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Faraday Discussions

P Gibson
The 2017 Faraday Discussion on the topic of "Catalysis for Fuels" was unique in the sense that it was the first Faraday Discussion to be held on the continent of Africa. "Catalysis" and "Fuels" are both topics that could be widely interpreted and the session topics proved to be a relevant spread of old and new i.e. Fischer-Tropsch chemistry, biomass refining, zeolite conversions and photocatalysis. Most of the papers were underpinned by fundamental studies, catalyst design approaches, reports of in operando characterization and detailed speciation and micro kinetic analyses...
March 17, 2017: Faraday Discussions
Shuai Wang, Iker Agirrezabal-Telleria, Aditya Bhan, Dante Simonetti, Kazuhiro Takanabe, Enrique Iglesia
This account illustrates concepts in chemical kinetics underpinned by the formalism of transition state theory using catalytic processes that enable the synthesis of molecules suitable as fuels from C1 and oxygenate reactants. Such feedstocks provide an essential bridge towards a carbon-free energy future, but their volatility and low energy density require the formation of new C-C bonds and the removal of oxygen. These transformations are described here through recent advances in our understanding of the mechanisms and site requirements in catalysis by surfaces, with emphasis on enabling concepts that tackle ubiquitous reactivity and selectivity challenges...
March 16, 2017: Faraday Discussions
Hitoshi Ishida, Akihiko Sakaba
The temperature dependence of photocatalytic CO2 reduction by trans(Cl)-Ru(bpy)(CO)2Cl2 (bpy: 2,2'-bipyridine) has been researched in ethanol (EtOH)/N,N-dimethylacetamide (DMA) solutions containing [Ru(bpy)3](2+) (a photosensitizer) and 1-benzyl-1,4-dihydronicotinamide (BNAH, an electron donor). The catalytic system efficiently reduces CO2 to carbon monoxide (CO) with formate (HCOO(-)) as a minor product. The mechanism of the catalysis consists of the electron-relay cycle and the catalytic cycle: in the former cycle the photochemically generated reduced species of the photosensitizer injects an electron to the catalyst, and in the latter the catalyst reduces CO2...
March 15, 2017: Faraday Discussions
Chong Liu, Shannon N Nangle, Brendan C Colón, Pamela A Silver, Daniel G Nocera
Interfacing the CO2-fixing microorganism, Ralstonia eutropha, to the energy derived from hydrogen produced by water splitting is a viable approach to achieving renewable CO2 reduction at high efficiencies. We employ (13)C-labeling to report on the nature of CO2 reduction in the inorganic water splitting|R. eutropha hybrid system. Accumulated biomass in a reactor under a (13)C-enriched CO2 atmosphere may be sampled at different time points during CO2 reduction. Converting the sampled biomass into gaseous CO2 allows the (13)C/(12)C ratio to be determined by gas chromatography-mass spectrometry...
March 15, 2017: Faraday Discussions
Nao Yukihira, Yuko Sugai, Masazumi Fujiwara, Daisuke Kosumi, Masahiko Iha, Kazuhiko Sakaguchi, Shigeo Katsumura, Alastair T Gardiner, Richard J Cogdell, Hideki Hashimoto
Fucoxanthin is a carotenoid that is mainly found in light-harvesting complexes from brown algae and diatoms. Due to the presence of a carbonyl group attached to polyene chains in polar environments, excitation produces an excited intra-molecular charge transfer. This intra-molecular charge transfer state plays a key role in the highly efficient (∼95%) energy-transfer from fucoxanthin to chlorophyll a in the light-harvesting complexes from brown algae. In purple bacterial light-harvesting systems the efficiency of excitation energy-transfer from carotenoids to bacteriochlorophylls depends on the extent of conjugation of the carotenoids...
March 15, 2017: Faraday Discussions
Liping Bai, Takashi Fujishiro, Gangfeng Huang, Jürgen Koch, Atsushi Takabayashi, Makio Yokono, Ayumi Tanaka, Tao Xu, Xile Hu, Ulrich Ermler, Seigo Shima
The greenhouse gas and energy carrier methane is produced on Earth mainly by methanogenic archaea. In the hydrogenotrophic methanogenic pathway the reduction of one CO2 to one methane molecule requires four molecules of H2 containing eight electrons. Four of the electrons from two H2 are supplied for reduction of an electron carrier F420, which is catalyzed by F420-reducing [NiFe]-hydrogenase under nickel-sufficient conditions. The same reaction is catalysed under nickel-limiting conditions by [Fe]-hydrogenase coupled with a reaction catalyzed by F420-dependent methylene tetrahydromethanopterin dehydrogenase...
March 15, 2017: Faraday Discussions
Tomoaki Takayama, Ko Sato, Takehiro Fujimura, Yuki Kojima, Akihide Iwase, Akihiko Kudo
CuGaS2, (AgInS2)x-(ZnS)2-2x, Ag2ZnGeS4, Ni- or Pb-doped ZnS, (ZnS)0.9-(CuCl)0.1, and ZnGa0.5In1.5S4 showed activities for CO2 reduction to form CO and/or HCOOH in an aqueous solution containing K2SO3 and Na2S as electron donors under visible light irradiation. Among them, CuGaS2 and Ni-doped ZnS photocatalysts showed relatively high activities for CO and HCOOH formation, respectively. CuGaS2 was applied in a powdered Z-scheme system combining with reduced graphene oxide (RGO)-incorporated TiO2 as an O2-evolving photocatalyst...
March 13, 2017: Faraday Discussions
Fiona A Black, Christopher J Wood, Simbarashe Ngwerume, Gareth H Summers, Ian P Clark, Michael Towrie, Jason E Camp, Elizabeth A Gibson
This article describes a comparison between the photophysical properties of two charge-transfer dyes adsorbed onto NiO via two different binding moieties. Transient spectroscopy measurements suggest that the structure of the anchoring group affects both the rate of charge recombination between the dye and NiO surface and the rate of dye regeneration by an iodide/triiodide redox couple. This is consistent with the performance of the dyes in p-type dye sensitised solar cells. A key finding was that the recombination rate differed in the presence of the redox couple...
March 13, 2017: Faraday Discussions
Gerald F Manbeck, Komal Garg, Tomoe Shimoda, David J Szalda, Mehmed Z Ertem, James T Muckerman, Etsuko Fujita
We prepared electron-rich derivatives of [Ir(tpy)(ppy)Cl](+) with modification of the bidentate (ppy) or tridentate (tpy) ligands in an attempt to increase the reactivity for CO2 reduction and the ability to transfer hydrides (hydricity). Density functional theory (DFT) calculations reveal that complexes with dimethyl-substituted ppy have similar hydricities to the non-substituted parent complex, and photocatalytic CO2 reduction studies show selective CO formation. Substitution of tpy by bis(benzimidazole)-phenyl or -pyridine (L3 and L4, respectively) induces changes in the physical properties that are much more pronounced than from the addition of methyl groups to ppy...
March 10, 2017: Faraday Discussions
Jose F Martinez, Nathan T La Porte, Catherine M Mauck, Michael R Wasielewski
The naphthalene-1,4:5,8-bis(dicarboximide) radical anion (NDI(-)˙), which is easily produced by mild chemical or electrochemical reduction (-0.5 V vs. SCE), can be photoexcited at wavelengths as long as 785 nm, and has an excited state (NDI(-)˙*) oxidation potential of -2.1 V vs. SCE, making it a very attractive choice for artificial photosynthetic systems that require powerful photoreductants, such as CO2 reduction catalysts. However, once an electron is transferred from NDI(-)˙* to an acceptor directly bound to it, a combination of strong electronic coupling and favorable free energy change frequently make the back electron transfer rapid...
March 10, 2017: Faraday Discussions
Yutaka Amao, Shusaku Ikeyama, Takayuki Katagiri, Kohei Fujita
Recently, CO2 utilization technology, including artificial photosynthesis, has received much attention. In this field, CO2 is used as a feedstock for fuels, polymers and in other chemical processes. Of note are malic enzymes (MEs) which catalyze the reaction of malic acid to pyruvic acid and CO2 with the co-enzyme NADP(+), and catalyze the reverse reaction of pyruvic acid and CO2 to malic acid with the co-enzyme NADPH. Thus, MEs are also an attractive biocatalyst for carbon-carbon bond formation from CO2. Studies of the visible light-induced malic acid production from pyruvic acid and CO2 using an electron donor, a photosensitizer, an electron mediator, ferredoxin-NADP(+) reductase, NADP(+), and ME have been reported...
March 9, 2017: Faraday Discussions
Dong-Il Won, Jong-Su Lee, Ha-Yeon Cheong, Minji Cho, Won-Jo Jung, Ho-Jin Son, Chyongjin Pac, Sang Ook Kang
Efficient hybrid photocatalysts for carbon dioxide reduction were developed from dye-sensitized TiO2 nanoparticles and their catalytic performance was optimized by ternary organic/inorganic components. Thus, the hybrid system consists of (E)-2-cyano-3-(5'-(5''-(p-(diphenylamino)phenyl)thiophen-2''-yl)thiophen-2'-yl)-acrylic acid as a sensitizer and fac-[Re(4,4'-bis(diethoxyphosphorylmethyl)-2,2'-bipyridine)(CO)3Cl] as a reduction catalyst (ReP), both of which have been fixed onto TiO2 semiconductors (s-TiO2, h-TiO2, d-TiO2)...
March 9, 2017: Faraday Discussions
Yusuke Tamaki, Osamu Ishitani
New supramolecular photocatalysts comprising an asymmetric bis-tridentate Ru(ii) complex that functions as a photosensitizer and a Ru(ii) carbonyl complex as the catalyst were designed. The complexes photocatalyzed the reduction of CO2 to CO or formic acid with high selectivity. The product distribution depended on the catalyst unit. CO and formic acid were the main products when using [Ru(BL)(Clbpy)(CO)](2+) (BL = bridging ligand, Clbpy = 4,4'-dichloro-2,2'-bipyridine) and Ru(BL)(CO)2Cl2 catalysts, respectively...
March 9, 2017: Faraday Discussions
Tohru Setoyama, Takahiko Takewaki, Kazunari Domen, Takashi Tatsumi
Curbing anthropogenic CO2 emissions is one of the most important issues in the 21st century in order to mitigate climate change. Although the installation of solar cells for energy supply is in progress and these are becoming popular as an efficient use of sunlight, they are mostly used by energy-related industrial sectors. In the common chemical industry, various fossil resources are used to emit a huge amount of CO2. We believe that the chemical industry can make an effort to curb CO2 emissions by changing its resources to more environmentally benign ones...
March 9, 2017: Faraday Discussions
Hohyun Jeong, Myung Jong Kang, Hyeyeong Jung, Young Soo Kang
Pyridine molecules have been used as a catalyst to reduce the activation energy of the CO2 reduction reaction. It has been reported that CO2 is reduced by pyridine catalysts at low overpotential around -0.58 V vs. SCE. Poly(4-vinylpyridine), which has pyridine functional groups shows similar catalytic properties to reduce CO2 at low overpotential like pyridinium catalysts. Different thickness of P(4-VP) coated Pt electrodes were analyzed to determine the catalytic properties for CO2 reduction. Cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy methods showed the catalytic CO2 reduction properties of a P(4-VP)/Pt electrode...
March 9, 2017: Faraday Discussions
Biaobiao Zhang, Quentin Daniel, Ming Cheng, Lizhou Fan, Licheng Sun
A water oxidation electrocatalyst with high activity is essential for promoting the overall efficiency of an integrated water splitting device. Herein, by investigating the prominent temperature dependence of electrocatalytic water oxidation catalyzed by first row transition metal oxides, we present how to elevate the operating temperature of the electrolyzer as an effective and universal method to improve its electrocatalytic performance. Consequently, a triple device model combining a photothermal collector with a photovoltaic (PV) cell coupled to a water splitting device is proposed to realize the comprehensive and efficient utilization of solar energy: solar heat + PV + electrolyzer...
March 9, 2017: Faraday Discussions
Mitsuo Shoji, Hiroshi Isobe, Takahito Nakajima, Yasuteru Shigeta, Michihiro Suga, Fusamichi Akita, Jian-Ren Shen, Kizashi Yamaguchi
Large-scale QM/MM calculations were performed to elucidate an optimized geometrical structure of a CaMn4O5 cluster with and without water insertion in the S3 state of the oxygen evolving complex (OEC) of photosystem II (PSII). The left (L)-opened structure was found to be stable under the assumption of no hydroxide anion insertion in the S3 state, whereas the right (R)-opened structure became more stable if one water molecule is inserted to the Mn4Ca cluster. The optimized Mna(4)-Mnd(1) distance determined by QM/MM was about 5...
March 9, 2017: Faraday Discussions
Nicolas Queyriaux, Eugen S Andreiadis, Stéphane Torelli, Jacques Pecaut, Brad S Veldkamp, Eric A Margulies, Michael R Wasielewski, Murielle Chavarot-Kerlidou, Vincent Artero
The design of molecular dyads combining a light-harvesting unit with an electroactive centre is highly demanded in the field of artificial photosynthesis. The versatile Copper-catalyzed Azide-Alkyne Cycloaddition (CuAAC) procedure was employed to assemble a ruthenium tris-diimine unit to an unprecedented azide-substituted copper diimine-dioxime moiety. The resulting Ru(II)Cu(II) dyad 4 was characterized by electrochemistry, (1)H NMR, EPR, UV-visible absorption, steady-state fluorescence and transient absorption spectroscopies...
March 9, 2017: Faraday Discussions
S Uto, K Kawakami, Y Umena, M Iwai, M Ikeuchi, J-R Shen, N Kamiya
Photosystem II (PSII) is a membrane protein complex that performs light-induced electron transfer and oxygen evolution from water. PSII consists of 19 or 20 subunits in its crystal form and binds various cofactors such as chlorophyll a, plastoquinone, carotenoid, and lipids. After initial light excitation, the charge separation produces an electron, which is transferred to a plastoquinone molecule (QA) and then to another plastoquinone (QB). PsbM is a low-molecular-weight subunit with one transmembrane helix, and is located in the monomer-monomer interface of the PSII dimer...
March 8, 2017: Faraday Discussions
Masaki Yoshida, Mio Kondo, Masaya Okamura, Mari Kanaike, Setsiri Haesuwannakij, Hidehiro Sakurai, Shigeyuki Masaoka
A series of group 8 metal complexes with the same molecular framework, [M(PY5Me2)L]n+ (M = Fe, Ru, and Os; PY5Me2 = 2,6-bis[1,1-bis(2-pyridyl)ethyl]pyridine; L = monodentate ligand), were successfully synthesized and structurally characterized. The spectroscopic and electrochemical properties as well as the catalytic activity for water oxidation of these complexes were investigated.
March 8, 2017: Faraday Discussions
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