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| 2. |
- Bolton, Kim, et al.
(author)
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DFT study of the adsorption and dissociation of water on Ni(111), Ni(110) and Ni(100) surfaces
- 2014
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In: Surface Science. - : Elsevier. - 0039-6028 .- 1879-2758. ; 627, s. 1-10
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Journal article (peer-reviewed)abstract
- Water adsorption and dissociation on catalytic metal surfaces play a key role in a variety of industrial processes, and a detailed understanding of this process and how it is effected by the surface structure will assist in developing improved catalysts. Hence, a comparative study of the adsorption and dissociation of water on Ni(111), Ni(110) and Ni(100) surfaces, which is often used as catalyst, has been performed using density functional theory. The results show that the adsorption energies and dissociation rates depend on the surface structure. The adsorption energies for H2O and OH decrease in the order Ni(110) > Ni(100) > Ni(111), and for the O and H atoms the adsorption energies decrease in the order Ni(100) > Ni(111) > Ni(110). In addition, the splitting of water to OH and H has lower activation energies over less packed Ni(110) and Ni(100) surfaces compared to the highly packed Ni(111) surface. The subsequent splitting of the OH to O and H also has the lowest activation energy on the Ni(110) surface. At 463 K, which is typical for industrial processes that include the water gas shift reaction, the H2O splitting is approximately 6000 and 10 times faster on the Ni(110) surface compared to the Ni(111) and Ni(100) surfaces, respectively, and OH splitting is 200 and 3000 times faster, respectively. The complete water dissociation reaction rate decreases in the order Ni(110) > Ni(100) > Ni(111).
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| 3. |
- Haghighatpanah, Shayesteh, et al.
(author)
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Computational studies of catalyst-free single walled carbon nanotube growth
- 2013
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In: Journal of Chemical Physics. - : American Institute of Physics. - 0021-9606 .- 1089-7690. ; 139:5, s. 054308-1
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Journal article (peer-reviewed)abstract
- Semiempirical tight binding (TB) and density functional theory (DFT) methods have been used to study the mechanism of single walled carbon nanotube (SWNT) growth. The results are compared with similar calculations on graphene. Both TB and DFT geometry optimized structures of relevance to SWNT growth show that the minimum energy growth mechanism is via the formation of hexagons at the SWNT end. This is similar to the result for graphene where growth occurs via the formation of hexagons at the edge of the graphene flake. However, due to the SWNT curvature, defects such as pentagons are more stable in SWNTs than in graphene. Monte Carlo simulations based on the TB energies show that SWNTs close under conditions that are proper for growth of large defect-free graphene flakes, and that a particle such as a Ni cluster is required to maintain an open SWNT end under these conditions. The calculations also show that the proper combination of growth parameters such as temperature and chemical potential are required to prevent detachment of the SWNTs from the Ni cluster or encapsulation of the cluster by the feedstock carbon atoms.
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| 4. |
- Mohsenzadeh, Abas, et al.
(author)
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A density functional theory study of hydrocarbon combustion and synthesis on Ni surfaces
- 2015
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In: Journal of Molecular Modeling. - : Springer Berlin/Heidelberg. - 1610-2940 .- 0948-5023. ; 21:3
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Journal article (peer-reviewed)abstract
- Combustion and synthesis of hydrocarbons may occur directly (CH → C + H and CO → C + O) or via a formyl (CHO) intermediate. Density functional theory (DFT) calculations were performed to calculate the activation and reaction energies of these reactions on Ni(111), Ni(110), and Ni(100) surfaces. The results show that the energies are sensitive to the surface structure. The dissociation barrier for methylidyne (CH → C + H: catalytic hydrocarbon combustion) is lower than that for its oxidation reaction (CH + O → CHO) on the Ni(110) and Ni(100) surfaces. However the oxidation barrier is lower than that for dissociation on the Ni(111) surface. The dissociation barrier for methylidyne dissociation decreases in the order Ni(111) > Ni(100) > Ni(110). The barrier of formyl dissociation to CO and H is almost the same on the Ni(111) and Ni(110) surfaces and is lower compared to the Ni(100) surface. The energy barrier for carbon monoxide dissociation (CO → C + O: catalytic hydrocarbon synthesis) is higher than that of for its hydrogenation reaction (CO + H → CHO) on all three surfaces. This means that the hydrogenation to CHO is favored on these nickel surfaces. The energy barrier for both reactions decreases in the order Ni(111) > Ni(100) > Ni(110). The barrier for formyl dissociation to CH + O decreases in the order Ni(100) > Ni(111) > Ni(110). Based on these DFT calculations, the Ni(110) surface shows a better catalytic activity for hydrocarbon combustion compared to the other surfaces, and Ni is a better catalyst for the combustion reaction than for hydrocarbon synthesis, where the reaction rate constants are small. The reactions studied here support the BEP principles with R2 values equal to 0.85 for C-H bond breaking/forming and 0.72 for C-O bond breaking /forming reactions.
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| 5. |
- Mohsenzadeh, Abas, et al.
(author)
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Bioethylene Production from Ethanol : A Review and Techno-economical Evaluation.
- 2017
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In: Challenges in Sustainability. - : Wiley-VCH Verlag GmbH & Co. KGaA. - 2297-6477. ; 4:2, s. 75-91
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Journal article (peer-reviewed)abstract
- Manufg. of bioethylene via dehydration of bioethanol is an alternative to the fossil-based ethylene prodn. and decreases the environmental consequences for this chem. commodity. A few industrial plants that utilize 1st generation bioethanol for the bioethylene prodn. already exist, although not functioning without subsidiaries. However, there is still no process producing ethylene from 2nd generation bioethanol. This study is divided into two parts. Different ethanol and ethylene prodn. methods, the process specifications and current technologies are briefly discussed in the first part. In the second part, a techno-economic anal. of a bioethylene plant was performed using Aspen plus and Aspen Process Economic Analyzer, where different qualities of ethanol were considered. The results show that impurities in the ethanol feed have no significant effect on the quality of the produced polymer-grade bioethylene. The capacity of the ethylene storage tank significantly affects the capital costs of the process. [on SciFinder(R)]
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| 6. |
- Mohsenzadeh, Abas
(author)
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Computational studies of nickel catalysed reactions relevant for hydrocarbon gasification
- 2015
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Doctoral thesis (other academic/artistic)abstract
- Sustainable energy sources are of great importance, and will become even more important in the future. Gasification of biomass is an important process for utilization of biomass, as a renewable energy carrier, to produce fuels and chemicals. Density functional theory (DFT) calculations were used to investigate i) the effect of co-adsorption of water and CO on the Ni(111) catalysed water splitting reaction, ii) water adsorption and dissociation on Ni(111), Ni(100) and Ni(110) surfaces, as well as iii) formyl oxidation and dissociation, iv) hydrocarbon combustion and synthesis, and v) the water gas shift (WGS) reaction on these surfaces.The results show that the structures of an adsorbed water molecule and its splitting transition state are significantly changed by co-adsorption of a CO molecule on the Ni(111) surface. This leads to less exothermic reaction energy and larger activation barrier in the presence of CO which means that far fewer water molecules will dissociate in the presence of CO.For the adsorption and dissociation of water on different Ni surfaces, the binding energies for H2O and OH decrease in the order Ni(110) > Ni(100) > Ni(111), and the binding energies for O and H atoms decrease in the order Ni(100) > Ni(111) > Ni(110). In total, the complete water dissociation reaction rate decreases in the order Ni(110) > Ni(100) > Ni(111).The reaction rates for both formyl dissociation to CH + O and to CO + H decrease in the order Ni(110) > Ni(111) > Ni(100). However, the dissociation to CO + H is kinetically favoured. The oxidation of formyl has the lowest activation energy on the Ni(111) surface.For combustion and synthesis of hydrocarbons, the Ni(110) surface shows a better catalytic activity for hydrocarbon combustion compared to the other surfaces. Calculations show that Ni is a better catalyst for the combustion reaction compared to the hydrocarbon synthesis, where the reaction rate constants are small.It was found that the WGS reaction occurs mainly via the direct pathway with the CO + O → CO2 reaction as the rate limiting step on all three surfaces. The activation barrier obtained for this rate limiting step decreases in the order Ni(110) > Ni(111) > Ni(100). Thus, the WGS reaction is fastest on the Ni(100) surface if O species are present on the surfaces. However, the barrier for desorption of water (as the source of the O species) is lower than its dissociation reaction on the Ni(111) and Ni(100) surfaces, but not on the Ni(110) surface. Therefore the direct pathway on the Ni(110) surface will dominate and will be the rate limiting step at low H2O(g) pressures. The calculations also reveal that the WGS reaction does not primarily occur via the formate pathway, since this species is a stable intermediate on all surfaces.All reactions studied in this work support the Brønsted-Evans-Polanyi (BEP) principles.
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| 7. |
- Mohsenzadeh, Abas, et al.
(author)
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DFT study of the water gas shift reaction on Ni (111), Ni (100) and Ni (110) surfaces
- 2016
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In: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 644, s. 53-63
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Journal article (peer-reviewed)abstract
- Density functional theory (DFT) calculations were used to study the water gas shift (WGS) reaction on Ni(111), Ni(100) and Ni(110) surfaces. The adsorption energy for ten species involved in thereaction together with activation barriers and reaction energies for the nine most important elementary steps were determined using the same model and DFT methods. The results reveal that these energies are sensitive to the surface structure. In spite of this, the WGS reaction occurs mainly via the direct (also referred to as redox) pathway with the CO + O → CO2 reaction as the rate determining step on all three surfaces. The activation barrier obtained for this rate limiting step decreases in the order Ni(110) > Ni(111) > Ni(100). Therefore, if O species are present on the surfaces then the WGSreaction is fastest on the Ni(100) surface. However, the barrier for desorption of H2O (which is the source of the O species) is lower than its dissociation reaction on the Ni(111) and Ni(100) surfaces, but not on the Ni(110) surface. Hence, at low H2O(g) pressures, the direct pathway on the Ni(110) surface will dominate and will be the rate limiting step. The calculations also show that the reason that the WGS reaction does not primarily occur via the formate pathway is that this species is a stable intermediate on all surfaces. The reactions studied here support the Brønsted-Evans-Polanyi (BEP) principles with an R2 value of 0.99. © 2015 Elsevier B.V. All rights reserved.
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| 8. |
- Mohsenzadeh, Abas, et al.
(author)
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Hydrocarbon combustion and synthesis on Ni(111), Ni(110) and Ni(100) surfaces : A comparative density functional theory study
- 2014
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Conference paper (other academic/artistic)abstract
- Combustion and synthesis of hydrocarbons may occur directly (CH → C + H and CO → C + O) via a formyl intermediate (CH + O → CHO followed by CHO → CO + H and CO + H → CHO followed by CHO → CH + O) . The activation and reaction energies of these reactions on the Ni(111), Ni(110) and Ni(100) surfaces were investigated using density functional theory (DFT). Calculations show that the barriers are sensitive to the surface structure. The barrier for CH dissociation (catalytic hydrocarbon combustion) is lower than that of for its oxidation reaction (CH + O → CHO) on the Ni(110) and Ni(100) surfaces. In contrast, the barrier for oxidation is lower than that for dissociation on the Ni(111) surface. This means CH will preferably dissociate on the Ni(110) and Ni(100) surfaces, but not on the Ni(111) surface. The barrier for dissociation increases in the order Ni(110) < Ni(100) < Ni(111). The barrier of CHO dissociation to CO and H is almost the same on the Ni(111) and Ni(110) surfaces and it is lower compared to the Ni(100) surface. The energy barrier for carbon monoxide dissociation (catalytic hydrocarbon synthesis) is higher than that of for its hydrogenation reaction on all three surfaces. This means that the hydrogenation to CHO favored over the nickel surfaces studied here. The barrier for both reactions increases in the order Ni(110) < Ni(100) < Ni(111). Formyl dissociation to CH + O barrier is the lowest on the Ni(110) surface and follows the order Ni(100) > Ni(111) > Ni(110). Our DFT results show that the Ni(110) surface has a larger catalytic activity compared to the other surfaces, and that Ni is a better catalyst for hydrocarbon combustion than synthesis.
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| 9. |
- Mohsenzadeh, Abas, et al.
(author)
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Oxidation and dissociation of formyl on Ni(111), Ni(110) and Ni(100) surfaces : A comparative density functional theory study
- 2014
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Conference paper (peer-reviewed)abstract
- Formyl (CHO) is an important adsorbate and a key intermediate in industrial processes such as water gas shift (WGS), Fischer Tropsch synthesis (FTS) and catalytic hydrocarbon combustion reactions. Density functional theory (DFT) with the PBE functional was used to calculate the adsorption, reaction and activation energies of formyl oxidation and dissociation on Ni(111), Ni(110) and Ni(100) surfaces. The results show that these energies are sensitive to the surface structure. The dissociation barrier for CHO → CH + O (FTS process) is higher than that for CHO → CO + H (catalytic combustion) on all three surfaces. This means that the dissociation to CO and H is kinetically favored. The dissociation reaction rate decreases in the order Ni(110) > Ni(111) > Ni(100) for both dissociation reactions. The formation of formate (CHO + O → HCOO), which is included in one of the pathways for the WGS reaction, has lowest activation energy on the Ni(111) surface, and the energy increases in the order Ni(111) < Ni(110) < Ni(100). However, the reaction rate at 463 K, which is a typical temperature for industrial processes that involve these reactions, is at least five orders of magnitude higher for the CHO → CO + H reaction than for the other two reactions, irrespective of the crystallographic structure of the Ni surface. This means that Ni surfaces studied here are better catalysts for this reaction. The results also show that the WGS reaction on a Ni catalyst does not primarily occur via the formate pathway.
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| 10. |
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