Selective gas detection with high-temperature operated metal oxides using catalytic filters

Metal oxide gas sensors in general, show high sensitivity but poor selectivity if pure sensor materials are used. The performance in terms of reproducibility may be enhanced by using very stable materials, which may be operated at quite high temperature but this does not help in the problem of selectivity. This paper discusses the use of gas pretreatment using filters operated at elevated temperatures to overcome this problem for special applications. Three different types of gas filters are discussed: a physical filter which is permeated by hydrogen only, a catalyst filter which removes disturbing solvent vapours by oxidation, and a gas conversion filter which ensures a defined NO/NO2 equilibrium. These filters relate to the applications of selective indoor CH4, H2, and automotive exhaust gas nitrogen oxide detection.