This review surveys recent advances in the applications of layered double hydroxides (LDHs) in heterogeneous catalysis. By virtue of the flexible tunability and uniform distribution of metal cations in the brucite-like layers and the facile exchangeability of intercalated anions, LDHs-both as directly prepared or after thermal treatment and/or reduction-have found many applications as stable and recyclable heterogeneous catalysts or catalyst supports for a variety of reactions with high industrial and academic importance. A major challenge in this rapidly growing field is to simultaneously improve the activity, selectivity and stability of these LDH-based materials by developing ways of tailoring the electronic structure of the catalysts and supports. Therefore, this Review article is mainly focused on the most recent developments in smart design strategies for LDH materials and the potential catalytic applications of the resulting materials.

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In this paper, a facile synthetic route of cobalt ferrite nanocrystals with narrow size distribution was reported.The key feature of this method involved a very rapid mixing of reducible metal cations with sodium borohydride and simultaneous reduction in a colloid mill, which is followed by a slow oxidation in a separate hydrothermal treatment. The microstructural and magnetic characteristics of the materials were characterized by powder X-ray diffraction (XRD), chemical analysis, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), transmission electron microscopy (TEM), Mo ¨ssbauer spectroscopy, and magnetometry. The results unambiguously indicated that the obtained products consisted of CoFe 2 O 4 nanocrystals with good monodispersity and high stoichiometry and that, especially, a 9 nm sample exhibited room-temperature superparamagnetism. The formation mechanism of nanocrystals was proposed. It is believed that the extreme forces, to which the nucleation mixture of metallic cobalt and iron obtained with a very short time was subjected in the colloid mill, prevented aggregation of the newly formed metal nuclei. Consequently, when the resulting metal nuclei were oxidized slowly in a separate hydrothermal treatment, CoFe 2 O 4 nanocrystals with narrow size range were obtained.

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As a promising renewable alternative to the production of petroleum-derived chemicals and energy, biomass transformation is attracting increasing attention in terms of green chemical processes and sustainable development. Specifically, selective aerobic oxidation of cellulose-derived 5-hydroxymethylfurfural (HMF) into high value-added 2,5-furandicarboxylic acid (FDCA) is regarded as one of the most attractive biomass transformations due to a wide range of its application prospects. Herein, we report the synthesis of a highly efficient and stable bimetallic AuPd nanocatalyst over the La-doped Ca−Mg−Al layered double hydroxide (La-CaMgAl-LDH) support for base-free aerobic oxidation of HMF to FDCA in water, which makes the biomass-based chemical process green and cost effective. Under optimized reaction conditions, the yield of FDCA can reach above 99%. Such encouraging performance of the catalyst is believed to be correlated with both the higher surface basicity of La-CaMgAl-LDH support and the synergy between Au−Pd atoms in the bimetallic AuPd nanoparticles, which can greatly favor the activation of reactants and reaction intermediates in the course of tandem oxidation reactions. The present work provides an effective strategy for developing highly efficient bimetallic catalysts with the enhanced stability by adjusting surface structures and compositions of supports for a wide range of base-free aerobic oxidation of other biomass-derived compounds in water.