NO Reduction by Activated Carbons. 7. Some Mechanistic Aspects of Uncatalyzed and Catalyzed Reaction

Abstract

In this last paper of a series devoted to uncatalyzed and catalyzed reduction of NO by carbon, we discuss some mechanistic aspects of this reaction, which is thought to be a viable alternative to selective catalytic reduction by ammonia or hydrocarbons. We present a summary of the results of isothermal and temperature-programmed reduction studies on a metal-free activated carbon and carbon loaded with K, Ca, Fe, Cu, Cr, Co, and Ni catalysts. All the results obtained on catalyzed NO reduction are consistent with a simple oxidation-reduction (redox) mechanism involving the following kinetically significant steps: (1) chemisorption of NO on the catalyst surface; (2) transfer of oxygen from the catalytically active sites to the carbon reactive sites; and(3) desorption of oxygen from the carbon surface. A comparison with the proposed mechanisms for selective catalytic reduction is offered, as well as a mechanistic interpretation of the NO reduction enhancement in the presence of O 2 .

Synthetic coal chars for the elucidation of NO heterogeneous reduction mechanisms

“…Moreover a deeper knowledge of the chemistry involved in the formation and the reduction of NO X is required. Many authors have performed NO heterogeneous reduction studies on carbonaceous materials using, mainly, chars from phenol-formaldehyde resins [4][5][6][7][8][9], graphites [10] and activated carbons [11][12][13]. The use of model compounds, with controlled heteroatom content and well defined functionalities, is a useful approach that has been used by other authors [14,15] to study the release of nitrogen compounds from char combustion.…”

Reaction Mechanism Study of the Di-Air System and Selectivity and Reactivity of NO Reduction in Excess O2

“…In the 1990's Illán-Gômez et al [17,18] reported that activated carbon is active in NO x reduction in a temperature window between 400 and 500 °C. A large fuel injection upstream of a catalyst bed might promote the carbon formation and this in turn might enhance the NO x reduction.…”

Next Generation Automotive DeNOx Catalysts: Ceria What Else?

“…Using carbon as a reductant offers obvious advantages, these include: (1) soot is present in the exhaust gas or produced from injected fuel and (2) its oxygen scavenging capability 22 1. Introduction [43,44]. The NO reduction by activated carbons originating from different raw materials shows that the NO reduction begins in the temperature range from 250 to 400 ∘ C and exhibits a sharp increase up to 100% conversion above 650 ∘ C [45].…”

“…The soot oxidation accelerated by the presence of NO [49]. Simultaneously, only up to 10-15% of NO is converted into N [43]. This method is regarded as a successful method to remove the soot, however, for NO reduction, this technology will be not able to meet any of the NO emission standards.…”