Rich surface Co(iii) ions-enhanced Co nanocatalyst benzene/toluene oxidation performance derived from CoIICoIII layered double hydroxide

Abstract

A hierarchical Co^II_2.8Co^III₁ layered double hydroxide (LDH) nanostructure was constructed through a facile topochemical transformation route under a dynamic oxygen atmosphere. Self-assembled coral-like CoAl LDH nanostructures via the homogeneous precipitation method were also inspected under different ammonia-releasing reagents and solvents. Benzene and toluene were chosen as probe molecules to evaluate their catalytic performance over the metal oxide CoCoO and CoAlO calcined from their corresponding LDH precursors. Nanocatalyst of trivalent Co ions replaced Al³⁺ ions in the bruited-like layer had a higher catalytic activity (T₉₉(benzene) = 210 °C and T₉₉(toluene) = 220 °C at a space velocity = 60 000 mL g⁻¹ h⁻¹). Raman spectroscopy, XPS and H₂-TPR demonstrated the existence of abundant high valence Co ions that serve as active sites. TPD verified the types of active oxygen species and surface acid properties. It was concluded that the high valence Co ions induced excellent low-temperature reducibility. Surface Lewis acid sites and the surface O_ads/O_latt molar ratio (0.61) played relevant roles in determining its catalytic oxidation performance. Our design in this work provides a promising approach for the development of nanocatalysts with exposed desirable defects.