After impregnation of the transition metals adding TiO2 powder or WO3/TiO2 powder, they were stirred by the magnetic stirrer and slowly heated to make TiO2 or TiO2/WO3 powder supported on transition metals. After the acquired substance was dried at 110 C for 12 h and fired at 600 C for 2 h, the sensor material was obtained by pulverizing the powder.