In the presence of Mo6+-doped α-MnO2 (Mo–MnO2), various sulfides could efficiently be oxidized to the corresponding sulfoxides as the major products. In addition, Mo–MnO2 could repeatedly be reused.

The efficient surface reaction and rapid ion diffusion of nanocrystalline metal oxides have prompted considerable research interest for the development of high functional materials. Herein, we present a novel low-temperature method to synthesize ultrasmall nanocrystalline spinel oxides by controlling the hydration of coexisting metal cations in an organic solvent. This method selectively led to Li–Mn spinel oxides by tuning the hydration of Li+ ions under mild reaction conditions (i.e., low temperature and short reaction time). These particles exhibited an ultrasmall crystallite size of 2.3 nm and a large specific surface area of 371 ± 15 m2 g−1. They exhibited unique properties such as unusual topotactic Li+/H+ ion exchange, high-rate discharge ability, and high catalytic performance for several aerobic oxidation reactions, by creating surface phenomena throughout the particles. These properties differed significantly from those of Li–Mn spinel oxides obtained by conventional solid-state methods.

The oxygenation of alkylarenes to the corresponding aryl ketones is an important reaction, and the development of efficient heterogeneous catalysts that can utilize O2 as the sole oxidant is highly desired. In this study, we developed an efficient alkylarene oxygenation process catalyzed by ultrafine transition‐metal‐containing Mn‐based oxides with spinel or spinel‐like structures (M‐MnOx, M=Fe, Co, Ni, Cu). These M‐MnOx catalysts were prepared by a low‐temperature reduction method in 2‐propanol‐based solutions using tetra‐n‐butyl ammonium permanganate (TBAMnO4) as the Mn source, and they exhibited high Brunauer–Emmett–Teller surface areas (typically >400 m2 g−1). Using fluorene as the model substrate, the catalytic activities of M‐MnOx and Mn3O4 were compared. The catalytic activities of M‐MnOx were significantly higher than that of Mn3O4, which demonstrates that the incorporation of transition metals in manganese oxide was critical. Among the series of M‐MnOx catalysts examined, Ni‐MnOx exhibited the highest catalytic activity for the oxygenation. In addition, the catalytic activity of Ni‐MnOx was higher than that of a physical mixture of Mn3O4 and NiO. Furthermore, Ni‐MnOx exhibited a broad substrate scope with respect to various types of structurally diverse (hetero)alkylarenes (16 examples). The observed catalysis was truly heterogeneous, and the Ni‐MnOx catalyst was reusable for the oxygenation of fluorene at least three times and its high catalytic performance was preserved, for example, the reaction rate, final product yield, and product selectivity. The present Ni‐MnOx‐catalyzed oxygenation process is possibly initiated by a single‐electron oxidation process, and herein a plausible oxygen‐transfer mechanism is proposed based on several pieces of experimental evidence.

Ultrasmall nanocrystallinem anganese binary oxides with various compositions and crystal structures were synthesized by ac onvenient, rational low-temperature method. These oxidesw ere obtained in 2-propanol-based solutions using the organic-solvent-soluble MnO 4À as am anganese source under controlled metal cation templateh ydration. Three-dimensional spinel oxides were generated selectively by suppressing the hydration of metal cation templates. One-dimensional tunnels and two-dimensional layered structuresp redominated under adequate and high hydration, respectively.T hese oxidesa cted as efficient reusable heterogeneous catalysts for primary alcohol ammoxidation and amidation using aqueous NH 3 as an itrogen source and O 2 (air) as at erminal oxidant. In particular, ultrasmall CoÀMn spinel oxide effectively catalyzed the ammoxidation of primary alcohols into their corresponding nitriles. The LiÀMn spinel oxide promoted the hydration of ammoxidation-derived nitriles, facilitating the one-pot conversion of primary alcohols into primary amides.

In the presence of hollandite-based catalysts, various sulfoxides and pyridine N-oxides could be converted into deoxygenated products under atmospheric H2 pressure.