New Model for a Pd-Doped SnO2-Based CO Gas Sensor and Catalyst Studied by Online in-Situ X-ray Photoelectron Spectroscopy

The functional mechanism of oxide-based gas sensors and the gas catalysis reaction are controversial topics. The traditional static photoelectron data collection technique is obviously not satisfied for this study. However, after appropriate remodification of the data collection system we propose a new, online XPS in-situ data collection technique for overcoming this difficulty. This online photoelectron collection technique was employed for the first time on this kind of study with SnO2-based gas sensors. The results we found are as follows: (1) For rutile SnO2 in powder form, its O1s peak of 531.8 eV would come from the lattice oxygen in the surface area, not from chemisorbed oxygen as proposed conventionally; (2) we observed that in the adsorptive process of CO onto Pd-doped SnO2, Pd, CO, and lattice oxygen in the surface area of SnO2 could form an intermediate product [Pd(CO)(4)]O-4, from which comes a unified new model for illustrating the mechanism of this kind gas sensor, on one hand, and the oxidation catalysis process, on the other; (3) we noticed a transient magnetic phenomenon during the adsorption process of CO onto SnO2. This could open a door for studying spin sensors.