Non-linear phenomena during CO oxidation in the mbar pressure range: a comparison between Pt/SiO2 and Pt(100)

We report a comparative study of unsteady behavior of CO oxidation over sil ica-supported platinum and Pt(100). Experiments were performed in a reactio n cell allowing the first direct comparison between both catalyst types und er the same conditions at pressures between 10 and 100 mTorr. The reaction is examined with mass spectrometry, time-resolved FT-IIE spectroscopy, and ellipsomicroscopy for surface imaging (EMSI). For the supported catalyst, o ur measurements concentrated on the reaction rate as a function of control parameters pressure and temperature and time-resolved FT-IR, EMSI was used to follow spatio-temporal pattern formation on the Pt(100) single crystal. The parameter space (partial pressures of the reactants, catalyst temperatu re, pumping speed of the reactor) for unsteady behavior of the CO oxidation is much wider for the supported catalyst. In certain parameter ranges, spa tio-temporal pattern formation governs the unsteady behavior of the single crystal, while for other parameters, very regular oscillations with no patt ern formation are observed. Time-resolved FTIR spectroscopy was used to fol low the CO coverages under reaction conditions, which stayed below 15% of t he maximum coverage (C) 1999 Elsevier Science Ltd. All rights reserved.