The selective oxidation of alkylaromatics is of vital importance for the production of high-added-value raw materials. The development of highly efficient heterogeneous catalytic oxidation systems under mild conditions has become an attractive research area. In this work, hybrid Co–Cu–Al layered double hydroxide/graphene (CoCuAl-LDH/graphene) nanocomposites, which were assembled successfully by a one-step coprecipitation route without the use of any additional reducing agents, were used as highly efficient catalysts for the liquid-phase selective oxidation of ethylbenzene using tert-butyl hydroperoxide as the oxidant. A series of characterizations revealed that graphene could stabilize CoCuAl-LDH nanoplatelets effectively in the nanocomposites, and in turn, highly dispersed CoCuAl-LDH could prevent the aggregation of the graphene nanosheets. By fine-tuning the mass ratio of graphene to CoCuAl-LDH, such nanocomposites offered a tunable catalytic oxidation performance. In particular, the nanocomposite with the graphene/CoCuAl-LDH mass ratio of 0.4:1 exhibited a remarkable catalytic performance with a considerable conversion (96.8 %) and selectivity to acetophenone (>95.0 %), which was mainly attributed to the synergism between the active CoCuAl-LDH component and the graphene matrix in the unique hetero-nanostructure. Moreover, the as-assembled nanocomposite catalysts displayed good recyclability and were active for the selective oxidation of other alkylaromatics.

With ever increasing demand of sustainable energy, biomass has been regarded as an ideal alternative to fossil resources. Herein, hierarchical three-dimensional nickel-based nanowalls on a nickel foam substrate were fabricated by a Ni–Zr–Al layered double hydroxide (NiZrAl–LDH) precursor route, which involved in situ growth of the Zr-containing precursor on the Ni foam strut through surface activation without an external nickel source. After calcination–reduction treatment, the nanowalls were applied as a structured catalyst for selectively hydrogenating biomass-derived levulinic acid to γ-valerolactone. Systematic characterization revealed that highly dispersed Ni nanoparticles could be generated on the platelet-like Zr-containing oxide matrix derived from hierarchical 3 D NiZrAl–LDH nanowalls. Under vapor-phase, solvent-free hydrogenation conditions (250 °C, ambient pressure), the yield and productivity for as-fabricated Ni-based structured catalyst could reach as high as 97.7 % and 5.747 kg_GVL kg_cat⁻¹ h⁻¹, respectively. Such high catalytic efficiency was reasonably attributable to highly dispersed Ni nanoparticles and abundant surface Lewis acid sites, as well as favorable heat-transfer nature of present catalytic system. Moreover, the newly developed structured nanowall-like Ni-based catalyst possesses high structural and chemical stability, which makes the vapor-phase hydrogenation process promising in terms of green sustainable chemistry.

The efficient gas-phase selective hydrogenation of a series of esters to the corresponding alcohols was achieved over well-dispersed aluminum-doped zirconia-supported copper nanocatalysts (Cu/Al-ZrO₂), which were prepared through a homogeneous coprecipitation route in the presence of cetyl trimethyl ammonium bromide. The characterization revealed that the structure and catalytic performance of Cu/Al-ZrO₂ nanocatalysts were profoundly affected by the addition of Al. Compared with the Al-free catalyst, Al-doped materials had higher specific surface areas and smaller copper nanoparticles. In particular, the results confirmed that the incorporation of Al into the ZrO₂ framework could form tetrahedrally coordinated Al³⁺ species, leading to the improvement of metal dispersion and the formation of more surface Lewis acid sites. In the gas-phase selective hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG), 100 % DMO conversion, 97.1 % EG selectivity, and a high turnover frequency of 16.9 h⁻¹ were achieved over Cu/Al-ZrO₂ catalyst with a Al/(Cu+Zr+Al) mass ratio of 0.1. The high efficiency of Cu/Al-ZrO₂ catalysts in DMO hydrogenation was attributed mainly to the surface synergistic catalytic effect between highly dispersed metallic copper species and strong Lewis acid sites, which promoted the hydrogenation reaction related to the ester groups, unlike the single case of Cu⁺Cu⁰ synergy reported previously that was found to control the extent of hydrogenation. The obtained catalysts displayed excellent catalytic performance in the gas-phase hydrogenation of other esters including dimethyl succinate, dimethyl maleate, dimethyl adipate, and 1,4-cycolhexane dicarboxylate.