Tracer studies on the reaction paths of the CO oxidation over platinum

Abstract

Transient production of carbon dioxide was monitored by mass spectrometry where a polycrystalline platinum foil covered by given amounts of carbon monoxide was exposed to various gas mixtures of carbon monoxide and oxygen at room temperature. The transient feature depended strongly on the amount of carbon monoxide preadsorbed and the pressure of the dosed gas. When the substrate was covered in advance with carbon monoxide labeled with carbon 13, the initial ratio of 13CO 2 to 12CO 2 in the carbon dioxide produced was equal to that of 13CO to 12CO in the carbon monoxide preadsorbed. The equality between them held true for all pressures and the compositions of the dosed gas and for the initial coverages of carbon monoxide studied. Carbon monoxide immediately prior to oxidation was concluded to be in a chemisorption state, i.e., carbon dioxide is produced via a Langmuir-Hinshelwood process, namely CO(a) + O(a) → CO 2. No contribution from an Eley-Rideal process, namely CO(g) + O(a) → CO 2, was observed.