Oxygen exchange on nanocrystalline tin dioxide modified by palladium

摘要

Temperature-programmed oxygen isotopic exchange study was performed on nanocrystalline tin dioxide-based materials synthesized via solgel route and modified by palladium. Such materials are widely used as resistive gas sensors. The experiments were carried out in a flow-reactor up to complete isotopic substitution of oxygen. Substantial rates of isotopic exchange for SnO _2 were observed from about 700 K. The distribution of isotopic molecules ~(16)O _2, ~(16)O ~(18)O and ~(18)O _2 corresponds to simple dioxygen heteroexchange mechanism with single lattice oxygen atom. The modification of SnO _2 by Pd introduced multiple heteroexchange mechanism with preliminary O _2 dissociation on the clusters surface. Spill-over of atomic oxygen from Pd to the surface of SnO _2 and fast exchange with lattice oxygen result in more than 100% increase of apparent heteroexchange rate. The exchange on SnO _2/Pd was shown to be a complex process involving partial deactivation of the catalytic centers at temperature higher than 750 K.