Oscillatory oxidation of co over Pd and Ir catalysts

Abstract

Oscillations in the rate of CO 2 production have been observed for the first time over Pd and Ir catalysts. The experiments were conducted near atmospheric pressure in a clean flow reactor system using polycrystalline Pd or Ir wire. For Pd, sustained oscillations were found over a wide range of gas compositions (0.05 < P CO P O 2 <2.0) and temperatures (230 < T g < 350° C), where P CO and P O 2 are the respective partial pressures of carbon monoxide and oxygen in the gas stream, and Tg is the temperature of the gas. For Ir, oscillations were found for 0.005 < P CO P O 2 < 0.025 and 180 < T g < 250° C. As proposed for CO oxidation over a Pt catalyst, it is believed that the oscillations occur between two branches of a Langmuir-Hinshelwood reaction mechanism, and that the slow formation and removal of subsurface oxygen drives the reaction between these two branches. These experiments suggest that oscillations in surface reactions are more general than previously suspected.