Abstract
In recent years, metal–organic frameworks (MOFs) have received increasing attention as selective oxidation catalysts and supports for their construction. In this short review paper, we survey recent findings concerning use of MOFs in heterogeneous liquid-phase selective oxidation catalysis with the green oxidant–aqueous hydrogen peroxide. MOFs having outstanding thermal and chemical stability, such as Cr(III)-based MIL-101, Ti(IV)-based MIL-125, Zr(IV)-based UiO-66(67), Zn(II)-based ZIF-8, and some others, will be in the main focus of this work. The effects of the metal nature and MOF structure on catalytic activity and oxidation selectivity are analyzed and the mechanisms of hydrogen peroxide activation are discussed. In some cases, we also make an attempt to analyze relationships between liquid-phase adsorption properties of MOFs and peculiarities of their catalytic performance. Attempts of using MOFs as supports for construction of single-site catalysts through their modification with heterometals will be also addressed in relation to the use of such catalysts for activation of H2O2. Special attention is given to the critical issues of catalyst stability and reusability. The scope and limitations of MOF catalysts in H2O2-based selective oxidation are discussed.
Highlights
In the quest for sustainable and green production of valuable chemicals, an important goal is the development of economic and ecologically sound oxidation processes using benign and readily available oxidizing agents [1,2,3]
Metal–organic frameworks (MOFs) are an emerging class of materials composed of metal ions or, more frequently, clusters connected by multidentate organic linkers into a regular porous structure
While studying catalytic activity of UiO-66 prepared by different methodologies and differing in their crystallinity for the oxidative desulfurization of fuel, Granadeiro and coworkers have found that all the samples reveal superior selectivity toward the formation of sulfones [78]
Summary
In the quest for sustainable and green production of valuable chemicals, an important goal is the development of economic and ecologically sound oxidation processes using benign and readily available oxidizing agents [1,2,3]. The majority of works in this area deal with the use of molecular oxygen or anhydrous alkyl hydroperoxides as oxidants while not so many are devoted to oxidation catalysis with H2 O2 This is not surprising if we remember that aqueous hydrogen peroxide possesses oxidizing and hydrolyzing and strong complexing ability, which is a threat to the structure of most MOFs, especially at elevated temperatures. Discoveries of MOFs having outstanding chemical and thermal stability, especially Zr-based ones, are currently changing the situation [44,45] In this short review paper, we survey recent findings concerning use of MOFs as heterogeneous catalysts for selective oxidations using H2 O2 , with special attention drawn to the mechanistic aspects of the oxidation reactions and stability/reusability issues.
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