Volatile Organic Compound Sensing with WO3-Based Gas Sensors: Surface Chemistry Basics

The sensing properties of WO3-based gas sensors were evaluated at an operating temperature of 150 °C in the presence of different volatile organic compounds (VOCs). Simultaneously to the sensing tests, operando diffuse-reflectance infrared Fourier transform spectra were acquired. Remarkably, no CO2 generation was observed under gas exposure for any of the target VOCs. Catalytic combustion properties of the WO3 toward acetone and ethanol at temperatures from 150 to 400 °C, both in dry and humid atmospheres, were additionally performed. Such measurements confirmed that no combustion occurred for ethanol (up to at least 300 °C) while it became detectable for acetone only starting from 250 °C. The reaction products are acetaldehyde and acetate in the case of ethanol exposure and acetate and formate in the case of acetone exposure. The oxidation catalytic effect of WO3 was confirmed for both toluene, where benzaldehyde and benzoate modes were observed, and acetylene (where acetaldehyde and ethenol were detected). The systematic absence of CO2 as a product and the identification of oxidized species are the basis of the proposed reaction mechanisms.