Titanium dioxide based high temperature carbon monoxide selective sensor

The anatase form of TiO2 has been examined for the sensing of CO and CH4 at temperatures of 873 K. Though, there were differences in the sensitivity of the anatase sensor towards CO and CH4, both gases showed considerable resistance changes. However, in the presence of lanthanum oxide and copper oxide (labeled as ALC sensor), the sensor showed minimal response towards CH4, while still exhibiting sensitivity towards CO. The insensitivity towards CH4 was also con®rmed by measuring the sensor response in the presence of both gases. In order to understand the basis for selective CO sensing, diffuse re ̄ectance infrared spectroscopy was carried out on the sensor materials at elevated temperatures. Lanthanum oxide was used to inhibit the anatase to rutile transformation. Infrared spectroscopic data strongly suggest that there is a layer of lanthanum oxide on the titania surface, which acts as a trap for the oxidation products of CO and CH4. Upon oxidation of CO on ALC, carbonate species were detected, whereas the reaction of CH4 produced negligible carbonate species. The insensitivity of the ALC sensor towards CH4 is proposed to be due to its rapid oxidation by O2 on the copper oxide. This ef®cient oxidation was responsible for lack of CH4 reaction on the anatase surface, thus, producing minimal resistance change. CO oxidation also occurred partially on the CuO surface but signi®cant reaction also occurred on the anatase surface and produced a change in resistance. # 2001 Elsevier Science B.V. All rights reserved.