liu.seSearch for publications in DiVA
Change search
Link to record
Permanent link

Direct link
BETA
Alternative names
Publications (10 of 102) Show all publications
Atakan, A., Erdtman, E., Mäkie, P., Ojamäe, L. & Odén, M. (2018). Time evolution of the CO2 hydrogenation to fuels over Cu-Zr-SBA-15 catalysts. Journal of Catalysis, 362, 55-64
Open this publication in new window or tab >>Time evolution of the CO2 hydrogenation to fuels over Cu-Zr-SBA-15 catalysts
Show others...
2018 (English)In: Journal of Catalysis, ISSN 0021-9517, E-ISSN 1090-2694, Vol. 362, p. 55-64Article in journal (Refereed) Published
Abstract [en]

Time evolution of catalytic CO2 hydrogenation to methanol and dimethyl ether (DME) has been investigated in a high-temperature high-pressure reaction chamber where products accumulate over time. The employed catalysts are based on a nano-assembly composed of Cu nanoparticles infiltrated into a Zr doped SiOx mesoporous framework (SBA-15): Cu-Zr-SBA-15. The CO2 conversion was recorded as a function of time by gas chromatography-mass spectrometry (GC-MS) and the molecular activity on the catalyst’s surface was examined by diffuse reflectance in-situ Fourier transform infrared spectroscopy (DRIFTS). The experimental results showed that after 14 days a CO2 conversion of 25% to methanol and DME was reached when a DME selective catalyst was used which was also illustrated by thermodynamic equilibrium calculations. With higher Zr content in the catalyst, greater selectivity for methanol and a total 9.5% conversion to methanol and DME was observed, yielding also CO as an additional product. The time evolution profiles indicated that DME is formed directly from methoxy groups in this reaction system. Both DME and methanol selective systems show the thermodynamically highest possible conversion.

Keywords
Cu-Zr-SBA-15, CO2 hydrogenation, Catalysis, Time evolution, Thermodynamics, Methanol, Dimethyl ether
National Category
Nano Technology Physical Chemistry
Identifiers
urn:nbn:se:liu:diva-147297 (URN)10.1016/j.jcat.2018.03.023 (DOI)000432770900007 ()
Note

Funding agencies: EUs Erasmus-Mundus program (The European School of Materials Doctoral Programme - DocMASE); Knut och Alice Wallenbergs Foundation [KAW 2012.0083]; Swedish Government Strategic Research Area (SFO Mat LiU) [2009 00971]; Swedish Energy Agency [42022-1]

Available from: 2018-04-16 Created: 2018-04-16 Last updated: 2018-06-14Bibliographically approved
Stenberg, P., Danielsson, Ö., Erdtman, E., Sukkaew, P., Ojamäe, L., Janzén, E. & Pedersen, H. (2017). Matching precursor kinetics to afford a more robust CVD chemistry: a case study of the C chemistry for silicon carbide using SiF4 as Si precursor. Journal of Materials Chemistry C, 5, 5818-5823
Open this publication in new window or tab >>Matching precursor kinetics to afford a more robust CVD chemistry: a case study of the C chemistry for silicon carbide using SiF4 as Si precursor
Show others...
2017 (English)In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 5, p. 5818-5823Article in journal (Refereed) Published
Abstract [en]

Chemical Vapor Deposition (CVD) is one of the technology platforms forming the backbone of the semiconductor industry and is vital in the production of electronic devices. To upscale a CVD process from the lab to the fab, large area uniformity and high run-to-run reproducibility are needed. We show by a combination of experiments and gas phase kinetics modeling that the combinations of Si and C precursors with the most well-matched gas phase chemistry kinetics gives the largest area of of homoepitaxial growth of SiC. Comparing CH4, C2H4 and C3H8 as carbon precursors to the SiF4 silicon precursor, CH4 with the slowest kinetics renders the most robust CVD chemistry with large area epitaxial growth and low temperature sensitivity. We further show by quantum chemical modeling how the surface chemistry is impeded by the presence of F in the system which limits the amount of available surface sites for the C to adsorb.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2017
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-137446 (URN)10.1039/c7tc00138j (DOI)000403571200024 ()
Note

Funding agencies: Knut & Alice Wallenberg Foundation (KAW) project Isotopic Control for Ultimate Material Properties; Swedish Foundation for Strategic Research project SiC - the Material for Energy-Saving Power Electronics [EM11-0034]; Swedish Government Strategic Research

Available from: 2017-05-16 Created: 2017-05-16 Last updated: 2018-10-08Bibliographically approved
Erdtman, E., Andersson, M., Lloyd Spetz, A. & Ojamäe, L. (2017). Simulations of the thermodynamics and kinetics of NH3 at the RuO2 (110) surface. Surface Science, 656, 77-85
Open this publication in new window or tab >>Simulations of the thermodynamics and kinetics of NH3 at the RuO2 (110) surface
2017 (English)In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 656, p. 9p. 77-85Article in journal (Refereed) Published
Abstract [en]

Ruthenium(IV)oxide (RuO2) is a material used for various purposes. It acts as a catalytic agent in several reactions, for example oxidation of carbon monoxide. Furthermore, it is used as gate material in gas sensors. In this work theoretical and computational studies were made on adsorbed molecules on RuO2 (110) surface, in order to follow the chemistry on the molecular level. Density functional theory calculations of the reactions on the surface have been performed. The calculated reaction and activation energies have been used as input for thermodynamic and kinetics calculations. A surface phase diagram was calculated, presenting the equilibrium composition of the surface at different temperature and gas compositions. The kinetics results are in line with the experimental studies of gas sensors, where water has been produced on the surface, and hydrogen is found at the surface which is responsible for the sensor response.

Place, publisher, year, edition, pages
Elsevier, 2017. p. 9
Keywords
Catalysis; Kinetics; Ruthenium dioxide; Sensor; Surface; Thermodynamics
National Category
Analytical Chemistry
Identifiers
urn:nbn:se:liu:diva-133425 (URN)10.1016/j.susc.2016.10.006 (DOI)000390969300012 ()
Available from: 2016-12-28 Created: 2016-12-28 Last updated: 2018-11-26
Danielsson, Ö., Li, X., Ojamäe, L., Janzén, E., Pedersen, H. & Forsberg, U. (2016). A model for carbon incorporation from trimethyl gallium in chemical vapor deposition of gallium nitride. Journal of Materials Chemistry, 4(4), 863-871
Open this publication in new window or tab >>A model for carbon incorporation from trimethyl gallium in chemical vapor deposition of gallium nitride
Show others...
2016 (English)In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 4, no 4, p. 863-871Article in journal (Refereed) Published
Abstract [en]

Gallium nitride (GaN) semiconductor material can become semi-insulating when doping with carbon. Semi-insulating buffer layers are utilized to prevent leakage currents in GaN high power devices. Carbon is inherently present during chemical vapor deposition (CVD) of GaN from the use of trimethyl gallium (TMGa) as precursor. TMGa decomposes in the gas phase, releasing its methyl groups, which could act as carbon source for doping. It is previously known that the carbon doping levels can be controlled by tuning the CVD process parameters, such as temperature, pressure and precursor flow rates. However, the mechanism for carbon incorporation from TMGa is not yet understood. In this paper, a model for predicting carbon incorporation from TMGa in GaN layers grown by CVD is proposed. The model is based on ab initio quantum chemical calculations of molecular adsorption and reaction energies. Using Computational Fluid Dynamics, with a chemical kinetic model for decomposition of the precursors and reactions in the gas phase, to calculate gas phase compositions at realistic process conditions, together with the proposed model, we obtain good correlations with measurements, for both carbon doping concentrations and growth rates, when varying the inlet NH3/TMGa ratio. When varying temperature (800 – 1050°C), the model overpredicts carbon doping concentrations at the lower temperatures, but predicts growth rates well, and the agreement with measured carbon doping concentrations is good above 1000°C.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2016
National Category
Physical Sciences Physical Chemistry
Identifiers
urn:nbn:se:liu:diva-118113 (URN)10.1039/c5tc03989d (DOI)000368839700027 ()
Note

Funding agencies: Swedish Foundation for Strategic Research (SSF); Swedish Defence Material Administration (FMV)

Vid tiden för disputation förelåg publikationen endast som manuskript

Available from: 2015-05-22 Created: 2015-05-22 Last updated: 2017-12-04Bibliographically approved
Liu, Y. & Ojamäe, L. (2016). C-13 Chemical Shift in Natural Gas Hydrates from First-Principles Solid-State NMR Calculations. The Journal of Physical Chemistry C, 120(2), 1130-1136
Open this publication in new window or tab >>C-13 Chemical Shift in Natural Gas Hydrates from First-Principles Solid-State NMR Calculations
2016 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 2, p. 1130-1136Article in journal (Refereed) Published
Abstract [en]

Natural gas hydrates (NGHs) are of interest both as a prospective energy resource and for possible technological applications. C-13 NMR technology is a powerful tool to characterize NGHs, and in this work, the trends and origins of C-13 NMR chemical shifts of hydrocarbon molecules in NGHs from quantum-chemical first-principles calculations on solid state phases are presented. The chemical shift is found to decrease as the size of the water cavities increases for single occupancy NGHs, and to increase as the amount of CH4 increases for the multioccupancy cases. In most cases, the chemical shift of NGHs monotonically increases as the external pressure increases. Furthermore, the chemical shift can be mainly attributed to the host-guest interaction together with a small contributions from water molecules for tight environments and mainly depends on host-guest interaction for loose environments. The theoretical results provide useful information for identification of the types of clathrate phases and guest molecules included in NGH samples taken from natural sites.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2016
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-125313 (URN)10.1021/acs.jpcc.5b11372 (DOI)000368754700035 ()
Note

Funding Agencies|Swedish Research Council (VR); Swedish Supercomputer Center (SNIC/NSC); China Scholarship Council [201206060016]

Available from: 2016-02-24 Created: 2016-02-19 Last updated: 2017-11-30
Andres Cisneros, G., Thor Wikfeldt, K., Ojamäe, L., Lu, J., Xu, Y., Torabifard, H., . . . Paesani, F. (2016). Modeling Molecular Interactions in Water: From Pairwise to Many Body Potential Energy Functions. Chemical Reviews, 116(13), 7501-7528
Open this publication in new window or tab >>Modeling Molecular Interactions in Water: From Pairwise to Many Body Potential Energy Functions
Show others...
2016 (English)In: Chemical Reviews, ISSN 0009-2665, E-ISSN 1520-6890, Vol. 116, no 13, p. 7501-7528Article, review/survey (Refereed) Published
Abstract [en]

Almost 50 years have passed from the first computer simulations of water, and a large number of molecular models have been proposed since then to elucidate the unique behavior of water across different phases. In this article, we review the recent progress in the development of analytical potential energy functions that aim at correctly representing many-body effects. Starting from the many-body expansion of the interaction energy, specific focus is on different classes of potential energy functions built upon a hierarchy of approximations and on their ability to accurately reproduce reference data obtained from state-of-the-art electronic structure calculations and experimental measurements. We show that most recent potential energy functions, which include explicit short-range representations of two-body and three-body effects along with a physically correct description of many-body effects at all distances, predict the properties of water from the gas to the condensed phase with unprecedented accuracy, thus opening the door to the long-sought "universal model" capable of describing the behavior of water under different conditions and in different environments.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2016
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:liu:diva-130380 (URN)10.1021/acs.chemrev.5b00644 (DOI)000379794000003 ()27186804 (PubMedID)
Note

Funding Agencies|Royal Swedish Academy of Sciences through Nobel Institutes for Physics and Chemistry; Swedish Research Council; Department of Physics at Stockholm University; Icelandic Research Fund; Army Research Laboratory [W911NF-12-2-0023]; Cluster of Excellence RESOLV - Deutsche Forschungsgemeinschaft (DFG) [EXC 1069]; Leverhulme Early Career Fellowship [1441]; Isaac Newton Trust; Wayne State University; National Institutes of Health [R01GM108583]; National Science Foundation [CHE-1453204, ACI-1053575]; National Energy Research Scientific Computing Center (NERSCC); Office of Science of the U.S. Department of Energy [DE-AC02-05CH11231]

Available from: 2016-08-15 Created: 2016-08-05 Last updated: 2017-11-28
Sukkaew, P., Ojamäe, L., Kordina, O., Janzén, E. & Danielsson, Ö. (2016). Thermochemical Properties of Halides and Halohydrides of Silicon and Carbon. ECS Journal of Solid State Science and Technology, 5(2), P27-P35
Open this publication in new window or tab >>Thermochemical Properties of Halides and Halohydrides of Silicon and Carbon
Show others...
2016 (English)In: ECS Journal of Solid State Science and Technology, ISSN 2162-8769, E-ISSN 2162-8777, Vol. 5, no 2, p. P27-P35Article in journal (Refereed) Published
Abstract [en]

Atomization energies, enthalpies of formation, entropies as well as heat capacities of the SiHnXm and CHnXm systems, with X being F, Cl and Br, have been studied using quantum chemical calculations. The Gaussian-4 theory (G4) and Weizman-1 theory as modified by Barnes et al. 2009 (W1RO) have been applied in the calculations of the electronic, zero point and thermal energies. The effects of low-lying electronically excited states due to spin orbit coupling were included for all atoms and diatomic species by mean of the electronic partition functions derived from the experimental or computational energy splittings. The atomization energies, enthalpies of formation, entropies and heat capacities derived from both methods were observed to be reliable. The thermochemical properties in the temperature range of 298-2500 K are provided in the form of 7-coefficient NASA polynomials. (C) The Author(s) 2015. Published by ECS. All rights reserved.

Place, publisher, year, edition, pages
ELECTROCHEMICAL SOC INC, 2016
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-124117 (URN)10.1149/2.0081602jss (DOI)000365748800023 ()
Note

Funding Agencies|Swedish Foundation for Strategic Research

Available from: 2016-01-22 Created: 2016-01-19 Last updated: 2017-11-30
Yazdanfar, M., Kalered, E., Danielsson, Ö., Kordina, O., Nilsson, D., Ivanov, I. G., . . . Pedersen, H. (2015). Brominated chemistry for chemical vapor deposition of electronic grade SiC. Chemistry of Materials, 27(3), 793-801
Open this publication in new window or tab >>Brominated chemistry for chemical vapor deposition of electronic grade SiC
Show others...
2015 (English)In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 27, no 3, p. 793-801Article in journal (Refereed) Published
Abstract [en]

Chlorinated chemical vapor deposition (CVD) chemistry for growth of homoepitaxial layers of silicon carbide (SiC) has paved the way for very thick epitaxial layers in short deposition time as well as novel crystal growth processes for SiC. Here, we explore the possibility to also use a brominated chemistry for SiC CVD by using HBr as additive to the standard SiC CVD precursors. We find that brominated chemistry leads to the same high material quality and control of material properties during deposition as chlorinated chemistry and that the growth rate is on average 10 % higher for a brominated chemistry compared to chlorinated chemistry. Brominated and chlorinated SiC CVD also show very similar gas phase chemistries in thermochemical modelling. This study thus argues that brominated chemistry is a strong alternative for SiC CVD since the deposition rate can be increased with preserved material quality. The thermochemical modelling also suggest that the currently used chemical mechanism for halogenated SiC CVD might need to be revised.

National Category
Chemical Sciences Physical Sciences
Identifiers
urn:nbn:se:liu:diva-111075 (URN)10.1021/acs.chemmater.5b00074 (DOI)000349934500016 ()
Available from: 2014-10-07 Created: 2014-10-07 Last updated: 2018-06-19Bibliographically approved
Liu, Y. & Ojamäe, L. (2015). CH-Stretching Vibrational Trends in Natural Gas Hydrates Studied by Quantum-Chemical Computations. The Journal of Physical Chemistry C, 119(30), 17084-17091
Open this publication in new window or tab >>CH-Stretching Vibrational Trends in Natural Gas Hydrates Studied by Quantum-Chemical Computations
2015 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 30, p. 17084-17091Article in journal (Refereed) Published
Abstract [en]

Vibrational Raman spectrosopy of hydrocarbon CH-stretching vibrations is often-used to study natural gas, hydrates., In this work, CH-stretching vibrational, Raman spectra of hydrocarbon molectles (CH4, C2H6, C(3)H6, C3H8, C4H8, i-C4H10, and n-C4H10) encapsulated in the water cages (D, ID, T, P, H, and I) of the SI, sII, sH, and sK crystal phases. are derived from quantum-chemical computations at the omega B97X-D/6-311++G(24,2p) level of theory. The trends of CH-stretching vibrational frequencies Of hydrocarbon Molecules in natural gas hydrates are found to follow the prediction by the loose cage tight cage model: as the size of Water cavity increases, the CH frequencies will first decrease and: then increase until equal to-that in the gas phase. In the "tight cage" situation, the frequency will be greater than in the gas phase; in the "loose cage" situation, the frequency will be smaller or asymptotic to that in the gas phase. Furthermore, the OH-stretching frequencies are sensitive to the H-bond configuration, and the varying strengths of H-bonds for different configurations are reflected by,the frequency distribution in the corresponding subspectra.

Place, publisher, year, edition, pages
American Chemical Society, 2015
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:liu:diva-120872 (URN)10.1021/acs.jpcc.5b01903 (DOI)000359031900007 ()
Note

Funding Agencies|Swedish Research Council (VR); Swedish Supercomputer Center (SNIC/NSC); China Scholarship Council [201206060016]

Available from: 2015-08-28 Created: 2015-08-28 Last updated: 2017-12-04
Liu, Y. & Ojamäe, L. (2014). C-C Stretching Raman Spectra and Stabilities of Hydrocarbon Molecules in Natural Gas Hydrates: A Quantum Chemical Study. Journal of Physical Chemistry A, 118(49), 11641-11651
Open this publication in new window or tab >>C-C Stretching Raman Spectra and Stabilities of Hydrocarbon Molecules in Natural Gas Hydrates: A Quantum Chemical Study
2014 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 118, no 49, p. 11641-11651Article in journal (Refereed) Published
Abstract [en]

The presence of specific hydrocarbon gas molecules in various types of water cavities in natural gas hydrates (NGHs) are governed by the relative stabilities of these encapsulated guest molecule-water cavity combinations. Using molecular quantum chemical dispersion-corrected hybrid density functional computations, the interaction (Delta E(host-)guest) and cohesive energies (Delta E-coh), enthalpies, and Gibbs free energies for the complexes of host water cages and hydrocarbon guest molecules are calculated at the pi B97X-D/6-311++G(2d,2p) level of theory. The zero-point energy effect of ?Ehost-guest and ?Ecoh is found to be quite substantial. The energetically optimal host-guest combinations for seven hydrocarbon gas molecules (CH4, C2H6, C3H6, C3H8, C4H8, i-C4H10, and n-C4H10) and various water cavities (D, ID, T, P, H, and I) in NGHs are found to be CH4@D, C2H6@T, C3H6@T, C3H8@T, C4H8@T/P/H, i-C4H10@H, and n-C4H10@H, as the largest cohesive energy magnitudes will be obtained with these host-guest combinations. The stabilities of various water cavities enclosing hydrocarbon molecules are evaluated from the computed cohesive Gibbs free energies: CH4 prefers to be trapped in a ID cage; C2H6 prefer T cages; C3H6 and C3H8 prefer T and H cages; C4H8 and i-C4H10 prefer H cages; and n-C4H10 prefer I cages. The vibrational frequencies and Raman intensities of the C-C stretching vibrational modes for these seven hydrocarbon molecules enclosed in each water cavity are computed. A blue shift results after the guest molecule is trapped from gas phase into various water cages due to the host-guest interactions between the water cage and hydrocarbon molecule. The frequency shifts to the red as the radius of water cages increases. The model calculations support the view that C-C stretching vibrations of hydrocarbon molecules in the water cavities can be used as a tool to identify the types of crystal phases and guest molecules in NGHs.

Place, publisher, year, edition, pages
American Chemical Society, 2014
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-113497 (URN)10.1021/jp510118p (DOI)000346320800021 ()25406092 (PubMedID)
Note

Funding Agencies|Swedish Research Council (VR); Swedish supercomputer center (NSC); State Scholarship Fund of China Scholarship Council [201206060016]

Available from: 2015-01-19 Created: 2015-01-19 Last updated: 2017-12-05
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-5341-2637

Search in DiVA

Show all publications