The rate equation for the overall reaction of NO and O 2 over Pt/Al 2 O 3 was determined to be r ¼ k f ½NO 1:05AE0:08 ½O 2 1:03AE0:08 ½NO 2 0:92AE0:07 ð1 À bÞ, with k f as the forward rate constant, b ¼ ð½NO 2 =K½NO½O 2 1=2 Þ, and K as the equilibrium constant for the overall reaction. An apparent activation energy of 82 kJ mol )1 ± 9 kJ mol )1 was observed. The inhibition by the product NO 2 makes it imperative to include the influence of NO 2 concentration in any analysis of the kinetics of this reaction. The reaction mechanism that fits our observed orders consists of the equilibrated dissociation of NO 2 to produce a surface mostly covered by oxygen, thereby inhibiting the equilibrium adsorption of NO, and the non-dissociative adsorption of O 2 , which is the proposed rate determining step.
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