Ioan Cezar Marcu
University of Bucharest, Romania
Title: Investigation of oxidation catalysts by in situ electrical conductivity measurements
Biography
Biography: Ioan Cezar Marcu
Abstract
The electronic and redox properties of oxide-based catalysts strongly influence their catalytic performance in oxidation reactions. A useful and highly sensitive technique to characterize them is the in situ electrical conductivity measurement. This allows to gain insight into the key features of the redox catalysts that determine their catalytic performance in order to better understand the origin of the catalytic effect and the reaction mechanism involved and, consequently, to improve the catalysts on a scientific basis or to rationally design efficient new ones. The oxidation catalysts are semiconducting metal oxides and function during catalysis via a heterogeneous redox mechanism involving the reduction and re-oxidation of the solid in the catalytic cycle. This behavior can be studied by following the evolution of the electrical conductivity of the oxide as a function of the nature of the gas phase in contact with this. For example, in the presence of oxygen the electrical conductivity of an n-type oxide decreases, while in the presence of reducing molecules, such as hydrocarbons, H2, CO, which consume lattice oxygen species, it increases. In this work, electrical conductivity studies of several oxide-based catalysts have been performed as a function of temperature and oxygen partial pressure. Also, temporal responses during sequential exposures to different gaseous atmospheres, including the reaction mixture, in conditions similar to those of catalysis were analyzed. Correlations between their redox properties and their catalytic performance in different oxidation reactions have been established and the origin of their catalytic behavior has been elucidated.