Pt-loaded Al2O3 catalytic filters for screen-printed WO3 sensors highly selective to benzene

We describe the fabrication of low-cost benzene sensors by using screen-printing technology. Two different types of catalytic filters were developed to enhance the sensitivity of tungsten oxide films to benzene. The first type of filter consists of a porous Al2O3 layer, loaded with a Pt layer on its surface. The second type of filter is based on a porous Al2O3 layer, with Pt homogeneously distributed in its bulk. These filters were used to coat WO3-based sensors. The presence of by-products resulting from the incomplete catalytic combustion of benzene in the catalytic filters (that could further interact with the WO3 film), explains the higher sensitivity of the coated sensors, as compared with the sensitivity of bare tungsten oxide sensors. In particular, it is shown that a very selective benzene sensor can be obtained by combining a coated and uncoated tungsten oxide sensor. This combined sensor, selectively detects benzene in a wide concentration range in the presence of interfering species such as ethanol, ammonia, nitrogen dioxide and water vapour.