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

Metal oxide gas sensors in general, show high sensitivity but poor selectiv ity if pure sensor materials are used. The performance in terms of reproduc ibility may be enhanced by using very stable materials, which may be operat ed at quite high temperature but this does not help in the problem of selec tivity. This paper discusses the use of gas pretreatment using filters oper ated at elevated temperatures to overcome this problem for special applicat ions. Three different types of gas filters are discussed: a physical filter which is permeated by hydrogen only, a catalyst filter which removes distu rbing solvent vapours by oxidation, and a gas conversion filter which ensur es a defined NO/NO2 equilibrium. These filters relate to the applications o f selective indoor CH4, H-2, and automotive exhaust gas nitrogen oxide dete ction. (C) 2000 Elsevier Science S.A. All rights reserved.