scholarly journals Reaction Mechanism for Methane-to-Methanol in Cu-SSZ-13: First-Principles Study of the Z2[Cu2O] and Z2[Cu2OH] Motifs

Catalysts ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 17
Author(s):  
Unni Engedahl ◽  
Adam A. Arvidsson ◽  
Henrik Grönbeck ◽  
Anders Hellman
Keyword(s):  
Liquid Fuel ◽  
Density Functional ◽  
Reaction Pathway ◽  
Direct Conversion ◽  
Reaction Conditions ◽  
Oxidation Of Methane ◽  
Small Pore ◽  
Desorption Step ◽  
Solution Gas ◽  
Stable Motif

As transportation continues to increase world-wide, there is a need for more efficient utilization of fossil fuel. One possibility is direct conversion of the solution gas bi-product CH4 into an energy-rich, easily usable liquid fuel such as CH3OH. However, new catalytic materials to facilitate the methane-to-methanol reaction are needed. Using density functional calculations, the partial oxidation of methane is investigated over the small-pore copper-exchanged zeolite SSZ-13. The reaction pathway is identified and the energy landscape elucidated over the proposed motifs Z2[Cu2O] and Z2[Cu2OH]. It is shown that the Z2[Cu2O] motif has an exergonic reaction path, provided water is added as a solvent for the desorption step. However, a micro-kinetic model shows that neither Z2[Cu2O] nor Z2[Cu2OH] has any notable activity under the reaction conditions. These findings highlight the importance of the detailed structure of the active site and that the most stable motif is not necessarily the most active.

scholarly journals New insights into the mechanism of Schiff base synthesis from aromatic amines in the absence of acid catalyst or polar solvents

2019 ◽  
Author(s):  
Pedro J Silva
Keyword(s):  
Transition State ◽  
Aromatic Amines ◽  
Density Functional ◽  
Large Scale ◽  
Reaction Pathway ◽  
Acid Catalyst ◽  
Functional Study ◽  
Computational Studies ◽  
Reaction Conditions ◽  
Polar Solvents

Extensive computational studies of the imine synthesis from amines and aldehydes in water have shown that the large-scale structure of water is needed to afford appropriate charge delocalisation and enable sufficient transition state stabilisation. These insights cannot, however, be applied to the understanding of the reaction pathway in apolar solvents due their inability to form extensive hidrogen-bonding networks. In this work, we perform the first computational studies of this reaction in apolar conditions. This density-functional study of the reaction of benzaldehyde with four closely related aromatic amines (aniline, o-toluidine, m-toluidine and p-toluidine) shows that an additional molecule of amine may provide enough stabilization of the first transition state even in the absence of a hydrogen bonding network. Our computations also show that the second reaction step cannot take place unless an extra proton is added to the system but, crucially, that reaction rate is so high that even picomolar amounts of protonated base are enough to achieve realistic rates. Additional computations show that those minute amounts of protonated base may be obtained under reaction conditions without the addition of extraneous acid through the auto-protolysis of the amines themselves. To our knowledge, this is the first report of a role for the auto-protolysis of anilines in their extensive reactional repertoire.

Direct conversion of fructose to 5-ethoxymethyl-furfural catalyzed by ultra stable Y zeolite

BioResources ◽  
2020 ◽  
Vol 15 (2) ◽  
pp. 3621-3635
Author(s):  
Guizhuan Xu ◽  
Shaohao Zhang ◽  
Zhangbin Zheng ◽  
Chen Wang ◽  
Shijie Wang ◽  
...  
Keyword(s):  
Heterogeneous Catalysts ◽  
Reaction Pathway ◽  
Direct Conversion ◽  
High Energy ◽  
High Energy Density ◽  
Y Zeolite ◽  
Reaction Conditions ◽  
One Pot ◽  
New Type ◽  
Optimum Reaction

5-Ethoxymethylfurfural (EMF) is a new type of biofuel with a high energy density and excellent fuel properties. One-pot production of EMF from renewable carbohydrate catalyzed by heterogeneous catalysts has the potential to be an attractive reaction pathway. In this study, fructose was directly converted to EMF in ethanol medium catalyzed by ultra stable Y zeolite (USY). The effects of different reaction conditions on EMF yields were investigated, and an optimum reaction condition was obtained by utilizing response surface methodology. Under the optimum reaction conditions, which were a temperature of 132 °C, substrate density of 60 g/L, and catalyst dosage of 2.1 wt%, a maximum EMF yield of 73.8 mol% with the prediction error of 1.6% was achieved in 25 min. Moreover, the reusability of USY and characterization were evaluated. This study demonstrated a promising strategy for EMF production from fructose.

scholarly journals New insights into the mechanism of Schiff base synthesis from aromatic amines in the absence of acid catalyst or polar solvents

2019 ◽  
Author(s):  
Pedro J Silva
Keyword(s):  
Transition State ◽  
Aromatic Amines ◽  
Density Functional ◽  
Large Scale ◽  
Reaction Pathway ◽  
Acid Catalyst ◽  
Functional Study ◽  
Computational Studies ◽  
Reaction Conditions ◽  
Polar Solvents

Extensive computational studies of the imine synthesis from amines and aldehydes in water have shown that the large-scale structure of water is needed to afford appropriate charge delocalisation and enable sufficient transition state stabilisation. These insights cannot, however, be applied to the understanding of the reaction pathway in apolar solvents due their inability to form extensive hidrogen-bonding networks. In this work, we perform the first computational studies of this reaction in apolar conditions. This density-functional study of the reaction of benzaldehyde with four closely related aromatic amines (aniline, o-toluidine, m-toluidine and p-toluidine) shows that an additional molecule of amine may provide enough stabilization of the first transition state even in the absence of a hydrogen bonding network. Our computations also show that the second reaction step cannot take place unless an extra proton is added to the system but, crucially, that reaction rate is so high that even picomolar amounts of protonated base are enough to achieve realistic rates. Additional computations show that those minute amounts of protonated base may be obtained under reaction conditions without the addition of extraneous acid through the auto-protolysis of the amines themselves. To our knowledge, this is the first report of a role for the auto-protolysis of anilines in their extensive reactional repertoire.

scholarly journals Self-Assembled Bimetallic Aluminum-Salen Catalyst for the Cyclic Carbonates Synthesis

Molecules ◽  
2021 ◽  
Vol 26 (13) ◽  
pp. 4097
Author(s):  
Wooyong Seong ◽  
Hyungwoo Hahm ◽  
Seyong Kim ◽  
Jongwoo Park ◽  
Khalil A. Abboud ◽  
...  
Keyword(s):  
Hydrogen Bonding ◽  
Self Assembly ◽  
Reaction Pathway ◽  
Kinetic Studies ◽  
Cyclic Carbonate ◽  
Reaction Conditions ◽  
Formation Reaction ◽  
X Ray ◽  
Carbonate Formation ◽  
Salen Aluminum

Bimetallic bis-urea functionalized salen-aluminum catalysts have been developed for cyclic carbonate synthesis from epoxides and CO2. The urea moiety provides a bimetallic scaffold through hydrogen bonding, which expedites the cyclic carbonate formation reaction under mild reaction conditions. The turnover frequency (TOF) of the bis-urea salen Al catalyst is three times higher than that of a μ-oxo-bridged catalyst, and 13 times higher than that of a monomeric salen aluminum catalyst. The bimetallic reaction pathway is suggested based on urea additive studies and kinetic studies. Additionally, the X-ray crystal structure of a bis-urea salen Ni complex supports the self-assembly of the bis-urea salen metal complex through hydrogen bonding.

scholarly journals Photochemistry of 1-Phenyl-4-Allyl-Tetrazol-5-One: A Theoretical Study Contribution towards Mechanism Elucidation

2021 ◽  
Vol 11 (9) ◽  
pp. 4045
Author(s):  
Amilcar Duque-Prata ◽  
Carlos Serpa ◽  
Pedro J. S. B. Caridade
Keyword(s):  
Density Functional ◽  
Reaction Pathway ◽  
Intramolecular Proton Transfer ◽  
Polarizable Continuum Model ◽  
Uv Spectra ◽  
Point Of View ◽  
Basis Set ◽  
Pathway Evolution ◽  
Photodegradation Mechanism ◽  
Energetic Point

The photodegradation mechanism of 1-phenyl-4-allyl-tetrazol-5-one has been studied using (time-dependent) density functional theory with the M06-HF, B3LYP, and PBE0 functionals and the VDZ basis set. All calculations have been carried out using the polarizable continuum model to simulate the solvent effects of methanol. The reaction pathway evolution on the triplet state has been characterised to validate a previously postulated experimental-based mechanism. The transition states and minimums have been initially located by local scanning in partial constrained optimisation, followed by a fully relaxed search procedure. The UV spectra has shown to be better described with PBE0 functional when compared with the experimental results, having the M06-HF a shift of 40 nm. From the energetic point of view, the postulated mechanism has been validated in this work showing a concerted photoextrusion of the N2 molecule. The intramolecular proton transfer occurs at a later stage of the mechanism after cyclization of the allyl group on a triplet biradical intermediate. The photoproduct observed experimentally, a pyrimidinone, has been characterised. The infrared spectroscopic reaction profile has also been proposed.

scholarly journals Prebiotic Route to Thymine from Formamide—A Combined Experimental–Theoretical Study

Molecules ◽  
2021 ◽  
Vol 26 (8) ◽  
pp. 2248
Author(s):  
Lukáš Petera ◽  
Klaudia Mrazikova ◽  
Lukas Nejdl ◽  
Kristyna Zemankova ◽  
Marketa Vaculovicova ◽  
...  
Keyword(s):  
Formic Acid ◽  
Quantum Chemical ◽  
Prebiotic Chemistry ◽  
Theoretical Study ◽  
Reaction Pathway ◽  
Hydrolysis Product ◽  
Current Paper ◽  
Reaction Conditions ◽  
Chemical Modeling ◽  
Chemistry Research

Synthesis of RNA nucleobases from formamide is one of the recurring topics of prebiotic chemistry research. Earlier reports suggest that thymine, the substitute for uracil in DNA, may also be synthesized from formamide in the presence of catalysts enabling conversion of formamide to formaldehyde. In the current paper, we show that to a lesser extent conversion of uracil to thymine may occur even in the absence of catalysts. This is enabled by the presence of formic acid in the reaction mixture that forms as the hydrolysis product of formamide. Under the reaction conditions of our study, the disproportionation of formic acid may produce formaldehyde that hydroxymethylates uracil in the first step of the conversion process. The experiments are supplemented by quantum chemical modeling of the reaction pathway, supporting the plausibility of the mechanism suggested by Saladino and coworkers.

Graph theory-based reaction pathway searches and DFT calculations for the mechanism studies of free radical-initiated peptide sequencing mass spectrometry (FRIPS MS): a model gas-phase reaction of GGR tri-peptide

2020 ◽  
Vol 22 (9) ◽  
pp. 5057-5069 ◽  
Author(s):  
Jae-ung Lee ◽  
Yeonjoon Kim ◽  
Woo Youn Kim ◽  
Han Bin Oh
Keyword(s):  
Graph Theory ◽  
Dft Calculations ◽  
Gas Phase ◽  
Density Functional ◽  
Reaction Pathway ◽  
Peptide Sequencing ◽  
Phase Reaction ◽  
Functional Theory ◽  
Fragmentation Mechanisms ◽  
Gas Phase Fragmentation

A new approach for elucidating gas-phase fragmentation mechanisms is proposed: graph theory-based reaction pathway searches (ACE-Reaction program) and density functional theory (DFT) calculations.

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