Improving the reducibility of CeO2/TiO2 by high-temperature redox treatment: the key role of atomically thin CeO2 surface layers

Abstract

CeO2/TiO2 catalysts treated in reaction environment at high temperatures evolve into complex and diverse systems, where several mixed oxides are formed. To analyze the redox behavior of this system, multiple oxidations and reducing thermal treatments have been applied. Results from the temperature-programmed reduction studies revealed a clear shift at lower temperatures on the reduction peak when the sample was previously reduced at high temperatures and oxidized under mild conditions. Meanwhile, the reduction peak was moved to high temperatures when the sample was previously reduced and oxidized at severe temperatures. The study, which was aimed at correlating this behavior with its chemical structure, was conducted using advanced electron microscopy, including high-resolution TEM and STEM imaging and spectroscopic techniques such as X-EDS and EELS. The data presented here comparing structures at the atomic level and chemical properties have uniquely unveiled that besides the cerium-titanium mixed oxides, a very thin layer up to a single monolayer was deposited along the TiO2 surface, which indeed was responsible for the improvement of the reducing temperature.