literature. The influence of the nature of the reducing agent, and the preparation and structure of the catalysts have also been discussed and rationalised for several other oxide systems. It is concluded for non-zeolitic oxides that species that are strongly adsorbed on the surface, such as nitrates/nitrites and acetates, could be key intermediates in the formation of various reduced and oxidised species of nitrogen, the further reaction of which leads eventually to the formation of molecular nitrogen. For the platinum group metal catalysts, the different mechanisms that have been proposed in the literature have been critically assessed. It is concluded that although there is indirect, mainly spectroscopic, evidence for various reaction intermediates on the catalyst surface, it is difficult to confirm that any of these are involved in a critical mechanistic step because of a lack of a direct quantitative correlation between infrared and kinetic measurements. A simple mechanism which involves the dissociation of NO on a reduced metal surface to give N(ads) and O(ads), with subsequent desorption of N2 and N2O and removal of O(ads) by the reductant can explain many of the results with the platinum group metal catalysts, although an additional contribution from organo-nitro-type species may contribute to the overall NOx reduction activity with these catalysts. It is concluded, after the investigation of hundreds of catalyst formulations, that many of the fundamental questions relating to lean deNOx reactions have been addressed and the main boundary conditions have been established. It seems clear that catalysts with sufficient activity, selectivity or stability to satisfy the demanding conditions that appertain in automotive applications are still far away. The rapidly growing interest in NOx storage systems reflects this situation, and it now seems to be the case that acceptable direct NOx reduction catalysts may be very difficult to find for lean-burn applications.

A review of the selective reduction of NOx, with hydrocarbons under lean-burn conditions with non-zeolitic oxide and platinum group metal catalysts

Transition metal-promoted silica and alumina catalysts for the selective reduction of nitrogen monoxide with propane

The effect of addition of alkali metals was investigated on the catalytic activity of cobalt oxide (Co3O4) for the direct decomposition of NO. Although Co3O4 was totally inactive, NO decomposition over Co3O4 was significantly promoted by the addition of alkali metals (Li, Na, K, Rb and Cs). Potassium was found to be the most effective additive. The addition of alkali metals increased not only the surface area but also the specific activity per unit surface area. This suggests that catalytically active sites are created on the Co3O4 surface as a result of interaction with alkali metals. The interface between alkali metals and Co3O4 is clearly essential in the NO decomposition reaction. Characterization of the catalyst using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and desorption of O2 (O2-TPD) revealed that traces of added alkali metals weaken the CoO bond strength and promote oxygen desorption from Co3O4, resulting in the formation of cobalt species with a slightly lower valence state. We conclude that these effects, caused by addition of alkali metals, are responsible for the activity enhancement of Co3O4.

Alkali metal-doped cobalt oxide catalysts for NO decomposition

Role of supported metals in the selective reduction of nitrogen monoxide with hydrocarbons over metal/alumina catalysts

Infrared study of catalytic reduction of nitrogen monoxide by propene over Ag/TiO2–ZrO2

The paper discusses the mechanism of the selective reduction of NO with propene based on the behavior of adsorbed species formed on Ag/TiO 2 -ZrO 2 catalyst, observed by in-situ FT-IR spectroscopy

Yoshiaki Kintaichi

Papers

Transition metal-promoted silica and alumina catalysts for the selective reduction of nitrogen monoxide with propane

Alkali metal-doped cobalt oxide catalysts for NO decomposition

Role of supported metals in the selective reduction of nitrogen monoxide with hydrocarbons over metal/alumina catalysts

Infrared study of catalytic reduction of nitrogen monoxide by propene over Ag/TiO2–ZrO2

Infrared study of catalytic reduction of nitrogen monoxide by propene over Ag/TiO2-ZrO2