CO oxidation on Pt(111) promoted by coadsorbed H2O

It is well established that CO2 is produced at temperatures similar to 300 K through the well known Langmuir-Hinshelwood mechanism, e.g. when CO and oxygen are coadsorbed on Pt(111) at temperatures 150-170 K and then heated. We demonstrate that the same coadsorbates after the addition of minute amounts (less than or equal to 0.1 ML) of H2O, causes CO2 production at 180-230 K. By analysis of temperature programmed reaction (TPR) spectra of desorbing H2O and CO2 for different O/CO/H2O coverage combinations, we suggest an autocatalytic reaction path where OH molecules, produced via the 2H(2)O + O-ad --> 3OH(ad) + H-ad reaction, induce low temperature CO oxidation. This result suggests a reinterpretation of earlier reported TPR spectra of low temperature CO2 production from CO + O coadsorbates. It also suggests that H2O may reduce the self poisoning by CO of supported Pt catalysts in e.g. vehicle emission cleaning. (C) 2001 Elsevier Science B.V. All rights reserved.