Samiran Bhattacharjee

Chromium terephthalate metal–organic framework MIL-101: synthesis, functionalization, and applications for adsorption and catalysis

The chromium terephthalate metal–organic framework, MIL-101 (MIL, Material Institut Lavoisier), is comprised of trimeric chromium(III) octahedral clusters interconnected by 1,4-benzenedicarboxylates, resulting in a highly porous 3-dimentional structure. The large pores (29 and 34 A) and high BET surface area (>3000 m2 g−1) with a huge cell volume (≈702 000 A3) together with the coordinatively unsaturated open metal sites that can be subjected to diverse post-synthesis functionalization or guest encapsulation, and excellent hydrothermal/chemical stability, make MIL-101 particularly attractive for applications, such as selective gas adsorption/separation, energy storage and heterogeneous catalysis. This paper reviews the current status of research and development on the synthesis, functionalization and applications of MIL-101 for adsorption/catalytic reactions.

Zeolitic Imidazolate Frameworks: Synthesis, Functionalization, and Catalytic/Adsorption Applications

Zeolitic imidazolate frameworks (ZIFs) are comprised of transition metal ions (Zn, Co) and a range of imidazolate linkers in a tetrahedral coordination similar to that in crystalline aluminosilicate zeolites. The high surface area, tunable nanoporosity that can be subject to functionalization and the excellent thermal/chemical stability of ZIFs are attractive for heterogeneous catalysis and selective gas adsorption/separation. This review presents the current trends in synthesis, surface modification and catalytic reactions/adsorption of ZIF-based materials with particular emphasis on ZIF-8, which is the most widely studied structure among ZIFs.

CrAPO-5 catalysts having a hierarchical pore structure for the selective oxidation of tetralin to 1-tetralone

A novel CrAPO-5 material having a unique microporous–mesoporous hierarchical pore structure (CrAPO-5H) was synthesized using an organosilane surfactant to conventional CrAPO-5 reaction mixture by a one-step hydrothermal process. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), N2-adsorption isotherm and UV-visible diffuse reflectance spectroscopy, and employed as a catalyst for the liquid phase oxidation of tetralin. CrAPO-5H produced higher activity than conventional microporous CrAPO-5. Acylperoxy radicals, in situ generated from trimethylacetaldehyde and O2, were more effective as oxidant than tert-butyl hydroperoxide (t-BuOOH); 88% conversion of tetralin with 97% selectivity to 1-tetralone was obtained with the former, whereas 57% conversion with 86% selectivity was achieved using the latter at 80 °C after 8 h. The effect of reaction temperature, Cr content, solvent, and the type of aldehyde employed for the in situ generation of acylperoxy radicals on catalytic performance was investigated. Activities of CrAPO-5H remained constant after 1st catalyst recycle. A hot filtration experiment coupled with a blank test revealed that oxidation proceeded mostly on Cr sites in the CrAPO-5H, but a minor contribution from trace amount of leached Cr could not be ruled out.

Post-synthesis functionalization of a zeolitic imidazolate structure ZIF-90: a study on removal of Hg(II) from water and epoxidation of alkenes

Thiol-functionalized ZIF-90 (ZIF-90-SH) was prepared via condensation of the free aldehyde group of ZIF-90 with 2-mercaptoethylamine to an imine through a one-step post-synthesis route. A subsequent reaction with manganese(II) acetate resulted in the formation of a new Mn(II)-immobilized hybrid material (ZIF-90-S[Mn]). This material was characterized by chemical analysis, X-ray diffraction, N2 adsorption–desorption, thermogravimetric analysis and Fourier transform infrared spectroscopy, which confirmed the successful functionalization of the as-synthesized ZIF-90. ZIF-90-SH employed as an adsorbent for the removal of Hg(II) ions from an aqueous solution at room temperature exhibited an adsorption capacity of ca. 22.4 mg g−1. The material showed 96–98% removal of Hg(II) ions in a low concentration range (0.1 to 10.0 mg L−1). ZIF-90-S[Mn] showed good catalytic activity and selectivity in the epoxidation of several important alkenes using molecular oxygen under atmospheric pressure. Recycling and hot filtration experiments coupled with a blank test showed that epoxidation proceeded over ZIF-90-S[Mn] on the external surface of the ZIF-90 matrices, where the active Mn(II) sites were located. The catalyst could be recycled up to four times without significant loss of efficiency.

Synthesis of a sulfonato-salen-nickel(II) complex immobilized in LDH for tetralin oxidation

A novel sulfonato-salen-nickel(II) complex has been immobilized on a Zn(II)-Al(III) layered double hydroxide (LDH) host. XRD, FT-IR, TGA and UV-vis spectroscopy, as well as chemical analysis, confirmed the successful incorporation of the nickel-salen complex within the LDH structure. BET surface area measurements, SEM and TEM were also used to characterize the heterogenized catalyst. The sulfonato-salen-nickel(II) complex-immobilized material, LDH-[nickel-salen], was found to be effective in the oxidation of tetralin, where a combination of trimethylacetaldehyde and dioxygen at atmospheric pressure was employed as the oxidant. At 72.3% conversion, tetralin was converted to 1-tetralone with 72.2% selectivity at 70 °C after 7 h. Tetralin oxidation using tert-butyl hydroperoxide afforded a lower conversion and selectivity of 1-tetralone than with trimethylacetaldehyde and dioxygen as the oxidant. The effect of various reaction parameters on catalytic performance was also investigated. A hot filtration experiment coupled with a blank test revealed that oxidation proceeded mostly on nickel-salen sites in LDH-[nickel-salen]. A reaction mechanism is proposed based on the experimental results.

Metal–Organic Frameworks for Catalysis

Metal–organic frameworks (MOFs) are a relatively new class of porous material, which are comprised of metal ions or clusters linked with poly-functional organic molecules. MOFs have been studied increasingly for heterogeneous catalysis applications because these hybrid materials have well-ordered tunable porous structures with exceptional textural properties and introduction of additional active sites can be carried out easily by relatively simple post-synthesis functionalization. This short review focuses on recent works on liquid phase catalytic reactions carried out over selected MOFs. The MOF membranes for catalysis and the potential of functionalized MOF materials for chiral reactions are also mentioned briefly.