Reactions of No_Xwith nitrogen hydrides

In this review, we consider the reactions of NO_x(x = 1, 2) with the nitrogen hydrides NH, NH₂and NH₃The reactions are relevant to the post-combustion, non-catalytic reduction of NO_xwith NH₃in the thermal de-NO_xprocess and with HNCO in the rapid reduction of NO_xas well as to the thermal decomposition of some high-energy materials, including ammonium dinitramide. The practical importance has motivated considerable theoretical interest in these reactions. We review numerous ab-initio molecular orbital studies of potential energy surfaces for NO_x+ NH_yand theoretical calculations of their kinetic parameters, such as thermal rate constants and branching ratios of various products. The most advanced theoretical calculations are carried out using the Gaussian-2 family of methods which provides the chemical accuracy (within 2 kcal mol^-1) for the energetics and molecular parameters of the reactants, products, intermediates and transition states. We present a detailed comparison of the theoretical results with available experimental data. We show that the reactions of NO_xwith NH and NH₂are very fast because they occur without a barrier and lead to the formation of multiple products which include radicals and stable molecules. The reactions of NO_xwith NH, taking place by the H abstraction to form NH and HNO_xare slow but still relevant to the NH₃de-NO_xsystem, because of their fast reverse processes which have not yet been measuredexperimentally.