Oxidation and hydrogenation catalysis plays a crucial role in the current chemical industry for the production of key chemicals and intermediates. Because of their easy separation and recyclability, supported catalysts are widely used in these two processes. Layered double hydroxides (LDHs) with the advantages of unique structure, composition diversity, high stability, ease of preparation and low cost have shown great potential in the design and synthesis of novel supported catalysts. This review summarizes the recent progress in supported catalysts by using LDHs as supports/precursors for catalytic oxidation and hydrogenation. Particularly, partial hydrogenation of acetylene, hydrogenation of dimethyl terephthalate, methanation, epoxidation of olefins, elimination of NOx and SOx emissions, and selective oxidation of biomass have been chosen as representative reactions in the petrochemical, fine chemicals, environmental protection and clean energy fields to highlight the potential application and the general functionality of LDH-based catalysts in catalytic oxidation and hydrogenation. Finally, we concisely discuss some of the scientific challenges and opportunities of supported catalysts based on LDH materials.

Co-containing layered double hydroxides (LDHs) are potential non-noble-metal catalysts for the aerobic oxidation of alcohols. However, the intrinsic activity of bulk LDHs is relatively low. In this work, we fabricated ultrathin and vacancy-rich nanosheets by exfoliating bulk CoAl-LDHs, which were then assembled with graphite oxide (GO) to a ord a hybrid CoAl-ELDH/GO catalyst. TEM, AFM, and positron annihilation spectrometry indicate that the thickness of the exfoliated LDH platelets is about 3 nm, with a large number of vacancies in the host layers. Fourier transformed XAFS functions show that the Co−O and Co••••Co coordination numbers (5.5 and 2.8, respectively) in the hybrid CoAl-ELDH/GO material are significantly lower than the corresponding values in bulk CoAl-LDHs (6.0 and 3.8, respectively). Furthermore, in addition to the oxygen vacancies (VO) and cobalt vacancies (VCo), CoAl-ELDH/GO also contains negatively charged VCo−Co−OH δ− sites and exposed lattice oxygen sites. CoAl-ELDH/GO shows excellent performance as a catalyst for the aerobic oxidation of benzyl alcohol, with a TOF of 1.14 h − 1 ; this is nearly five times that of the unexfoliated bulk CoAl-LDHs (0.23 h − 1) precursor. O2-TPD and DRIFT spectroscopy declare that the oxygen storage capacity and mobility are facilitated by the oxygen vacancies and surface lattice oxygen sites. Meanwhile, DFT calculations of adsorption energy show that benzyl alcohol is strongly adsorbed on the oxygen vacancies and negatively charged VCo−Co−OH δ− sites. A kinetic isotope e ect study further illustrates that the vacancy-rich CoAl-ELDH/GO catalyst accelerates the cleavage of the O−H bond in benzyl alcohol. Finally, we show that the hybrid CoAl-ELDH/GO material exhibits excellent catalytic activity and selectivity in the oxidation of a range of other benzylic and unsaturated alcohols.

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The catalytic upgrading of biomass-derived feedstocks to valuable chemicals generally requires catalysts with integrated active sites and tuned structures for selective activation of their multifunctional groups. Herein, we fabricated different Cu-based catalysts with multiple interfaces by facile reduction of layered double hydroxides (LDHs), aimed at controlling the reaction pathway and product selectivity in the hydrogenation of 5-(hydroxymethyl)­furfural (HMF), an important biomass-based platform molecule. These Cu catalysts were characterized by XRD, Raman, TPR, HAADF-STEM, and in situ XAFS. For Cu/MgAlO x , derived from CuMg5Al2-LDHs, Cu particles were partially encapsulated by a MgAlO x support, thus forming highly intimate Cu–MgAlO x interfaces. On Co@Cu/CoAlO x , derived from CuCo x Al2-LDHs, together with a Cu–CoAlO x interface, partially reduced ultrasmall Co clusters were mounted around Cu particles to form a metallic Co–Cu interface, which is tunable by varying the Cu/Co ratio. As expected, Cu/MgAlO x was only active in CO hydrogenation to produce 2,5-bis­(hydroxymethyl)­furan (DHMF) in a 92.7% yield, while Co@Cu/3CoAlO x sequentially catalyzed the CO hydrogenation and C–OH hydrogenolysis to yield as high as 98.5% 2,5-dimethylfuran (DMF), in sharp contrast to Co@Cu/5CoAlO x , which further broke the CC bonds of DMF to yield 83.6% 2,5-dimethyltetrahydrofuran (DMTHF). The dependence of the reaction pathway and product selectivity on the composition and properties of the interface was revealed by identifying various intermediates using in situ IR. Specifically, HMF transformed into an O-bound intermediate on the Cu sites over the Cu–MgAlO x , while the unsaturated interfacial Cu–CoAlO x structure served as dual active sites to form a C,O-bound intermediate, thus leading to different products. In addition, the tunable Cu–Co interfacial sites remarkably influenced the adsorption modes of CC bonds in the furan ring. This work provides a rationale for controlling the reaction pathway and product selectivity for complicated biomass reactions via the controllable construction of multiple interfaces.

Using a laser monitoring observation technique, the solubilities of terephthalaldehydic acid, p-toluic acid, benzoic acid, terephthalic acid, and isophthalic acid in N-methyl-2-pyrrolidone were determined by the synthetic method from (295.65 to 371.35) K. The experimental results were correlated by an empirical equation.

Au-Pd nanoalloys supported on Mg-Al mixed metal oxides prepared using sol-immobilisation are found to be highly efficient and reusable catalysts for the solvent-free oxidation of benzyl alcohol using molecular oxygen under low pressure. When using this support alloying Pd with Au resulted in an increase in both activity and selectivity to benzaldehyde and moreover an improved resistance to catalyst deactivation compared with the monometallic Pd and Au catalysts. The turnover number for the Au/Pd 1:1 molar ratio catalyst achieved 13,000 after 240 min and the selectivity to benzaldehyde was maintained at 93%; this high catalytic activity can be retained in full after three successive uses. The ensemble and electronic effect of Au-Pd nanoalloys were studied by IR spectroscopy using CO chemisorption, XPS and HRTEM. Moreover, the bifunctional nature of the acid-base MgAl-MMO support was found to be important as the acid sites are considered to be responsible for the improvement of catalytic activity; while, the basic sites gave rise to high selectivity. A possible mechanism with Au-Pd nanoparticles as the active sites has been proposed, illustrating that the oxidation of benzyl alcohol can proceed through the cooperation between the Au-Pd nanoalloys and the base/acid sites on the surface of the support.

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