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Highly dispersed molybdenum trioxide were loaded in three-dimensional dendritic mesoporous silica nanospheres (MoO3@3D-DMSNs) by one-pot method. The mesoporous silica nanospheres with central radical channels were obtained through the interaction of bisurfactant and molybdenum source and the as-synthesized MoO3@3D-DMSNs were characterized by specific tests. As a result, the as-prepared MoO3@3D-DMSNs exhibited better catalytic performance for epoxidation of olefins. When the molar ratio value of Mo and Si is 5%, the specific surface area (SBET = 185.8 m2/g) and pore volume (Vp = 0.46 cm3/g) of MoO3@3D-DMSNs reach a maximum, and the catalytic activity is the best for the epoxidation of cyclooctene. The conversion could reach 84% with a selectivity above 98% after 6 h. The better catalytic performance can be maintained after five reaction-regeneration cycles. The dendritic mesoporous structure can be well preserved after recycling. Additionally, olefins with electron-absorbing group exhibit better catalytic activity with MoO3@3D-DMSNs-5 as catalyst. Hence, MoO3@3D-DMSNs catalysts with the center-radial oriented channel exhibit good activity and stability. The central radial channel can effectively disperse the active center MoO3 and play a key role in the transmission and accessibility of substrates, and it would have a good application prospect in the catalytic reactions.

A facile post-synthetic strategy was developed to functionalize the preformed hollow mesoporous silica spheres by encapsulating the molybdenum dioxide (MoO2) nanoparticles inside the interior cavity. Hollow mesoporous silica spheres were prepared and employed as carriers, and the encapsulation of MoO2 nanoparticles was achieved through a one-pot hydrothermal protocol. After characterization, the encapsulated MoO2 nanoparticles were certified to be ultrafine and highly dispersed, which greatly promoted the catalytic activity. The as-prepared catalysts were utilized in epoxidation of alkenes and exhibited as a promising catalyst in this reaction. After reacting for 10 h, the optimal catalyst MoO2@SiO2-1 achieved a conversion above 95% and selectivity above 95%, respectively. Moreover, the catalysts also exhibited good reusability, conversion of 78% and selectivity of 89% (reaction time 4 h) were still obtained after recycling for 5 times. Meanwhile, the employed facial and efficient hydrothermal approach could be expanded to other molybdenum modified heterogeneous catalysts in various applications. Keywords: Post-synthesis, Ultrafine, Molybdenum dioxide, Alkene, Epoxidation

Functionalization of vegetable oils (VOs) including edible, non-edible, and waste cooking oil (WCOs) to epoxides (EVOs) is receiving great attention by many researchers from academia and industry because they are renewable, versatile, sustainable, non-toxic, and eco-friendly, and they can partially or totally replace harmful phthalate plasticizers. The epoxidation of VOs on an industrial scale has already been developed by the homogeneous catalytic system using peracids. Due to the drawbacks of this method, other systems including acidic ion exchange resins, polyoxometalates, and enzymes are becoming alternative catalysts for the epoxidation reaction. We have reviewed all these catalytic systems including their benefits and drawbacks, reaction mechanisms, intensification of each system in different ways as well as the physicochemical properties of VOs and EVOs and new findings in recent years. Finally, the current methods including titrimetric methods as well as ATR-FTIR and 1H NMR for determination of conversion, epoxidation, and selectivity of epoxidized vegetable oils (EVOs) are also briefly described.

Polymeric carbon nitride (C3N4) is currently the most potential nonmetallic photocatalyst, but it suffers from low catalytic activity due to rapid electron–hole recombination behavior and low specific surface area. The morphology control of C3N4 is one of the effective methods used to achieve higher photocatalytic performance. Here, bulk, lamellar and coralloid C3N4 were synthesized using different chemical methods. The as-prepared coralloid C3N4 has a higher specific surface area (123.7 m2 · g−1) than bulk (5.4 m2 · g−1) and lamellar C3N4 (2.8 m2 · g−1), thus exhibiting a 3.15- and 2.59-fold higher photocatalytic efficiency for the selective oxidation of benzyl alcohol than bulk and lamellar C3N4, respectively. Optical characterizations of the photocatalysts suggest that coralloid C3N4 can effectively capture electrons and accelerate carrier separation, which is caused by the presence of more nitrogen vacancies. Furthermore, it is demonstrated that superoxide radicals (·O2 −) and holes (h+) play major roles in the photocatalytic selective oxidation of benzyl alcohol using C3N4 as a photocatalyst.

A general thermal decomposition strategy is reported to fabricate MoO3@SiO2 nanoreactors, with a mesoporous silica shell and embedded MoO3 nanoparticles. The novel preparation procedure involves mixing certain mass ratio of (NH4)6Mo7O24·4H2O (AMM) and hollow mesoporous silica spheres (HMSS) by grinding, fusion and thermal decomposition of (NH4)6Mo7O24·4H2O under calcination and removing the residual via filtration. The as-prepared MoO3@SiO2 nanoreactors were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), N2 adsorption/desorption and X-ray photoelectron spectra (XPS). The nanoreactors were utilized in epoxidation of alkenes and displayed high catalytic activity and stability. The mass ratio of AMM and HMSS greatly affected the properties and catalytic performance of the nanoreactors. The optimal mass ratio of AMM: HMSS has been confirmed as 1/2. After reacting for 12 h with H2O2 (50 wt%) as oxidant, conversion and selectivity of optimal MoO3@SiO2-400-1/2 almost reached up to 98% and 99%, respectively. Furthermore, the catalyst still had high conversion (78%) and selectivity (95%) at 4 h epoxidation of cyclooctene after recycling for 6 runs. Kinetics study was also carried out and demonstrated the epoxidation of alkenes follows the first order model.

In this study, the flower-like Bi2WO6 with oxygen vacancies were synthesized by using the anionic and cationic dual surfactants strategy. The study results indicate that the synergistic effect of dual surfactants provides more oxygen vacancies for Bi2WO6, which leads to a narrower band gap, an expanded light response range, and an improved separation efficiency of photogenerated charges in Bi2WO6. In the experiment of photocatalytic selective oxidation benzyl alcohol, Bi2WO6 with dual surfactants shows excellent photocatalytic activity. Especially when the molar rate of CTAB to SDS is 2, the conversion of benzyl alcohol overs 90%, which is 1.74-fold than that of pure Bi2WO6. Meanwhile, Bi2WO6 with dual surfactants also exhibits better photocatalytic efficiency for other aromatic alcohols. Furthermore, the free radical capture experiments show that superoxide radical (•O2−) and hole (h+) play a major role in the photocatalytic selective oxidation of benzyl alcohol.

A lamellar porous Mo-modified carbon nitride polymers (CN-Mo) was successfully prepared by a simple bottom-up method, which involves molecule self-assembly by hydrogen bonding between uracil and melamine. Analysis Results of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectra (XPS) show that Mo element has been doped in the skeleton of carbon nitride. The optical characterization results of the as-prepared photocatalysts show that, CN-Mo has a suitable band structure that can promote the separation of carriers and expands the absorption of light. Compared with CN, CN-Mo has better photocatalytic activity for epoxidation of olefins. When the mass value (relative to melamine) of ammonium molybdate tetrahydrate is 2 %, the photocatalytic efficiency is the best for the epoxidation of styrene. And the conversion rate of styrene reaches 38.4 % and the selectivity of styrene oxide is up to 83.2 %. In addition, it can maintain the better photocatalytic performance for the epoxidation of styrene after five reaction-regeneration cycles. This finding provides an effective development direction for photocatalytic olefins epoxidation under mild conditions.

The efficient catalysts were designed to allow the entry and release of reactants and products into the mesoporous SBA-15 in which the active sites, peroxophosphotungstate, were entrapped by silylation with three different silylating agents (C3, C5, and C8 arm). The as-prepared catalysts were characterized by elemental analysis, ICP analysis, TGA, XRD, N2 adsorption/desorption, SEM, TEM, and FT-IR spectra. Their catalytic performances were tested for the epoxidation of soybean oil using different parameters such as temperature, H2O2 to unsaturation molar ratio, catalyst loading and stirring speed. The resulting epoxidized soybean oil was analyzed qualitatively and quantitatively by FT-IR and 1HNMR. The results confirmed that the catalyst silylated with C8 arm is promising for the synthesis of epoxides of long-chain carbon and reusable at least three times without obvious decrease in activity. Moreover, use of H2O2 oxidant and free of solvent in the epoxidation reaction are the main advantages of these catalysts.

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.