An Update on the Thermochemistry and Kinetics of the Carbon-NO Reaction

SALGADO, A.; RADOVIC, L.; GARCIA, X.:
Proceeding The first latino american workshop on carbon materials for energy and the environment, Vol.1 131-132 (2014).

Abstract

Carbon-based energy generation processes will inevitably continue to be an important part of the worldwide energy resources, with much greater emphasis placed on air quality management. Our research is part of an effort to improve existing technologies and reduce contaminants such as NOx. Use of carbon itself is of great interest here, either as a reducing agent (e.g., 2C + 2NO→C + CO2 + N2), or better still, as a catalyst (2C + 2NO→N2 + O2 + 2C).

We use computational quantum chemistry (DFT, Gaussian) to confront thermochemically and kinetically feasible pathways of monomer versus dimer reaction mechanisms proposed in the experimental literature. The focus is on analysis of reactant (NO and (NO)2) adsorption and product (N2) desorption. Our results are consistent with the expectation that electron density distribution at graphene edges plays a key role in the relative abundance of N2O as an intermediate or final product of NO reduction. Thus for example, O-down dimer structures adsorbed on reactive sites are the most favorable configurations that lead to both desorption of N2 and formation of C(O) and C(O2) surface complexes. Furthermore, when two contiguous zigzag sites are available, onlya quintet (with its four unpaired electrons!) can stabilize the adsorbed dimer structure, albeit at a high energy cost (e.g., 71 kcal/mol less stable than the triplet); in contrast, desorption of N2O occurs upon the formation of a triplet or a singlet, the latter being 17 kcal/mol less stable than the ground-state triplet. Experimental studies on potassium-catalyzed NO reduction are in agreement with our results and, perhaps surprisingly, implicate the participation of N2O in the main reaction pathways.

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