CO oxidation over Pd supported catalysts —In situ study of the electric and catalytic properties

•Pd/TiO2 and Pd/SnO2/TiO2 catalysts were prepared by the impregnation and tested in CO oxidation.•The surface dynamics was studied by in situ electrical conductivity measurements.•Two reaction mechanism are involved.•At low temperatures the CO conversion is related with the presence of the oxidized form of palladium.•At t>150°C the reaction follows the Langmuir-Hinshelwood mechanism.