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 o f the anatase sensor towards CO and CH4, both gases showed considerable res istance changes. However, in the presence of lanthanum oxide and copper oxi de (labeled as ALC sensor), the sensor showed minimal response towards CH4, while still exhibiting sensitivity towards CO. The insensitivity towards C H4 was also confirmed by measuring the sensor response in the presence of b oth gases. In order to understand the basis for selective CO sensing, diffu se reflectance infrared spectroscopy was carried out on the sensor material s at elevated temperatures. Lanthanum oxide was used to inhibit the anatase to rutile transformation. Infrared spectroscopic data strongly suggest tha t 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 AL C, carbonate species were detected, whereas the reaction of CH4 produced ne gligible carbonate species. The insensitivity of the ALC sensor towards CH4 is proposed to be due to its rapid oxidation by O-2 on the copper oxide. T his efficient oxidation was responsible for lack of CH4 reaction on the ana tase surface, thus, producing minimal resistance change. CO oxidation also occurred partially on the CuO surface but significant reaction also occurre d on the anatase surface and produced a change in resistance. (C) 2001 Else vier Science B.V. All rights reserved.