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Influence of Cobalt Crystal Structures on Activation of Nitrogen Molecule: A First-Principles Study
No full textIdentification of the structure sensitivity of nitrogen molecule (N-2) activation and ammonia synthesis on metal surfaces is important for the mechanistic understanding and rational design of more efficient catalysts. In the present work, density functional theory calculations together with microkinetic simulations were performed to study the influence of cobalt crystal structures including hexagonal close-packed (HCP) and face-centered cubic (FCC) on nitrogen molecule dissociation and ammonia synthesis. Molecular and dissociative adsorption energies of N-2 as well as dissociation barriers are calculated for a total of ten cobalt surfaces. It is found that molecular adsorption energies on Co surfaces vary modestly on the order of 0.25 eV, whereas dissociative adsorption energies and the corresponding barriers vary considerably in magnitude by about 0.80 eV. First-principles microkinetic simulations show that HCP Co displays higher activity than FCC cobalt for nitrogen molecule dissociation and ammonia synthesis due to the higher intrinsic activity and density of active sites of HCP cobalt. Nitrogen molecule dissociation is the rate-determining step of ammonia synthesis due to the weak interaction between nitrogen and cobalt. The crystal phase sensitivity of nitrogen molecule dissociation on cobalt is compared with the dissociation of an isoelectronic molecule, carbon monoxide on cobalt, ruthenium, and nickel. This work provides valuable insights into nitrogen molecule dissociation and ammonia synthesis on cobalt catalysts with different crystal phases, and highlights the interplay between activated molecules and catalyst composition on the crystal phase sensitivity
Task-specific ionic liquids as corrosion inhibitors on carbon steel in 0.5 M HCl solution: An experimental and theoretical study
No full textThis study investigated corrosion inhibition of task-specific ionic liquids, 1-(4-sulfonic acid) butyl-3-ethyl imidazolium hydrogen sulfate and 1-(4-sulfonic acid) butyl-3-decyl imidazolium hydrogen sulfate, for carbon steel in 0.5 M HCl by electrochemical tests, SEM, UV-vis, XPS, contact angle measurements, molecular orbital theory, and MD simulations. The inhibition efficiency of both ionic liquids increased with concentration, and the latter one shows higher inhibition efficiency of 97.9% due to the weaker hydrophilicity caused by increased alkyl tail. The mechanism of inhibition was found to be through adsorption onto the steel surface with cycling donation and back-donation of electrons
Synthesis of an open-cage fullerene-based unidirectional H-bonding network and its coordination with titanium
No full textOpen-cage fullerene derivatives with up to three hydroxyl groups on the rim of an orifice were prepared through modification of functional groups followed by controlled stepwise reduction of carbonyl groups on the rim. The hydroxyl groups form a unidirectional H-bond network and show a weak but clear interaction with a water molecule trapped inside the fullerene cage. Titanium ions coordinated with the hydroxyl and carbonyl groups to form a TiL2 type of complex
Characterization of the substrate scope of an alcohol dehydrogenase commonly used as methanol dehydrogenase
No full textMany alcohol dehydrogenases (ADHs) catalyze oxidation of a broad scope of alcohols. When an NAD-dependent ADH oxidizes methanol, albeit at a poor rate, it may be treated as methanol dehydrogenase (MDH). One ADH from Geobacillus stearothermophilus DSM 2334 (GsADH) has been widely used as MDH, but its actual substrate scope remains less characterized. Here we purified recombinant GsADH from Escherichia coli and determined its crystal structure. We collected kinetics data of this enzyme towards a number of short chain alcohols, and found that isopropanol is by far the most favorable substrate. Moreover, molecular docking analysis suggested that substrate preference is mainly attributed to the conformer energy of the protein-substrate complex. Our data clarified the substrate scope of GsADH and provided structural insights, which may facilitate more efficient cofactor regeneration and rational metabolic engineering
Selective cleavage of lignin and lignin model compounds without external hydrogen, catalyzed by heterogeneous nickel catalysts
No full textSelective hydrogenolysis of the C-aryl-O bonds in lignin is a key strategy for the generation of fuels and chemical feedstocks from biomass. Currently, hydrogenolysis has been mainly conducted using hydrogen, which is flammable and not sustainable or economical. Herein, an external hydrogen-free process for aryl ethers hydrogenolysis in lignin models and dioxasolv lignin over nickel nanoparticles supported on Al2O3, is reported. Kinetic studies reveal that the transfer hydrogenolysis activity of the three model compounds decreased in the following order: benzyl phenyl ether (a-O-4), 2-phenylethyl phenyl ether (b-O-4) and diphenyl ether (4-O-5), which linearly corresponds to their binding energies and the activation energies. The main reaction route for the three model compounds was the cleavage of the ether bonds to produce aromatic alkanes and phenol, and the latter was further reduced to cyclohexanol. Dioxasolv lignin depolymerization results exhibit a significant Caryl-O decrease over the Ni nanoparticles supported on Al2O3 with iso-propanol as the hydrogen source through 2D-HSQC-NMR analysis, which confirmed the transfer hydrogenolysis conclusion in the model study. This work provides an economical and environmentally-friendly method for the selective cleavage of lignin and lignin model compounds into value-added chemicals
Identification of different carbenium ion intermediates in zeolites with identical chabazite topology via(13)C-C-13 through-bond NMR correlations
No full textC-13-C-13 through-bond NMR correlation experiments reveal the stabilization of different carbenium ion intermediates in two zeolites possessing identical CHA topology (H-SAPO-34 and H-SSZ-13) during the methanol to olefins reaction
