From Core–Shell to Yolk–Shell: Improved Catalytic Performance toward CoFe2O4@ Hollow@ Mesoporous TiO2 toward Selective Oxidation of Styrene

Copper-decorated core-shell structured ordered mesoporous containing cobalt ferrite nanoparticles as high-performance heterogeneous catalyst toward synthesis of tetrazole

The present work describes the synthesis of copper immobilization on CoFe2O4/MCM-41 as a catalyst, which is created by attaching copper and ligand (N-phenyl anthranilic acid (PA)) on the surface of CoFe2O4/MCM-41 (CoFe2O4/MCM-41/PA/Cu). The synthesized CoFe2O4/MCM-41 support and immobilized copper were identified by FTIR, TEM, VSM, SEM XRD, and nitrogen adsorption-desorption analysis. The results showed that MCM-41 silica was coated with magnetite nanoparticles and copper was successfully immobilized on this structure. The catalytic performance of synthesized catalyst was tested in the synthesis of tetrazole. It was shown that the solid catalyst exhibited a strong magnetic response and showed good catalytic activity in the synthesis of tetrazole. The catalytic test showed that copper supported on CoFe2O4/MCM-41 hybrid showed much better catalytic activity than copper supported on CoFe2O4, indicating that MCM-41 plays an important role in CoFe2O4/MCM-41 hybrid for the synthesis of tetrazole. Separation of the solid catalyst from the reaction mixture was easily performed by external magnetism without apparent mass loss. And the catalyst could be reused six times for the synthesis of heterogeneous tetrazole.

Modulating Charges of Dual Sites in Multivariate Metal-Organic Frameworks for Boosting Selective Aerobic Epoxidation of Alkenes

Selective aerobic epoxidation of alkenes without any additives is of great industrial importance but still challenging because the competitive side reactions including C═C bond cleavage and isomerization are difficult to avoid. Here, we show fabricating Cu(I) single sites in pristine multivariate metal-organic frameworks (known as CuCo-MOF-74) via partial reduction of Cu(II) to Cu(I) ions during solvothermal reaction. Impressively, CuCo-MOF-74 is characteristic with single Cu(I), Cu(II), and Co(II) sites, and they exhibit the substantially enhanced selectivity of styrene oxide up to 87.6% using air as an oxidant at almost complete conversion of styrene, ∼25.8% selectivity increased over Co-MOF-74, as well as good catalytic stability. Contrast experiments and theoretical calculation indicate that Cu(I) sites contribute to the substantially enhanced selectivity of epoxides catalyzed by Co(II) sites. The adsorption of two O₂ molecules on dual Co(II) and Cu(I) sites is favorable, and the projected density of state of the Co-3d orbital is closer to the Fermi level by modulating with Cu(I) sites for promoting the activation of O₂ compared with dual-site Cu(II) and Co(II) and Co(II) and Co(II), thus contributing to the epoxidation of the C═C bond. When other kinds of alkenes are used as substrates, the excellent selectivity of various epoxides is also achieved over CuCo-MOF-74. We also prove the universality of fabricating Cu(I) sites in other MOF-74 with various divalent metal nodes.

Metal-Organic Frameworks Decorated Cu2O Heterogeneous Catalysts for Selective Oxidation of Styrene

The selective oxidation of styrene with highly efficient, environmentally benign, and cost-effective catalysts are of great importance for sustainable chemical processes. Here, we develop an in situ self-assembly strategy to decorate Cu-based metal-organic framework (MOF) Cu-BDC-NH2 nanocrystals on Cu2O octahedra to construct a series of Cu2O@Cu-BDC-NH2 catalysts for selective oxidation of styrene. Using H2O2 as green oxidants, the optimized sample of Cu2O@Cu-BDC-NH2-8h could achieve 85% styrene conversion with 76% selectivity of benzaldehyde under a mild condition of 40 °C. The high performance of the as-prepared heterogeneous catalysts was attributed to the well-designed Cu+/Cu2+ interface between Cu2O and Cu-BDC-NH2 as well as the porous MOF shells composed of the uniformly dispersed Cu-BDC-NH2 nanocrystals. The alkaline properties of Cu2O and the –NH2 modification of MOFs enable the reaction to be carried out in a base-free condition, which simplifies the separation process and makes the catalytic system more environmentally friendly. Besides the Cu2O octahedra (od-Cu2O), the Cu2O cuboctahedrons (cod-Cu2O) were synthesized by adjusting the added polyvinyl pyrrolidone, and the obtained cod-Cu2O@Cu-BDC-NH2 composite also showed good catalytic performance. This work provides a useful strategy for developing highly efficient and environmentally benign heterogeneous catalysts for the selective oxidation of styrene.

Kinetic Study of Styrene Oxidation over Titania Catalyst Supported on Sulfonated Fish Bone-derived Carbon

The kinetic evaluation of titania supported sulfonated fish bone-derived carbon (TiO2/SFBC) as a catalyst in styrene oxidation by aqueous hydrogen peroxide was carried out. The catalysts were prepared by carbonation of fishbone powder at varying temperatures 500, 600 and 700 °C, respectively for 2 h, followed by sulfonation with sulfuric acid (1M) for 24 h and impregnated by varied titania concentration 500, 1000 and 1500 µmol. The physical properties of catalysts were characterized using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Scanning Electron Microscope-Energy Dispersive X-Ray (SEM-EDX) and the nitrogen adsorption-desorption analysis. The catalytic activity result showed that TiO2/SFBC can be used as a potential catalyst in styrene oxidation. Worth noting that the sulfonation process has not only transformed the TiO2/FBC particulates (without sulfonation) to cuboid-shaped TiO2/SFBC (with sulfonation) but also contributed to the high selectivity of benzaldehyde. On the other hand, carbonization at different temperatures has an indistinct effect on catalytic performance due to their similar surface areas. The styrene conversion rate responded positively with the increasing amount of titania in the functionalized composites. The styrene oxidation by aqueous H2O2 unraveled the first-order reaction with the activation energy of ⁓63.5 kJ. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Confinement of nano-gold in 3D hierarchically structured gadolinium-doped ceria mesocrystal: synergistic effect of chemical composition and structural hierarchy in CO and propane oxidation

Gadolinium-doped ceria hierarchical gold catalyst shows four-fold TOF increase compared to undoped non-hierarchical system, proving the synergistic effect of doping and structural hierarchy in propane oxidation.