Covalent functionalization of graphene oxide with molybdenum-carboxylate complexes: New reusable catalysts for the epoxidation of olefins

Nickel Nanoparticles Decorated on Glucose-Derived Carbon Spheres as a Novel, Non-Palladium Catalyst for Epoxidation of Olefin

Carbon spheres supporting nickel nanoparticles (NPs), generated by the integration of hydrothermal and microwave irradiation techniques, catalyzed the epoxidation of 1-octene, cyclooctene, styrene, allyl alcohol, and cyclohexene. The average particle sizes of the carbon spheres (CSs) and nickel oxide species immobilized on the CSs were 240 nm and 26 nm, respectively. The fabricated composites incorporating nickel NPs showed higher activity in the cyclohexene epoxidation process. The cyclohexene conversion was enhanced by raising the Ni loading to 10%. Within 14 h, the cyclohexene conversion had grown to 98%. This robust catalytic activity can be attributed to the efficient distribution of Ni species on the CSs, the facile lowering of the surface, and the development of uniformly nanosized species. The composite exhibited good recyclability across at least five cycles (which is not a simple task involving nickel-nanoparticle-based catalysts that are employed in water), and no nickel species leached into the solution, making the total system environmentally benign and cost-effective.

Synthesis and Structure-Activity Characterization of a Single-Site MoO2 Catalytic Center Anchored on Reduced Graphene Oxide

Molecularly derived single-site heterogeneous catalysts can bridge the understanding and performance gaps between conventional homogeneous and heterogeneous catalysis, guiding the rational design of next-generation catalysts. While impressive advances have been made with well-defined oxide supports, the structural complexity of other supports and the nature of the grafted surface species present an intriguing challenge. In this study, single-site Mo(═O)₂ species grafted onto reduced graphene oxide (rGO/MoO₂) are characterized by XPS, DRIFTS, powder XRD, N₂ physisorption, NH₃-TPD, aqueous contact angle, active site poisoning assay, Mo EXAFS, model compound single-crystal XRD, DFT, and catalytic performance. NH₃-TPD reveals that the anchored MoO₂ moiety is not strongly acidic, while Mo 3d_5/2 XPS assigns the oxidation state as Mo(VI), and XRD shows little rGO periodicity change on MoO₂ grafting. Contact angle analysis shows that MoO₂ grafting consumes rGO surface polar groups, yielding a more hydrophobic surface. The rGO/MoO₂ DRIFTS assigns features at 959 and 927 cm^-1 to the symmetric and antisymmetric Mo═O stretching modes, respectively, of an isolated cis-(O═Mo═O) moiety, in agreement with DFT computation. Moreover, the Mo EXAFS rGO/MoO₂ structural data are consistent with isolated (C-O)₂-Mo(═O)₂ species having two Mo═O bonds and two Mo-O bonds at distances of 1.69(3) and 1.90(3) Å, respectively. rGO/MoO₂ is also more active than the previously reported AC/MoO₂ catalyst, with reductive carbonyl coupling TOFs approaching 1.81 × 10³ h^-1. rGO/MoO₂ is environmentally robust and multiply recyclable with 69 ± 2% of the Mo sites catalytically significant. Overall, rGO/MoO₂ is a structurally well-defined and versatile single-site Mo(VI) dioxo heterogeneous catalytic system.

A recyclable cobalt(iii)–ammonia complex catalyst for catalytic epoxidation of olefins with air as the oxidant

A recyclable [Co(NH₃)₆]Cl₃ complex was synthesized to catalyze the epoxidation of α-pinene. With air as the oxidant, [Co(NH₃)₆]Cl₃ obtained 97.4% conversion of α-pinene and 98.3% selectivity of epoxide.

Recent Progress in Application of Molybdenum-Based Catalysts for Epoxidation of Alkenes

Epoxides are important industrial intermediates applied in a variety of industrial processes. During the production of epoxides, catalysts have played an irreplaceable and unique role. In this review, the historic progress of molybdenum-based catalysts in alkene epoxidation are covered and an outlook on future challenge discussed. Efficient catalysts are demonstrated including soluble molybdenum complexes, polyoxometalates catalysts, molybdenum-containing metal organic frameworks, silica supported molybdenum-based catalysts, polymer supported molybdenum-based catalysts, magnetic molybdenum-based catalysts, hierarchical molybdenum-based catalysts, graphene-based molybdenum containing catalysts, photocatalyzed epoxidation catalysts, and some other systems. The effects of different solvents and oxidants are discussed and the mechanisms of epoxidation are summarized. The challenges and perspectives to further enhance the catalytic performances in alkenes epoxidation are presented.