Search

2-Methylfuran obtained viathe hydrogenation of furfural is an important biomass-derived liquid fuel. However, the large-scale production of 2-methylfuran from furfural requires cost-effective, active, and selective heterogeneous catalysts. Herein, we have performed experimental and DFT investigations on MFe2O4(M = Cu2+, Ni2+, and Fe2+) inverse spinel catalysts to selectively hydrogenate furfural into 2-methylfuran viatransfer hydrogenation, and to determine the nature of active sites. CuFe2O4afforded 99.4% furfural conversion and 97.6% 2-methylfuran selectivity at 200 °C in 1.5 h. In contrast, NiFe2O4and Fe3O4catalysts afforded furfuryl alcohol as a major product. The comprehensive characterization of the catalysts revealed that the acidity of these inverse spinel catalysts originates from the Lewis acid sites. Further, the strength of Lewis acid sites and the associated catalytic activity trend directly correlate with the binding energy of Fen+ions in MFe2O4catalysts. DFT calculations revealed the energetically favorable interactions of furfural and furfural alcohol with the Fe3+sites of Fe3O4and Fe sites (most likely Fe3+) of CuFe2O4and NiFe2O4catalysts, whereas Cu2+and Ni2+sites present in CuFe2O4and NiFe2O4catalysts have stronger interactions with the isopropanol molecule. Hence, it is proposed that the Fe3+sites present in CuFe2O4are the active Lewis acid centers to selectively convert furfural into 2-methylfuran viatransfer hydrogenation. Literature reports on the metal oxide catalyzed transfer hydrogenation of furfural into 2-methylfuran are rare. The present findings on the elucidation of the active sites of cost-effective, recyclable mixed metal oxide catalysts for the selective transfer hydrogenation of furfural into 2-methylfuran using isopropanol are attractive from the green chemistry perspective, and therefore extremely important for the academic catalysis community and to industrialists.

The selective carbon capture and utilization (CCU) as a one-carbon (C1) feedstock offers dual advantages for mitigating the rising atmospheric CO2content and producing fine chemicals/fuels. In this context, herein, we report the application of a porous bipyridine-functionalized, pyrene-based covalent organic framework (Pybpy-COF) for the stable anchoring of catalytic Ag(0) nanoparticles (NPs) and its catalytic investigation for fixation of CO2to commodity chemicals at ambient conditions. Notably, Ag@Pybpy-COF showed excellent catalytic activity for the carboxylation of various terminal alkynes to corresponding alkynyl carboxylic acids/phenylpropiolic acids via C–H bond activation under atmospheric pressure conditions. Besides, carboxylative cyclization of various propargylic amines with CO2to generate 2-oxazolidinones, an important class of antibiotics, has also been achieved under mild conditions. This significant catalytic activity of Ag@Pybpy-COF with wide functional group tolerance is rendered by the presence of highly exposed, alkynophilic Ag(0) catalytic sites decorated on the pore walls of high surface area (787 m2g–1) Pybpy-COF. Further, density functional theory calculations unveiled the detailed mechanistic path of the Ag@Pybpy-COF-catalyzed transformation of CO2to alkynyl carboxylic acids and 2-oxazolidinones. Moreover, the catalyst showed high recyclability for several cycles of reuse without significant loss in its catalytic activity and structural rigidity. This work demonstrates the promising application of Pybpy-COF for stable anchoring of Ag NPs for successful transformation of CO2to valuable commodity chemicals at ambient conditions.

The continuous depletion of lithium resources has drawn great attention toward the development of nonlithium rechargeable batteries having electrode materials that prove to be promising in delivering advantages of cost-effectiveness, a high charge/discharge rate, and excellent storage capacity. Because of its planar honeycomb structure, a 2-D monolayer of siligraphene SiC7has been explored as an electrode material for Na-ion batteries on the basis of its geometric, structural, and electrochemical properties by employing van der Waals corrected first-principles calculations based on density functional theory. Its dynamic and thermal stability is well validated using phonon dispersion spectra and ab initiomolecular dynamics. A direct band gap of 0.7 eV presents it as a semiconductor material effective to be used as an electrode. Potential adsorption sites on the surface of SiC7are studied for their effective storage capacity. Bader charge analysis revealed the charge transfer between the monolayers upon adsorption of Na ions. A high Na storage capacity of 696 mA h/g is obtained along with a low diffusion barrier of 0.8 eV, which further facilitates easy diffusivity of Na ions through the monolayers. Additionally, a working voltage of 0.84 V reveals that SiC7will be a potential candidate for anodes in Na-ion batteries.

The need for sustainable energy fuel is much higher than before. The use of hydrogen as a fuel is impeded due to its low storage capacity in the storage medium. In this work, a newly designed metal–carbyne framework (MCF) is decorated with Li atoms with an average Li binding energy of 1.94 eV. Two Li atoms are used to decorate each carbyne linker of the MCF. Here, using density functional theory calculations, we systematically investigated the adsorption of H2in Li-decorated MCF, namely MCFLi8. It is found that four H2molecules are adsorbed in the molecular form on each Li in MCFLi8by Niu’s charge polarization mechanism. Our findings revealed that the Li-decorated MCF exhibits a high hydrogen storage capacity at ambient conditions with adsorption–desorption energy ranging between 0.2 and 0.6 eV. Hirshfeld charge analysis and electrostatic potential maps show the charge transfer mechanism during the hydrogen adsorption. Born–Oppenheimer molecular dynamics simulations reveal the reversibility of adsorbed hydrogen at ideal pressure and temperature conditions. Thermodynamic usable capacity of adsorbed hydrogen at adsorption and desorption conditions is determined by calculating hydrogen occupation number. The gravimetric hydrogen density of 11.1 wt % is found for complete H2adsorbed in MCFLi8. This study suggests that Li-decorated MCF can be a promising hydrogen storage material.

Highly porous, polyhedral metal–organic frameworks (MOFs) of Co(II)/Ni(II), {[M6(TATAB)4(DABCO)3(H2O)3]·12DMF·9H2O}n(where M = Co(II) (1)/Ni(II) (2), H3TATAB = 4,4′,4″-s-triazine-1,3,5-triyl-tri-p-aminobenzoic acid, and DABCO = 1,4-diazabicyclo[2.2.2]octane) have been synthesized solvothermally. Both MOFs 1and 2show a 2-fold interpenetrated 3D framework structure composed of dual-walled cages of dimension ∼ 30 Å functionalized with a high density of Lewis acidic Co(II)/Ni(II) metal sites and basic -NH- groups. Interestingly, MOF 1shows selective adsorption of CO2with high heat of adsorption (Qst) value of 39.7 kJ/mol that is further supported by theoretical studies with computed binding energy (BE) of 41.17 kJ/mol. The presence of the high density of both Lewis acidic and basic sites make MOFs 1/2ideal candidate materials to carry out co-catalyst-free cycloaddition of CO2to epoxides. Consequently, MOFs 1/2act as excellent recyclable catalysts for cycloaddition of CO2to epoxides for high-yield synthesis of cyclic carbonates under co-catalyst-free mild conditions of 1 bar of CO2. Further, MOF 1was recycled for five successive cycles without substantial loss in catalytic activity. Herein, rational design of rare examples of 3D polyhedral MOFs composed of Lewis acidic and basic sites exhibiting efficient co-catalyst-free conversion of CO2has been demonstrated.

Hydrogen is the most promising candidate for a sustainable energy source in the transport sector. However, the storage of hydrogen is a major problem. Calix[4]arene (CX) is functionalized with Ti and Li metals on the delocalized π electrons of benzene rings, and the metal-functionalized system is studied for hydrogen storage efficiency by applying density functional theory using the M06 hybrid functional and 6-311G(d,p) basis set. The calculated binding energy indicates Ti coordinates with CX strongly while Li coordinates weakly and the binding of CX and metal is through Dewar mechanism. On saturation with hydrogen, each Ti atom traps four H2molecules while each Li atom traps three H2molecules on CX. Hydrogen molecules are adsorbed on the metal atoms by Kubas–Niu–Rao–Jena interaction. The global reactivity index obtained for the system obeys the maximum hardness and minimum electrophilicity principle. Molecular dynamics simulations are performed using spin-polarized generalized gradient approximation with the Perdew–Burke–Ernzerhof functional including Grimme diffusion parameter on H2saturated systems. The dissociation of H2molecules in the Ti-functionalized CX system begins from 273 K, while all the H2molecules are desorbed by 473 K. The storage capacity is found to be 8.7 wt % for Ti and 10.1 wt % for Li-functionalized CX. When the Ti atom is intercalated between the two CX moieties, the storage capacity does not reduce significantly. This study reveals that the Ti-functionalized CX is a potential reversible hydrogen storage material.

An organocatalytic enantioselective (3 + 3)-cycloaddition reaction of racemic cyclopropane carbaldehydes and aryl hydrazones has been demonstrated for the first time. A wide range of enantioenriched tetrahydropyridazines with an exocyclic double bond were obtained with moderate to good yields and good to excellent enantiomeric excesses. Mechanistic investigations hinted toward a matched/mismatched kinetic resolution, and control experiments and DFT calculations unveiled that 1,3-aryl migration was concerted and intramolecular and proceeds via a four-membered transition state.

Context.A recent modeling study of brightness ratios for CO rotational transitions in gas typical of the diffuse ISM by Liszt found the role of H collisions to be more important than previously assumed. This conclusion was based on recent quantum scattering calculations using the so-called WKS potential energy surface (PES) which reported a large cross section for the important 0$\rightarrow$1 rotational transition. This result is in contradiction to one obtained using the earlier BBH PES for which the cross section is quite small and which is consistent with an expected homonuclear-like propensity for even $\Delta J$transitions.