Intrinsic kinetics mechanisms for the catalytic reduction of NO by Na-loaded char

Abstract

An insight into the interaction between NO and Na-loaded char is essential to improve the catalytic ability of Na to NO reduction, which will be useful to lower NO emissions during thermal utilization of sodium-containing fuels. Here, the intrinsic kinetics mechanisms for the catalytic reduction of NO by Na-loaded char were discussed in details. Using density functional theory (DFT) calculations, possible reaction pathways were first obtained, followed by evaluation of the rate coefficients through transition state theory (TST) calculations. On this basis, the analyses of both sensitivity and rate of products (ROP) were performed to illustrate the intrinsic kinetic mechanism for the NO reduction by Na-loaded char in a certain combustion condition, with an emphasis on the effects of temperature and NO-to-CO stoichiometric ratio. Results indicated that the catalytic active center –ONa plays an important role in the catalytic reduction of NO by Na-loaded char. Specifically, in most cases, the interaction of NO with Na-loaded char largely depends on the elementary reaction of CNO-Na+NO+CO→21-IM3+CO2. As the stoichiometric ratio of NO to CO increases, the CO-Na+2NO→8-IM4+N2 becomes increasingly dominant. Moreover, higher temperature causes the CNO-Na+NO→20-P + N2O as the dominant reaction. Nonetheless, one thing that these reactions have in common is that they are all related to the catalytic active center –ONa. Therefore, the NO reduction Na-loaded char largely depends on the interaction of NO with the carbonaceous surface containing –ONa. Inspired by this, a conceptual approach was proposed to improve the catalytic performance of Na on NO reduction, and it has been shown to be theoretically feasible. To summarize, the combination of DFT, TST and kinetic calculations is useful to clarify the interaction between NO with Na-loaded char, and it gives a basis for the development of micro-kinetic model.