Deactivation mechanism and anti-deactivation modification of SnO2-based catalysts for methane gas sensors

Abstract

Hexamethyldisiloxane (HMDSO) is one of the most serious poisons in the field of catalysts. In this research, the deactivation of SnO2 and Pd/SnO2 catalysts by HMDSO was studied. Surface modification with Ag/Al2O3 was used to improve the resistance of the catalyst to HMDSO deactivation. To intrinsically investigate the deactivation mechanism of the catalyst, the morphology, structure and surface state of the catalyst were characterized by SEM, EDS, HRTEM, XPS, Raman, and PL. HMDSO decomposed on the SnO2 catalyst surface, yielding organosilicon and silicates (SixOy, y/x<2). On the surface of the Pd/SnO2, in addition to the organosilicon and silicates, the decomposition products of HMDSO also contained SiO2. SixOy can be further oxidized at highly active sites associated with bridging OVs on the Pd/SnO2 surface, forming SiO2. With the decomposition of HMDSO on the surfaces of the SnO2 and Pd/SnO2 catalysts, the reduction in OVs and clogging of the pores led to irreversible deactivation of the catalysts for CH4 detection. However, for the Pd/SnO2 catalyst surface-modified by Ag/Al2O3, deactivation by HMDSO exposure was reversible. HMDSO decomposed on the surface of the Ag and Al2O3 support. In addition, Al2O3 acts as a filter layer which prevent the penetration of HMDSO and its decomposition products. Therefore, the inner sensing layer was protected by the surface-modification layer from HMDSO deactivation.