CO oxidation on Pt(111) promoted by coadsorbed H sub 2 O

It is well established that CO sub 2 is produced at temperatures approx =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 ( < =0.1 ML) of H sub 2 O, causes CO sub 2 production at 180-230 K. By analysis of temperature programmed reaction (TPR) spectra of desorbing H sub 2 O and CO sub 2 for different O/CO/H sub 2 O coverage combinations, we suggest an autocatalytic reaction path where OH molecules, produced via the 2H sub 2 O + O sub ad - > 3OH sub ad + H sub ad reaction, induce low temperature CO oxidation. This result suggests a reinterpretation of earlier reported TPR spectra of low temperature CO sub 2 production from CO + O coadsorbates. It also suggests that H sub 2 O may reduce the self poisoning by CO of supported Pt catalysts in e.g. vehicle emission cleaning.