Periodic forcing of NO reduction on a Pt(100) surface

The influence of a cycled gas feed on reactions of the automotive catalytic converter has been investigated under low pressure conditions (p < 10(-3) mbar) with a Pt(100) surface as catalyst. Catalytic NO reduction with CO or H-2 as reducing agent was studied in binary mixtures. The reactions were forced around the unstable high rate branch of the rate vs. T hysteresis by applying a square-wave modulation of P-co (p(H2)). For the NO+CO reaction the yield vs frequency dependence exhibits a pronounced maximum. The pressure modulation causes a periodic structural transformation 1 x 1 <----> hex. The frequency dependence of the yield is largely related to the average concentration of defects which are created during the phase transition.