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The hydrogen-donor solvent (H-donor) used in direct coal liquefaction (DCL) plays a critical role in both the oil yield and distribution of the products. However, the mechanism of the reaction between H-donor and coal in the DCL is unclear. In this study, the reaction of H-donor and coal in the DCL was investigated using the model compounds tetralin (H-donor) and diphenylmethane (DPM, coal). Density functional theory calculations were employed to examine both pyrolytic radical and solvent-mediated hydrogenolysis mechanisms. Based on the computed results, a modified solvent-mediated hydrogenolysis mechanism was proposed, namely the synergistic double-hydrogen-transfer mechanism, in which the β- and α-hydrogen atoms simultaneously transfer from tetralin to the ipso- and meta-carbon atoms of DPM. The calculated energy barriers of hydrogen transfer were lower than most of the bond dissociation enthalpies for coal. The energy barriers range of the synergistic double-hydrogen-transfer reaction did not correlate with the dissociation enthalpies of Caryl−Calkyl bond, although they were consistent with the order of the hydrogen-donating abilities of different solvents. This study may provide a theoretical guidance to improve the efficiency of H-donor in the DCL.

The low-temperature coal tar contains a considerable number of oxygen-containing compounds, which results in poor quality. The catalytic hydrodeoxygenation of oxygen-containing compound to an added-value chemical compound is one of the most efficient methods to upgrade coal tar. In this study, density functional theory calculations are employed to assess and analyze in detail the hydrodeoxygenation of dibenzofuran, as a model compound of coal tar, on the Ni (1 1 1) surface. The obtained results indicate that dibenzofuran can be firstly hydrogenated to tetrahydrodibenzofuran and hexahydrodibenzofuran. The five-membered-ring opening reaction of tetrahydrodibenzofuran is more straightforward than that of hexahydrodibenzofuran (Ea = 0.71 eV vs. 1.66 eV). Then, both pathways generate an intermediate 2-cyclohexylphenoxy compound. One part of 2-cyclohexylphenoxy is hydrogenated to 2-cyclohexylphenol and consecutively hydrogenated to cyclohexylcyclohexanol, and another part is directly hydrogenated to cyclohexylcyclohexanone. The hydrogenated intermediates of 2-cyclohexylphenol have higher deoxygenation barriers than 2-cyclohexylphenol and cyclohexylcyclohexanol. During the hydrogenation process of cyclohexylcyclohexanone to cyclohexylcyclohexanol, the intermediate 26, formed by adding H to O atom of cyclohexylcyclohexanone, exhibits the lowest deoxygenation barrier of 1.08 eV. High hydrogen coverage may promote the hydrogenation of tetrahydrodibenzofuran, hexahydrodibenzofuran, and intermediate 26 to generate dodecahydrodibenzofuran and cyclohexylcyclohexanol. This dibenzofuran hydrodeoxygenation reaction mechanism corroborates well with previous experimental results and provides a theoretical basis for further optimization of the design of nickel-based catalysts.

Catalytic hydrodeoxygenation is an efficient method to upgrade the quality of low-temperature coal tar and coal liquefied oil. However, only limited researches are performed on the mechanism of hydrodeoxygenation and, therefore, innovation of more efficient and stable catalysts is less progressed and still remains a challenging subject. In this study, density functional theory calculations are carried out to get a deeper insight in the mechanism of dibenzofuran hydrodeoxygenation on the Pt(111) surface. Calculated energies and activation barriers indicate that five-membered-ring opening of tetrahydrodibenzofuran is easier than that of hexahydrodibenzofuran. Then, the generated intermediate can be preferentially hydrogenated through a non-consecutive pathway to 2-cyclohexylphenol, and would result in multiple radical species. The dehydroxylation of that intermediate formed by adding five hydrogen atoms to the phenyl ring of 2-cyclohexylphenol shows a moderate reaction barrier of 1.07 eV; whereas, dehydroxylation of cyclohexylcyclohexanol needs a higher energy barrier of 2.04 eV. For the hydrodeoxygenation of dibenzofuran on the Pt(111) surface, the target product bicyclohexane is most likely to be formed through a radical intermediate. This investigation may provide a potent theoretical guidance to design new catalyst for hydrodeoxygenation of coal to liquid.

By adding different proportions of N-butylimidazole and carboxyethylthiosuccinic acid (CETSA), three hybrid systems of ionic liquids were synthesized and named ILHS1, ILHS2 and ILHS3. Using the weight loss method, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and contact angle test, it was determined that ILHS2 had the best corrosion inhibition among the three ionic liquid systems, and that the inhibition efficiency reached up to 90.63% when the concentration was 10 mM in 1 M HCl at 308 K. The adsorption isotherm was consistent with Langmuir adsorption, and combined with molecular dynamics simulation (MD), it was proved that mixed adsorption occurred on the metal interface. Polarization curves showed that the ionic liquid mixture systems could inhibit the corrosion of both poles, meaning that the anions and cations could act synergistically, and that the anions played a major role. The elemental and molecular structures of ILHS1, ILHS2 and ILHS3 were investigated using 1H NMR, which indicated that the three carboxyl groups on CETSA were regionally selective and combined with imidazole cations to form ionic liquid mixture systems.

The electron-rich nature of vinyl ethers (CH2═CHOR) enables their versatile reactivity patterns with transition metal catalysts. Furthermore, they are highly attractive monomers for the synthesis o...

The polymerization mechanism of functionalized styrene derivatives, viz., p-NMe2 (pMNS)-, o-/p-OCH3 (o/pMOS)-, and p-SCH3 (pMTS)-substituted styrene, catalyzed by cationic rare-earth-metal catalysts has been comparatively studied through density functional theory (DFT) calculations. Having achieved an agreement between theory and experiment, it is found that large steric hindrance as a main factor prevents oMOS from undergoing o-C–H activation relevant to step-growth polymerization, while the nonoccurrence of C–H activation of pMNS and pMTS can be explained by the relatively less dispersion of charge distribution in the four-center transition states. In addition, the electron-donating pyridine side arm weakened the interaction between pMOS and the metal center and meanwhile increased the steric hindrance, preventing the C–H activation. Therefore, the simultaneous occurrence of C–H activation (step-growth polymerization) and C═C insertion (chain-growth polymerization) are affected by multiple factors such ...

The isoprene/ethylene copolymerization catalyzed by cationic rare earth metal complexes [(η5-C5Me5)Sc(CH2SiMe3)]+ (A) had afforded alternating isoprene-ethylene copolymer with rich 3,4-polyisoprene microstructures, whereas no isoprene-ethylene copolymer was observed by using analogous [(PNPPh)Sc(CH2SiMe3)]+ (B) under the same conditions. Theoretical calculations in this work have revealed that, in the case of A, successive 3,4-insertion of isoprene resulted in a noncovalent interaction between the C = C double bond of penultimate unit and the metal center, suppressing the further insertion of monomers due to higher energy barrier and endergonic character. On the other hand, the ethylene pre-inserted species with alkyl active site is more suitable for the subsequent kinetically and thermodynamically favorable isoprene insertion and copolymerization is therefore realized. In the case of B, the experimentally observed cis-1,4-specific homopolymerization of isoprene was the outcome of both kinetic and thermodynamic control. And, the unfavorable ethylene insertion into the isoprene pre-inserted species with allyl active site could account for the experimental finding that no isoprene-ethylene copolymer was obtained. These computational results are expected to provide some hints for the design of rare earth copolymerization catalysts.

Biochar-supported nickel (Ni/BC) catalysts have potential applications in steam reforming of tar during biomass gasification. However, the industrial application of Ni/BC catalysts is restricted by their rapid deactivation caused by the gasification of biochar support and deposition of carbon on the active Ni metal. In this study, the effect of boron doping was explored on the performance of Ni/BC catalysts in steam reforming of toluene as a tar model compound. A series of Ni/BC and boron-doped Ni/BC catalysts were prepared by impregnating Ni salts on raw and acid-washed biomass as the starting materials and used in steam reforming of toluene as the tar model compound. It was found that boron doping significantly prolonged the lifetime of Ni/BC catalysts by interacting with Ni and the biochar support simultaneously. It is believed that boron doping lowered the gasification consumption rate of the biochar support in three ways: transforming the inherent K into more stable borates, inhibiting the desorption of CO and CO2, and forming B2O3 as the active site blocker. Furthermore, boron doping also reduced coke deposition on the Ni particles.

The Sonogashira cross-coupling reaction is one of the most important and widely used sp2–sp carbon–carbon bond formation reactions in organic synthesis. Up to now, the exact mechanism of the palladium/copper-catalyzed Sonogashira reaction is far from being fully understood, mainly due to the difficulties in clarifying the combination behavior of the two metal catalysts. In this study, DFT calculations have been performed to elucidate the mechanism of the copper-cocatalyzed Sonogashira cross-coupling reaction, where bis(triphenylphosphino)palladium was used as a catalyst and Cs2CO3 was applied as a base. In an agreement between theory and experiment, the Cu cycle could favorably generate an I–-coordinated copper acetylide as the catalytically active species rather than the generally considered neutral copper acetylide. In addition, the transmetalation is calculated to be the rate-determining step. The results reported herein are expected to have broad mechanistic implications for other bimetal-catalyzed re...

DFT calculations have been conducted for investigating the relation between the electronic states and catalytic properties of iminopyridine-ligated cationic iron complexes in the stereoselective polymerization of isoprene. Iminopyridine ligand is found to be redox-inert in this catalytic system. The neutral pre-catalyst and active cationic species present as a high spin quintet and the open-shell unpaired 3d-electrons reside on Fe center. The trans and cis polymerization of isoprene catalyzed by the complexes [(octyl-iminopyridine)FeII(Me)]+ (A1) and [(supermesityl-iminopyridine)FeII(Me)]+ (A2) could be attributed to the electronic and steric effects in the transition states, respectively.

Because of the steric bulkiness and the η5/κ1-constrained-geometry-configuration (CGC) geometry, the entire range of pyridyl-methylene-fluorenyl-stabilized rare earth metal bisalkyl complexes, (Flu-CH2-Py)Ln(CH2SiMe3)2(THF)x (Flu = fluorenyl; Py = pyridyl; for 1, Ln = Sc and x = 0; for 2–11, Ln = Lu, Tm, Er, Ho, Y, Dy, Tb, Gd, Nd, or Pr and x = 1), and monoalkyl complex, (Flu-CH2-Py)2La(CH2SiMe3) (THF) (12), has been successfully achieved for the first time via the sequential salt metathesis reactions. Activated by [Ph3C][B(C6F5)4] and AliBu3, complexes 1–9 showed high activity and perfect syndioselectivity for styrene polymerization, while the large Nd- and Pr-attached precursors 10 and 11 exhibited slightly decreased syndioselectivity but rather low activity; the monoalkyl La precursor 12 was completely inert. The activity increased with the decrease in the rare earth metal size, in striking contrast to the literature that has shown that a large metal facilitates a high activity, which was also not a re...

Recent in vivo and in vitro experiments indicated that methoxylated polybrominated diphenyl ethers (MeO-PBDEs) can be biotransformed into hydroxylated PBDEs (HO-PBDEs) that are more toxic than PBDEs and MeO-PBDEs. Nevertheless, the enzymatic transformation mechanism is not clear. We hypothesized that cytochrome P450 enzymes (CYPs) play a key role in the transformation and employed the density functional theory calculations to unveil the mechanism. The transformation of a model compound, 6-MeO-BDE-47, catalyzed by the active center of CYPs (Compound I), was computed. For the first time, our results show that the energy barriers for the addition of Compound I to the C atoms on the phenyl of 6-MeO-BDE-47 are much higher than that for hydroxylation of the methoxyl, indicating that O-demethylation is a dominating metabolic pathway. This is in line with experimental observations performed by others. The pathways for the transformation of 6-MeO-BDE-47 catalyzed by Compound I were clarified. A C-H bond of the methoxyl is activated by Compound I, followed by radical rebound to form carbinol intermediates, then the carbinols decompose to form 6-HO-BDE-47 with the assistance of water molecules. The computational method can be potentially employed to develop models that predict biotransformation of xenobiotics catalyzed by CYPs.

Transition-metal-catalyzed copolymerization reactions of olefins with polar-functionalized comonomers are highly important and also highly challenging. A second-coordination-sphere strategy was developed to address some of the difficulties encountered in these copolymerization reactions. A series of α-diimine ligands bearing nitrogen-containing second coordination spheres were prepared and characterized. The properties of the corresponding nickel and palladium catalysts in ethylene polymerizations and copolymerizations were investigated. In the nickel system, significant reduction in polymer branching density was observed, while lower polymer branching densities, as well as a wider range of polar monomer substrates, were achieved in the palladium system. Control experiments and computational results reveal the critical role of the metal-nitrogen interaction in these polymerization and copolymerization reactions.

Precisely controlling the stereochemistry of a copolymerization by single catalyst, and achieving copolymers with predicted sequences, is a challenging project in organometallic and macromolecular sciences. This article reports that the copolymerization of isoprene and butadiene with the 3,4- and cis-1,4 different regioselectivities has been accessed through employing a pyridylmethylene functionalized fluorenyl ligated yttrium cationic species. The thus unprecedented regularity combination is attributed mainly to the backbiting interaction of the penultimate unit of the polymer chain to the active central metal ion according to the DFT calculation. Moreover, the compositions can be adjusted by regulating the monomer feed ratio according to the copolymerization kinetics study.