Effect of the introduction of oxide ion vacancies into cubic fluorite-type rare earth oxides on the NO decomposition catalysis

摘要

Cubic fluorite-type solid solutions based on Pr6O11 and CeO2 were synthesized and oxide anion vacancies were intentionally introduced into the cubic fluorite-type lattice through the charge compensating mechanism by Mg2+ and/or Ca2+ doping into their lattices. The oxide anion vacancies bring about positive effect on NO decomposition catalysis. The reason for the increase in the catalytic activity was attributed to defect fluorite-type structures close to the C-type cubic one, because C-type cubic rare earth oxides, in which one-quarter of the oxygen atoms in the fluorite-type structure are removed, show high NO decomposition activity. In particular, the positive effect of the formation of oxide anion vacancies was significant for Pr6O11 and its solid solutions, because the molar volume of Pr6O11 is larger than that of CeO2, and Pr6O11 contains Pr3+ as well as Pr4+ and thereby a small amount of oxide anion vacancies exist inherently in the lattice. (C) 2014 Elsevier Inc. All rights reserved.