Effect of Water Concentration and Acidity on the Synthesis of Porous Chromium Benzenedicarboxylates

Methanation of CO2 Using MIL-53-Based Catalysts: Ni/MIL-53–Al2O3 versus Ni/MIL-53

MIL-53 and the MIL-53–Al2O3 composite synthesized by a solvothermal procedure, with water as the only solvent besides CrCl3 and benzene-1,4-dicarboxylic acid (BDC), were used as catalytic supports to obtain the novel MIL-53-based catalysts Ni(10 wt.%)/MIL-53 and Ni(10 wt.%)/MIL-53–Al2O3. Ni nanoparticle deposition by an adapted double-solvent method leads to the uniform distribution of metallic particles, both smaller (≤10 nm) and larger ones (10–30 nm). MIL-53–Al2O3 and Ni/MIL-53–Al2O3 show superior thermal stability to MIL-53 and Ni/MIL-53, while MIL-53–Al2O3 samples combine the features of both MIL-53 and alumina in terms of porosity. The investigation of temperature’s effect on the catalytic performance in the methanation process (CO2:H2 = 1:5.2, GHSV = 4650 h−1) revealed that Ni/MIL-53 is more active at temperatures below 300 °C, and Ni/MIL-53–Al2O3 above 300 °C. Both catalysts show maximum CO2 conversion at 350 °C: 75.5% for Ni/MIL-53 (methane selectivity of 93%) and 88.8% for Ni/MIL-53–Al2O3 (methane selectivity of 98%). Stability tests performed at 280 °C prove that Ni/MIL-53–Al2O3 is a possible candidate for the CO2 methanation process due to its high CO2 conversion and CH4 selectivity, corroborated by the preservation of the structure and crystallinity of MIL-53 after prolonged exposure in the reaction medium.

Iron and chromium MOFs as sustainable catalysts for transfer hydrogenation of carbonyl compounds and biomass conversions

Fe and Cr based MOFs (MIL-88B) act as efficient and reusable catalysts for transfer hydrogenation of carbonyl compounds including bio-derived substrates.

Hybrid MIL-101(Cr)@MIL-53(Al) composite for carbon dioxide capture from biogas

In this study, hybrids of nanoporous MIL-101(Cr) and MIL-53(Al) were synthesized using a hydrothermal method for various time periods, ranging from 8 to 40 h. The prepared materials were characterized by powder X-ray diffraction (PXRD) and elemental analysis, and their specific surface areas were measured by N₂ sorption at 77 K using the Brunauer–Emmett–Teller (BET) method. To investigate the practical application of these materials, the pure carbon dioxide and methane adsorption capacities of the samples were determined using the volumetric method. The Langmuir model was used to fit the CO₂ and CH₄ isotherms. Extended Langmuir (EL) equations and the ideal adsorbed solution theory (IAST) models were used to obtain the CO₂/CH₄ selectivity. The sample with the highest BET specific surface area was selected as a candidate for further investigations. The thermal stability of the selected sample was investigated by thermogravimetric analysis (TGA). Scanning electron microscopy (SEM) was used to characterize the sample morphology. XRD results showed that the sample synthesized over the shortest time corresponded to MIL-101(Cr), while the sample synthesized over the longest time was in agreement with MIL-53(Al). Samples synthesized for time periods between these two limits were assumed to be composites of both MIL-53(Al) and MIL-101(Cr). TGA results indicated that the hybrid materials were thermally stable at temperatures about 100 °C higher than for pure MIL-101(Cr). The BET specific surface area (1746 m² g⁻¹) and CO₂ adsorption capacity (16 mmol g⁻¹) of the selected hybrid sample were about 50% and 35% higher, respectively, compared with those of pure MIL-53(Al), but 30% and 20% lower, respectively, compared with those of pure MIL-101(Cr). Binary adsorption modeling showed the high selectivity of the MIL-101(Cr) and MIL-53(Al) hybrid material for CO₂ with a minimum separation factor of about 60 at 298 K. This value was much higher than those reported previously and those observed in this work for the original MIL-101(Cr) or MIL-53(Al). These results demonstrated that the hybrid of MIL-101(Cr) and MIL-53(Al) was a promising material for selective CO₂ capture from natural and biogas.

In this study, hybrids of nanoporous MIL-101(Cr) and MIL-53(Al) were synthesized using a hydrothermal method for various time periods, ranging from 8 to 40 h.

Microwave induced “egg yolk” structure in Cr/V-MIL-53

Using a one pot microwave procedure, mixed-metal “egg yolk” MOFs are created, with a core of (Cr/V)-MIL-53 and a shell of Cr-MIL-53.

Substitution reactions in metal–organic frameworks and metal–organic polyhedra

This review summarizes the advances in the study of substitution reactions in metal–organic frameworks (MOFs) and metal–organic polyhedra (MOPs).

Organophophorous ester degradation by chromium(III) terephthalate metal-organic framework (MIL-101) chelated to N,N-dimethylaminopyridine and related aminopyridines

Porous materials based on chromium(III) terephthalate metal organic frameworks (MOF) MIL-101(Cr) and their complexes with dialkylaminopyridines (DAAP) were synthesized via a DAAP-MOF complexation, and tested for hydrolytic degradation of organophosphorous esters such as diethyl 4-nitrophenyl phosphate (paraoxon). Elemental analysis, TGA, XRD, FT-IR, TEM, SEM, and nitrogen adsorption measurements indicated that the DAAP units were incorporated into MIL-101 pores by complexation, keeping the parent framework intact. The DAAP-MOF enabled facile paraoxon hydrolysis in water/acetonitrile mixtures under ambient conditions (100% conversion after 24 h at pH 10). The MOF-DAAP complexes showed synergistic effects, being 7-fold and 47-fold more active than the parent MIL-101 or DAAP materials, respectively. The high hydrolysis reaction turnover was realized by simultaneous action of the Lewis acid Cr(III) center of the MOF as well as the electron-rich nucleophile, DAAP. This study demonstrates a simple and efficient method of generating catalytically active MOF materials for environmental detoxification as well as defensive applications.

Adsorptive removal of methyl orange from aqueous solution with metal-organic frameworks, porous chromium-benzenedicarboxylates

Two typical highly porous metal-organic framework (MOF) materials based on chromium-benzenedicarboxylates (Cr-BDC) obtained from Material of Institute Lavoisier with special structure of MIL-101 and MIL-53 have been used for the adsorptive removal of methyl orange (MO), a harmful anionic dye, from aqueous solutions. The adsorption capacity and adsorption kinetic constant of MIL-101 are greater than those of MIL-53, showing the importance of porosity and pore size for the adsorption. The performance of MIL-101 improves with modification: the adsorption capacity and kinetic constant are in the order of MIL-101 Collapse

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Affiliation(s)

Enamul Haque Department of Chemistry, Kyungpook National University, Daegu 702-701, Republic of Korea
Ji Eun Lee
In Tae Jang
Young Kyu Hwang
Jong-San Chang
Jonggeon Jegal
Sung Hwa Jhung

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