scholarly journals Balancing the Activity and Selectivity of Propane Oxidative Dehydrogenation on NiOOH (001) and (010)

2020 ◽  
Vol 26 (5) ◽  
pp. 341-351
Author(s):  
Lisheng Li ◽  
Hua Wang ◽  
Jinyu Han ◽  
Xinli Zhu ◽  
Qingfeng Ge
Keyword(s):  
Oxidative Dehydrogenation ◽  
Density Functional ◽  
Activation Barrier ◽  
Propane Oxidative Dehydrogenation ◽  
Functional Theory ◽  
Activation Barriers ◽  
Propylene Oxidation ◽  
Propane Odh ◽  
High Activation Barrier ◽  
Allylic Radical

Abstract Propane oxidative dehydrogenation (ODH) is an energy-efficient approach to produce propylene. However, ODH suffers from low propylene selectivity due to a relatively higher activation barrier for propylene formation compared with that for further oxidation. In this work, calculations based on density functional theory were performed to map out the reaction pathways of propane ODH on the surfaces (001) and (010) of nickel oxide hydroxide (NiOOH). Results show that propane is physisorbed on both surfaces and produces propylene through a two-step radical dehydrogenation process. The relatively low activation barriers of propane dehydrogenation on the NiOOH surfaces make the NiOOH-based catalysts promising for propane ODH. By contrast, the weak interaction between the allylic radical and the surface leads to a high activation barrier for further propylene oxidation. These results suggest that the catalysts based on NiOOH can be active and selective for the ODH of propane toward propylene.

Facile formation of azines from reactions of singlet methylene and dimethylcarbene with precursor diazirines: theoretical explorations

1999 ◽  
Vol 77 (5-6) ◽  
pp. 540-549 ◽  
Author(s):  
Gennady V Shustov ◽  
Michael TH Liu ◽  
K N Houk
Keyword(s):  
Density Functional Theory ◽  
Ab Initio ◽  
Ring Opening ◽  
Density Functional ◽  
Activation Barrier ◽  
Thermal Reaction ◽  
Orbital Theory ◽  
Functional Theory ◽  
Activation Barriers ◽  
Singlet Methylene

The reactions of the singlet methylene (1a) and dimethylcarbene (1b), with their diazirine precursors, diazirine (2a), and dimethyldiazirine (2b), have been studied theoretically using ab initio and density functional theory. The reaction has no activation barriers for the parent system (1a + 2a) and proceeds via a reactive complex and a transition state with a small negative enthalpy of activation Δ Hnot =298 = -1.1 kcal mol-1, ΔSnot =298 = -34.4 cal mol-1 K-1, ΔG°298 = 9.2 kcal mol-1) for the dimethyl derivatives (1b + 2b). The formation of N-methylene diazirinium ylides (3a,b) is exothermic by 64-80 kcal mol-1. The isomer, 1,3-diazabicyclo[1.1.0]butane (4a), is more stable (5-12 kcal mol-1) than isomer 3a, but can neither be formed by direct thermal reaction of 1a with 2a nor undergo the direct rearrangement into formaldazine (5a). The rearrangement of ylides 3a,b into azines 5a,b proceeds by conrotatory C3-N1 ring opening. The predicted activation barrier of ca. 15 kcal mol-1 for the ring opening in ylide 3b is in excellent agreement with experimental data. The formation of pyridinium ylides from carbenes and pyridine is also studied.Key words: diazirinium ylide, ab initio MO (molecular orbital) theory, density functional theory, pyridinium ylide, CIS (singles configuration interaction) transition energies.

Mechanisms for the formation of epoxide and chlorine-containing products in the oxidation of ethylene by chromyl chloride: a density functional study

1999 ◽  
Vol 77 (9) ◽  
pp. 1476-1491 ◽  
Author(s):  
Maricel Torrent ◽  
Liqun Deng ◽  
Miquel Duran ◽  
Miquel Solà ◽  
Tom Ziegler
Keyword(s):  
Density Functional Theory ◽  
Reaction Mechanisms ◽  
Density Functional ◽  
Activation Barrier ◽  
Activation Energies ◽  
Functional Study ◽  
Functional Theory ◽  
Activation Barriers ◽  
Density Functional Study ◽  
Chromyl Chloride

The reaction between CrO2Cl2 and ethylene leading to the formation of epoxide and chlorohydrin precursors or directly to 1,2-dichloroethane has been studied by density functional theory. The formation of the epoxide precursor (Cl2(O)Cr-OC2H4) was found to take place via a [3+2] addition of ethylene to two Cr=O bonds followed by rearrangement of the five-membered diol to the epoxide product. The alternative mechanisms involving a direct addition of oxygen to ethylene or the [2+2] addition of the olefin to a Cr=O bond were found to have much higher activation energies. The formation of the chlorohydrin precursor (Cl(O)Cr-OCH2=CHCl) was found to take place via a [3+2] addition to one Cr—Cl and one Cr=O bond. Pathways involving initial [2+2] addition to a Cr—Cl or Cr=O bond had much higher activation barriers. The generation of 1,2-dichloroethane is highly unfavorable with an endothermicity of 44.7 kcal/mol and an even higher activation barrier. It is suggested that the formation of epoxide and chlorohydrin from the respective precursors requires the addition of H2O.Key words: reaction mechanisms, epoxide, oxidation of ethylene, chromyl chloride, DFT.

scholarly journals Adsorption and Reaction Mechanisms of Direct Palladium Synthesis by ALD Using Pd(hfac)2 and Ozone on Si (100) Surface

Processes ◽  
2021 ◽  
Vol 9 (12) ◽  
pp. 2246
Author(s):  
Chunyu Cheng ◽  
Yiming Zou ◽  
Jiahui Li ◽  
Amanda Jiamin Ong ◽  
Ronn Goei ◽  
...  
Keyword(s):  
Reaction Mechanisms ◽  
Palladium Nanoparticles ◽  
Density Functional ◽  
Noble Metals ◽  
Activation Barrier ◽  
Atomic Layer ◽  
Activation Barriers ◽  
Layer Deposition ◽  
High Activation Barrier ◽  
Palladium Metal

Palladium nanoparticles made by atomic layer deposition (ALD) normally involve formaldehyde or H2 as a reducing agent. Since formaldehyde is toxic and H2 is explosive, it is advantageous to remove this reducing step during the fabrication of palladium metal by ALD. In this work we have successfully used Pd(hfac)2 and ozone directly to prepare palladium nanoparticles, without the use of reducing or annealing agents. Density functional theory (DFT) was employed to explore the reaction mechanisms of palladium metal formation in this process. DFT results show that Pd(hfac)2 dissociatively chemisorbed to form Pd(hfac)* and hfac* on the Si (100) surface. Subsequently, an O atom of the ozone could cleave the C–C bond of Pd(hfac)* to form Pd* with a low activation barrier of 0.46 eV. An O atom of the ozone could also be inserted into the hfac* to form Pd(hfac-O)* with a lower activation barrier of 0.29 eV. With more ozone, the C–C bond of Pd(hfac-O)* could be broken to produce Pd* with an activation barrier of 0.42 eV. The ozone could also chemisorb on the Pd atom of Pd(hfac-O)* to form O3-Pd(hfac-O)*, which could separate into O-Pd(hfac-O)* with a high activation barrier of 0.83 eV. Besides, the activation barrier was 0.64 eV for Pd* that was directly oxidized to PdOx by ozone. Based on activation barriers from DFT calculations, it was possible to prepare palladium without reducing steps when ALD conditions were carefully controlled, especially the ozone parameters, as shown by our experimental results. The mechanisms of this approach could be used to prepare other noble metals by ALD without reducing/annealing agents.

Reaction Prediction using Density Functional Theory Calculations: A Study into the Synthesis of Safranal via Diels-Alder Reactions

2011 ◽  
Vol 66 (11) ◽  
pp. 1141-s1241
Author(s):  
Gabriele Wagner ◽  
Nadia Vahdati ◽  
Ashley Howkins ◽  
Louisa Cubitt
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Activation Barrier ◽  
Exothermic Reaction ◽  
Density Functional Theory Calculations ◽  
Alder Reaction ◽  
Diels Alder ◽  
Functional Theory ◽  
Diels Alder Reaction ◽  
High Activation Barrier

Two pathways for the synthesis of safranal (2,6,6-trimethyl-cyclohexa-1,3-diene-1-carbaldehyde) via a Diels-Alder reaction are proposed and analyzed for their feasibility by Density Functional Theory (DFT) calculations on a B3LYP/6-31G* level of theory. Pathway A involving the reaction of 3-methyl-2-butenal with 4-methoxypenta-1,3-diene is predicted to produce the desired regioisomers, although with low stereoselectivity. Due to the high activation barrier (23 kcal mol−1), the reaction will require harsher conditions than the related known reaction of Z-2-butenal and 1-methoxy-1,3- butadiene with a calculated ΔEa of 17 kcal mol−1. Replacement of the methoxy group at the diene by OAc, OSiMe3 or pyrrolidinyl does not enhance the reactivity any further. Preliminary experiments confirm these results, although the reaction conditions need to be improved for the reaction to be of synthetic use. In the reaction of methoxyethene with 3-formyl-2,4-dimethylpenta-1,3-diene (pathway B), the homo- and hetero-Diels-Alder pathways were compared. The desired homo-Diels-Alder reaction is predicted to give the correct regioisomer in an exothermic reaction. However, the activation barrier is high (30 kcal mol−1) and the reaction unlikely to proceed. The hetero-Diels-Alder reaction requires less activation energy (23 kcal mol−1) and is expected to dominate, although the thermodynamic driving force is low. The preferred regioisomeric product is the 2-methoxy-3,4-dihydropyran, in agreement with related reactions studied experimentally

scholarly journals A Computational Study of Direct CO2 Hydrogenation to Methanol on Pd Catalysts

2021 ◽  
Author(s):  
Igor Kowalec ◽  
Lara Kabalan ◽  
Richard Catlow ◽  
Andrew Logsdail
Keyword(s):  
Density Functional ◽  
Negative Charge ◽  
Computational Study ◽  
Adsorbed Species ◽  
Pd Catalysts ◽  
Functional Theory ◽  
Activation Barriers ◽  
Rate Determining Step ◽  
Adsorption Energies ◽  
Insight Into

<p>We investigate the mechanism of direct CO<sub>2</sub> hydrogenation to methanol on Pd (111), (100) and (110) surfaces using density functional theory (DFT), providing insight into the reactivity of CO<sub>2</sub> on Pd-based catalysts. The initial chemisorption of CO<sub>2</sub>, forming a partially charged CO<sub>2</sub><sup>δ-</sup>, is weakly endothermic on a Pd (111) surface, with an adsorption energy of 0.06 eV, and slightly exothermic on Pd (100) and (110) surfaces, with adsorption energies of -0.13 and -0.23 eV, respectively. Based on Mulliken analysis, we attribute the low stability of CO<sub>2</sub><sup>δ-</sup><sub> </sub>on the Pd (111) surface to a negative charge that accumulates on the surface Pd atoms interacting directly with the CO<sub>2</sub><sup>δ-</sup><sub> </sub>adsorbate. For the reaction of the adsorbed species on the Pd surface, HCOOH hydrogenation to H<sub>2</sub>COOH is predicted to be the rate determining step of the conversion to methanol in all cases, with activation barriers of 1.35, 1.26, and 0.92 eV on Pd (111), (100) and (110) surfaces, respectively.<br></p>

scholarly journals Mechanical bending effects on hydrogen storage of Ni decorated (8, 0) boron nitride nanotube : DFT study

2019 ◽  
Vol 16 (1) ◽  
pp. 299-325
Author(s):  
Atef Elmahdy ◽  
Hayam Taha ◽  
Mohamed Kamel ◽  
Menna Tarek
Keyword(s):  
Boron Nitride ◽  
Hydrogen Storage ◽  
Density Functional ◽  
Boron Nitride Nanotubes ◽  
Department Of Energy ◽  
Functional Theory ◽  
Activation Barriers ◽  
The Us ◽  
Adsorption Energies ◽  
Mechanical Bending

The influence of mechanical bending to tuning the hydrogen storage of Ni-functionalized of zigzag type of boron nitride nanotubes (BNNTs) has been investigated using density functional theory (DFT) with reference to the ultimate targets of the US Department of Energy (DOE). Single Ni atoms prefer to bind strongly at the axial bridge site of BN nanotube, and each Ni atom bound on BNNT may adsorb up to five, H2 molecules, with average adsorption energies per hydrogen molecule of )-1.622,-0.527 eV( for the undeformed B40N40-? = 0 , ) -1.62 , 0-0.308 eV( for the deformed B40N40-? = 15, ) -1.589,  -0.310 eV( for the deformed B40N40-? = 30, and ) -1.368-  -0.323 eV( for the deformed B40N40-? = 45 nanotubes respectively. with the H-H bonds between H2 molecules significantly elongated. The curvature attributed to the bending angle has effect on average adsorption energies per H2 molecule. With no metal clustering, the system gravimetric capacities are expected to be as large as 5.691 wt % for 5H2 Ni B40N40-? = 0, 15, 30, 45. While the desorption activation barriers of the complexes nH2 + Ni B40N40-? = 0 (n = 1-4) are outside the (DOE) domain (-0.2 to -0.6 eV), the complexes nH2 + Ni- B40N40-? = 0 (n = 5) is inside this domain. For nH2 + Ni- B40N40-? = 15, 30, 45 with (n = 1-2) are outside the (DOE) domain, the complexes nH2 + Ni- B40N40-? = 15, 30, 45 with (n = 3-5) are inside this domain. The hydrogen storage of the irreversible 4H2+ Ni- B40N40-? = 0, 2H2+ Ni- B40N40-? = 15, 30, 45 and reversible 5H2+ Ni- B40N40-? = 0, 3H2+ Ni- B40N40-? = 15, 30, 45 interactions are characterized in terms of density of states, pairwise and non-pairwise additivity, infrared, Raman, electrophilicity and molecular electrostatic potentials. Our calculations expect that 5H2- Ni- B40N40-j = 0, 15, 30, 45 complexes are promising hydrogen storage candidates.

A density functional theory study on the performance of graphene and N-doped graphene supported Au3 cluster catalyst for acetylene hydrochlorination

2016 ◽  
Vol 94 (10) ◽  
pp. 842-847 ◽  
Author(s):  
Fei Zhao ◽  
Yang Wang ◽  
Lihua Kang
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Energy Gap ◽  
Activation Barrier ◽  
Similar Reaction ◽  
Functional Theory ◽  
Acetylene Hydrochlorination ◽  
Doped Graphene ◽  
Calculated Activation ◽  
Calculated Activation Barrier

Density functional theory (DFT) calculation was used to investigate the mechanism of Au3 clusters, separately supported on pure graphene (Au3/graphene) and one graphitic N-doped graphene (Au3/N-graphene). These supported Au3 clusters were used to catalyze acetylene hydrochlorination. Results show that the graphene supporter could obviously enhance the adsorption of reactants. Also, N-atom doping could broaden the energy gap between the HOMO of graphene and the LUMO of Au3, leading to the significantly attenuated interaction between the Au3 cluster and graphene by more than 19 kcal/mol (1 cal = 4.184 J). The two catalysts possessed extremely similar reaction mechanisms with activation energy values of 23.26 and 23.89 kcal/mol, respectively. The calculated activation barrier declined in the order of Au3 < Au3/N-graphene < Au3/graphene, suggesting that Au3/N-graphene could be a potential catalyst for acetylene hydrochlorination.

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