Catalytic membrane sensors. A thin film modified H-2 resistive sensor for multi-molecular detection

A so-called "catalytic membrane sensor" (CMS) is being developed to impart selectivity and reactivity to the surface of an existing sensor by modifyin g it with a series of thin films. The proposed "sandwich-type" modification involves deposition of a catalyst layer between two size selective sol-gel layers on a Pd/Ni resistive H-2 sensor. The role of the catalyst is to con vert organic materials to H-2 and organic by-products by a dehydrogenation mechanism. The roles of the membranes are to impart chemical specificity by molecular sieving of the analyte and the converted product streams as well as to control access to the underlying Pd/Ni sensor. The "sandwich" modifi cation will mediate the sensor response and avoid potential poisoning effec ts. Ultimately, an array of these CMS elements encompassing different catal ysts and membranes will further enable improvements in selectivity and spec ificity via pattern recognition methodologies. This report details the synt hesis of the various thin film solutions (i.e., catalyst precursors, sol-ge l solution), the generation of the catalyst through ion-exchange, a compari son of the double alkoxide versus standard catalyst precursors, and the pro cessing required to generate a CMS. This paper also details the novel and s urprising experimental data concerning the increased selectivity and durabi lity observed for the sol-gel modified H-2 gas sensing resistors. The utili ty of the CMS component as a multi-molecular detector will be reported late r.