In situ XAS probes partially oxidized platinum generating high activity for CO oxidation

In situ x-ray absorption spectroscopy identified partially oxidized platinum as the active phase for generating high activity during carbon monoxide oxidation over Pt/Al2O3. CO covers and poisons metallic platinum, which results in a low catalytic activity. The conversion in CO abruptly increased during ignition, switching from low activity to high activity, accompanied by oxidation as observed in the increased intensity of the XANES. EXAFS analysis indicated breaking of Pt-Pt bonds and the appearance of a Pt-O scatterer. The partially oxidized catalyst had a lower oxygen coordination number and shorter Pt-O bond length than bulk PtO2, suggesting that a strongly defected platinum oxide was formed with a coordination possibly lower than octahedral. From infrared data, ignition was accompanied by the abrupt disappearance of CO adsorbed on metallic particles. The reverse changes happen with the sudden decrease in CO conversion during extinction: partially oxidized catalyst becomes reduced and covered with CO.