Surface behaviour of alumina supported tin dioxide and its reactivity towards carbon monoxide oxidation

Metal Oxide gas sensors are widely used for detection of reducing gases like CO, which are oxidized on the surface of the sensor, with an increase of the density of the catalyst free electrons and an increase of the related conductance: this makes such devices an important tool in solving environmental problems. Among these sensors, those based on SnO2 supported on Al2O3 play an important role because of the ntype semiconducting behaviour of SnO2 and of its capabilities of catalyzing surface CO oxidation, through the above mentioned mechanism. Therefore, it appeared interesting to prepare a SnO2/Al2O3 catalyst, to analyse it with the methods of heterogeneous catalytic investigations, namely to characterize its catalytic reactivity and its surface interactions with CO. Its activity was then investigated by means of steady and non steady techniques, paying attention to characterise surface behaviour by means of TPR, and TPD above all of O2. Moreover the surface interactions between catalyst superficial layers and reactants or products were examined with XPS technique. Finally these features were analyzed on the basis of the behaviour of the sensing properties of a commercial sensor in the same range of temperature.