Influence of catalytic reactivity on the response of metal-oxide-silicon carbide sensor to exhaust gases

Catalytic metal insulator silicon carbide, MISiC, Schottky diodes are promi sing devices for on board exhaust diagnosis in cars. These sensors show a d irect or indirect sensitivity to gases like H-2, CO, HC (hydrocarbons) and O-2. The catalytic reactivity of the sensor will effect the gas sensing con ditions. In some situations knowledge about the reactivity of the catalytic surface may give more information about the exhaust gas composition. For i nstance, the sensor signal normally moves to a lower voltage in an ambient containing H-2 and HC, however, under certain conditions when exposed to ri ch gas mixtures, the HC response is opposite the one for H-2. Measurements performed by the MISiC sensors on simulated exhaust gas mixtures, either ri ch or lean, are shown here. Some fundamental studies of the HC response hav e been performed. Reaction limitation conditions are suggested as an explan ation for the response of HC opposite the one of H-2. (C) 1999 Elsevier Sci ence S.A. All rights reserved.