Surface Science I15 (1982) L11 I-L1 16 North-Holland Publishing Company Llll SURFACE SCIENCE LETTERS zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHG COMMENTS ON “ISOTHERMAL SUSTAINED OSCILLATIONS IN A VERY SIMPLE SURFACE REACTION” BY C.G. TAKOUDIS, L.D. SCHMIDT AND R. ARIS * M. BOUILLON, R. DAGONNIER, P. DUFOUR and Martine DUMONT ** Fuircul~Pdes Screr~ces. U%w-sitk de I’Etat. B-7000 Mow Belgium Received 4 August I98 I : accepted for publication 3 December 198 I The oscillating CO oxidation on Pt is examined as a possible candidate for the Takoudis. Schmidt and Aris (TSA) model. Moreover the results of our Monte Carlo simulation of this model reaction are tentatively compared to TSA numerical results. In a recent paper Takoudis, Schmidt and Aris (TSA) [I] propose a kinetic model for bimolecular surface reactions that exhibit isothermal sustained oscillations. The most challenging feature of this model consists in the inclu- sion, in the kinetics, of a “Langmuir-Hinshelwood” (LH) mechanism requiring two adjacent vacant sites. This note has two objectives: (i) a detailed examination of the CO oxidation on Pt as a possible candidate for the TSA model as suggested by these authors; (ii) a comparison between TSA numerical results and those we have obtained by a Monte Carlo simulation of a surface reaction involving a four-site LH mechanism and for the parameter values specific of the oscillations displayed in ref. [l]. Let us first set the model equations along TSA lines. These authors consider the surface reaction A+iB n ” - products, n = 1 or 2, (1) that involves the following steps (k,P,. E,) A+S (k-,5_,) AS, (hzpz/‘). El) B,, + zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA nS (k.z?E_,) zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDC nBS, n= 1 or2, (3) AS+BS+2S (A,. E,J,, - 4s + products, (4) * Work partly supported by the IRIS Program sponsored by the Belgian Ministry for Science Policy. ** Charge de Recherches au.Fond National Beige de la Recherche Scientifique. 0039-6028/82/0000-0/$02.75 0 1982 North-Holland