Thermal reduction of NO by H₂: Kinetic measurement and computer modeling of the HNO + NO reaction

The kinetics and mechanism of the thermal reduction of NO by H₂ have been investigated by FTIR spectrometry in the temperature range of 900 to 1225 K at a constant pressure of 700 torr using mixtures of varying NO/H₂ ratios. In about half of our experimental runs, CO was introduced to capture the OH radical formed in the system with the well‐known, fast reaction, OH + CO → H + CO₂. The rates of NO decay and CO₂ formation were kinetically modeled to extract the rate constant for the rate‐controlling step, (2) HNO + NO → N₂O + OH. Combining the modeled values with those from the computer simulation of earlier kinetic data reported by Hinshelwood and co‐workers (refs. [3] and [4]), Graven (ref.[5]), and Kaufman and Decker (ref. [6]) gives rise to the following expression: (Formula Presented.) . This encompasses 45 data points and covers the temperature range of 900 to 1425 K. RRKM calculations based on the latest ab initio MO results indicate that the reaction is controlled by the addition/stabilization processes forming the HN(O)NO intermediate at low temperatures and by the addition/isomerization/decomposition processes producing N₂O + OH above 900 K. The calculated value of k₂ agrees satisfactorily with the experimental result. © 1995 John Wiley & Sons, Inc.