Enhancing the catalytic oxidation capacity of Pt/TiO2 using a light pre-treatment approach

Abstract

The role of UV light pre-treatment in enhancing Pt/TiO2 activity for the catalytic oxidation of formic acid in an aqueous environment and under ambient conditions has been examined. The impact of light pre-treatment, relaxation time (the period between light pre-treatment and formic acid addition) and re-illumination on the oxidation rate were considered. Pre-illuminating Pt/TiO2 provided an almost seven-fold increase in the formic acid oxidation rate compared with the untreated case. The oxidation rate decreased with increasing relaxation time, whereby after 16h of relaxation it had stabilised at a value still around three times greater than the untreated sample. Re-illuminating the Pt/TiO2 led to a complete recovery of the transient element of the activity. The Pt deposits were observed to undergo partial oxidation over the course of the reaction and, when coupled with a lower activity being observed upon purging the system with N2, imply the participation of dissolved oxygen in the overall oxidation mechanism. The findings suggest the platinum deposits can inject electrons into adsorbed molecular oxygen where the oxygen remains in an active state ready for oxidising the formic acid. Pre-treating the catalyst with light accentuates this effect as additional photogenerated electrons are drawn into the Pt deposits from the TiO2 and transferred to and held by the adsorbed oxygen. Striking features of this particular system is the light pre-treatment effect prevails for an unexpectedly long period (in the order of hours) and is completely recoverable with re-illumination.