Effects of Pd- and Pt-loading on the Gas-sensing Properties of SnO₂ Subjected to Surface Chemical Modification with Diethoxydimethylsilane

Abstract

Pd- and Pt-loaded SnO₂ sensors were subjected to repeated surface chemical modification with diethoxydimethylsilane (DEMS) to modify the gas-sensing properties of the DEMS-modified SnO₂ sensor to H₂, CH₄ and C₃H₈ with the noble metal sensitizers. Variations in temperature programmed desorption (TPD) chromatograms of oxygen and water as well as in oxidation activities were also investigated in relation to the mechanism of the modification of the gas-sensing properties. Pt/SnO₂ was superior to Pd/SnO₂ in the H₂ sensing, and the sensitivity to H₂ increased with repeated surface modification, accompanied by a mazked increase in the H₂ oxidation activity. On the other hand, Pd/SnO₂ was superior to Pt/SnO₂ in the C₃H₈ and CH₄ sensing, and Pd/SnO₂ subjected to three times modification with DEMS exhibited the maximum sensitivity of S=180 to C₃H₈ at 350°C and S=38 to CH₄ at 400°C. Then, the response and recovery rate of the hydrocazbon sensing was satisfactorily fast at 400°C. However, the sensitivity to hydrocarbon decreased with further modification, although the catalytic activity for hydrocarbon oxidation was not so much influenced by the modification, in accordance with the almost unchanged amount of PdO species measured by TPD. The variations in gas-sensing and oxidation properties are discussed in terms of the effects of Pd- and Pt-loading and of the SiO₂ component introduced by the surface modification with DEMS.