Studies of sol–gel TiO2 and Pt/TiO2 catalysts for NO reduction by CO in an oxygen-rich condition

The textural properties, morphological features, surface basicity and oxygen reduction behaviours of titania and Pt supported titania catalysts synthesized via a sol–gel method were studied by means of N₂ physisorption, SEM, TEM, CO₂-TPD and H₂-TPR techniques. Mesostructured TiO₂ shows a very narrow pore size distribution that uniformly centred at about 4 nm. High resolution TEM images confirmed that most of Pt particles on Pt/TiO₂-SG had a size smaller than 2 nm. Both the titania support and Pt loaded catalysts chiefly contained weak basic sites with small amount of strong basic sites. Loading Pt did not significantly alter the surface reduction characters of titania, indicating a weak interaction between Pt metals and titania support. Catalytic evaluation revealed that the selectivity of NO reduction over titania was insensitive to variation of textural property. On the bare titania, low NO conversion but high selectivity to N₂O was obtained. However, the Pt/TiO₂-SG catalysts exhibited high NO conversion and high selectivity to N₂, which is assumed to relate to NO dissociation catalysed by the metallic Pt clusters. In addition, when the reaction temperature was above 200 °C, 3–11% NO₂ was yielded over the Pt/TiO₂-SG catalysts, which was discussed on a basis of reaction competition, metal-support interaction and NO dissociation.