[Display omitted] • Understanding industrial catalysts needs correlative operando spectroscopies. • Pt on ceria appears oxidized independent of CO coverage and oxidation activity. • CO oxidation occurs at the platinum-ceria boundary when platinum is CO self-poisoned. • Protracted catalytic extinction is caused by a shift of main CO oxidation route. • CO oxidation over small alumina supported Pt particles follows the classical extinction behavior with a drop in catalytic activity caused by a sudden CO self-poisoning. • Highly dispersed platinum on alumina show classical kinetic phase transitions. Industrially relevant, highly dispersed, Pt/ceria and reference Pt/alumina catalysts with narrow Pt particle size distributions have been prepared, characterised ex situ and studied for CO oxidation by operando infrared and X-ray absorption spectroscopy. At high CO conversions, spectator CO ad-species on ionic platinum are observed while the CO oxidation proceeds on Pt particles in a high oxidation state exhibiting significant Pt O coordination. During the protracted catalytic extinction, the CO coverage builds up gradually while the Pt oxidation state and Pt O coordination remain high because of interactions with ceria. The observed CO oxidation at high CO coverage is suggested to involve sites at the platinum-ceria boundary that cannot be CO self-poisoned. This behaviour is in stark contrast to that of Pt/alumina, which shows removal of platinum oxides formed during CO oxidation and the classical drop in catalytic activity caused by rapid CO self-poisoning when reaching a critical temperature. [ABSTRACT FROM AUTHOR]