Simulation of oscillatory behaviour in the NO+H-2 reaction on a partially reconstructed Pt(100) surface

Our recently developed mathematical model for the description of the NO+H-2 /Pt(100)-(1 x 1) reaction [J. Chem. Phys. 108 (1998) 3740] is extended to i nclude the adsorbate-induced (1 x 1)double left right arrow hex phase trans ition of a Pt(100) surface. Under certain pressure and temperature conditio ns, the phase transition is of critical importance for the kinetics of the reaction, since the two phases exhibit strongly different catalytic activit y. The model successfully reproduces the experimentally observed non-linear phenomena: rate hysteresis during a heat-cool cycle and oscillatory behavi our, including periodic and chaotic oscillations. In agreement with experim ent, rate oscillations occur in the vicinity of the hex double right arrow( 1 x 1) phase transition as the hex-reconstructed surface is cooled down in a NO+H-2 atmosphere. At relatively high temperatures, oscillations take pla ce on a largely hex-reconstructed surface. Decreasing the temperature cause s an increase in the adsorbate coverage and, as a result, an increase in th e fraction of the (1 x 1) phase. At relatively low temperatures, oscillatio ns take place on a surface that is completely in the (1 x 1) structure. Thu s, the simulation results show that the (1 x 1)double left right arrow hex surface phase transition of Pt( 100) is not essential for producing oscilla tory behaviour, even if oscillations may proceed on a largely hex-reconstru cted surface. The requirement of vacant sites for NO dissociation on Pt( 10 0)-(I x 1) is the most important step in the oscillation mechanism for the NO+H-2/Pt(100) system. (C) 1998 Elsevier Science B.V. All rights reserved.