Surface activation by Pt-nanoclusters on titania for gas sensing applications

Platinum supported on titania was prepared by two impregnation procedures using platinum chloride as a precursor. The catalytic precursor has been introduced before and after titania structural stabilisation, followed in both cases by a calcination process for chemical stabilisation. Anatase surface reactivity towards platinum is higher than rutile since better catalytic incorporation has been observed, by X-ray fluorescence (XRF) analyses, when introduced in anatase phase. Likewise, X-ray photoelectron spectroscopy (XPS) measurements show that the surface concentration of platinum nanoclusters is improved when adding the precursor in anatase phase. Depending on the additive concentration and the stabilisation temperature, platinum nanoclusters exhibit grain sizes between 2 and 4 nm, as shown by high resolution TEM (HRTEM) micrographs. However, concentrations higher than 2.5 at.% Pt/Ti, lead to a clustering phenomena to grain sizes up to 200 nm. Pt/TiO2 with 2.4 at.% metal content and calcined at 1100 °C shows maximum density of Pt nanoparticles and enhanced sensing behaviour. The response of thick-film Pt/TiO2 layers under gas exposures has been monitored showing that their suitability for in situ control of combustion processes is strongly related to the technological procedure used in sensor fabrication.