Ppm level methane detection using micro-thermoelectric gas sensors with Pd/Al₂O₃ combustion catalyst films

The CH₄ combustion performance of a micro-thermoelectric gas sensor (TGS) with Pd-Al₂O₃ catalysts prepared using two different methods, impregnation and colloid mixing, has been investigated. Three crystal phases of Al₂O₃, α, θ, and γ, were used for the catalyst support; the Pd/θ-Al₂O₃ catalyst showed the best combustion performance. The Pd/θ-Al₂O₃ catalyst exhibited the best dispersion of Pd nanoparticles as analyzed by both a pulse adsorption technique and transmission electron microscopy. The effect of the catalyst thickness on the H₂ and CH₄ detection performance of the TGS using this Pd/θ-Al₂O₃ catalyst prepared using a colloid mixing method was investigated. It was found that the response voltage, ΔV, of the TGS to CH₄ increased with increasing film thickness, but the ΔV to H₂ decreased. The TGS with the Pd/θ-Al₂O₃ catalyst whose thickness was 35 μm could detect as low as 1 ppm of CH₄ in air by the thermoelectric conversion of the combustor heat to an electrical voltage.