Selective detection of methane by HZSM-5 zeolite/Pd-SnO2 gas sensors

Abstract Gas sensors based on Pd-loaded SnO2 were prepared with printed zeolite films on the top of the sensor layer to enhance selective response to methane. As expected, Pd-loaded SnO2 has a sensitive response to CH4 and VOCs, such as ethanol and acetone vapors. Pt catalyst was dispersed onto the surface to promote the catalytic activity of zeolite. According to the catalytic characterizations, it was indicated that interfered gases, CO and ethanol were catalytically oxidized into CO2 and water vapor. Whereas the catalytic combustion of methane is a negligible and sensitive response to the interested analyte, CH4 was significantly promoted. Thus, the selective response to CH4 was greatly improved even in a mixture of methane with CO and VOCs. Based on the power-law response to oxygen, it was found that the resistive responses of all sensors were highly oxygen-dependent, suggesting that oxygen adsorbates on the surface were involved in the sensing process and no difference with zeolite coated sensors. Thus, it can be concluded that zeolite films printed onto the sensing layer surface serve as a catalytic filter and responsible for the enhanced sensitive and selective response of methane.