Details of a Researcher - Thomas, Morgan

Papers - Thomas, Morgan

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Effect of cation side-chain structure on the physicochemical properties of pyrrolidinium-based electrolytes upon mixing with sodium salt

Yoshifumi Hirotsu, Morgan L. Thomas, Yuko Takeoka, Masahiro Rikukawa, Masahiro Yoshizawa-Fujita

Science and Technology of Advanced Materials (Taylor & Francis Ltd) 26 ( 1 ) 2466417 2025.12

Accepted, ISSN 1468-6996

In recent years, the development of next-generation secondary batteries employing resource-abundant metals such as Na has garnered significant attention. However, the high reactivity of Na raises safety concerns, necessitating the development of safer devices. To address this, ionic liquids (ILs) and organic ionic plastic crystals (OIPCs) have emerged as promising novel electrolytes. Despite their potential, studies investigating the influence of cation structures on various properties remain scarce, particularly in composites where Na salts are introduced into OIPCs. This study focuses on the effects of cation species and Na-salt concentration in OIPCs, specifically in N,N-diethylpyrrolidinium bis(fluorosulfonyl)amide ([C₂epyr][FSA]) and N-ethyl-N-isopropylpyrrolidinium bis(fluorosulfonyl)amide ([Cᵢ₃epyr][FSA]), with the addition of sodium bis(fluorosulfonyl)amide (NaFSA). The phase transition behavior, dissociation state of Na salts, and electrochemical properties exhibited significant differences based on the cationic structure of the OIPCs. The combination of each OIPC with Na salt resulted in liquid mixtures, and the ionic conductivity increased significantly as the Na salt concentration increased. High ionic conductivities were achieved with [C₂epyr][FSA]/NaFSA (20 mol%) and [Cᵢ₃epyr][FSA]/NaFSA (10 mol%), showing values of 2.7 × 10⁻³ and 2.2 × 10⁻³ S cm⁻¹ at 25 degrees C, respectively. Linear sweep voltammetry results indicated superior oxidative stability in the [Ci₃epyr][FSA] system. Solvation numbers of Na⁺, influenced by differences in cationic side-chain structures, were determined to be 2.7 for the [C₂epyr]⁺ system and 2.9 for the [Cᵢ₃epyr]⁺ system. The results suggest that controlling solvation numbers is a critical factor in the molecular design of high-performance ionic conductors.

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A Simple Regeneration Process Using a CO₂‐Switchable‐Polarity Solvent for Cellulose Hydrogels

Arata Matsui, Deandra Ayu Putri, Morgan L. Thomas, Yuko Takeoka, Masahiro Rikukawa, Masahiro Yoshizawa-Fujita

ChemSusChem (Wiley-VCH Verlag GmbH) 18 ( 6 ) e202401848 2024.11

Accepted, ISSN 1864-5631

<jats:p>Cellulose is one of the main components of plant cell walls, abundant on earth, and can be acquired at a low cost. Furthermore, there has been increasing interest in its use in environmentally friendly, carbon‐neutral, sustainable materials. It is expected that the applications of cellulose will expand with the development of a simple processing method. In this study, we dissolved cellulose in aqueous N‐butyl‐N‐methylpyrrolidinium hydroxide solution ([C4mpyr][OH]/H2O) and investigated the cellulose regeneration process based on changes in solubility upon application of CO2 gas. We investigated the effect of transformation of the anion chemical structure on cellulose solubility by flowing CO2 gas into [C4mpyr][OH]/H2O and conducted pH, FT‐IR, and 13C NMR measurements. We observed that the changes in anion structure allowed for the modulation of cellulose solubility in [C4mpyr][OH]/H2O, thus establishing a simple and safe cellulose regeneration process. This regeneration process was also applied to enable the production of cellulose hydrogels. The hydrogel formed using this method was revealed to have higher mechanical strength than an analogous hydrogel produced using the same dissolution solvent with the addition of a cross‐linker. The ability to produce cellulose‐based hydrogels of different mechanical properties is expected to expand the possible applications.</jats:p>

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Evaluation of the Solid-Electrolyte Interphase Formation in a Bis(fluorosulfonyl)amide Based Ionic Liquid in the Presence Lithium Ion Using Different Redox Probes

Shunosuke Momose, Morgan L. Thomas, Nobuyuki Serizawa, Yasushi Katayama

ECS Transactions 2024.09

Accepted

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Efficient Exploration of Highly Conductive Pyrrolidinium-Based Ionic Plastic Crystals Using Materials Informatics

Takuto Ootahara, Kan Hatakeyama-Sato, Morgan L. Thomas, Yuko Takeoka, Masahiro Rikukawa, Masahiro Yoshizawa-Fujita

ACS Applied Electronic Materials (American Chemical Society (ACS)) 6 ( 8 ) 5866 - 5878 2024.07

Accepted, ISSN 2637-6113

Organic ionic plastic crystals (OIPCs), which are soft crystals with plasticity and ionic conductivity, are expected to be applied as solid electrolytes in battery applications. Further improvement of ionic conductivity is necessary for practical use as an electrolyte for energy storage devices. Materials Informatics (MI) is a method of incorporating information science in materials development. In this research, MI is being used to develop OIPCs with high ionic conductivity. By using informatics science in addition to chemical knowledge, this research can be carried out efficiently and innovatively. The synthesis of eight new compounds resulted in six of them being solid at room temperature, while two of them were in a liquid state, namely, ionic liquids. We evaluated the phase transition temperatures and ionic conductivity for each compound. Notably, N-ethyl-N-methylpyrrolidinium trifluoro(trifluoromethyl)borate ([C₂mpyr][CF₃BF₃]) exhibited a high ionic conductivity of 1.75 × 10⁻⁴ S cm⁻¹ at 25 degrees C, which is one of the highest values reported among OIPCs to date. The combination of an experimental and MI based approach revealed an improved understanding of the relationship between ion size and ionic conductivity for a series of pyrrolidinium-based OIPCs, and it is expected that further improvements to this approach will yield greater understanding of structure-property relationships.

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Boosting the Ionic Conductivity of Pyrrolidinium-Based Ionic Plastic Crystals by LLZO Fillers

Kotoko Ariga, Shuho Akakabe, Ryotaro Sekiguchi, Morgan L. Thomas, Yuko Takeoka, Masahiro Rikukawa, Masahiro Yoshizawa-Fujita

ACS Omega (American Chemical Society (ACS)) 9 ( 20 ) 22203 - 22212 2024.05

Accepted, ISSN 2470-1343

Organic ionic plastic crystals (OIPCs) have attracted attention as novel organic solid electrolyte materials, but their insufficient mechanical strength and ionic conductivity have prevented their application. In this study, a lithium salt, lithium bis(fluorosulfonyl)amide (LiFSA), and an inorganic solid electrolyte, Li₇La₃Zr₂O₁₂ (LLZO), were added to an OIPC, N,N-diethylpyrrolidinium bis(fluorosulfonyl)amide ([C₂epyr][FSA]). The fabricated organic-inorganic hybrid solid electrolytes were evaluated thermally, mechanically, and electrochemically to reveal which factors affect the properties of the electrolytes. All samples showed excellent thermal stability regardless of LiFSA or LLZO concentration, and they were found to be highly plastic and ion-conductive solids at a wide range of temperatures. It was also revealed that the addition of LLZO raised the nanoindentation stiffness (H-IT) of the [C₂epyr][FSA]/LiFSA composites. The ionic conductivity of the hybrid electrolytes was higher than that of the pristine OIPC, reaching a value of 2.1 × 10⁻⁴ S cm⁻¹ at 25 degrees C upon addition of appropriate amounts of LiFSA and LLZO. Overall, samples with higher LiFSA concentration and moderate LLZO concentration exhibited higher ionic conductivity. Cyclic voltammetry results showed that the [C₂epyr][FSA]/LiFSA/LLZO composites were lithium-ion conductors. These findings indicate that by optimizing the concentrations of lithium salt and LLZO, it would be possible to realize their applications as solid electrolytes.

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Hydrothermal processing of waste pine wood into industrially useful products

Jyoti S. Gokhale, Moreshwar P. Hude, Ganapati D. Yadav, Morgan Thomas, Janusz Kozinski, Ajay K. Dalai

Journal of the Indian Chemical Society (Elsevier {BV}) 99 ( 9 ) 100647 - 100647 2022.09

Accepted, ISSN 00194522

An ongoing major outbreak of mountain pine beetle in Western Canada has provided a clear opportunity to utilize waste pinewood as a source of renewable energy. Therefore hydrothermal processing of waste pinewood as a feedstock for bio-oil and biochar production using subcritical and supercritical water technology was carried out in semi-batch mode to investigate the effect of pressure (200–400 bar) and temperature (300–400 °C) on the yield and composition of bio-oil. The pinewood samples have very high cellulose and hemicellulose content but low ash content and are thus a formidable feedstock for bioenergy production. The optimum conditions for the hydrothermal processing of the pinewood in a tubular reactor were found to be 400 °C and 250 bars with respect to biochar and bio-oil yield based on the highest calorific value analysis. Detailed characterization of bio-oil and biochar was performed using GCMS, NMR, SEM, calorific value, and elemental analysis, respectively. The critical components of bio-oil were found to be phenols, methoxyphenols, hydroxymethyl furfural (HMF), and vanillin, whereas as compared to the raw pine wood, the biochar was considerably lower H:C and O:C ratios than those of the unprocessed pinewood. The analyses of bio-oil by means of GCMS and ¹H NMR showed that it was mainly composed of heterocyclic compounds, phenols, aldehydes and acids.

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Rheological and Ionic Transport Properties of Nanocomposite Electrolytes Based on Protic Ionic Liquids and Silica Nanoparticles

Mayeesha Marium, Mahfuzul Hoque, Muhammed Shah Miran, Morgan L. Thomas, Izuru Kawamura, Kazuhide Ueno, Kaoru Dokko, Masayoshi Watanabe

Langmuir (American Chemical Society ({ACS})) 36 ( 1 ) 148 - 158 2020.01

Accepted, ISSN 07437463

In this study, the effect of hydrophilic silica nanoparticle (AEROSIL 200) addition on the rheological and transport properties of several protic ionic liquids (PILs) consisting of protonated 1,8-diazabicyclo[5.4.0]undec-7-ene cation (DBU) was studied. Interactions between the surface silanol groups of the silica nanoparticles and the ions of these PILs affected the nature of particle aggregation and the hydrogen bonding environment, which was reflected in the nonlinear rheological behaviors and transport properties of their colloidal suspensions. In contrast to shear-thinning gels formed by colloidal suspensions of the silica nanoparticles in [DBU][TFSA] ([TFSA] = [N(SO₂CF₃)₂]), [DBU][TfO] ([TfO] = [CF₃SO₃]), and [DBU][TFA] ([TFA] = [CF₃CO₂]), a shear-thickening stable suspension was formed in the [DBU][MSA] ([MSA] = [CH₃SO₃]) system. A relatively strong interaction between the silanol groups and the ions of [DBU] [MSA] and the ability of this PIL to form a thicker solvation layer through hydrogen bonding were assumed to be responsible for this unique behavior. Moreover, the [DBU][MSA]-silica system showed a large enhancement in the conductivity at a certain silica concentration. This enhancement was not observed in the other PIL-silica composites that exhibited shear-thinning behavior. Even though diffusion of ions was found to be restricted in the presence of silica, a preferentially stronger interaction between [MSA] anions and the silica surface resulted in an increase in the number of charge carriers.

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Role of Cation Structure in CO₂ Separation by Ionic Liquid/Sulfonated Polyimide Composite Membrane

Eri Hayashi, Kei Hashimoto, Morgan L. Thomas, Seiji Tsuzuki, Masayoshi Watanabe

Membranes (MDPI AG) 9 ( 7 ) 81 - 81 2019.07

Accepted

The development of suitable separation technologies for the separation of carbon dioxide is a pressing technological requirement. The application of ion gel membranes for this purpose continues to stimulate a great deal of research, and in this study we focus on the chemical structure of the ionic liquid component in the ion gel, and its interactions with the sulfonated polyimide polymer. Whilst such membranes are known to give promising carbon dioxide separation properties together with mechanical strength and thin-film-processability, we further elaborate on how changing the cation of the ionic liquid from a typical imidazolium cation to a protic variant effects the physicochemical, thermal, and structural properties of the membranes, and how these changes further influence the carbon dioxide separation properties. We compare and contrast our findings with our earlier study on protic and aprotic ammonium-based ionic liquids, and highlight that for CO₂ absorption behavior in the imidazolium systems, the importance of directionality of interactions (ion pairs exhibit a large energy stabilization only for a specific geometrical arrangement of cation and anion, e.g., hydrogen bonding rather than Coulombic interaction) between cation and anion applies not only to the protic system, but also to the nominally aprotic cation. Finally, we demonstrate that the phase separation behavior in the ion gels is an important factor in determining the carbon dioxide separation behavior.

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Sulfolane-Based Highly Concentrated Electrolytes of Lithium Bis(trifluoromethanesulfonyl)amide: Ionic Transport, Li-Ion Coordination, and Li–S Battery Performance

Azusa Nakanishi, Kazuhide Ueno, Daiki Watanabe, Yosuke Ugata, Yoshiharu Matsumae, Jiali Liu, Morgan L. Thomas, Kaoru Dokko, Masayoshi Watanabe

Journal of Physical Chemistry C (American Chemical Society) 123 ( 23 ) 14229 - 14238 2019.05

Accepted, ISSN 1932-7447

Following our recent study demonstrating predominant Li-ion hopping conduction in sulfolane (SL)-based highly concentrated electrolytes with LiBF4, LiClO4, and lithium bis(fluorosulfonyl)amide, herein a systematic study on transport properties and Li-ion coordination of SL-based electrolytes with lithium bis(trifluoromethanesulfonyl)amide was performed. In the highly concentrated region, Li ions clearly diffuse faster than SL and TFSA anions. The two oxygen atoms of the SL sulfonyl group tend to coordinate to two different neighboring Li ions and TFSA anions form ionic clusters with Li ions, verifying the previous observation of the unusual Li-ion conduction and its relevance to the SL-and anion-bridged, chainlike Li-ion coordination structure for the SL-based concentrated systems with other Li salts. Moreover, addition of hydrofluoroether (HFE) to the SL-based concentrated electrolytes greatly enhances diffusion coefficients but fragments the chainlike Li-ion coordination to smaller clusters, leading to a reduced contribution of Li-ion hopping to the overall Li-ion conduction. The SL-based concentrated electrolyte and its mixtures with HFE showed lower lithium polysulfide solubility and higher rate capability for lithium-sulfur (Li-S) cells compared with previously reported tetraglyme-based electrolytes. The SL-based electrolytes were found to manifest a significant improvement in Li-ion mass transfer as a sparingly solvating electrolyte, enabling the solid-state sulfur redox reactions in high-performance Li-S batteries.

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Application of Protic Ionic Liquids to CO₂ Separation in a Sulfonated Polyimide-derived Ion Gel Membrane

Eri Hayashi, Morgan L. Thomas, Kei Hashimoto, Seiji Tsuzuki, Akika Ito, Masayoshi Watanabe

ACS Applied Polymer Materials (American Chemical Society) 1 ( 6 ) 1579 - 1589 2019.05

Accepted, ISSN 2637-6105

It is of great interest to determine whether a relatively easily prepared and inexpensive protic ionic liquid (PIL) could be used in place of an aprotic ionic liquid (AIL) in a composite membrane for CO₂ separation. We prepared mechanically reliable sulfonated polyimide (SPI) composite membranes with a PIL, [N124][NTf₂] (N,N,N-butylethylmethylammonium bis(trifluoromethylsulfonyl)amide) by a solution casting method, and their mechanical, thermal, and gas separation (CO₂ and N₂) properties were compared with those of membranes incorporating an isomeric AIL, [N1123][NTf₂] ([N1123](+), N,N,N,N-ethyldimethylpropylammonium). We discussed the influence of the presence or absence of active protons in the ILs on CO₂ separation characteristics and the applicability of the PIL to a CO₂ separation membrane. The SPI/PIL membrane exhibited a slightly lower selectivity, but higher permeability, than the SPI/AIL membrane. It is supposed that these differences originate from the difference in membrane structure and CO₂ interactions between PIL and AIL, which was investigated through a combination of ab initio calculations, CO₂ solubility measurements, and dynamic mechanical analysis. The [N124][NTf₂](PIL)/SPI membranes showed a CO₂ permeability (PCO₂ = 240 Barrer) with a relatively high selectivity (alpha(CO₂/N₂) = 23) at 30 degrees C, which indicates that a PIL/SPI composite membrane can be employed for CO₂ separation. We also explored CO₂ separation under elevated temperatures and humidified conditions for confirming the applicability of the SPI/PIL membrane. Finally, the effect of PIL structures was studied by using [N122][NTf₂] ([N122](+), N,N,N-diethylmethylammonium) in comparison with [N124][NTf₂]. Composite [N122][NTf₂]/SPI membranes exhibited a comparable selectivity and an improved permeability. We anticipate these results will unveil a new paradigm in functional ion gels for critical CO₂ separation technology, toward utilization of effective, benign materials.

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Li-ion Hopping Conduction in Highly Concentrated Lithium Bis(fluorosulfonyl)Amide/Dinitrile Liquid Electrolytes

Yosuke Ugata, Morgan L. Thomas, Toshihiko Mandai, Kazuhide Ueno, Kaoru Dokko, Masayoshi Watanabe

Physical Chemistry Chemical Physics (Royal Society of Chemistry) 21 ( 19 ) 9759 - 9768 2019.04

Accepted, ISSN 1463-9076

Li+ ion hopping conduction in highly concentrated solutions of lithium bis(fluorosulfonyl) amide (LiFSA) dissolved in dinitrile solvents, namely succinonitrile, glutaronitrile, and adiponitrile, was investigated. Phase behaviors of the LiFSA/dinitrile binary mixtures assessed by differential scanning calorimetry suggested that LiFSA and the dinitriles form stable solvates in a molar ratio of 1 : 2. For succinonitrile, a glass forming room temperature liquid is formed when [LiFSA]/[succinonitrile] 4 1. The corresponding glutaronitrile and adiponitrile mixtures have melting points below 60 degrees C. The self-diffusion coefficients of Li+, FSA(-), and dinitrile measured with pulsed field gradient NMR suggested that Li+ ion diffuses faster than anion and dinitrile in the liquids of composition [LiFSA]/[dinitrile] = 1/0.8, indicating emergence of Li+ ion hopping conduction. X-ray crystallography for the LiFSA-(dinitrile)(2) solvates and Raman spectroscopy for the liquids with composition [LiFSA]/[dinitrile] > 1 revealed that the two cyano groups of the dinitrile coordinate to two different Li+ ions and form solvent-bridged structures of (Li+-dinitrile-Li+). In addition, the Raman spectra suggested that ionic aggregates (Li+-FSA(-)-Li+) are formed in the liquids with composition [LiFSA]/[dinitrile] > 1. Although there is frequent ligand (dinitrile and/or anion) exchange for each Li+ ion in the liquid state, the polymeric network structures (solvent-bridged structure and ionic aggregates) restrict the facile motion of ligands because each ligand is interacting with multiple Li+ ions in the highly concentrated electrolytes. This induces the faster diffusion of the Li+ ion than that of the ligands, i. e., hopping conduction of Li+ through ligand exchange. Electrochemical measurements clarified that the [LiFSA]/[succinonitrile] = 1/0.8 electrolyte possesses a relatively high Li+ transport ability (limiting current density > 7 mA cm(-2)) thanks to the Li+ hopping conduction, regardless of its extremely high viscosity (3142 mPa s) and relatively low conductivity (0.26 mS cm(-1)) at room temperature. Furthermore, this electrolyte was shown to have a high Li+ transference number (>0.6), exhibited reversible Li metal deposition/dissolution i.e. suppression of reductive decomposition of the solvent, and could be successfully applied to graphite and LiNi1/3Mn1/3Co1/3O2 half-cells.

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Ionic transport in highly concentrated lithium bis(fluorosulfonyl)amide electrolytes with keto ester solvents: structural implications for ion hopping conduction in liquid electrolytes

Shinji Kondou, Morgan L. Thomas, Toshihiko Mandai, Kazuhide Ueno, Kaoru Dokko, Masayoshi Watanabe

Physical Chemistry Chemical Physics (Royal Society of Chemistry ({RSC})) 21 ( 9 ) 5097 - 5105 2019.02

Accepted, ISSN 14639076

Recent studies have suggested that a Li ion hopping or ligand- or anion-exchange mechanism is largely involved in Li ion conduction of highly concentrated liquid electrolytes. To understand the determining factors for the Li ion hopping/exchange dominant conduction in such liquid systems, ionic diffusion behavior and Li ion coordination structures of concentrated liquid electrolytes composed of lithium bis(fluorosulfonyl)amide (Li[FSA]) and keto ester solvents with two carbonyl coordinating sites of increasing intramolecular distance (methyl pyruvate (MP), methyl acetoacetate (MA), and methyl levulinate (ML)) were studied. Diffusivity measurements of MP- and MA-based concentrated electrolytes showed faster Li ion diffusion than the solvent and FSA anion, demonstrating that Li ion diffusion was dominated by the Li ion hopping/exchange mechanism. A solvent-bridged, chain-like Li ion coordination structure and highly aggregated ion pairs (AGGs) or ionic clusters e.g. Li-x[FSA](y)((y-x)-) forming in the electrolytes were shown to contribute to Li ion hopping conduction. By contrast, ML, with greater intramolecular distance between the carbonyl moieties, is more prone to form a bidentate complex with a Li cation, which increased the contribution of the vehicle mechanism to Li ion diffusion even though similar AGGs and ionic clusters were also observed. The clear correlation between the unusual Li ion diffusion and the solvent-bridged, chain-like structure provides an important insight into the design principles for fast Li ion conducting liquid electrolytes that would enable Li ion transport decoupled from viscosity-controlled mass transfer processes.

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Direct Evidence for Li Ion Hopping Conduction in Highly Concentrated Sulfolane-Based Liquid Electrolytes

Kaoru Dokko, Daiki Watanabe, Yosuke Ugata, Morgan L. Thomas, Seiji Tsuzuki, Wataru Shinoda, Kei Hashimoto, Kazuhide Ueno, Yasuhiro Umebayashi, Masayoshi Watanabe

The Journal of Physical Chemistry B (American Chemical Society ({ACS})) 122 ( 47 ) 10736 - 10745 2018.11

Accepted, ISSN 15206106

We demonstrate that Li+ hopping conduction, which cannot be explained by conventional models i.e., Onsager's theory and Stokes' law, emerges in highly concentrated liquid electrolytes composed of LiBF4 and sulfolane (SL). Self-diffusion coefficients of Li+ (D-Li), BF4- (D-BF4), and SL (D-SL) were measured with pulsed-field gradient NMR. In the concentrated electrolytes with molar ratios of SL/LiBF4 <= 3, the ratios D-SL/D-Li and D-BF4/D-Li become lower than 1, suggesting faster diffusion of Li+ than SL and BF4-, and thus the evolution of Li+ hopping conduction. X-ray crystallographic analysis of the LiBF4/SL (1:1) solvate revealed that the two oxygen atoms of the sulfone group are involved in the bridging coordination of two different Li+ ions. In addition, the BF4- anion also participates in the bridging coordination of Li+. The Raman spectra of the highly concentrated LiBF4-SL solution suggested that Li+ ions are bridged by SL and BF4- even in the liquid state. Moreover, detailed investigation along with molecular dynamics simulations suggests that Li+ exchanges ligands (SL and BF4-) dynamically in the highly concentrated electrolytes, and Li+ hops from one coordination site to another. The spatial proximity of coordination sites, along with the possible domain structure, is assumed to enable Li+ hopping conduction. Finally, we demonstrate that Li+ hopping suppresses concentration polarization in Li batteries, leading to increased limiting current density and improved rate capability compared to the conventional concentration electrolyte. Identification and rationalization of Li+ ion hopping in concentrated SL electrolytes is expected to trigger a new paradigm of understanding for such unconventional electrolyte systems.

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Enhanced Electrochemical Stability of Molten Li Salt Hydrate Electrolytes by the Addition of Divalent Cations

Shinji Kondou, Erika Nozaki, Shoshi Terada, Morgan L. Thomas, Kazuhide Ueno, Yasuhiro Umebayashi, Kaoru Dokko, Masayoshi Watanabe

The Journal of Physical Chemistry C (American Chemical Society ({ACS})) 122 ( 35 ) 20167 - 20175 2018.09

Accepted, ISSN 19327447

Water can be an attractive solvent for Li-ion battery electrolytes owing to numerous advantages such as high polarity, nonflammability, environmental benignity, and abundance, provided that its narrow electrochemical potential window can be enhanced to a similar level to that of typical nonaqueous electrolytes. In recent years, significant improvements in the electrochemical stability of aqueous electrolytes have been achieved with molten salt hydrate electrolytes containing extremely high concentrations of Li salt. In this study, we investigated the effect of divalent salt additives (magnesium and calcium bis(trifluoromethanesulfonyl)amides) in a molten salt hydrate electrolyte (21 mol kg(-1) lithium bis(trifluoromethanesulfonyl)amide) on the electrochemical stability and aqueous lithium secondary battery performance. We found that the electrochemical stability was further enhanced by the addition of the divalent salt. In particular, the reductive stability was increased by more than 1 V on the Al electrode in the presence of either of the divalent cations. Surface characterization with X-ray photoelectron spectroscopy suggests that a passivation layer formed on the Al electrode consists of inorganic salts (most notably fluorides) of the divalent cations and the less-soluble solid electrolyte interphase mitigated the reductive decomposition of water effectively. The enhanced electrochemical stability in the presence of the divalent salts resulted in a more-stable charge-discharge cycling of LiCoO2 and Li4Ti5O12 electrodes.

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Critically Examining the Role of Nanocatalysts in Li-O₂ Batteries: Viability toward Suppression of Recharge Overpotential, Rechargeability, and Cyclability

Raymond A. Wong, Chunzhen Yang, Arghya Dutta, O. Minho, Misun Hong, Morgan L. Thomas, Keisuke Yamanaka, Toshiaki Ohta, Keiko Waki, Hye Ryung Byon

ACS Energy Letters (American Chemical Society) 3 ( 3 ) 592 - 597 2018.03

Accepted, ISSN 2380-8195

In lithium-oxygen (Li-O2) batteries, nanocatalysts have been widely employed as a means to suppress the large recharge overpotential and to possibly improve cyclability. However, these studies have consistently been mired with ambiguity relating to the possible exacerbation of side reactions, which in turn has brought into question the role of such catalysts in Li-O2 cells. Here, we shed light on the viability of nanocatalysts by examining the use of Ru, Pt, Pd, Co3O4, and Au nanoparticles supported on carbon nanotubes in Li-O2 cells. We show that while there can be noticeable reduction in overpotential with catalysts, the facile decomposition of Li2O2 is not accompanied by a decrease in side reactions, and as a consequence, there is no notable improvement in rechargeability or cyclability. Instead, highly active catalysts can exhibit nonselectivity for all oxidation reactions including Li2O2 and the electrolyte. This work underscores the importance of metrics beyond simple consideration of the recharge overpotential and the necessity of pursuing approaches that can promote reversible Li-O2 electrochemistry.

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Protic ionic liquids with primary alkylamine-derived cations: The dominance of hydrogen bonding on observed physicochemical properties

Mahfuzul Hoque, Morgan L. Thomas, Muhammed Shah Miran, Mio Akiyama, Mayeesha Marium, Kazuhide Ueno, Kaoru Dokko, Masayoshi Watanabe

RSC Advances (Royal Society of Chemistry) 8 ( 18 ) 9790 - 9794 2018.03

Accepted, ISSN 2046-2069

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Magnesium bis(trifluoromethanesulfonyl)amide complexes with triglyme and asymmetric homologues: Phase behavior, coordination structures and melting point reduction

Kei Hashimoto, Soma Suzuki, Morgan L. Thomas, Toshihiko Mandai, Seiji Tsuzuki, Kaoru Dokko, Masayoshi Watanabe

Physical Chemistry Chemical Physics (Royal Society of Chemistry) 20 ( 12 ) 7998 - 8007 2018.02

Accepted, ISSN 1463-9076

The phase behavior of binary mixtures of triglyme (G3) and Mg[TFSA]2 (TFSA: bis(trifluoromethanesulfonyl)amide) was investigated, towards the development of a Mg2+-based room-temperature solvate ionic liquid (SIL) electrolyte. In a 1:1 molar ratio, G3 and Mg[TFSA]2 form a thermally stable complex (decomposition temperature, Td: 240 °C) with a melting point (Tm) of 70 °C, which is considerably lower than that of the analogous tetraglyme (G4) system (137 °C). X-ray crystallography of a single crystal of [Mg(G3)][TFSA]2 revealed that a single Mg2+ cation is coordinated by a single, distorted, tetradentate G3 molecule from one side, and two monodentate [TFSA]- anions, with transoid conformation, from the reverse side to form an ion pair. Raman spectra of [Mg(G3)][TFSA]2 in the molten state revealed the presence of different coordination structures, as the liquid exhibits changes in the vibrational modes corresponding to G3 and the [TFSA]- anion compared to those observed for the solid. Investigation of the ion pair stabilization energies by DFT calculations suggests that higher stability cation complexes and ion pairs co-exist in the molten state than those observed in the crystalline state. These results imply that the coordination structures of the ion pairs play a key role in providing SILs with low Tm. To decrease the Tm further, several asymmetric homologues of G3, which have higher conformational flexibility than G3, were investigated. Notably, a 1:1 mixture of Mg[TFSA]2 with G3Bu (where one of the terminal methyl groups of G3 is substituted for a butyl group) formed a thermally stable complex (Td: 251 °C) without any distinct Tm and showed reasonable ionic conductivity at room-temperature, indicating partial dissociation of ions. In this electrolyte, which showed high oxidative stability, quasi-reversible Mg deposition/dissolution was achieved, indicating that Mg2+-based room-temperature SILs can be utilized as a new class of Mg electrolyte.

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Electrolyte Composition in Li/O₂ Batteries with LiI Redox Mediators: Solvation Effects on Redox Potentials and Implications for Redox Shuttling

Azusa Nakanishi, Morgan L. Thomas, Hoi Min Kwon, Yuki Kobayashi, Ryoichi Tatara, Kazuhide Ueno, Kaoru Dokko, Masayoshi Watanabe

Journal of Physical Chemistry C (American Chemical Society) 122 ( 3 ) 1522 - 1534 2018.01

Accepted, ISSN 1932-7447

© 2018 American Chemical Society. The use of LiI as redox mediator for the charge reaction in nonaqueous Li/O2 cells has been widely studied recently, as a possible means to fulfill the great promise of the Li/O2 system as a high energy density "beyond Li-ion" battery. In this work, we highlight the importance of considering the redox potential for both the I-/I3- and I3-/I2 redox couples and how the electrolyte solvent (here tetraglyme (G4) and dimethyl sulfoxide (DMSO)) and concentration (here 1.0 and 2.8 M) have a profound influence on these potentials. Through a combination of galvanostatic cycling, electrochemical mass spectrometry, and cyclic voltammetry, we thus consider the influence of solvent and electrolyte concentration on both the redox mediation and redox shuttle processes and suggest that this important aspect must be considered for further studies with mediators in Li/O2 and related systems. We demonstrate that, in our system, 100 mM LiI in 1.0 M Li[TFSA]/DMSO provides the most effective redox mediation among the electrolytes we have studied but conversely exhibits the highest degree of redox shuttling (in the absence of O2). The balance between effective limitation of redox shuttle and ease of mediator diffusion to discharge products is of great importance and should be considered in any future cell design utilizing a mediator.

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Simple combination of a protic salt and an iron halide: Precursor for a Fe, N and S co-doped catalyst for the oxygen reduction reaction in alkaline and acidic media

Mahfuzul Hoque, Shiguo Zhang, Morgan L. Thomas, Zhe Li, Soma Suzuki, Ayumi Ando, Masato Yanagi, Yoshio Kobayashi, Kaoru Dokko, Masayoshi Watanabe

Journal of Materials Chemistry A (Royal Society of Chemistry) 6 ( 3 ) 1138 - 1149 2017.12

Accepted, ISSN 2050-7496

The major bottleneck for widespread realization of fuel cells has been the usage of precious-metal-based electrocatalysts, such as Pt/C or Pt-alloy/C, at the cathode. Owing to the high cost and limited natural resources of platinum, nonprecious metal catalysts, such as iron-doped carbons, have emerged as promising substitute catalyst materials. Protic salts and protic ionic liquids can provide a simple, quick, and cost-effective approach for fabricating iron-doped carbons without any additives or high-surface-area carbon supports. We demonstrate here the fabrication of an efficient electrocatalyst based on a protic salt, 1,10-phenanthrolinium dihydrogen sulfate ([Phen][2HSO4]), in combination with iron(iii) chloride, FeCl3, via nanocasting. A predominantly mesoporous architecture with a narrow pore size distribution was achieved owing to the suitability of the precursors and silica template. The material also exhibited in situ formation of Fe-N bonds in the nitrogen and sulfur co-doped carbons. We found that maximizing the content of this motif was beneficial towards efficient conversion of oxygen into water in alkaline media. The prototype catalyst after post treatment (acid leaching and 2nd carbonization) also exhibited efficient reduction of oxygen in acidic media. The contribution of Fe-N bonds to the observed activity in acidic solution was less than in alkaline solution. The simplicity of the synthesis of the protic salt and the versatility of the ionic liquid platform make this molecular-level carbon precursor a unique candidate for future development of iron doped catalysts for fuel cells.

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Oxygen Reduction Reaction in Highly Concentrated Electrolyte Solutions of Lithium Bis(trifluoromethanesulfonyl)amide/Dimethyl Sulfoxide

Ryoichi Tatara, David G. Kwabi, Thomas P. Batcho, Michal Tulodziecki, Kenta Watanabe, Hoi-Min Kwon, Morgan L. Thomas, Kazuhide Ueno, Carl V. Thompson, Kaoru Dokko, Yang Shao-Horn, Masayoshi Watanabete

JOURNAL OF PHYSICAL CHEMISTRY C (AMER CHEMICAL SOC) 121 ( 17 ) 9162 - 9172 2017.05

Accepted, ISSN 1932-7447

The performance of current Liair batteries is greatly limited by critical obstacles such as electrolyte decomposition, high charging overpotentials, and limited cycle life. Thus, much effort is devoted to fundamental studies to understand the mechanisms of discharge/charge processes and overcome the above-mentioned obstacles. In particular, the search for new stable electrolytes is vital for long-lasting and highly cyclable batteries. The highly reactive lithium superoxide intermediate (LiO2) produced during discharge process can react with the electrolyte and produce a variety of byproducts that will shorten battery life span. To study this degradation mechanism, we investigated oxygen reduction reaction (ORR) in highly concentrated electrolyte solutions of lithium bis(trifluoromethanesulfonyl)amide (Li[TFSA])/dimethyl sulfoxide (DMSO). On the basis of rotating ring disk electrode measurements, we showed that LiO2 dissolution can be limited by increasing lithium salt concentration over 2.3 mol dm(-3). Our Raman results suggested that this phenomenon can be related to lack of free DMSO molecules and increasing DMSO-Li+ interactions with higher Li+ concentration. X-ray diffraction measurements for the products of ORR suggested that the side reaction of DMSO with Li2O2 and/or LiO2 could be suppressed by decreasing the solubility of LiO2 in highly concentrated electrolytes.

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Effect of Anion in Glyme-based Electrolyte for Li-O₂ Batteries: Stability/Solubility of Discharge Intermediate

Hoi-Min Kwon, Morgan L. Thomas, Ryoichi Tatara, Azusa Nakanishi, Kaoru Dokko, Masayoshi Watanabe

CHEMISTRY LETTERS (CHEMICAL SOC JAPAN) 46 ( 4 ) 573 - 576 2017.04

Accepted, ISSN 0366-7022

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Suppression of Water Absorption by Molecular Design of Ionic Liquid Electrolyte for Li-Air Battery

Morgan L. Thomas, Yoshiki Oda, Ryoichi Tatara, Hoi-Min Kwon, Kazuhide Ueno, Kaoru Dokko, Masayoshi Watanabe

ADVANCED ENERGY MATERIALS (WILEY-V C H VERLAG GMBH) 7 ( 3 ) art - 1601753 2017.02

Accepted, ISSN 1614-6832

In this study, the effect of water on the oxygen reduction reaction is initially investigated in aprotic ionic liquids by cyclic voltammetry, revealing that the presence of water significantly deteriorates the reversibility of the oxygen reduction reaction and oxygen evolution reaction, which will be detrimental to performance of a practical lithium-air battery. In order to prevent moisture intrusion from ambient air, a hydrophobic electrolyte is then designed and the moisture content in the electrolyte exposed to ambient air is greatly suppressed, to less than 1 wt% at 30 degrees C and 90% RH (relative humidity). Charge and discharge tests using the hydrophobic electrolyte are reversible for several cycles even in O-2 with a RH of 28%. This approach for enhancing the hydrophobicity of the electrolyte, and thus the inherent equilibrium moisture content, for the Li-air battery demonstrates the possibility for improved stability to ambient moisture.

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Stability of Glyme Solvate Ionic Liquid as an Electrolyte for Rechargeable Li-O₂ Batteries

Hoi-Min Kwon, Morgan L. Thomas, Ryoichi Tatara, Yoshiki Oda, Yuki Kobayashi, Azusa Nakanishi, Kazuhide Ueno, Kaoru Dokko, Masayoshi Watanabee

ACS APPLIED MATERIALS & INTERFACES (AMER CHEMICAL SOC) 9 ( 7 ) 6014 - 6021 2017.02

Accepted, ISSN 1944-8244

A solvate ionic liquid (SIL) was compared with a conventional organic solvent for the electrolyte of the Li-O-2 battery. An equimolar mixture of triglyme (G3) and lithium bis(trifluoromethanesulfonyl)amide (Li[TFSA]), and a G3/Li[TFSA] mixture containing excess glyme were chosen as the SIL and the conventional electrolyte, respectively. Charge behavior and accompanying gas evolution of the two electrolytes was investigated by electrochemical mass spectrometry (ECMS). From the linear sweep voltammetry performed on an as-prepared cell, we demonstrate that the SIL has a higher oxidative stability than the conventional electrolyte and, furthermore, offers the advantage of lower volatility, which would benefit an open-type lithium-O-2 cell design. Moreover, CO2 evolution during galvanostatic charge was less in the SIL, which implies less side reaction. However, O-2 evolution during charge did not reach the theoretical value in either of the two electrolytes. Several mass spectral fragments were generated during the charge process, which provided evidence for side reactions of glyme-based electrolytes. We further relate the difference in observed discharge product morphology for these electrolytes to the solubility of the superoxide intermediate, determined by rotating ring disk electrode (RRDE) measurements.

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Sulfur-Based Catholyte Solution with a Glass-Ceramic Membrane for Li-S Batteries

Lina Wang, Yu Zhao, Morgan L. Thomas, Arghya Dutta, Hye Ryung Byon

CHEMELECTROCHEM (WILEY-V C H VERLAG GMBH) 3 ( 1 ) 152 - 157 2016.01

Accepted, ISSN 2196-0216

Shuttling of soluble polysulfide species within electrodes is one of the most challenging issues in lithium-sulfur (Li-S) batteries. The resulting deposition of polysulfide species reduces the conductivity of the metallic Li electrode and the quantity of active material. Here, we demonstrate pronounced suppression of polysulfide shuttle using a sulfide-impermeable glass-ceramic membrane, which is employed as separator between the positive and negative electrodes. As a result, highly stable Li-S electrochemistry occurs in the sulfur-dissolving tetrahydrofuran catholyte solution, which provides good capacity retention and Coulombic efficiency for cycling. This demonstration holds promise for practical next-generation batteries with marked reversibility and the possibility to increase the energy density when equipped with a catholyte flow-through mode.

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Selective aerobic oxidation of para-xylene in sub- and supercritical water. Part 3: effects of geometry and mixing in laboratory scale continuous reactors

Eduardo Perez, Morgan L. Thomas, Duncan Housley, Paul A. Hamley, Joan Fraga-Dubreuil, Jun Li, Edward Lester, Martyn Poliakoff

RSC ADVANCES (ROYAL SOC CHEMISTRY) 6 ( 14 ) 11289 - 11294 2016.01

Accepted, ISSN 2046-2069

In this paper we report a strong dependence of the observed performance of the catalyst on the geometry and the configuration of laboratory scale reactors in the continuous aerobic oxidation of p-xylene in supercritical water. Small differences, such as the length of the feed pipes protruding into the reactor, have a very large effect on the observed yields and selectivities as well as on the reproducibility of the results. Different reactor designs also exert an influence on the perceived catalyst performance. We demonstrate that these effects are consistent with the relative efficiency of mixing of the reactant streams in the different reactors. The overall conclusion is that caution is required when comparing sets of data derived from studying such reactions even in apparently similar experimental arrangements.

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In situ synchrotron-based X-ray powder diffraction and micro-Raman study of biomass and residue model compounds at hydrothermal conditions

Morgan L. Thomas, Ian S. Butler, Janusz A. Kozinski

ENERGY SCIENCE & ENGINEERING (WILEY) 3 ( 3 ) 189 - 195 2015.05

Accepted, ISSN 2050-0505

The applications of synchrotron X-ray powder diffraction (XRPD) and laser micro-Raman techniques in an examination of the dissolution, transformation, and gasification of pure cellulose and models for biomass residue under hydrothermal conditions in a diamond-anvil cell are reported. The results contribute to the measurement of in situ time-resolved profiles of biomass reactions, catalyst stability, and residue formation that occur in aqueous fluids at near-and supercritical conditions.

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A perfluorinated moiety-grafted carbon nanotube electrode for the non-aqueous lithium-oxygen battery

Morgan L. Thomas, Keisuke Yamanaka, Toshiaki Ohta, Hye Ryung Byon

CHEMICAL COMMUNICATIONS (ROYAL SOC CHEMISTRY) 51 ( 19 ) 3977 - 3980 2014.12

Accepted, ISSN 1359-7345

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A structured three-dimensional polymer electrolyte with enlarged active reaction zone for Li-O₂ batteries

Nadege Bonnet-Mercier, Raymond A. Wong, Morgan L. Thomas, Arghya Dutta, Keisuke Yamanaka, Chihiro Yogi, Toshiaki Ohta, Hye Ryung Byon

SCIENTIFIC REPORTS (NATURE PUBLISHING GROUP) 4 ( 1 ) art - 7127 2014.11

Accepted, ISSN 2045-2322

The application of conventional solid polymer electrolyte (SPE) to lithium-oxygen (Li-O-2) batteries has suffered from a limited active reaction zone due to thick SPE and subsequent lack of O-2 gas diffusion route in the positive electrode. Here we present a new design for a three-dimensional (3-D) SPE structure, incorporating a carbon nanotube (CNT) electrode, adapted for a gas-based energy storage system. The void spaces in the porous CNT/SPE film allow an increased depth of diffusion of O-2 gas, providing an enlarged active reaction zone where Li+ ions, O-2 gas, and electrons can interact. Furthermore, the thin SPE layer along the CNT, forming the core/shell nanostructure, aids in the smooth electron transfer when O-2 gas approaches the CNT surface. Therefore, the 3-D CNT/SPE electrode structure enhances the capacity in the SPE-based Li-O-2 cell. However, intrinsic instability of poly(ethylene oxide) (PEO) of the SPE matrix to superoxide (O-2(center dot-)) and high voltage gives rise to severe side reactions, convincing us of the need for development of a more stable electrolyte for use in this CNT/SPE design.

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In Situ Synthesis of Bipyramidal Sulfur with 3D Carbon Nanotube Framework for Lithium-Sulfur Batteries

Lina Wang, Yu Zhao, Morgan L. Thomas, Hye Ryung Byon

ADVANCED FUNCTIONAL MATERIALS (WILEY-V C H VERLAG GMBH) 24 ( 15 ) 2248 - 2252 2014.04

Accepted, ISSN 1616-301X

A one-pot synthesis of three-dimensional carbon nanotube frameworks with bipyramidal sulfur particles and the application of these materials for a cathode in lithium-sulfur (Li-S) battery are reported. By simple mixing of multi-walled carbon nanotubes (MWCNTs), sulfur powder, and capping agents in water/tetrahydrofuran, micrometer bipyramidal sulfur particles enclosed with MWCNTs are synthesized. The MWCNTs spontaneously form a 3D conducting network inside and outside the sulfur particle. Along the edge of MWCNT framework, a sulfur particle-free region is present, which comprises approximate to 35 vol% based on the total volume. These sulfur-MWCNT bipyramidal particles are mixed with conductive carbon additive to prepare binder-free cathode for Li-S cells. The Li-S cells deliver a specific discharge capacity of approximate to 1600 mAh g(-1) at 0.05 C on the first cycle. In particular, these Li-S cells show high rate stability and Coulombic efficiency with deep discharge and charge (1.0-3.0 V vs Li/Li+). This resultant performance can arise from 1) homogeneous distribution of the conducting MWCNT framework and the carbon additive coating layer on the sulfur particle, which allow rapid Li+ ion/electrolyte diffusion and mitigation of polysulfide shuttle, respectively, and 2) the sulfur-free buffer space accommodating volume expansion. It is expected that this new cathode design with the simple synthetic process can reduce the number of preparation steps, thus allowing the construction of a low-cost Li-S battery.

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Utilisation Of Waste Wood For Bioenergy Using Supercritical Water Technology

M.L. Thomas, P. Aggarwal, M.P. Hude, J.B. Sontakke, A.K. Dalai, I.S. Butler, J.A. Kozinski

Proceedings of the World Engineers’ Convention paper - 339 2011.09

Accepted

Hydrothermal Raman microscopy studies of manganese carbonyls

Courtney Calahoo, Mirela M. Barsan, Morgan L. Thomas, Janusz A. Kozinski, Ian S. Butler

VIBRATIONAL SPECTROSCOPY (ELSEVIER SCIENCE BV) 57 ( 1 ) 2 - 7 2011.09

Accepted, ISSN 0924-2031

We present here the application of Raman microscopy in providing simultaneous visual and spectroscopic characterisation of the physical and chemical changes occurring in organometallic materials while undergoing hydrothermal treatment. The effect of water at elevated pressures and temperatures on three prototype manganese carbonyls, Mn-2(CO)(10), (eta(5)-C5H5)Mn(CO)(3) and Mn(CO)(5)Br, was investigated. A Bassett-type hydrothermal diamond-anvil cell (HDAC) was used to subject each compound to conditions of at least 22.1 MPa and 374 degrees C (i.e., beyond the critical point of water), while Raman microscopy was used to monitor the structural changes occurring during the heating and cooling cycles of the cell. The hydrothermal studies showed that Mn-2(CO)(10), (eta(5)-C5H5)Mn(CO)(3) and Mn(CO)(5)Br dissolved in subcritical water at 150, 125 and 225 degrees C. respectively. Moreover, Mn(CO)(5)Br is also believed to have dimerized to Mn-2(CO)(8)Br-2 when the cell temperature was increased to 425 degrees C. (C) 2011 Elsevier B.V. All rights reserved.

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Frontiers In Energy Science And Engineering: A Canadian Perspective

M.L. Thomas, J.A. Kozinski

Proceedings of the World Engineers’ Convention paper - 447 2011.09

Accepted

Selective aerobic oxidation of para-xylene in sub- and supercritical water. Part 2. The discovery of better catalysts

Eduardo Perez, Joan Fraga-Dubreuil, Eduardo Garcia-Verdugo, Paul A. Hamley, Morgan L. Thomas, Chong Yan, W. Barry Thomas, Duncan Housley, Walt Partenheimer, Martyn Poliakoff

GREEN CHEMISTRY (ROYAL SOC CHEMISTRY) 13 ( 9 ) 2397 - 2407 2011.07

Accepted, ISSN 1463-9262

An extensive and systematic study has been carried out on the catalytic effect of more than 20 elements on the aerobic oxidation of p-xylene to terephthalic acid in super-and subcritical water. Reactions have been performed in a continuous reactor under catalyst unsaturated conditions. Reaction product, by-products and intermediates have been quantified as well as the burn (the amount of CO2 originating from total oxidation of p-xylene). CuBr2 has been found to be a superior catalyst to MnBr2, which has been widely used in the literature for this reaction in water at high temperatures. At catalyst unsaturated conditions (i.e. with low concentrations of catalyst), MnBr2 gives a terephthalic acid yield of 36.1% whereas CuBr2 enhances this value to 55.6%. A strong synergistic effect has been found between CuBr2 and other metals and sources of bromide. Indeed, we show that Cu/Co/Br, Cu/Co/NH4/Br and other mixtures give better results than CuBr2 reaching a terephthalic acid yield of 70.5% for the four component catalyst. The compositions of the catalyst as well as the reactor temperature have been optimized and their effects on the analyzed compounds are discussed. A substantial amount of additional data is included in the electronic supplementary information.

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Advanced Analytical Methods in the Study of Waste Combustion: Recent Advances with in situ Synchrotron-based Measurements

M.L. Thomas, A.K. Dalai, I.S. Butler, J.A. Kozinski

Proceedings of the Combustion Institute / Canadian Section Spring Technical Meeting 329 - 332 2011.05

Accepted

Entwicklung eines Prozesses zur Herstellung von 2-Methyltetrahydrofuran als Kraftstoffkomponente

A. Harwardt, M. Thomas, F. Geilen, W. Leitner, W. Marquardt

Chemie Ingenieur Technik (Wiley-Blackwell) 81 ( 8 ) 1202 - 1203 2009.08

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Catalysis in High Temperature Water

Morgan L. Thomas

2008.07

A dramatic switch in selectivity in the catalytic dehydrogenation of 4-vinylcyclohexene in high pressure steam; a cautionary lesson for continuous flow reactions

Morgan L. Thomas, Joan Fraga-Dubreuil, A. Stuart Coote, Martyn Poliakoff

GREEN CHEMISTRY (ROYAL SOC CHEMISTRY) 10 ( 2 ) 197 - 201 2007.11

Accepted, ISSN 1463-9262

We report an investigation of the continuous oxidative dehydrogenation of 4-vinylcyclohexene (VCH) in high pressure steam. Oxidative dehydrogenation reactions such as this are often limited by unselective or total oxidation. We find that these side-reactions not only occur in this case, but can also have a major influence on the selectivity; a small increase in flow rate results in a complete switch in selectivity of the reaction. Our results suggest that styrene (ST) is formed as the initial product but that unless the H-2 is sequestered, ST may then be hydrogenated to yield ethylbenzene (EB).
The observation of periodic temperature spikes near the surface of the catalyst bed indicate cycles of propagating flames occur in a relatively small volume of the reactor, leading to total oxidation of some VCH and removal of O-2, which would otherwise sequester the H-2. These flames give rise to the large variations in the observed product selectivity. We suggest that these observations may not be restricted to this reaction system and reactor configuration, and may occur in other situations where small-scale continuous flow oxidation reactors are used.

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