Low-temperature NO-adsorption properties of manganese oxide octahedral molecular sieves with different potassium content

In this study, we synthesized hollandite-type manganese oxide octahedral molecular sieves (OMS) with different potassium content (KxMn8O16; K-OMS-2). Owing to crystal growth, the specific surface area of K-OMS-2 decreased with an increase in the K concentration for x > 1.5. The K-OMS-2 samples with x < 1.5 exhibited NO adsorption at low temperatures because of an oxidation reaction of NO. The amount of adsorbed NO depended on the oxidation activity of K-OMS-2 instead of the specific surface area (i.e., the number of NO adsorption sites). The amount of NO that was adsorbed at 323 K was correlated to the increase in the amount of oxygen released from K-OMS-2. It is assumed that the thermally unstable oxygen sites acted as oxidation sites for NO at low temperatures and thus increased the amount of adsorbed NO. (C) 2016 Elsevier B.V. All rights reserved.