The development and characterization of titania based gas sensors for combustion process monitoring

Gas sensors that utilize metal oxide materials are widely used in industry to monitor combustion processes. While they are inexpensive to fabricate and robust in high temperature environments, many of these devices are not selective towards the species of interest when placed in a stream composed of multiple gases.; A titania-based sensor was modified in various ways with Pt-Y zeolite in order to create a device that was selective towards hydrocarbons in the presence of CO. To understand this property, gas chromatography was used to study the products formed when CO and propane were passed through a bed of Pt-Y. The device using Pt-Y and titania was then compared to a sensor that used titania doped with colloidal platinum. The sensors using colloidal platinum on titania had a greater conductance that those devices that used Pt-Y and were not able to selectively detect propane in the presence of CO. A model based on the oxidation state of the platinum metal was proposed to explain these results.; The effects of humidity on a titania based gas sensor were studied using electrical measurements. It was found that high humidity had a relatively small effect on the sensor conductance when compared to gases like CO. To explain these results, diffuse reflectance infrared spectroscopy was performed on a hydrated titania surface that was heated to various levels. The infrared data showed that hydroxyl groups and water were formed on the titania surface at high temperature, with bridging hydroxyl groups being the first to form. These spectroscopic studies were correlated to the electrical measurements in order to propose a mechanism involving the displacement of adsorbed oxygen species by water.; In order to eliminate the response of a titania sensor to fluctuations in humidity, a siliceous zeolite was fabricated on an alumina support. It was determined with electrical measurements that this hydrophobic membrane was effective in stopping water from permeating the membrane. In addition, it was found that CO transversed this membrane quickly relative to propane which permeated at a much slower rate. To quantify the diffusion phenomenon, gas permeation experiments were conducted in which nitrogen, oxygen, CO, and propane were each exposed to a membrane individually. A model explaining the permeance of these gases was then proposed.