Oxidation chemistry and electrical activity of Pt on titania: development of a novel zeolite-filter hydrocarbon sensor

The change in resistance of semiconducting metal oxides upon exposure to gases is the basis for many gas sensors. Additives to the metal oxide provide a route to control selectivity and sensitivity for gas detection. Additives are often added to modify the chemical reactivity on the metal oxide surface. However, as the temperatures at which the sensing reactions are carried out increases, there is the possibility that the additive can also interact with the metal oxide and alter its electrical properties. In this paper, using Pt on titania as the model system, we examine how direct incorporation of Pt into TiO2 alters the chemical and electrical properties upon CO and propane exposure as compared to Pt in a microporous zeolite dispersed in TiO2. These results have allowed us to develop a novel Pt-zeolite filter-TiO2 sensor that responds selectively to hydrocarbons in the presence of CO. We propose that the response to propane is from the water that is liberated as a result of the oxidation reaction, and this hypothesis is based on the observation that the resistance of TiO2 at temperatures of 500–600 °C decreases upon exposure to water vapor.