Chemistry Research
https://hdl.handle.net/10023/52
2024-03-29T08:49:13ZReversed crystal growth
https://hdl.handle.net/10023/16784
In the last decade, reversed growth route has been found in many crystal growth processes. In these systems, a single crystal does not develop from a single nucleus. The precursor molecules/ions or nanocrystallites aggregate into some large amorphous or polycrystalline particles. Multiple-nucleation on surface of the amorphous particles or surface re-crystallization of the polycrystalline particles then takes place, forming a single crystal shell with a regular morphology. Finally, the crystallization extends from the surface to the core to form single crystals. This non-classical crystal growth route often results in some special morphologies, such as core-shell structures, hollow single crystals, sandwich structures, etc. This article gives a brief review of the research in the reversed crystal growth and demonstrates that investigation of detailed mechanisms of crystal growth enables us to better understand the formation of many novel morphologies of the crystals. Some unsolved problems are also discussed.
2018-12-22T00:00:00ZZhou, WuzongIn the last decade, reversed growth route has been found in many crystal growth processes. In these systems, a single crystal does not develop from a single nucleus. The precursor molecules/ions or nanocrystallites aggregate into some large amorphous or polycrystalline particles. Multiple-nucleation on surface of the amorphous particles or surface re-crystallization of the polycrystalline particles then takes place, forming a single crystal shell with a regular morphology. Finally, the crystallization extends from the surface to the core to form single crystals. This non-classical crystal growth route often results in some special morphologies, such as core-shell structures, hollow single crystals, sandwich structures, etc. This article gives a brief review of the research in the reversed crystal growth and demonstrates that investigation of detailed mechanisms of crystal growth enables us to better understand the formation of many novel morphologies of the crystals. Some unsolved problems are also discussed.Finding and proving the exact ground state of a generalized Ising model by convex optimization and MAX-SAT
https://hdl.handle.net/10023/12857
Lattice models, also known as generalized Ising models or cluster expansions, are widely used in many areas of science and are routinely applied to the study of alloy thermodynamics, solid-solid phase transitions, magnetic and thermal properties of solids, fluid mechanics, and others. However, the problem of finding and proving the global ground state of a lattice model, which is essential for all of the aforementioned applications, has remained unresolved for relatively complex practical systems, with only a limited number of results for highly simplified systems known. In this paper, we present a practical and general algorithm that provides a provable periodically constrained ground state of a complex lattice model up to a given unit cell size and in many cases is able to prove global optimality over all other choices of unit cell. We transform the infinite-discrete-optimization problem into a pair of combinatorial optimization (MAX-SAT) and nonsmooth convex optimization (MAX-MIN) problems, which provide upper and lower bounds on the ground state energy, respectively. By systematically converging these bounds to each other, we may find and prove the exact ground state of realistic Hamiltonians whose exact solutions are difficult, if not impossible, to obtain via traditional methods. Considering that currently such practical Hamiltonians are solved using simulated annealing and genetic algorithms that are often unable to find the true global energy minimum and inherently cannot prove the optimality of their result, our paper opens the door to resolving longstanding uncertainties in lattice models of physical phenomena. An implementation of the algorithm is available at https://github.com/dkitch/maxsat-ising
This paper was supported primarily by the US Department of Energy (DOE) under Contract No. DE-FG02-96ER45571. In addition, some of the test cases for ground states were supported by the Office of Naval Research under contract N00014-14-1-0444.
2016-10-21T00:00:00ZHuang, WenxuanKitchaev, Daniil A.Dacek, Stephen T.Rong, ZiqinUrban, AlexanderCao, ShanLuo, ChuanCeder, GerbrandLattice models, also known as generalized Ising models or cluster expansions, are widely used in many areas of science and are routinely applied to the study of alloy thermodynamics, solid-solid phase transitions, magnetic and thermal properties of solids, fluid mechanics, and others. However, the problem of finding and proving the global ground state of a lattice model, which is essential for all of the aforementioned applications, has remained unresolved for relatively complex practical systems, with only a limited number of results for highly simplified systems known. In this paper, we present a practical and general algorithm that provides a provable periodically constrained ground state of a complex lattice model up to a given unit cell size and in many cases is able to prove global optimality over all other choices of unit cell. We transform the infinite-discrete-optimization problem into a pair of combinatorial optimization (MAX-SAT) and nonsmooth convex optimization (MAX-MIN) problems, which provide upper and lower bounds on the ground state energy, respectively. By systematically converging these bounds to each other, we may find and prove the exact ground state of realistic Hamiltonians whose exact solutions are difficult, if not impossible, to obtain via traditional methods. Considering that currently such practical Hamiltonians are solved using simulated annealing and genetic algorithms that are often unable to find the true global energy minimum and inherently cannot prove the optimality of their result, our paper opens the door to resolving longstanding uncertainties in lattice models of physical phenomena. An implementation of the algorithm is available at https://github.com/dkitch/maxsat-isingChemistry and Brexit
https://hdl.handle.net/10023/12567
2017-12-07T00:00:00ZCole-Hamilton, David JohnThe corrosion behavior of a sputtered micrograin film on Fe-5Cr-5Si alloy in H2-CO2-H2S mixture at 700 °C
https://hdl.handle.net/10023/10788
The corrosion behaviors of as-cast Fe-5Cr-5Si alloy with and without sputtered Fe-5Cr-5Si film in H2-CO2-H2S mixture at 700 °C are studied. The corrosion scale forming on the as-cast alloy is non-protective and mainly composed of FeS outer layer and FeS + FeCr2O4 + Fe2SiO4 inner layer. However, a continuous Cr2O3 + SiO2 layer which possesses favorable protectiveness forms at the coating/alloy interface for the coated alloy, even though FeS layer and FeS + FeCr2O4 + Fe2SiO4 mixed layer also form. The formation mechanism of the Cr2O3 + SiO2 layer on the coated alloy is discussed thoroughly.
Financial support from the NSFC (Projects NO. 59071129 & 51501135) is acknowledged.
2017-10-01T00:00:00ZLiu, L. L.Li, W. B.Guo, Q. Q.Ni, C. S.Niu, Y.The corrosion behaviors of as-cast Fe-5Cr-5Si alloy with and without sputtered Fe-5Cr-5Si film in H2-CO2-H2S mixture at 700 °C are studied. The corrosion scale forming on the as-cast alloy is non-protective and mainly composed of FeS outer layer and FeS + FeCr2O4 + Fe2SiO4 inner layer. However, a continuous Cr2O3 + SiO2 layer which possesses favorable protectiveness forms at the coating/alloy interface for the coated alloy, even though FeS layer and FeS + FeCr2O4 + Fe2SiO4 mixed layer also form. The formation mechanism of the Cr2O3 + SiO2 layer on the coated alloy is discussed thoroughly.Electronic nature of zwitterionic alkali metal methanides, silanides and germanides - a combined experimental and computational approach
https://hdl.handle.net/10023/9838
Zwitterionic group 14 complexes of the alkali metals of formula [C(SiMe2OCH2CH2OMe)3M], (M- 1 ), [Si(SiMe2OCH2CH2OMe)3M], (M- 2 ), [Ge(SiMe2OCH2CH2OMe)3M], (M- 3 ), where M = Li, Na or K, have been prepared, structurally characterized and their electronic nature was investigated by computational methods. Zwitterions M- 2 and M- 3 were synthesized via reactions of [Si(SiMe2OCH2CH2OMe)4] ( 2 ) and [Ge(SiMe2OCH2CH2OMe)4] ( 3 ) with MOBut (M = Li, Na or K), resp., in almost quantitative yields, while M- 1 were prepared from deprotonation of [HC(SiMe2OCH2CH2OMe)3] (1) with LiBut, NaCH2Ph and KCH2Ph, resp. X-ray crystallographic studies and DFT calculations in the gas-phase, including calculations of the NPA charges confirm the zwitterionic nature of these compounds, with the alkali metal cations being rigidly locked and charge separated from the anion by the internal OCH2CH2OMe donor groups. Natural bond orbital (NBO) analysis and the second order perturbation theory analysis of the NBOs reveal significant hyperconjugative interactions in M- 1 -M- 3 , primarily between the lone pair and the antibonding Si-O orbitals, the extent of which decreases in the order M- 1 > M- 2 > M- 3 . The experimental basicities and the calculated gas-phase basicities of M- 1 -M- 3 reveal the zwitterionic alkali metal methanides M- 1 to be significantly stronger bases than the analogous silanides M- 2 and germanium M- 3 .
This project was funded in part by the NSF (grant no. 1407681; Project SusChEM: IUPAC) as part of the IUPAC International Funding Call on “Novel Molecular and Supramolecular Theory and Synthesis Approaches for Sustainable Catalysis”. Support was also provided by the TTU Department of Chemistry & Biochemistry cluster Robinson whose purchase was funded by the NSF (CRIF-MU CHE-0840493).
2017-02-01T00:00:00ZLi, H.Aquino, A. J. A.Cordes, D. B.Hase, W. L.Krempner, C.Zwitterionic group 14 complexes of the alkali metals of formula [C(SiMe2OCH2CH2OMe)3M], (M- 1 ), [Si(SiMe2OCH2CH2OMe)3M], (M- 2 ), [Ge(SiMe2OCH2CH2OMe)3M], (M- 3 ), where M = Li, Na or K, have been prepared, structurally characterized and their electronic nature was investigated by computational methods. Zwitterions M- 2 and M- 3 were synthesized via reactions of [Si(SiMe2OCH2CH2OMe)4] ( 2 ) and [Ge(SiMe2OCH2CH2OMe)4] ( 3 ) with MOBut (M = Li, Na or K), resp., in almost quantitative yields, while M- 1 were prepared from deprotonation of [HC(SiMe2OCH2CH2OMe)3] (1) with LiBut, NaCH2Ph and KCH2Ph, resp. X-ray crystallographic studies and DFT calculations in the gas-phase, including calculations of the NPA charges confirm the zwitterionic nature of these compounds, with the alkali metal cations being rigidly locked and charge separated from the anion by the internal OCH2CH2OMe donor groups. Natural bond orbital (NBO) analysis and the second order perturbation theory analysis of the NBOs reveal significant hyperconjugative interactions in M- 1 -M- 3 , primarily between the lone pair and the antibonding Si-O orbitals, the extent of which decreases in the order M- 1 > M- 2 > M- 3 . The experimental basicities and the calculated gas-phase basicities of M- 1 -M- 3 reveal the zwitterionic alkali metal methanides M- 1 to be significantly stronger bases than the analogous silanides M- 2 and germanium M- 3 .Comparison between phosphine and NHC-modified Pd catalysts in the telomerization of butadiene with methanol – a kinetic study combined with model-based experimental analysis
https://hdl.handle.net/10023/9289
The telomerization of butadiene with methanol was investigated in the presence of different palladium catalysts modified either with triphenylphosphine (TPP) or 1,3-dimesityl-imidazol-2-ylidene (IMes) ligand. When pure butadiene was used as substrate, a moderate selectivity for the Pd-TPP catalyst toward the desired product 1-methoxy-2,7-octadiene (1-Mode) of around 87 % was obtained, while the IMes carbene ligand almost exclusively formed 1-Mode with 97.5 % selectivity. The selectivity remained unchanged when the pure butadiene feed was replaced by synthetic crack-C4 (sCC4), a technical feed of 45 mol% butadiene and 55 mol% inerts (butenes and butanes). The TPP-modified catalyst showed a lower reaction rate, which was attributed to the expected dilution effect caused by the inerts. Surprisingly, the IMes-modified catalyst showed a higher rate with sCC4 compared to the pure feed. By means of a model-based experimental analysis, kinetic rate equations could be derived. The kinetic modeling supports the assumption that the two catalyst systems follow different kinetic rate equations. For the Pd-TPP catalyst, the reaction kinetics were related to the Jolly mechanism. In contrast, the Jolly mechanism had to be adapted for the Pd-IMes catalyst as the impact of the base seems to differ strongly from that for the Pd-TPP catalyst. The Pd-IMes system was found to be zero order in butadiene at moderate to high butadiene concentrations and first order in base while the nucleophilicity of the base is influenced by the methanol amount resulting in a negative reaction order for methanol.
The authors thank the European Community within its project SYNFLOW (FP7; grant agreement n8 NMP2-LA-2010-246461) for financial support.
2015-01-01T00:00:00ZHopf, LisaRecker, SebastianNiedermaier, MatthiasKiermaier, StephanStrobel, VinzentMaschmeyer, DietrichCole-Hamilton, DavidMarquardt, WolfgangWasserscheid, PeterHaumann, MarcoThe telomerization of butadiene with methanol was investigated in the presence of different palladium catalysts modified either with triphenylphosphine (TPP) or 1,3-dimesityl-imidazol-2-ylidene (IMes) ligand. When pure butadiene was used as substrate, a moderate selectivity for the Pd-TPP catalyst toward the desired product 1-methoxy-2,7-octadiene (1-Mode) of around 87 % was obtained, while the IMes carbene ligand almost exclusively formed 1-Mode with 97.5 % selectivity. The selectivity remained unchanged when the pure butadiene feed was replaced by synthetic crack-C4 (sCC4), a technical feed of 45 mol% butadiene and 55 mol% inerts (butenes and butanes). The TPP-modified catalyst showed a lower reaction rate, which was attributed to the expected dilution effect caused by the inerts. Surprisingly, the IMes-modified catalyst showed a higher rate with sCC4 compared to the pure feed. By means of a model-based experimental analysis, kinetic rate equations could be derived. The kinetic modeling supports the assumption that the two catalyst systems follow different kinetic rate equations. For the Pd-TPP catalyst, the reaction kinetics were related to the Jolly mechanism. In contrast, the Jolly mechanism had to be adapted for the Pd-IMes catalyst as the impact of the base seems to differ strongly from that for the Pd-TPP catalyst. The Pd-IMes system was found to be zero order in butadiene at moderate to high butadiene concentrations and first order in base while the nucleophilicity of the base is influenced by the methanol amount resulting in a negative reaction order for methanol.Disorder driven structural and dielectric properties of silicon substituted strontium titanate
https://hdl.handle.net/10023/9153
A systematic study on structural, microstructural, optical, dielectric, and electrical properties of phase-pure silicon-modified SrTiO3 polycrystalline electroceramics synthesized using high energy solid state reaction techniques is presented. The asymmetry and splitting in the x-ray diffractometer spectra and the observation of first order transverse optical TO2 and longitudinal optical LO4 modes in Raman spectra (nominally forbidden) revealed the distortion in the cubic lattice as a result of breaking of inversion symmetry due to doping. A bandgap Eg of 3.27 eV was determined for the sample by diffuse reflectance spectroscopy. A high dielectric constant of -400 and very low dielectric loss of -0.03 were obtained at 100 kHz near ambient conditions. The temperature dependence of the dielectric data displayed features of high temperature relaxor ferroelectric behavior as evidence of existence of polar nano-regions. The ac conductivity as a function of frequency showed features typical of universal dynamic response and obeyed a power law σac = σdc+Aωn . The temperature dependent dc conductivity followed an Arrhenius relation with activation energy of 123 meV in the 200–500 K temperature range. The linear dielectric response of Pt/SrSi0.03Ti0.97O3/Pt dielectric capacitors was well characterized. The measured leakage current was exceptionally low, 13 nA/cm2 at 8.7 kV/cm, revealing an interface blocked bulk conduction mechanism.
Financial support from NSF Grant No. NSF-RII-0701525 was acknowledged. S.D. is thankful to DOD for doctoral fellowship under Grant No. W911NF-11-1-0204. S.P.P. is grateful to NSF for financial assistance under Grant No: NSF-EFRI RESTOR # 1038272.
2015-07-17T00:00:00ZDugu, SitaPavunny, Shojan P.Sharma, YogeshScott, James F.Katiyar, Ram S.A systematic study on structural, microstructural, optical, dielectric, and electrical properties of phase-pure silicon-modified SrTiO3 polycrystalline electroceramics synthesized using high energy solid state reaction techniques is presented. The asymmetry and splitting in the x-ray diffractometer spectra and the observation of first order transverse optical TO2 and longitudinal optical LO4 modes in Raman spectra (nominally forbidden) revealed the distortion in the cubic lattice as a result of breaking of inversion symmetry due to doping. A bandgap Eg of 3.27 eV was determined for the sample by diffuse reflectance spectroscopy. A high dielectric constant of -400 and very low dielectric loss of -0.03 were obtained at 100 kHz near ambient conditions. The temperature dependence of the dielectric data displayed features of high temperature relaxor ferroelectric behavior as evidence of existence of polar nano-regions. The ac conductivity as a function of frequency showed features typical of universal dynamic response and obeyed a power law σac = σdc+Aωn . The temperature dependent dc conductivity followed an Arrhenius relation with activation energy of 123 meV in the 200–500 K temperature range. The linear dielectric response of Pt/SrSi0.03Ti0.97O3/Pt dielectric capacitors was well characterized. The measured leakage current was exceptionally low, 13 nA/cm2 at 8.7 kV/cm, revealing an interface blocked bulk conduction mechanism.Taking a molecular motor for a spin : helicase mechanism studied by spin labelling and PELDOR
https://hdl.handle.net/10023/7926
The complex molecular motions central to the functions of helicases have long attracted attention. Protein crystallography has provided transformative insights into these dynamic conformational changes, however important questions about the true nature of helicase configurations during the catalytic cycle remain. Using pulsed EPR (PELDOR or DEER) to measure interdomain distances in solution, we have examined two representative helicases: PcrA from superfamily 1 and XPD from superfamily 2. The data show that PcrA is a dynamic structure with domain movements that correlate with particular functional states, confirming and extending the information gleaned from crystal structures and other techniques. XPD in contrast is shown to be a rigid protein with almost no conformational changes resulting from nucleotide or DNA binding, which is well described by static crystal structures. Our results highlight the complimentary nature of PELDOR to crystallography and the power of its precision in understanding the conformational changes relevant to helicase function.
Welcome Trust programme grant [WT091825MA to M.F.W., J.H.N.]; Wellcome Trust multi-user equipment grant [099149/Z/12/Z]. Royal Society Wolfseon Merit Award (to M.F.W., J.H.N.). Funding for open access charge: Wellcome Trust [WT091825MA].
2015-12-10T00:00:00ZConstantinescu Aruxandei, DianaPetrovic-Stojanovska, BiljanaSchiemann, OlavNaismith, JimWhite, Malcolm FThe complex molecular motions central to the functions of helicases have long attracted attention. Protein crystallography has provided transformative insights into these dynamic conformational changes, however important questions about the true nature of helicase configurations during the catalytic cycle remain. Using pulsed EPR (PELDOR or DEER) to measure interdomain distances in solution, we have examined two representative helicases: PcrA from superfamily 1 and XPD from superfamily 2. The data show that PcrA is a dynamic structure with domain movements that correlate with particular functional states, confirming and extending the information gleaned from crystal structures and other techniques. XPD in contrast is shown to be a rigid protein with almost no conformational changes resulting from nucleotide or DNA binding, which is well described by static crystal structures. Our results highlight the complimentary nature of PELDOR to crystallography and the power of its precision in understanding the conformational changes relevant to helicase function.Understanding of CO2 electrochemical reduction reaction process via high temperature solid oxide electrolysers
https://hdl.handle.net/10023/7374
The CO2 electrochemical reduction via SOEC was studied for a range of cathode materials in various operational conditions. The influences of the fuel gas composition, operating potential and temperature on cathode behavior are discussed and compared on different cathodes. The dissociative adsorption and surface diffusion of active species from CO2 reduction reaction was found to contribute dominantly to the LSCM-based cathode working in CO2-CO mixtures. Efforts were also made to obtain a high performance and durable cathode for high temperature CO2 electrolyser by employing a gradient LSCM-YSZ cathode and by adopting wet impregnation in cathode preparation. The latter was to more effective in enhancing the cathode electro-catalytic activity. A competitive cathode to Ni-YSZ cermet was fabricated by infiltrating 0.5wt% Pd and GDC into porous LSCM and YSZ layers.
The authors thank the University of St Andrews and RCUK Energy Supergen programme on H-Delivery and EPSRC Platform and Senior fellowship programs for funding.
2015-07-17T00:00:00ZYue, XianglingIrvine, John Thomas SirrThe CO2 electrochemical reduction via SOEC was studied for a range of cathode materials in various operational conditions. The influences of the fuel gas composition, operating potential and temperature on cathode behavior are discussed and compared on different cathodes. The dissociative adsorption and surface diffusion of active species from CO2 reduction reaction was found to contribute dominantly to the LSCM-based cathode working in CO2-CO mixtures. Efforts were also made to obtain a high performance and durable cathode for high temperature CO2 electrolyser by employing a gradient LSCM-YSZ cathode and by adopting wet impregnation in cathode preparation. The latter was to more effective in enhancing the cathode electro-catalytic activity. A competitive cathode to Ni-YSZ cermet was fabricated by infiltrating 0.5wt% Pd and GDC into porous LSCM and YSZ layers.In situ tailored nickel nano-catalyst layer for internal reforming hydrocarbon fueled SOFCs
https://hdl.handle.net/10023/7372
Conventional Ni cermet anodes suffer from carbon deposition when they are directly used with hydrocarbon fuels due to the negative effects of pyrolysis and Boudouard reactions. In this work, the use of a non-stoichiometric perovskite, La0.8Ce0.1Ni0.4Ti0.6O3, as a reforming layer in reducing atmospheres led to the surface being highly populated with homogeneously exsolved Ni nano particles. This catalyst layer was applied to Ni-GDC anode supported and ScSZ electrolyte supported cells to prevent carbon deposition and to stabilize operation with dry methane. The catalyst layer showed both excellent attachment to the Ni-GDC anode and resistance to carbon deposition. The performance of the Ni-GDC anode-supported cells with the catalyst layer was about 1.1 W/cm2 in hydrogen fuel which is similar to that seen without the use of a catalyst layer. For the ScSZ electrolyte supported cells, the catalyst layer improved the power density and stability when in operation with dry methane.
The authors gratefully thank the Engineering and Physical Sciences Research Council (EPSRC) SuperGen Hydrogen Fuel Cells Challenges Flame SOFC Project (Grant No EP/K021036/1) for financial support
2015-07-17T00:00:00ZMyung, JaehaNeagu, DragosTham, MarkIrvine, John Thomas SirrConventional Ni cermet anodes suffer from carbon deposition when they are directly used with hydrocarbon fuels due to the negative effects of pyrolysis and Boudouard reactions. In this work, the use of a non-stoichiometric perovskite, La0.8Ce0.1Ni0.4Ti0.6O3, as a reforming layer in reducing atmospheres led to the surface being highly populated with homogeneously exsolved Ni nano particles. This catalyst layer was applied to Ni-GDC anode supported and ScSZ electrolyte supported cells to prevent carbon deposition and to stabilize operation with dry methane. The catalyst layer showed both excellent attachment to the Ni-GDC anode and resistance to carbon deposition. The performance of the Ni-GDC anode-supported cells with the catalyst layer was about 1.1 W/cm2 in hydrogen fuel which is similar to that seen without the use of a catalyst layer. For the ScSZ electrolyte supported cells, the catalyst layer improved the power density and stability when in operation with dry methane.Development of tailored porous microstructures for infiltrated catalyst electrodes by aqueous tape casting methods
https://hdl.handle.net/10023/7371
Recent SOFC research has shown that impregnating fine catalyst structures into porous scaffolds to be an extremely promising route for electrode development. It is clear that in optimising the advantages offered by this technique there will be an obvious link between the morphology of the porous scaffold and the infiltrated catalyst. There are significant potential benefits to using aqueous systems for the manufacture of the scaffold. They include the potential for a far larger range of pore formers which may be employed to create specific pore morphologies and also reduced environmental burdens, such as exhaust handling, worker exposure and disposal. Recent and ongoing activities to develop such systems at University of St Andrews will be described. Areas of discussion will be effects of ceramic particle size, the size ratio of pore former to ceramic particle, pore former type and loading and how these interact with other tape constituents both on the behaviour during processing and on the final fired morphology. Better understanding of these complex relationships will help in designing optimised porous structures in the future.
The authors acknowledge the EPSRC Hydrogen and Fuel Cells Supergen Fuels Cells Challenge Programme project EP/M014304/1 “Tailoring of microstructural evolution in impregnated SOFC electrodes” and the University of St Andrews for funding this work.
2015-07-17T00:00:00ZCassidy, MarkDoherty, D.J.Yue, XianglingIrvine, John Thomas SirrRecent SOFC research has shown that impregnating fine catalyst structures into porous scaffolds to be an extremely promising route for electrode development. It is clear that in optimising the advantages offered by this technique there will be an obvious link between the morphology of the porous scaffold and the infiltrated catalyst. There are significant potential benefits to using aqueous systems for the manufacture of the scaffold. They include the potential for a far larger range of pore formers which may be employed to create specific pore morphologies and also reduced environmental burdens, such as exhaust handling, worker exposure and disposal. Recent and ongoing activities to develop such systems at University of St Andrews will be described. Areas of discussion will be effects of ceramic particle size, the size ratio of pore former to ceramic particle, pore former type and loading and how these interact with other tape constituents both on the behaviour during processing and on the final fired morphology. Better understanding of these complex relationships will help in designing optimised porous structures in the future.Utilisation of coal in direct carbon fuel cells
https://hdl.handle.net/10023/7370
Hybrid Direct Carbon Fuel Cells merge Solid Oxide Fuel Cell (SOFC) and MCFC technologies, using a solid oxide electrolyte to separate the cathode and anode compartments, while a molten carbonate electrolyte is utilised to extend the anode/electrolyte region. Oxygen is reduced to O2- ions at the cathode and transported across the solid electrolyte membrane to the anode compartment, where carbon is oxidised to CO2. Molten carbonate could enhance the carbon oxidation in two ways as a fuel carrier or as an electrochemical mediator. The maximum energy density can be achieved by fully oxidising carbon to CO2 offering very high efficiencies. This concept has been demonstrated using a wide range of carbons and carbon-rich fuels such as coal, plastics, carbon colloids, activated carbons and charcoals. In a short stack of 3 cells delivered a maximum power output at 650°C of 5.4 W, at over 100mWcm-2. The underlying chemical processes in DCFCs are complex involving a series of catalytic and electrochemical reactions of a complex fuel. Coal and biochars are quite far from pure carbon comprising of high hydrogen content and often significant oxygen, sulphur and nitrogen contents as well as inorganic, ash components. Here we report on the pyrolysis and oxidation reactions and processes that occur in situ and in DCFC relevant conditions. Of key importance is interplay between carbon and its oxides as direct oxidation of carbon to carbon dioxide delivers the ultimate efficiency. There is a change in process above 750°C where the reverse Boudouard reaction becomes dominant and our focus is on understanding the lower temperature electrochemical processes.
The authors thank the Research fund for coal and steel for supporting this research, Grant Agreement Number: RFCR CT-2011-00004.
2015-01-01T00:00:00ZIrvine, John Thomas SirrFuente Cuesta, AidaMottram, AndrewJiang, CairongSavaniu, Cristian DanielJain, Sneh LataHybrid Direct Carbon Fuel Cells merge Solid Oxide Fuel Cell (SOFC) and MCFC technologies, using a solid oxide electrolyte to separate the cathode and anode compartments, while a molten carbonate electrolyte is utilised to extend the anode/electrolyte region. Oxygen is reduced to O2- ions at the cathode and transported across the solid electrolyte membrane to the anode compartment, where carbon is oxidised to CO2. Molten carbonate could enhance the carbon oxidation in two ways as a fuel carrier or as an electrochemical mediator. The maximum energy density can be achieved by fully oxidising carbon to CO2 offering very high efficiencies. This concept has been demonstrated using a wide range of carbons and carbon-rich fuels such as coal, plastics, carbon colloids, activated carbons and charcoals. In a short stack of 3 cells delivered a maximum power output at 650°C of 5.4 W, at over 100mWcm-2. The underlying chemical processes in DCFCs are complex involving a series of catalytic and electrochemical reactions of a complex fuel. Coal and biochars are quite far from pure carbon comprising of high hydrogen content and often significant oxygen, sulphur and nitrogen contents as well as inorganic, ash components. Here we report on the pyrolysis and oxidation reactions and processes that occur in situ and in DCFC relevant conditions. Of key importance is interplay between carbon and its oxides as direct oxidation of carbon to carbon dioxide delivers the ultimate efficiency. There is a change in process above 750°C where the reverse Boudouard reaction becomes dominant and our focus is on understanding the lower temperature electrochemical processes.Electrochemical impedance spectroscopy investigation of the anodic functionalities and processes in LSCM-CGO-Ni systems
https://hdl.handle.net/10023/7367
Electrochemical impedance spectroscopy was used to characterize anode compositions made of (La0.75Sr0.25)0.97Cr0.5Mn0.5O3 (LSCM) and gadolinia doped ceria (CGO) with and without additional submicron Ni, or exsoluted Ni nanoparticles. In addition, the effects of the anode gas flow rate and the working temperature were investigated. Higher content of the ionic conductor leads to a decrease of the impedance in the frequency range from 100 Hz to 10 Hz. The effect of the catalyst component was investigated while keeping the electronic conductivity unchanged in the tested materials. Enhanced catalytic activity was demonstrated to considerably decrease the impedance especially in the frequency range between 100 Hz to 1 Hz. The change in the gas flow rate affects mainly the impedance bellow 1 Hz.
2015-01-01T00:00:00ZBoulfrad, SamirNechache, A.Cassidy, MarkTraversa, E.Irvine, John Thomas SirrElectrochemical impedance spectroscopy was used to characterize anode compositions made of (La0.75Sr0.25)0.97Cr0.5Mn0.5O3 (LSCM) and gadolinia doped ceria (CGO) with and without additional submicron Ni, or exsoluted Ni nanoparticles. In addition, the effects of the anode gas flow rate and the working temperature were investigated. Higher content of the ionic conductor leads to a decrease of the impedance in the frequency range from 100 Hz to 10 Hz. The effect of the catalyst component was investigated while keeping the electronic conductivity unchanged in the tested materials. Enhanced catalytic activity was demonstrated to considerably decrease the impedance especially in the frequency range between 100 Hz to 1 Hz. The change in the gas flow rate affects mainly the impedance bellow 1 Hz.Collimation of fast electrons in critical density plasma channel
https://hdl.handle.net/10023/6348
Significantly collimated fast electron beam with a divergence angle 10° (FWHM) is generated through the interaction of ultra-intense laser light with a uniform critical density plasma in experiments and 2D PIC simulations. In the experiment, the uniform critical density plasma is created by ionizing an ultra-low density foam target. The spacial distribution of the fast electron is observed by Imaging Plate. 2D PIC simulation and post process analysis reveal magnetic collimation of energetic electrons along the plasma channel.
2015-01-01T00:00:00ZIwawaki, T.Habara, H.Baton, S.Morita, K.Fuchs, J.Chen, S.Nakatsutsumi, M.Rousseaux, C.Filippi, F.Nazarov, W.Tanaka, K.A.Significantly collimated fast electron beam with a divergence angle 10° (FWHM) is generated through the interaction of ultra-intense laser light with a uniform critical density plasma in experiments and 2D PIC simulations. In the experiment, the uniform critical density plasma is created by ionizing an ultra-low density foam target. The spacial distribution of the fast electron is observed by Imaging Plate. 2D PIC simulation and post process analysis reveal magnetic collimation of energetic electrons along the plasma channel.Simulated biogas for nickel-based solid oxide fuel cells
https://hdl.handle.net/10023/6070
Biogas is composed of variable gases including hydrogen, nitrogen and sulphur, with methane and carbon dioxide as the main components. The common ratio of methane to carbon dioxide is 60/40 in volume and this high amount of methane causes carbon deposition when biogas is used in solid oxide fuel cells. To prevent carbon deposition, dry reforming, steam reforming or partial oxidation is the common method. In this paper, a nickel cermet solid oxide fuel cell was investigated with a simulated biogas based on 63% CH4 and 37% CO2, which was obtained by presuming 80% fuel utilisation and 25% recirculation of anode gas. Supplied with a 30 ml/min of simulated biogas, the cell generated a maximum power density of 856 mW cm-2 at 850 °C. The cell ran stably at loads of 100 mA cm-2, 300 mA cm-2and 500 mA cm-2 over a period of 16 hours at each level.
2014-01-01T00:00:00ZMa, J.Jiang, C.Cassidy, M.Irvine, J.T.S.Biogas is composed of variable gases including hydrogen, nitrogen and sulphur, with methane and carbon dioxide as the main components. The common ratio of methane to carbon dioxide is 60/40 in volume and this high amount of methane causes carbon deposition when biogas is used in solid oxide fuel cells. To prevent carbon deposition, dry reforming, steam reforming or partial oxidation is the common method. In this paper, a nickel cermet solid oxide fuel cell was investigated with a simulated biogas based on 63% CH4 and 37% CO2, which was obtained by presuming 80% fuel utilisation and 25% recirculation of anode gas. Supplied with a 30 ml/min of simulated biogas, the cell generated a maximum power density of 856 mW cm-2 at 850 °C. The cell ran stably at loads of 100 mA cm-2, 300 mA cm-2and 500 mA cm-2 over a period of 16 hours at each level.Optimisation of engineered Escherichia coli biofilms for enzymatic biosynthesis of L-halotryptophans
https://hdl.handle.net/10023/5241
Engineered biofilms comprising a single recombinant species have demonstrated remarkable activity as novel biocatalysts for a range of applications. In this work, we focused on the biotransformation of 5-haloindole into 5-halotryptophan, a pharmaceutical intermediate, using Escherichia coli expressing a recombinant tryptophan synthase enzyme encoded by plasmid pSTB7. To optimise the reaction we compared two E. coli K-12 strains (MC4100 and MG1655) and their ompR234 mutants, which overproduce the adhesin curli (PHL644 and PHL628). The ompR234 mutation increased the quantity of biofilm in both MG1655 and MC4100 backgrounds. In all cases, no conversion of 5-haloindoles was observed using cells without the pSTB7 plasmid. Engineered biofilms of strains PHL628 pSTB7 and PHL644 pSTB7 generated more 5-halotryptophan than their corresponding planktonic cells. Flow cytometry revealed that the vast majority of cells were alive after 24 hour biotransformation reactions, both in planktonic and biofilm forms, suggesting that cell viability was not a major factor in the greater performance of biofilm reactions. Monitoring 5-haloindole depletion, 5-halotryptophan synthesis and the percentage conversion of the biotransformation reaction suggested that there were inherent differences between strains MG1655 and MC4100, and between planktonic and biofilm cells, in terms of tryptophan and indole metabolism and transport. The study has reinforced the need to thoroughly investigate bacterial physiology and make informed strain selections when developing biotransformation reactions.
This study was funded by a UK Biotechnology & Biological Sciences Research Council grant (BB/I006834/1) to MJS, RJMG and TWO and a quota PhD studentship to LH. The Accuri C6 instrument was awarded to TWO as a BD Accuri Creativity Award.
2013-11-04T00:00:00ZPerni, S.Hackett, L.Goss, R.J.M.Simmons, M.J.Overton, T.W.Engineered biofilms comprising a single recombinant species have demonstrated remarkable activity as novel biocatalysts for a range of applications. In this work, we focused on the biotransformation of 5-haloindole into 5-halotryptophan, a pharmaceutical intermediate, using Escherichia coli expressing a recombinant tryptophan synthase enzyme encoded by plasmid pSTB7. To optimise the reaction we compared two E. coli K-12 strains (MC4100 and MG1655) and their ompR234 mutants, which overproduce the adhesin curli (PHL644 and PHL628). The ompR234 mutation increased the quantity of biofilm in both MG1655 and MC4100 backgrounds. In all cases, no conversion of 5-haloindoles was observed using cells without the pSTB7 plasmid. Engineered biofilms of strains PHL628 pSTB7 and PHL644 pSTB7 generated more 5-halotryptophan than their corresponding planktonic cells. Flow cytometry revealed that the vast majority of cells were alive after 24 hour biotransformation reactions, both in planktonic and biofilm forms, suggesting that cell viability was not a major factor in the greater performance of biofilm reactions. Monitoring 5-haloindole depletion, 5-halotryptophan synthesis and the percentage conversion of the biotransformation reaction suggested that there were inherent differences between strains MG1655 and MC4100, and between planktonic and biofilm cells, in terms of tryptophan and indole metabolism and transport. The study has reinforced the need to thoroughly investigate bacterial physiology and make informed strain selections when developing biotransformation reactions.Calculation of a standard reformed biogas composition and testing on SOFC anode powders
https://hdl.handle.net/10023/5174
A standard reformed biogas composition, based on a 63% CH4 37% CO2 input biogas, was defined by calculation. It is designed to resemble the composition of biogas that would enter a real SOFC stack, assuming 80% fuel utilization, and 25% recirculation of the anode off-gas. It is thermodynamically impervious to coking above 720°C. This gas composition was then used to test the catalytic reforming performance of nickel powder and La0.8Ce0.1Ni0.4Ti0.6O3-δ at 900°C in the standard reformed biogas. No coking was seen on the powder samples by visual inspection after this test. The La0.8Ce0.1Ni0.4Ti0.6O3-δ is designed to exsolve Ni nanoparticles when reduced. SEM pictures of the post-test sample show some small particles that may be exsolved nanoparticles, but further investigation is needed to confirm this. Ni powder was the better reforming catalyst, but sintered extensively in the 3 h test. The La0.8Ce0.1Ni0.4Ti0.6O3-δ also showed reforming capability, and much better microstructural stability in the standard reformed biogas.
2013-01-01T00:00:00ZGamble, Stephen RichardNeagu, DragosIrvine, John Thomas SirrA standard reformed biogas composition, based on a 63% CH4 37% CO2 input biogas, was defined by calculation. It is designed to resemble the composition of biogas that would enter a real SOFC stack, assuming 80% fuel utilization, and 25% recirculation of the anode off-gas. It is thermodynamically impervious to coking above 720°C. This gas composition was then used to test the catalytic reforming performance of nickel powder and La0.8Ce0.1Ni0.4Ti0.6O3-δ at 900°C in the standard reformed biogas. No coking was seen on the powder samples by visual inspection after this test. The La0.8Ce0.1Ni0.4Ti0.6O3-δ is designed to exsolve Ni nanoparticles when reduced. SEM pictures of the post-test sample show some small particles that may be exsolved nanoparticles, but further investigation is needed to confirm this. Ni powder was the better reforming catalyst, but sintered extensively in the 3 h test. The La0.8Ce0.1Ni0.4Ti0.6O3-δ also showed reforming capability, and much better microstructural stability in the standard reformed biogas.Dodeka(ethylene)octamine
https://hdl.handle.net/10023/1753
2011-03-21T00:00:00ZBuehl, MichaelFlash vacuum pyrolysis of α-acyl-o-methoxybenzylidenetriphenylphosphoranes to give 2-substituted benzofurans
https://hdl.handle.net/10023/670
The title stabilised ylides, readily prepared in one step from acid chlorides, are converted upon FVP at 850 °C into 2-substituted benzofurans. When the acyl group is aromatic it appears unchanged as the 2- substituent in the product while for aliphatic examples degradation processes may lead to 2-alkenyl products.
2000-01-01T00:00:00ZAitken, R. AlanThe title stabilised ylides, readily prepared in one step from acid chlorides, are converted upon FVP at 850 °C into 2-substituted benzofurans. When the acyl group is aromatic it appears unchanged as the 2- substituent in the product while for aliphatic examples degradation processes may lead to 2-alkenyl products.