Heterogeneous oxidation of alcohols with hydrogen peroxide catalyzed by polyoxometalate metal–organic framework

Co@Co Cages Engineered from Hollowing MOFs for Enhanced Hydrogen Evolution Reaction Performance

Advances in hollow engineering of metal-organic frameworks (MOFs) have enabled a variety of applications in catalysts, sensors, and batteries, but the hollow derivatives are often limited to hydroxides, oxides, selenides, and sulfides with the presence of additional elements from the environment. Here we have successfully synthesized hollow metallic Co@Co cages through a facile two-step strategy. Interestingly, the Co@Co(C) cages with a small amount of residual carbon show excellent catalytic performance due to the abundant exposed active sites and fast charge transfer. During the hydrogen evolution reaction, the overpotential of Co@Co(C) is as low as ∼54 mV at the current density of 10 mA cm^-2, which is close to that of ∼38 mV for the Pt/C electrodes. The two-step synthesis strategy opens up opportunities for increasing the number of catalytic active sites and rates of charge/mass transfer while pushing the limits of materials utilization beyond that achieved in existing MOF-based nanostructures.

MOF/POM hybrids as catalysts for organic transformations

Insertion of molecular metal oxides, e.g. polyoxometalates (POMs), into metal-organic frameworks (MOFs) opens up new research opportunities in various fields, particularly in catalysis. POM/MOF composites have strong acidity, oxygen-rich surface, and redox capacity due to typical characteristics of POMs and the large surface area, highly organized structures, tunable pore size, and shape are due to MOFs. Such hybrid materials have gained a lot of attention due to astonishing structural features, and hence have potential applications in organic catalysis, sorption and separation, proton conduction, magnetism, lithium-ion batteries, supercapacitors, electrochemistry, medicine, bio-fuel, and so on. The exceptional chemical and physical characteristics of POMOFs make them useful as catalysts in simple organic transformations with high capacity and selectivity. Here, the thorough catalytic study starts with a brief introduction related to POMs and MOFs, and is followed by the synthetic strategies and applications of these materials in several catalytic organic transformations. Furthermore, catalytic conversions like oxidation, condensation, esterification, and some other types of catalytic reactions including photocatalytic reactions are discussed in length with their plausible catalytic mechanisms. The disadvantages of the POMOFs and difficulties faced in the field have also been explored briefly from our perspectives.

POM@MOF Hybrids: Synthesis and Applications

The hybrid materials that are created by supporting or incorporating polyoxometalates (POMs) into/onto metal–organic frameworks (MOFs) have a unique set of properties. They combine the strong acidity, oxygen-rich surface, and redox capability of POMs, while overcoming their drawbacks, such as difficult handling, a low surface area, and a high solubility. MOFs are ideal hosts because of their high surface area, long-range ordered structure, and high tunability in terms of the pore size and channels. In some cases, MOFs add an extra dimension to the functionality of hybrids. This review summarizes the recent developments in the field of POM@MOF hybrids. The most common applied synthesis strategies are discussed, together with major applications, such as their use in catalysis (organocatalysis, electrocatalysis, and photocatalysis). The more than 100 papers on this topic have been systematically summarized in a handy table, which covers almost all of the work conducted in this field up to now.

Heterogeneous catalysis by tungsten-based heteropoly compounds

In this review, the recent works on heterogeneous catalytic applications of polyoxotungstates in liquid-phase organic reactions are reviewed.

Sandwich type polyoxometalates encapsulated into the mesoporous material: synthesis, characterization and catalytic application in the selective oxidation of sulfides

The A-type sandwich polyoxometalates of [(HOSn^IVOH)₃(PW₉O₃₄)₂]¹²⁻ (P₂W₁₈Sn₃) and [(OCe^IVO)₃(PW₉O₃₄)₂]¹²⁻ (P₂W₁₈Ce₃) were immobilized for the first time into the porous metal–organic framework MIL-101(Cr). FT-IR, powder X-ray diffraction, SEM-EDX, ICP analysis, N₂ adsorption and thermogravimetric analysis collectively confirmed immobilization and good distribution of polyoxometalates into cages of MIL-101(Cr). The catalytic activities of the homogeneous P₂W₁₈Sn₃ and P₂W₁₈Ce₃ and the corresponding heterogeneous catalysts were examined in the oxidation of sulfides to sulfones with H₂O₂ as the oxidant at room temperature. The effects of different dosages of polyoxometalates, type of solvent, reaction time, amount of catalyst and oxidant in this catalytic system were investigated. The new P₂W₁₈Sn₃@MIL-101 and P₂W₁₈Ce₃@MIL-101 nanocomposites exhibited good recyclability and reusability in at least five consecutive reaction cycles without significant loss of activity or selectivity.

The A-type sandwich POMs of [(HOSn^IVOH)₃(PW₉O₃₄)₂]^12– (P₂W₁₈Sn₃) and [(OCe^IVO)₃(PW₉O₃₄)₂]^12– (P₂W₁₈Ce₃) were immobilized for the first time into the porous MIL-101 MOF. Their catalytic activities were examined in the oxidation of sulfides to sulfones at room temperature.

Recent advances in the field of selective epoxidation of vegetable oils and their derivatives: a review and perspective

The present critical review reports the recent progress of the last 15 years in the selective epoxidation of vegetable oils and their derivatives, in particular unsaturated fatty acids (UFAs) and fatty acid methyl esters (FAMEs).