Experimental evidence of propagating waves in hydrogen oxidation on platinum-group metals (Pt, Rh, Ir)

Abstract

The H2(g) + Oads reaction on nanoplanes of Pt-, Rh- and Ir-tips with a radius of ∼103 A was studied by FEM with a resolution of ∼20 A, and the critical conditions (Pi, T) under which this reaction is accompanied by the formation of a propagating wave front with a sharp boundary between the Hads- and Oads-layers were determined. The H2 + O2 reaction on a Pt-tip under steady-state conditions was studied by FIM with a lateral atomic resolution of ∼5 A, and images of H2O molecules (H2O+ ions) visualizing the spatial distribution of catalytically active sites (platinum atoms) were obtained for the first time. The origin of the kinetic self-oscillations in isothermal H2 oxidation in situ was investigated in detail. The regular chemical waves were found to be initiated by the reversible phase transition (Pt(100)-hex ↔ 1 × 1) of the Pt(100) nanoplane surface. A stepwise H2O formation mechanism involving OHads-groups was deduced from HREELS and TDS for the Hads + Oads reaction on the Pt(111) and Pt(100) single crystal surfaces.