Revealing the key oxidative species generated by Pt-loaded metal oxides under dark and light conditions.

The role of key oxidative species in formic acid oxidation using neat and platinum-loaded TiO 2 , CeO 2 and SiO 2 was investigated. The catalytic reactions under three different illumination conditions; dark catalysis (i.e. no illumination), dark catalysis with UV light pre-treatment (denoted as pre-30) and photocatalysis (i.e. continuous UV illumination), were studied. The activities of neat TiO 2 , CeO 2 and SiO 2 were low under dark and pre-30 conditions while under illumination (photocatalysis) the semiconductor metal oxides, TiO 2 and CeO 2 showed much higher oxidation rates. For the Pt-loaded catalysts, the key active species were surface active oxygen (PtO ads and O − ads ) under the dark catalytic condition with and without light pre-treatment while under photocatalytic condition, photogenerated holes and electrons are believed to form hydroxyl radicals ( OH) and superoxide radicals ( O 2 − ), respectively, for CeO 2 , TiO 2 , Pt/TiO 2 and Pt/CeO 2 . Unexpectedly, Pt/SiO 2 showed the highest activity under the dark catalytic condition. The cuboctahedral shape of the Pt deposits on the SiO 2 surface, which promote a greater number of sharp edges/corners at the interface, is believed to have been advantageous for dissociating and activating adsorbed oxygen species compared to the Pt deposits on TiO 2 and CeO 2 . The Pt deposit shape is thought to be responsible for the observed high activity of Pt/SiO 2 for the dark catalytic oxidation of formic acid. [ABSTRACT FROM AUTHOR]