THE MECHANISM OF KINETIC OSCILLATIONS IN CATALYTIC-OXIDATION OF CO ON PT(210)

Under isothermal conditions at low pressure (10(-4) Torr), the catalytic oxidation of CO on a Pt(210) surface exhibits kinetic oscillations which have been investigated using Video-LEED, measurement of the CO2 production rate and the variation of work function. An induction period of approximately 30 to 60 min, which has been shown to be due to a facetting of the surface exists before the appearance of kinetic oscillations. If reaction conditions are chosen which correspond to the high rate branch of Langmuir Hinshelwood kinetics, the Pt(210) surface facets into (310) and (110) orientations. The facetting process is associated with a decrease in catalytic activity caused by a lowering of the oxygen sticking coefficient. In situ LEED experiments demonstrated that the oscillations in the reaction rate are associated with periodic intensity variations of the half-order LEED beams belonging to (110) facets. Thus, the oscillations appear to be driven by the CO-induced 1 x 1 reversible 1 x 2 phase transition on (110) facets in the same way as has been verified for the system Pt(110)/CO + O2. The involvement of a facetting process explains the characteristics properties of kinetic oscillations on Pt(210) such as the relatively low high-temperature limit of almost-equal-to 500 K, the existence of an induction period and the period length which is on the order of minutes.