The reduction of graphene oxide

To investigate the initial chemical events associated with high-temperature gas-phase oxidation of hydrocarbons, we have expanded the ReaxFF reactive force field training set to include additional transition states and chemical reactivity of systems relevant to these reactions and optimized the force field parameters against a quantum mechanics (QM)-based training set. To validate the ReaxFF potential obtained after parameter optimization, we performed a range of NVT−MD simulations on various hydrocarbon/O2 systems. From simulations on methane/O2, o-xylene/O2, propene/O2, and benzene/O2 mixtures, we found that ReaxFF obtains the correct reactivity trend (propene > o-xylene > methane > benzene), following the trend in the C−H bond strength in these hydrocarbons. We also tracked in detail the reactions during a complete oxidation of isolated methane, propene, and o-xylene to a CO/CO2/H2O mixture and found that the pathways predicted by ReaxFF are in agreement with chemical intuition and our QM results. We o...

ReaxFF Reactive Force Field for Molecular Dynamics Simulations of Hydrocarbon Oxidation

Dang Sheng Su,*,†,‡ Siglinda Perathoner, and Gabriele Centi* †Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Science, 72 Wenhua Road, Shenyang 110006, China ‡Department of Inorganic Chemistry, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany Dipartimento di Ingegneria Elettronica, Chimica ed Ingegneria Industriale, University of Messina and INSTM/CASPE (Laboratory of Catalysis for Sustainable Production and Energy), Viale Ferdinando Stagno, D’Alcontres 31, 98166 Messina, Italy

Nanocarbons for the Development of Advanced Catalysts

The density functional theory method (M05-2X/6-31G(d)) was used to investigate reaction mechanisms for deoxygenation of graphene oxides (GOs) with hydrazine or heat treatment. Three mechanisms were identified as reducing epoxide groups of GO with hydrazine as a reducing agent. No reaction path was found for the hydrazine-mediated reductions of the hydroxyl, carbonyl, and carboxyl groups of GO. We instead discovered the mechanisms for dehydroxylation, decarbonylation, and decarboxylation using heat treatment. The hydrazine de-epoxidation and thermal dehydroxylation of GO have opposite dependencies on the reaction temperature. In both reduction types, the oxygen functionalities attached to the interior of an aromatic domain in GO are removed more easily, both kinetically and thermodynamically, than those attached at the edges of an aromatic domain. The hydrazine-mediated reductions of epoxide groups at the edges are suspended by forming hydrazino alcohols. We provide atomic-level elucidation for the deoxyge...

Hydrazine and Thermal Reduction of Graphene Oxide: Reaction Mechanisms, Product Structures, and Reaction Design

A detailed chemical kinetic mechanism has been developed to describe the oxidation of small hydrocarbon and oxygenated hydrocarbon species. The reactivity of these small fuels and intermediates is of critical importance in understanding and accurately describing the combustion characteristics, such as ignition delay time, flame speed, and emissions of practical fuels. The chosen rate expressions have been assembled through critical evaluation of the literature, with minimum optimization performed. The mechanism has been validated over a wide range of initial conditions and experimental devices, including flow reactor, shock tube, jet-stirred reactor, and flame studies. The current mechanism contains accurate kinetic descriptions for saturated and unsaturated hydrocarbons, namely methane, ethane, ethylene, and acetylene, and oxygenated species; formaldehyde, methanol, acetaldehyde, and ethanol.

A Hierarchical and Comparative Kinetic Modeling Study of C1 − C2 Hydrocarbon and Oxygenated Fuels

Kinetics and mechanisms for reactions of OH with methanol and ethanol have been investigated at the CCSD(T)/6-311 + G(3df, 2p)//MP2/6-311 + G(3df, 2p) level of theory. The total and individual rate constants, and product branching ratios for the reactions have been computed in the temperature range 200–3000 K with variational transition state theory by including the effects of multiple reflections above the wells of their pre-reaction complexes, quantum-mechanical tunneling and hindered internal rotations. The predicted results can be represented by the expressions k1 = 4.65 × 10−20 × T2.68 exp(414/T) and k2 = 9.11 × 10−20 × T2.58 exp(748/T) cm3 molecule−1 s−1 for the CH3OH and C2H5OH reactions, respectively. These results are in reasonable agreements with available experimental data except that of OH + C2H5OH in the high temperature range. The former reaction produces 96–89% of the H2O + CH2OH products, whereas the latter process produces 98–70% of H2O + CH3CHOH and 2–21% of the H2O + CH2CH2OH products in the temperature range computed (200–3000 K).

Theoretical study on the kinetics for OH reactions with CH3OH and C2H5OH

Quantum chemical studies of the dissociative adsorption mechanisms and kinetics of OHx (x = 1, 2) on graphite (0001) surface models were carried out with emphasis on the influence of surface defects. Finite-size model systems for Stone−Wales type (SW), mono- (1V), and divacancy (2V) defects are studied in addition to the defect-free (0D) surface models. Horizontal and vertical bulk effects have been considered by variation of the model system size and number of graphene layers. Potential energy surfaces for dissocative adsorption of one and two OH radicals on pristine graphite and for H2O adsorption on 1V, 2V, and SW defects are presented at the dispersion-augmented density functional tight binding (DFTB−D), integrated ONIOM(B3LYP/6-31+G(d):DFTB−D), and density functional theory B3LYP/6-31+G(d) levels of theory. OH is found to oxidatively erode the graphite surface by producing gaseous CO and hydrogenated vacancy defects (L1H1V), while water is found to react only with monovacancy defects. The rate consta...

Quantum chemical study of the dissociative adsorption of OH and H2O on pristine and defective graphite (0001) surfaces : Reaction mechanisms and kinetics

The kinetics and mechanisms for the unimolecular decomposition reactions of formic acid and oxalic acid have been studied computationally by the high-level G2M(CC1) method and microcanonical RRKM theory. There are two reaction pathways in the decomposition of formic acid:  The dehydration process starting from the Z conformer is found to be the dominant, whereas the decarboxylation reaction starting from the E conformer is less competitive. The predicted rate constants for the dehydration and decarboxylation reactions are in good agreement with the experimental data. The calculated CO/CO2 ratio, 13.6−13.9 between 1300 and 2000 K, is in close agreement with the ratio of 10 measured experimentally by Hsu et al. (In The 19th International Symposium on Combustion; The Combustion Institute:  Pittsburgh, PA, 1983; p 89). For oxalic acid, its isomer with two intramolecular hydrogen bonds is the most stable structure, similar to earlier reports. Two primary decomposition channels of oxalic acid producing CO2 + HO...

https://ir.nctu.edu.tw:443/bitstream/11536/10546/1/000248121400027.pdf

Computational study on the kinetics and mechanisms for the unimolecular decomposition of formic and oxalic acids.

The properties, interactions, and reactions of cyclic water clusters (H2O)n=1-5 on model systems for a graphite surface have been studied using pure B3LYP, dispersion-augmented density functional tight binding (DFTB-D), and integrated ONIOM(B3LYP:DFTB-D) methods. Coronene C24H12 as well as polycircumcoronenes C96H24 and C216H36 in monolayer, bilayer, and trilayer arrangements were used as model systems to simulate ABA bulk graphite. Structures, binding energies, and vibrational frequencies of water clusters on mono- and bilayer graphite models have been calculated, and structural changes and frequency shifts due to the water cluster−graphite interactions are discussed. ONIOM(B3LYP:DFTB-D) with coronene and water in the high level and C96H24 in the low level mimics the effect of extended graphite π-conjugation on the water−graphite interaction very reasonably and suggests that water clusters only weakly interact with graphite surfaces, as suggested by the fact that water is an excellent graphite lubricant....

Water clusters on graphite: methodology for quantum chemical a priori prediction of reaction rate constants.

Kinetics for the reaction of OH radical with CH2O has been studied by single-point calculations at the CCSD(T)/6-311+G(3df, 2p) level based on the geometries optimized at the B3LYP/6-311+G(3df, 2p) and CCSD/6-311++G(d,p) levels. The rate constant for the reaction has been computed in the temperature range 200–3000 K by variational transition state theory including the significant effect of the multiple reflections above the OH··OCH2 complex. The predicted results can be represented by the expressions k1 = 2.45 × 10-21T2.98 exp (1750/T) cm3 mol−1 s−1 (200–400 K) and 3.22 × 10-18T2.11 exp(849/T) cm3 mol−1 s−1 (400–3000 K) for the H-abstraction process and k2 = 1.05 × 10-17T1.63 exp(−2156/T) cm3 mol−1 s−1 in the temperature range of 200–3000 K for the HO-addition process producing the OCH2OH radical. The predicted total rate constants (k1 + k2) can reproduce closely the recommended kinetic data for OH + CH2O over the entire range of temperature studied. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 322–326, 2006

Shucheng Xu

Papers

Theoretical study on the kinetics for OH reactions with CH3OH and C2H5OH

Quantum chemical study of the dissociative adsorption of OH and H2O on pristine and defective graphite (0001) surfaces : Reaction mechanisms and kinetics

Computational study on the kinetics and mechanisms for the unimolecular decomposition of formic and oxalic acids.

Water clusters on graphite: methodology for quantum chemical a priori prediction of reaction rate constants.

Ab initio study of the OH + CH2O reaction: The effect of the OH··OCH2 complex on the H-abstraction kinetics