The kinetics and kinetic deuterium isotope effects have been precisely measured for the reaction of nitrous oxide with hydrogen on Ru/Al2O3, Rh/Al2O3, Ir/Al2O3, and Pt/Al2O3 catalysts. The reaction apparently proceeds through the two following elementary steps: N2O + M → N2 + M=O (reaction 1) and M=O + H2 → M + H2O (reaction 2). In reaction 1, an N2O molecule attacks the vacant metal site on the surface (M) to form an N2 molecule and an adsorbed oxygen atom (M=O). In reaction 2, the reaction of the surface oxygen atom with an H2 molecule takes place to form an H2O molecule and the vacant metal site. The activation energy for reaction 1 increases in the order Ru/Al2O3 < Rh/Al2O3 < Ir/Al2O3 < Pt/Al2O3, whereas for reaction 2 the activation energy decreases in the order Ru/Al2O3 > Rh/Al2O3 > Ir/Al2O3. The preexponential factors of the rate constant for both reactions 1 and 2 do not vary significantly from one catalyst to another, although the value for reaction 1 is ∼104 times smaller than that for reaction 2. The experimental results have been satisfactorily explained with the transition-state theory coupled with the above-mentioned reaction mechanism.
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