Knowledge of the catalytic performances of different crystalline phases of a material is vital for the development of superior catalysts. In this study, different phases of MnO 2 (α, β, γ, and δ) have been prepared by the oxidation of Mn 2+, and their catalytic performances were evaluated using the aerobic oxidation of benzyl alcohol to benzaldehyde as a model reaction. α-MnO 2 promoted the reaction to the highest yield. However, when the yields were normalized by the corresponding surface areas, δ-MnO 2 exhibited the highest specific activity and α-MnO 2 the lowest, indicating that the diverse microstructures resulting from the crystalline phase have a profound effect on catalytic performance. α-MnO 2 showed the highest catalytic stability, resulting from its unchanged composition and morphology after use. Informed by the experimental results, a possible reaction mechanism involving the Mars-van Krevelen process was proposed. This work provides useful information for the development of effective catalysts for aerobic oxidation.

Ethanol is a kind of green and sustainable liquid fuel with high energy density, which has a promising application prospect in liquid fuel cells. Improving the anti-poisoning ability and C−C bond cleavage ability of Pt-based catalysts is critical for achieving efficient ethanol oxidation reaction. Here, Pt−Sn nanosheets preferentially exposed with metastable (100) facets rather than thermodynamically stable (111) facets were synthesized through a simple hydrothermal method. Our experiment results demonstrated that the as-synthesized (100) faceted Pt−Sn nanosheets exhibited a good electrocatalytic performance, i.e., higher CO 2 selectivity and better stability when compared with Pt−Sn nanoparticles with irregular morphology and commercial Pt/ C. The electrochemical in situ infrared spectroscopy tests revealed that the Pt−Sn nanosheets alleviate the binding strength of reaction intermediates and further promote the electrooxidation of intermediates, thereby displaying a good CO 2 selectivity at a lower potential and over a wide range of potentials. This work demonstrates the important roles of the facet effect and alloying effect in electrocatalytic properties of noble metal catalysts.