The reduction mechanism of NO and its content on the selectivity of reactions were investigated using isotope labelled nitrogen species(15N),which is useful for the selective reduction of nitrate to N2on industry scale. NO participates in the reduction reaction by adsorbing on catalytic active sites of Pd-In, yielding intermediate(nitrous oxide) and products(N2and NH3). The concentration of NO governs the eventual product selectivity. When NO content is high, the interaction of adsorbed NO takes the dominan...