Low-Temperature NO_x Storage Capability of YBaCo₄O_7+δ Originating from Large Oxygen Nonstoichiometry

Abstract

Insights into NO x storage materials have emerged as key components in NO x abatement technologies. Recently, the pursuit of promising materials has been conducted mostly among perovskite- and its derived-structured transition metal oxides involving metal-oxygen octahedral units. There is, however, little information on the outcomes of consideration among other oxide families having different polyhedral units as potential candidates for NO x storage materials. Here, we report that a Swedenborgite-structured oxide, YBaCo4O7+δ, can be a prominent candidate to be used without any platinum group metal loadings. Superior NO x storage capabilities at rather a lower temperature of 100 °C are demonstrated. The present oxide achieves a higher catalytic oxidation of NO to NO2 than a conventional platinum- and barium-impregnated catalyst (Pt/Ba/Al2O3) below 400 °C. It is anticipated that the oxide can be easily modified by taking advantage of chemical flexibilities, e.g., in terms of iso- and/or aliovalent substitutions, toward more efficient catalytic materials in NO x abatement industries.

Experimental and Computational Insights into the Catalytic Mechanism of Y1–xBaxCoO3−δ Perovskite Oxides with a Controlled Crystal Structure

“…Among metal oxides, perovskite oxides are widely used in various catalytic reactions because they can be combined with various elements. − Recently, we determined that Co- and Mn-doped SrTiO 3 have high performances for CO oxidation and NO x storage reactions and that the reaction mechanism can be controlled based on the elements added to SrTiO 3 . − In Co-doped SrTiO 3 catalysts, the lattice oxygens of the oxides are involved in CO oxidation, and the reaction proceeds via the Mars–van Krevelen (MvK) mechanism (CO + O L → CO 2 + V O , O 2 + 2 V O → 2O L ; O L : Lattice oxygen, V O : Oxygen vacancy). , In contrast, for Mn-doped catalysts, the contribution of lattice oxygens to CO oxidation was negligible, and the reaction proceeded on the oxide surface according to the Langmuir–Hinshelwood (L–H) mechanism in which CO and O 2 in the gas phase were activated on the surface of the catalyst to form CO 2 . Thus, the effects of doping elements on perovskite materials have been frequently discussed.…”