Preparation and characterization of MoOx-SnO2 nano-sized materials for catalytic and gas sensing applications

This work gives results about the preparation and characterization of a series of MoOx/SnO2 powders at increasing Mo content with the aim of studying their surface properties, their catalytic performances in the NOx, abatement by hydrocarbons and, eventually, their sensing abilities to NO2/hydrocarbons mixtures. The goal of obtaining powders made by regularly shaped and nano-sized particles with a uniform spreading of MoOx species at the surface of the SnO2 particles is attained, as shown by XRD, SEM, HRTEM and XPS measurements. FTIR spectroscopy gives information on the MoOx, species and on the way they are affected in the presence of NO/O-2 or NO2 atmospheres. NOx surface species formed were carefully investigated and individuated and some related surface reactions have been proposed. Catalytic measurements show that the activity seems slightly dependent on Mo concentration but that, for temperature up to 300 degrees C the N-2 production increases, while for temperature higher than 300 degrees C, the N-2 production decreases with the Mo loading. In any case the specific activity increases with the temperature, the maximum being at 350 degrees C. Electrical measurements show that all materials, in absence of hydrocarbons, are good NO2 sensors at working temperatures in the range 150-250 degrees C and that the response to NO2/hydrocarbon mixtures is still good and selective for the NO2 gas at working temperature of 150 degrees C and 200 degrees C. At variance. at 250 degrees C the ability to sense NO2 is drastically reduced.