Abstract: A plate-type NO.sub.x gas sensor having a WO.sub.3 sensing film which are capable of preventing temperature variation of a sensing thin film depending on gas flow to decrease heat loss thereof, whereby extending the life span of batteries of a portable gas sensor. The plate-type NO.sub.x gas sensor includes a Pt thin film electrode formed on a front surface of an alumina substrate, a tungsten oxide thin film for sensing NO.sub.x gas deposited on the front surface of the substrate on which the Pt thin film electrode is formed, a heater formed on a back surface of the alumina substrate for holding a portion of the tungsten oxide thin film for sensing NO.sub.x gas within a predetermined temperature range, a conducting wire for connecting between the Pt thin film electrode and the heater and a sheet made of at least one material selected from a group composed of Al.sub.2 O.sub.

Abstract: A catalyst for cleaning exhaust gases has a first catalyst layer having as an active metal on an elemental support at least one noble metal selected from the group consisting of platinum, rhodium and palladium and a second catalyst layer having iridium as an active metal which is provided as a overlayer on the first catalyst layer.