New insight into the enhanced activity of ordered mesoporous nickel oxide in formaldehyde catalytic oxidation reactions

Highly ordered mesoporous materials synthesized by a nanocasting method offer vast opportunities in catalytic applications. However, considerable debates remain as to the mechanism by which the mesoporous structure results in enhanced performance. We demonstrate new insights into the role of ordered mesoporous metal oxides in the catalytic oxidation reaction by preparing nickel (II) oxide (NiO) rather than a multiple valence compound such as Co3O4 as model catalyst. Mesoporous NiO using KIT-6 as a template (m-NiO-k) achieved total formaldehyde (HCHO) mineralization at 90 degrees C using oxygen (O-2) as oxidant, while bulk NiO (b-NiO-c) oxidized HCHO completely at 170 degrees C. Moreover, using ozone (O-3) as oxidant, m-NiO-k attained increased HCHO conversion by similar to 34% with a twofold increase in CO2 selectivity and a 100% O-3 decomposition rate. We conclude that the surface sodium functionalization of m-NiO significantly promotes the total oxidation of HCHO with O-2, likely via contribute to hydroxyl regeneration during reaction. Furthermore, the extra active oxygen species and undercoordinated NiO on the mesoporous surface owing to the properties of mesoporous structures contribute almost exclusively to the high activity and selectivity in the simultaneous catalytic removal of HCHO and O-3, which are also involved in the further enhanced activity for HCHO oxidation using m-NiO with O-2. These findings provide additional new insight into engineering efficient mesoporous metal oxides for VOCs catalysis under mild condition. Furthermore, they provide an innovative perspective on optimizing other reactions employing nanocast mesoporous catalysts. (C) 2018 Elsevier Inc. All rights reserved.