Browsing by Author "Chen, Hsin-Tsung"

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A first-principles analysis for sulfur tolerance of CeO2 in solid oxide fuel cells
(2007-07-26)
Chen, Hsin-Tsung
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Choi, YongMan
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Liu, Meilin
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Lin, M. C.
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應用化學系分子科學碩博班
The mechanism for H2S-CeO2(111) interactions in solid oxide fuel cells (SOFCs) has been investigated by using periodic density functional theory (DFT) calculations. In order to properly characterize the effect of the localization of Ce-4f states on the interactions, DFT + U calculations were applied. Adsorption of H2S, SH, and atomic S was initially examined to locate energetically favorable intermediates. The species adsorb favorably at the Ce-top, O-top, and Ce-O bridging sites, respectively. Potential energy profiles for the H2S-CeO2 (111) interactions along the three product channels producing H-2, H2O, and SO2 were constructed using the nudged elastic band (NEB) method. Calculations show that H2S weakly bounds on CeO2(111) with a small binding energy, followed by dehydrogenation processes, forming surface sulfur species with an exothermicity of 29.9 kcal/mol. Molecular-level calculations demonstrated that the SO2-forming pathway is energetically most favorable.
A theoretical study of surface reduction mechanisms of CeO2 (111) and (110) by H-2
(2007-04-23)
Chen, Hsin-Tsung
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Choi, Yong Man
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Liu, Meilin
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Lin, M. C.
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應用化學系分子科學碩博班
Reaction mechanisms for the interactions between CeO2(111) and (110) surfaces are investigated using periodic density functional theory (DFT) calculations. Both standard DFT and DFT+U calculations to examine the effect of the localization of Ce4f states on the redox chemistry of H-2-CeO2 interactions are described. For mechanistic studies, molecular and dissociative local minima are initially located by placing an H-2 molecule at various active sites of the CeO2 surfaces. The binding energies of physisorbed species optimized using the DFT and DFT+U methods are very weak. The dissociative adsorption reactions producing hydroxylated surfaces are all exothermic; exothermicities at the DFT level range from 4.1 kcalmol(-1) for the (111) to 26.5 kcalmol(-1) for the (110) surface, while those at the DFT+U level are between 65.0 kcalmol(-1) for the (111) and 81.8kcalmol(-1) for the (110) surface. Predicted vibrational frequencies of adsorbed OH and H2O species on the surfaces are in line with available experimental and theoretical results. Potential energy profiles are constructed by connecting molecularly adsorbed and dissociatively adsorbed intermediates on each CeO2 surface with tight transition states using the nudged elastic band (NEB) method. It is found that the U correction method plays a significant role in energetics, especially for the intermediates of the exit channels and products that are partially reduced. The surface reduction reaction on CeO2(110) is energetically much more favorable. Accordingly, oxygen vacancies are more easily formed on the (110) surface than on the (111) surface.
Adsorption and dissociation of the HCl and Cl-2 molecules on W(111) surface: A computational study
(2008-08-14)
Chen, Hui-Lung
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Ju, Shin-Pon
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Chen, Hsin-Tsung
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Musaev, Djamaladdin G.
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Lin, M. C.
The adsorption and dissociation of Cl-2 and HCl molecules on W(111) surface have been studied at the density functional theory (DFT) level in conjunction with the projector augmented wave (PAW) method. The molecular structures and surface-adsorbent interaction energies of W(111)/Cl, W(111)/H, W(111)/Cl-2, and W(111)/HCl systems are predicted. In these studies, four adsorption sites, such as top (T), bridge (B), shallow (S), and deep (D) sites, of the W(111) surface are considered. It is shown that the Cl-2 and HCl molecules adsorb to the W(111) surface by the end-on manner (by their Cl-Cl or H-Cl bonds perpendicular to the W surface), and their dissociative adsorptions occur without intrinsic energy barriers and are exothermic by 80.46 and 53.72 kcal/mol, for Cl-2 and HCl, respectively. Molecular dynamics studies show that the dissociation of Cl-2 and HCl molecules on the W(111) surface occur in asymmetric fashion: at the beginning adsorbate forms a strong bond between one of their atoms and W centers, followed by the dissociation of the Cl-Cl (and/or H-Cl) bond and formation of the second bond between the atoms of adsorbate and the W center. For the Cl-2 molecule, both Cl atoms are preferred to adsorb at the top W centers. For the HCl molecule, after the dissociation of the H-Cl bond the Cl atom still occupies the top adsorption site, but the H atom prefers to move to the position between the top and shallow W centers. The rate constants for the dissociative adsorption of Cl-2 and HCl have been predicted with variational RRKM theory.
Adsorption Configurations and Reactions of Nitric Acid on TiO(2) Rutile (110) and Anatase (101) surfaces
(2009-04-16)
Chang, Ching Yi
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Chen, Hsin-Tsung
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Lin, M. C.
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應用化學系分子科學碩博班
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Institute of Molecular science
The adsorption and reactions of the monomer and dimer of nitric acid on TiO(2) rutile (110) and anatase (101) surfaces have been studied by first-principles density functional theory with ultrasoft pseudopotential approximation. The most stable configuration of HNO(3) on the rutile surface is a molecular monodentate adsorbed on the 5-fold coordinated Ti atom with the hydrogen bonded to a neighboring surface bridging oxygen with the adsorption energy of 6.7 kcal/mol. It can dissociate its H atom to a nearest bridged oxygen with almost no barrier to produce NO(3)(a) + H(a). The rotation of NO(3) requires a barrier of 12.2 kcal/mol to form the didentate configuration, Ti(5c)-ON(O)-Ti(5c)H-O(2),(a), which adsorbs on two 5-fold coordinated Ti atoms with the adsorption energy of 16.5 kcal/mol. In the case of the adsorption of 2HNO(3) molecules, the most stable configuration, 2(Ti(5c)-ON(O)OH...O(2c)(a)), has a structure similar to two single HNO(3) adsorbates on two 5-fold coordinated Ti atoms with the adsorption energy of 12.8 kcal/mol, which is about twice that of the single HNO(3) molecule. The result suggests that the interaction of the two planar HNO(3) adsorbates is negligible. The dehydration from 2(Ti(5c)-ON(O)OH...O(2)c(a)) forming N(2)O(5)(a) + H(2)O(a) requires an energy barrier of 46.2 kcal/mol, indicating that the dimerization of the two HNO(3)(a) is difficult. Similar adsorption phenomena appear on the anatase (101) surface. In addition, we find that the coadsorption of hydrogen plays a significant role in the adsorption energies of adsorbates, especially for the NO(3) radical, which may be employed as a linker between semiconductor quantum dots such as InN and the TiO(2) surface.
Adsorption Configurations and Reactions of Nitric Acid on TiO2 Rutile (110) and Anatase (101) surfaces
(2009-04-16)
Chang, Ching Yi
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Chen, Hsin-Tsung
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Lin, M. C.
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應用化學系分子科學碩博班
;
Institute of Molecular science
The adsorption and reactions of the monomer and dimer of nitric acid on TiO2 rutile (110) and anatase (101) surfaces have been studied by first-principles density functional theory with ultrasoft pseudopotential approximation. The most stable configuration of HNO3 on the rutile surface is a molecular monodentate adsorbed on the 5-fold coordinated Ti atom with the hydrogen bonded to a neighboring surface bridging oxygen with the adsorption energy of 6.7 kcal/mol. It can dissociate its H atom to a nearest bridged oxygen with almost no barrier to produce NO3(a) + H(a). The rotation of NO3 requires a barrier of 12.2 kcal/mol to form the didentate configuration, Ti-5c-ON(O)-Ti5cH-O-2,(a), which adsorbs on two 5-fold coordinated Ti atoms with the adsorption energy of 16.5 kcal/mol. In the case of the adsorption of 2HNO(3) molecules, the most stable configuration, 2(Ti-5c-ON(O)OH...O-2c(a)), has a structure similar to two single HNO3 adsorbates on two 5-fold coordinated Ti atoms with the adsorption energy of 12.8 kcal/mol, which is about twice that of the single HNO3 molecule. The result suggests that the interaction of the two planar HNO3 adsorbates is negligible. The dehydration from 2(Ti-5c-ON(O)OH...O(2)c(a)) forming N2O5(a) + H2O(a) requires an energy barrier of 46.2 kcal/mol, indicating that the dimerization of the two HNO3(a) is difficult. Similar adsorption phenomena appear on the anatase (101) surface. In addition, we find that the coadsorption of hydrogen plays a significant role in the adsorption energies of adsorbates, especially for the NO3 radical, which may be employed as a linker between semiconductor quantum dots such as InN and the TiO2 surface.
Characterization of O-2-CeO2 interactions using in situ Raman spectroscopy and first-principle calculations
(2006-09-11)
Choi, Y. M.
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Abernathy, Harry
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Chen, Hsin-Tsung
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Lin, M. C.
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Liu, Meilin
Interactions between O-2 and CeO2 are examined experimentally using in situ Raman spectroscopy and theoretically using density-functional slob-model calculations. Two distinct oxygen bonds appear at 825 and 1131 cm(-1), corresponding to peroxo- and superoxo-like species, respectively, when partially reduced CeO2 is exposed to 10% O-2. Periodic density-functional theory (DFT) calculations aid the interpretation of spectroscopic observations and provide energetic and geometric information for the dioxygen species adsorbed on CeO2. The O-2 adsorption energies on unreduced CeO2 surfaces ore endothermic (0.91 < Delta E-ads < 0.98 eV), while those on reduced surfaces are exothermic (-4. 0 < Delta E-ads < -0.9 eV), depending on other relevant surface processes such as chemisorption and diffusion into the bulk. Partial reduction of surface Ce4+ to Ce3+ (together with formation of oxygen vacancies) alters geometrical parameters and, accordingly, leads to a shift in the vibrational frequencies of adsorbed oxygen species compared to those on unreduced CeO2. Moreover, the location of oxygen vacancies affects the formation and subsequent dissociation of oxygen species on the surfaces. DFT predictions of the energetics support the experimental observation that the reduced surfaces are energetically more favorable than the unreduced surfaces for oxygen adsorption and reduction.
Computational Investigation of O(2) Reduction and Diffusion on 25% Sr-Doped LaMnO(3) Cathodes in Solid Oxide Fuel Cells
(2011-06-07)
Chen, Hsin-Tsung
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Raghunath, P.
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Lin, M. C.
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應用化學系
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應用化學系分子科學碩博班
The oxygen reduction reaction (ORR) and diffusion mechanisms on 25% Sr-doped LaMnO(3) (LSM) cathode materials as well as their kinetic behavior have been studied by using spin-polarized density functional theory (DFT) calculations. Bader charge and frequency analyses were carried out to identify the oxidation state of adsorbed oxygen species. DFT and molecular dynamics (MD) results show that the fast O(2) adsorption/reduction process via superoxide and peroxide intermediates is energetically favorable on the Mn site rather than on the Sr site. Furthermore, the higher adsorption energies on the Mn site of the (110) surface compared to those on the (100) surface imply that the former is more efficient for O(2) reduction. Significantly, we predict that oxygen vacancies enhance O(2) reduction kinetics and that the O-ion migration through the bulk is dominant over that on cathode.
Computational Investigation of O-2 Reduction and Diffusion on 25% Sr-Doped LaMnO3 Cathodes in Solid Oxide Fuel Cells
(2011-06-07)
Chen, Hsin-Tsung
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Raghunath, P.
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Lin, M. C.
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應用化學系
;
應用化學系分子科學碩博班
The oxygen reduction reaction (ORR) and diffusion mechanisms on 25% Sr-doped LaMnO3 (LSM) cathode materials as well as their kinetic behavior have been studied by using spin-polarized density functional theory (DFT) calculations. Bader charge and frequency analyses were carried out to identify the oxidation state of adsorbed oxygen species. DFT and molecular dynamics (MD) results show that the fast O-2 adsorption/reduction process via superoxide and peroxide intermediates is energetically favorable on the Mn site rather than on the Sr site. Furthermore, the higher adsorption energies on the Mn site of the (110) surface compared to those on the (100) surface imply that the former is more efficient for O-2 reduction. Significantly, we predict that oxygen vacancies enhance O-2 reduction kinetics and that the O-ion migration through the bulk is dominant over that on cathode.
Computational Investigation of the Adsorption and Reactions of SiHx (x=0-4) on TiO2 Anatase (101) and Rutile (110) Surfaces
(2013-06-15)
Huang, Wen-Fei
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Chen, Hsin-Tsung
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Lin, M. C.
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應用化學系
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應用化學系分子科學碩博班
The adsorption and reactions of the SiHx (x = 0-4) on Titanium dioxide (TiO2) anatase (101) and rutile (110) surfaces have been studied by using periodic density functional theory in conjunction with the projected augmented wave approach. It is found that SiHx (x = 0-4) can form the monodentate, bidentate, or tridentate adsorbates, depending on the value of x. H coadsorption is found to reduce the stability of SiHx adsorption. Hydrogen migration on the TiO2 surfaces is also discussed for elucidation of the SiHx decomposition mechanism. Comparing adsorption energies, energy barriers, and potential energy profiles on the two TiO2 surfaces, the SiHx decomposition can occur more readily on the rutile (110) surface than on the anatase (101) surface. The results may be used for kinetic simulation of Si thin-film deposition and quantum dot preparation on titania by chemical vapor deposition (CVD), plasma enhanced CVD, or catalytically enhanced CVD. (C) 2013 Wiley Periodicals, Inc.
Computational study on kinetics and mechanisms of unimolecular decomposition of succinic acid and its anhydride
(2008-07-24)
Chen, Hsin-Tsung
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Chang, Jee-Gong
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Musaev, Djamaladdin G.
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Lin, M. C.
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應用化學系分子科學碩博班
The mechanisms and kinetics of unimolecular decomposition of succinic acid and its anhydride have been studied at the G2M(CC2) and microcanonical RRKM levels of theory. It was shown that the ZsgsZ conformer of succinic acid, with the Z-acid form and the gauche conformation around the central C-C bond, is its most stable conformer, whereas the lowest energy conformer with the E-acid form, ECGsZ, is only 3.1 kcal/mol higher in energy than the ZsgsZ. Three primary decomposition channels of succinic acid producing H2O + succinic anhydride with a barrier of 51.0 kcal/mol, H2O + OCC2H3COOH with a barrier of 75.7 kcal/mol and CO2 + C2H5COOH with a barrier of 71.9 kcal/mol were predicted. The dehydration process starting from the ECGCZ-conformer is found to be dominant, whereas the decarboxylation reaction starting from the ZsgsZ-conformer is only slightly less favorable. It was shown that the decomposition of succinic anhydride occurs via a concerted fragmentation mechanism (with a 69.6 kcal/mol barrier), leading to formation of CO + CO2 + C2H4 products. On the basis of the calculated potential energy surfaces of these reactions, the rate constants for unimolecular decomposition of succinic acid and its anhydride were predicted. In addition, the predicted rate constants for the unimolecular decomposition Of C2H5COOH by decarboxylation (giving C2H6 + CO2) and dehydration (giving H3CCHCO + H2O) are in good agreement with available experimental data.
Computational study on the kinetics and mechanisms for the unimolecular decomposition of formic and oxalic Acids
(2007-07-26)
Chang, Jee-Gong
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Chen, Hsin-Tsung
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Xu, Shucheng
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Lin, M. C.
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應用化學系分子科學碩博班
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 + HOCOH with barriers of 33-36 kcal/mol and CO2 + CO + H2O with a barrier of 39 kcal/mol were found. At high temperatures, the latter process becomes more competitive. The rate constant predicted for the formation of CO2 and HOCOH (the precursor of HCOOH) agrees well with available experimental data. The mechanism for the isomerization of HOCOH to HCOOH is also discussed.
Computational Study on the Mechanisms and Rate Constants for the O(P-3,D-1) + OCS Reactions
(2019-10-03)
Chen, Hsin-Tsung
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Pham, Tien, V
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Lin, M. C.
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交大名義發表
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應用化學系
The mechanisms and kinetics of O(P-3,D-1) + OCS(X-1 Sigma(+)) reactions have been studied by the high-level G2M(CC2) and CCSD(T)/6-311+G(3df)//B3LYP/6-311+G(3df) methods in conjunction with the transition-state theory and variational Rice-Ramsperger-Kassel-Marcus theory calculations. The result shows that the triplet surface proceeds directly by abstraction and substitution channels to produce SO(P-3) + CO(X-1 Sigma(+)) and S(P-3) + CO2(X-1 Sigma(+)(g)) bypassing the barriers of 7.6 and 9.1 kcal.mol(-1) at the G2M(CC2)//B3LYP/6-311+G(3df) level, respectively, while two stable intermediates, LM1 (OSCO1) and LM2 (SC(O)O-1), are formed barrierlessly from O(D-1 ) + OCS(X-1 Sigma(+)) in the singlet surface, which lie at -40.5 and -50.1 kcal.mol(-1) relative to O(P-3) + OCS(X-1 Sigma(+)) reactants and decompose to CO (X-1 Sigma(+)) + SO (a(1)Delta) and S(D-1) + CO2(X-1 Sigma g(+)). LM1 and LM2 may also be produced by singlet-triplet surface crossings via MSX1 and MSX2; the predicted total rate constant for the O(P-3) + OCS(X-1 Sigma(+)) reaction including the crossings, 9.2 X 10(-11) exp(-5.18 kcal-mol(-1)/RT) cm(3) molecule(-1) s(-1), is in good agreement with available experimental data. The branching ratio of the CO2 product channel, 0.22-0.32, between 1200 and 1600 K, is also in excellent agreement with the value of 0.2-0.3 measured by Isshiki et al. (J. Phys. Chem. A. 2003, 107, 2464).
Density Functional Studies of the Adsorption and Dissociation of NO(x) (x=1, 2) Molecules on the W(111) Surface
(2009-04-02)
Chen, Hsin-Tsung
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Chen, Hui-Lung
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Ju, Shin-Pon
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Musaev, Djamaladdin G.
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Lin, M. C.
Adsorption and dissociation of NOx (x = 1, 2) molecules on the W(111) surface have been investigated by using the density functional theory (DFT) with the projector-augmentcd wave (PAW) approach in periodic boundary conditions. The adsorption structures, vibrational frequencies, and binding energies of NO(2), NO, N, and 0 on the W(111) surface were predicted. It was shown that the most favorable adsorption geometry of W(111)/NO(2) is the WNO(2) (IV-mu(3)-N2, OI, OI) configuration with NO(2) at the 3-fold-shallow site of the surface and has an adsorption energy of 79.4 kcal/mol. For W(111)NO, WNO(II-mu(2)-N1, O1) with NO at the bridge site is energetically the most favorable one and has an adsorption energy of 74.4 kcal/mol. The N and 0 atoms are bound preferentially at the bridge and top sites, respectively. The potential energy profiles for the decomposition of NO(2) on W(111) were constructed using the nudged elastic band (NEB) method. The barriers for the stepwise NO(2)-deoxygenation process to N((ads)) + 20((ads)) are calculated to be only 0.5-3.7 (for the first step of the reaction, ON-O bond activation) and 0.2-3.0 (for the second step of the reaction, N-O bond activation of the coordinated NO molecule) kcal/mol, with an overall exothermicity of 177.0-185.2 kcal/mol. These findings show that NO,) can easily decompose on the W(111) surface. The rate constants for NO(2) and NO dissociation on the surface were also predicted.
Density Functional Studies of the Adsorption and Dissociation of NOx (x=1, 2) Molecules on the W(111) Surface
(2009-04-02)
Chen, Hsin-Tsung
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Chen, Hui-Lung
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Ju, Shin-Pon
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Musaev, Djamaladdin G.
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Lin, M. C.
Adsorption and dissociation of NOx (x = 1, 2) molecules on the W(111) surface have been investigated by using the density functional theory (DFT) with the projector-augmentcd wave (PAW) approach in periodic boundary conditions. The adsorption structures, vibrational frequencies, and binding energies of NO2, NO, N, and 0 on the W(111) surface were predicted. It was shown that the most favorable adsorption geometry of W(111)/NO2 is the WNO2 (IV-mu(3)-N2, OI, OI) configuration with NO2 at the 3-fold-shallow site of the surface and has an adsorption energy of 79.4 kcal/mol. For W(111)NO, WNO(II-mu(2)-N1, O1) with NO at the bridge site is energetically the most favorable one and has an adsorption energy of 74.4 kcal/mol. The N and 0 atoms are bound preferentially at the bridge and top sites, respectively. The potential energy profiles for the decomposition of NO2 on W(111) were constructed using the nudged elastic band (NEB) method. The barriers for the stepwise NO2-deoxygenation process to N-(ads) + 20((ads)) are calculated to be only 0.5-3.7 (for the first step of the reaction, ON-O bond activation) and 0.2-3.0 (for the second step of the reaction, N-O bond activation of the coordinated NO molecule) kcal/mol, with an overall exothermicity of 177.0-185.2 kcal/mol. These findings show that NO,) can easily decompose on the W(111) surface. The rate constants for NO2 and NO dissociation on the surface were also predicted.
Density Functional Theory Study of the Adsorption and Reaction of H(2)S on TiO(2) Rutile (110) and Anatase (101) Surfaces
(2009-11-26)
Huang, Wen-Fei
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Chen, Hsin-Tsung
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Lin, M. C.
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應用化學系分子科學碩博班
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Institute of Molecular science
The adsorption and reaction of H(2)S on TiO(2) rutile (110) and anatase (101) surfaces have been investigated by using periodic density functional theory (DFT) in conjunction with the projected augmented wave (PAW) approach. Adsorption mechanisms of H(2)S, HS, and S on both surfaces were analyzed. It was found that H(2)S, HS, S, and H preferentially adsorb at the Ti(5c), O(2c), (Ti(5c))(2), and O(2c) sites, respectively, on the rutile surface, and at the Ti(5c), (Ti(5c))(2), (-O(2c))(-Ti(5c)), and O(2c), sites, respectively, on the anatase surface. Potential energy profiles of the adsorption processes on both Surfaces producing H(2) and H(2)O were constructed using the nudged elastic band (NEB) method. Forming Surface sulfur species by a complete O <-> S exchange at the rutile Surface is endothermic by 15.4 kcal/mol and requires a high energy barrier of 35.5 kcal/mol, while it is endothermic by 5.0 kcal/mol and requires it lower energy barrier of 12.4 kcal/mol at the anatase surface. The rate constants for the dehydrogenation and dehydration processes have been predicted.
Density Functional Theory Study of the Adsorption and Reaction of H2S on TiO2 Rutile (110) and Anatase (101) Surfaces
(2009-11-26)
Huang, Wen-Fei
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Chen, Hsin-Tsung
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Lin, M. C.
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應用化學系分子科學碩博班
;
Institute of Molecular science
The adsorption and reaction of H2S on TiO2 rutile (110) and anatase (101) surfaces have been investigated by using periodic density functional theory (DFT) in conjunction with the projected augmented wave (PAW) approach. Adsorption mechanisms of H2S, HS, and S on both surfaces were analyzed. It was found that H2S, HS, S, and H preferentially adsorb at the Ti-5c, O-2c, (Ti-5c)(2), and O-2c sites, respectively, on the rutile surface, and at the Ti-5c, (Ti-5c)(2), (-O-2c)(-Ti-5c), and O-2c, sites, respectively, on the anatase surface. Potential energy profiles of the adsorption processes on both Surfaces producing H-2 and H2O were constructed using the nudged elastic band (NEB) method. Forming Surface sulfur species by a complete O <-> S exchange at the rutile Surface is endothermic by 15.4 kcal/mol and requires a high energy barrier of 35.5 kcal/mol, while it is endothermic by 5.0 kcal/mol and requires it lower energy barrier of 12.4 kcal/mol at the anatase surface. The rate constants for the dehydrogenation and dehydration processes have been predicted.
Kinetics and Mechanisms for the Adsorption, Dissociation, and Diffusion of Hydrogen in Ni and Ni/YSZ Slabs: A DFT Study
(2012-04-03)
Weng, Meng Hsiung
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Chen, Hsin-Tsung
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Wang, Yao-Chun
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Ju, Shin-Pon
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Chang, Jee-Gong
The adsorption, dissociation, and diffusion of hydrogen in Ni(100) and Ni(100)/YSZ(100) slabs with two different interfaces (Ni/cation and Ni/O interface) have been studied by the density functional theory (DFT) with the Perdew-Wang functional. The H-2 molecule is found to preferentially absorb on a Top (T) site with side-on configuration on the Ni(100) surface, while the H-atom is strongly bound at a fcc Hollow (H) site. The barrier for the H-2 dissociation on both surfaces is calculated to be only similar to 0.1 eV. The potential energy pathways of H diffusion on pure Ni and Ni/YSZ with the two different interfaces are studied. Our calculated results show that the H-atom diffusion occurs via surface path rather than the bulk path. For the bulk path in Ni/YSZ, H-atom migration can occur more readily at the Ni/cation interface compared to the Ni/O interface. The existence of vacancy in the interface region is found to improve the mobility of H-atoms at the interface of Ni/YSZ slab. The rate constants for hydrogen dissociation and diffusion in pure Ni and Ni/YSZ are predicted.
Reaction Dynamics of O((1)D,(3)P) + OCS Studied with Time-Resolved Fourier Transform Infrared Spectroscopy and Quantum Chemical Calculations
(2009-11-26)
Chiang, Hung-Chu
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Wang, Niann-Shiah
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Tsuchiya, Soji
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Chen, Hsin-Tsung
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Lee, Yuan-Pern
Time-resolved infrared emission of CO(2) and OCS was observed in reactions O((1)P) + OCS and O((1)D) + OCS with a step-scan Fourier transform spectrometer. The CO(2) emission involves Delta nu(3) = -1 transitions from highly vibrationally excited states, whereas emission of OCS is mainly from the transition (0, 0 degrees, 1) (0, 0, 0); the latter derives its energy via near-resonant V-V energy transfer from highly excited CO(2). Rotationally resolved emission lines of CO (v <= 4 and J <= 30) were also observed in the reaction O((1)D) + OCS. For O((3)P) + OCS, weak emission Of CO(2) diminishes when Ar is added, indicating that O((3)P) is translationally hot to overcome the barrier for CO(2) formation. The band contour of CO(2) agrees with a band shape simulated on the basis of a Dunharn expansion model of CO(2); the average vibrational energy of CO(2) in this channel is 49% of the available energy. This vibrational distribution fits with that estimated through a statistical partitioning of energy E* congruent to 18 000 +/- 500 cm(-1) into all vibrational modes of CO(2). For the reaction of O((1)D) + OCS, approximately 51% of the available energy is converted into vibrational energy of CO(2), and a statistical prediction using E* congruent to 30 000 +/- 500 cm(-1) best fits the data. The mechanisms of these reactions are also investigated with the CCSD(T)/6-311+G(3df)//B3LYP/6-311+G(3df) method. The results indicate that the triplet O((3)P) + OCS(X(1)Sigma(+)) surface proceeds via direct abstraction and substitution channels with barriers of 27.6 and 36.4 kJ mol(-1), respectively, to produce SO(X(3)Sigma(-)) + CO(X(1)Sigma(+)) and S((3)P) + CO(2)(X(1)A(1)), whereas two intermediates, OSCO and SC(O)O, are formed from the singlet O((1)D) + OCS(X(1)Sigma(+)) surface without barrier, followed by decomposition to SO(a(1)Delta) + CO(X(1)Sigma(+)) and S((1)D) + CO(2)(X(1)A(1)), respectively. For the ground-state reaction O((3)P) + OCS(X(1)Sigma(+)), the singlet-triplet curve crossings play important roles in the observed kinetics and chemiluminescence.
Reaction Dynamics of O(D-1,P-3) + OCS Studied with Time-Resolved Fourier Transform Infrared Spectroscopy and Quantum Chemical Calculations
(2009-11-26)
Chiang, Hung-Chu
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Wang, Niann-Shiah
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Tsuchiya, Soji
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Chen, Hsin-Tsung
;
Lee, Yuan-Pern
Time-resolved infrared emission of CO2 and OCS was observed in reactions O(P-1) + OCS and O(D-1) + OCS with a step-scan Fourier transform spectrometer. The CO2 emission involves Delta nu(3) = -1 transitions from highly vibrationally excited states, whereas emission of OCS is mainly from the transition (0, 0 degrees, 1) (0, 0, 0); the latter derives its energy via near-resonant V-V energy transfer from highly excited CO2. Rotationally resolved emission lines of CO (v <= 4 and J <= 30) were also observed in the reaction O(D-1) + OCS. For O(P-3) + OCS, weak emission Of CO2 diminishes when Ar is added, indicating that O(P-3) is translationally hot to overcome the barrier for CO2 formation. The band contour of CO2 agrees with a band shape simulated on the basis of a Dunharn expansion model of CO2; the average vibrational energy of CO2 in this channel is 49% of the available energy. This vibrational distribution fits with that estimated through a statistical partitioning of energy E* congruent to 18 000 +/- 500 cm(-1) into all vibrational modes of CO2. For the reaction of O(D-1) + OCS, approximately 51% of the available energy is converted into vibrational energy of CO2, and a statistical prediction using E* congruent to 30 000 +/- 500 cm(-1) best fits the data. The mechanisms of these reactions are also investigated with the CCSD(T)/6-311+G(3df)//B3LYP/6-311+G(3df) method. The results indicate that the triplet O(P-3) + OCS(X-1 Sigma(+)) surface proceeds via direct abstraction and substitution channels with barriers of 27.6 and 36.4 kJ mol(-1), respectively, to produce SO(X-3 Sigma(-)) + CO(X-1 Sigma(+)) and S(P-3) + CO2(X(1)A(1)), whereas two intermediates, OSCO and SC(O)O, are formed from the singlet O(D-1) + OCS(X-1 Sigma(+)) surface without barrier, followed by decomposition to SO(a(1)Delta) + CO(X-1 Sigma(+)) and S(D-1) + CO2(X(1)A(1)), respectively. For the ground-state reaction O(P-3) + OCS(X-1 Sigma(+)), the singlet-triplet curve crossings play important roles in the observed kinetics and chemiluminescence.
The adsorption and reactions of SiClx (x=0-4) on hydroxylated TiO2 anatase (101) surface: A computational study on the functionalization of titania with Cl2Si(O)O adsorbate
(1970-01-01)
Huang, Wen-Fei
;
Chen, Hsin-Tsung
;
Lin, M. C.
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應用化學系分子科學碩博班
;
Institute of Molecular science
"The adsorption and reactions of the SiClx (x = 0-4) on the hydroxylated TiO2 anatase (101) surface have been investigated by using periodic density functional theory calculations in conjunction with the projected augmented wave (PAW) approach. The adsorption and reactions tend to occur more readily on the 'O-w' site derived from water than the 'O-s' site from TiO2 as revealed by the potential energy profiles and adsorption energies. The stepwise reactions of SiClx can be achieved by dehydrochlorination taking place by three paths: Ow-path, cross-path, and O-s-path. The Ow-path is the lowest energy path, in which Cl3Si-O-w(a) and Cl2Si-(O-w)O-w(a) are the main products formed by spontaneous reactions. The ready formation and the high stability of Cl2Si-(O-w)O-w(a) suggest that it can be employed as a molecular linker for Si and other semiconductor quantum dot growth on titania through its high reactivity towards SiHx radicals and metal alkyls, respectively. (C) 2012 Elsevier B.V. All rights reserved."