New uniform solid catalyst for the low-temperature oxidation of carbon monoxide: a triple-layered rare earth perovskite containing Co and Cu ions

Abstract

Oxygen reactivity and catalytic activity of the cobalt-containing layered defect perovskites, YBa₂Cu₂CoO_7+δ and LaBa₂Cu₂CoO_7+δ, in comparison with LaBa₂Cu₃O_7-δ have been investigated employing temperature-programmed desorption (TPD) and temperature-programmed surface reactions (TPSR) in the stoichiometric and catalytic mode using carbon monoxide as a probe molecule. TPD studies showed evidence for the presence of two distinct labile oxygen species, one at (0 0 1/2) sites and the other at (0 1/2 0) sites in LaBa₂Cu₂CoO_7+δ against a single labile species at (0 1/2 0) in the case of two other oxides. The activation energies for the catalytic oxidation of carbon monoxide by oxygen over LaBa₂Cu₃O_7−δ, YBa₂Cu₂CoO_7+δ, and LaBa₂Cu₂CoO_7+δ have been estimated to be 24.2, 15.9, and 13.6 kcal/mol, respectively. The reactivity and catalytic activity of the oxide systems have been interpreted in terms of the structural changes brought about by substituents, guided by a directing effect of the larger rare earth cation. TPSR profiles, structural analysis, and infrared spectroscopic investigations suggest that the oxygen present at (0 0 1/2) sites in the case of LaBa₂Cu₂CoO_7+δ is accessible to catalytic oxidation of CO through a Mars-Van Krevelen pathway. Catalytic conversion of CO to CO₂ over LaBa₂Cu₂CoO_7+δ occurs at 200 °C. The enhanced reactivity is explained in terms of changes brought about in the coordination polyhedra around transition metals, enhanced basal plane oxygen diffusivity, and redox potentials of the different transition metal cations.