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ACS Catalysis

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https://www.readbyqxmd.com/read/29333330/amorphous-cobalt-vanadium-oxide-as-a-highly-active-electrocatalyst-for-oxygen-evolution
#1
Laurent Liardet, Xile Hu
The water-splitting reaction provides a promising mechanism to store renewable energies in the form of hydrogen fuel. The oxidation half-reaction, the oxygen evolution reaction (OER), is a complex four-electron process that constitutes an efficiency bottleneck in water splitting. Here we report a highly active OER catalyst, cobalt vanadium oxide. The catalyst is designed on the basis of a volcano plot of metal-OH bond strength and activity. The catalyst can be synthesized by a facile hydrothermal route. The most active pure-phase material (a-CoVO x ) is X-ray amorphous and provides a 10 mA cm-2 current density at an overpotential of 347 mV in 1 M KOH electrolyte when immobilized on a flat substrate...
January 5, 2018: ACS Catalysis
https://www.readbyqxmd.com/read/29333329/stable-pd-doped-ceria-structures-for-ch4-activation-and-co-oxidation
#2
Ya-Qiong Su, Ivo A W Filot, Jin-Xun Liu, Emiel J M Hensen
Doping CeO2 with Pd atoms has been associated with catalytic CO oxidation, but current surface models do not allow CO adsorption. Here, we report a new structure of Pd-doped CeO2(111), in which Pd adopts a square planar configuration instead of the previously assumed octahedral configuration. Oxygen removal from this doped structure is favorable. The resulting defective Pd-doped CeO2 surface is active for CO oxidation and is also able to cleave the first C-H bond in methane. We show how the moderate CO adsorption energy and dynamic features of the Pd atom upon CO adsorption and CO oxidation contribute to a low-barrier catalytic cycle for CO oxidation...
January 5, 2018: ACS Catalysis
https://www.readbyqxmd.com/read/29226012/hydride-transfer-versus-deprotonation-kinetics-in-the-isobutane-propene-alkylation-reaction-a-computational-study
#3
Chong Liu, Rutger A van Santen, Ali Poursaeidesfahani, Thijs J H Vlugt, Evgeny A Pidko, Emiel J M Hensen
The alkylation of isobutane with light alkenes plays an essential role in modern petrochemical processes for the production of high-octane gasoline. In this study we have employed periodic DFT calculations combined with microkinetic simulations to investigate the complex reaction mechanism of isobutane-propene alkylation catalyzed by zeolitic solid acids. Particular emphasis was given to addressing the selectivity of the alkylate formation versus alkene formation, which requires a high rate of hydride transfer in comparison to the competitive oligomerization and deprotonation reactions resulting in catalyst deactivation...
December 1, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/29226011/role-of-conformational-dynamics-in-the-evolution-of-retro-aldolase-activity
#4
Adrian Romero-Rivera, Marc Garcia-Borràs, Sílvia Osuna
Enzymes exist as ensembles of conformations that are important for function. Tuning these populations of conformational states through mutation enables evolution toward additional activities. Here we computationally evaluate the population shifts induced by distal and active site mutations in a family of computationally designed and experimentally optimized retro-aldolases. The conformational landscape of these enzymes was significantly altered during evolution, as pre-existing catalytically active conformational substates became major states in the most evolved variants...
December 1, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/29226010/mechanism-of-cobalt-catalyzed-co-hydrogenation-2-fischer-tropsch-synthesis
#5
Wei Chen, Ivo A W Filot, Robert Pestman, Emiel J M Hensen
Fischer-Tropsch (FT) synthesis is one of the most complex catalyzed chemical reactions in which the chain-growth mechanism that leads to formation of long-chain hydrocarbons is not well understood yet. The present work provides deeper insight into the relation between the kinetics of the FT reaction on a silica-supported cobalt catalyst and the composition of the surface adsorbed layer. Cofeeding experiments of 12C3H6 with 13CO/H2 evidence that CH x surface intermediates are involved in chain growth and that chain growth is highly reversible...
December 1, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/29226009/mechanism-of-cobalt-catalyzed-co-hydrogenation-1-methanation
#6
Wei Chen, Robert Pestman, Bart Zijlstra, Ivo A W Filot, Emiel J M Hensen
The mechanism of CO hydrogenation to CH4 at 260 °C on a cobalt catalyst is investigated using steady-state isotopic transient kinetic analysis (SSITKA) and backward and forward chemical transient kinetic analysis (CTKA). The dependence of CH x residence time is determined by 12CO/H2 → 13CO/H2 SSITKA as a function of the CO and H2 partial pressure and shows that the CH4 formation rate is mainly controlled by CH x hydrogenation rather than CO dissociation. Backward CO/H2 → H2 CTKA emphasizes the importance of H coverage on the slow CH x hydrogenation step...
December 1, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/29142780/molecular-mechanism-of-enzymatic-chlorite-detoxification-insights-from-structural-and-kinetic-studies
#7
Irene Schaffner, Georg Mlynek, Nicola Flego, Dominic Pühringer, Julian Libiseller-Egger, Leighton Coates, Stefan Hofbauer, Marzia Bellei, Paul G Furtmüller, Gianantonio Battistuzzi, Giulietta Smulevich, Kristina Djinović-Carugo, Christian Obinger
The heme enzyme chlorite dismutase (Cld) catalyzes the degradation of chlorite to chloride and dioxygen. Although structure and steady-state kinetics of Clds have been elucidated, many questions remain (e.g., the mechanism of chlorite cleavage and the pH dependence of the reaction). Here, we present high-resolution X-ray crystal structures of a dimeric Cld at pH 6.5 and 8.5, its fluoride and isothiocyanate complexes and the neutron structure at pH 9.0 together with the pH dependence of the Fe(III)/Fe(II) couple, and the UV-vis and resonance Raman spectral features...
November 3, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/29109904/visible-light-photocatalytic-decarboxylation-of-%C3%AE-%C3%AE-unsaturated-carboxylic-acids-facile-access-to-stereoselective-difluoromethylated-styrenes-in-batch-and-flow
#8
Xiao-Jing Wei, Wout Boon, Volker Hessel, Timothy Noël
The development of synthetic methodologies which provide access to both stereoisomers of α,β-disubstituted olefins is a challenging undertaking. Herein, we describe the development of an operationally simple and stereoselective synthesis of difluoromethylated styrenes via a visible-light photocatalytic decarboxylation strategy using fac-Ir(ppy)3 as the photocatalyst. Meta- and para-substituted cinnamic acids provide the expected E-isomer. In contrast, ortho-substituted cinnamic acids yield selectively the less stable Z-product, whereas the E-isomer can be obtained via continuous-flow processing through accurate control of the reaction time...
October 6, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/29104813/photocatalytic-indole-diels-alder-cycloadditions-mediated-by-heterogeneous-platinum-modified-titanium-dioxide
#9
Spencer P Pitre, Juan C Scaiano, Tehshik P Yoon
Indole alkaloids represent an important class of molecules, with many naturally occurring derivatives possessing significant biological activity. One area that requires further development in the synthesis of indole derivatives is the Diels-Alder reaction. In this work, we expand on our previously developed heterogeneous protocol for the [4+2] cycloaddition of indoles and electron-rich dienes mediated by platinum nanoparticles supported on titanium dioxide semiconductor particles (Pt(0.2%)@TiO2) with visible-light irradiation...
October 6, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/29038742/methylene-c-sp-3-h-arylation-of-aliphatic-ketones-using-a-transient-directing-group
#10
Kai Hong, Hojoon Park, Jin-Quan Yu
Palladium-catalyzed methylene β-C(sp(3))-H arylation of aliphatic ketones using a transient directing group is developed. The use of α-benzyl β-alanine directing group that forms a six-membered chelation with palladium is crucial for promoting the methylene C(sp(3))-H bond activation.
October 6, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/29034122/methanol-on-anatase-tio2-101-mechanistic-insights-into-photocatalysis
#11
Martin Setvin, Xiao Shi, Jan Hulva, Thomas Simschitz, Gareth S Parkinson, Michael Schmid, Cristiana Di Valentin, Annabella Selloni, Ulrike Diebold
The photoactivity of methanol adsorbed on the anatase TiO2 (101) surface was studied by a combination of scanning tunneling microscopy (STM), temperature-programmed desorption (TPD), X-ray photoemission spectroscopy (XPS), and density functional theory (DFT) calculations. Isolated methanol molecules adsorbed at the anatase (101) surface show a negligible photoactivity. Two ways of methanol activation were found. First, methoxy groups formed by reaction of methanol with coadsorbed O2 molecules or terminal OH groups are photoactive, and they turn into formaldehyde upon UV illumination...
October 6, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/29034121/atomically-dispersed-pd-o-species-on-ceo2-111-as-highly-active-sites-for-low-temperature-co-oxidation
#12
Giulia Spezzati, Yaqiong Su, Jan P Hofmann, Angelica D Benavidez, Andrew T DeLaRiva, Jay McCabe, Abhaya K Datye, Emiel J M Hensen
Ceria-supported Pd is a promising heterogeneous catalyst for CO oxidation relevant to environmental cleanup reactions. Pd loaded onto a nanorod form of ceria exposing predominantly (111) facets is already active at 50 °C. Here we report a combination of CO-FTIR spectroscopy and theoretical calculations that allows assigning different forms of Pd on the CeO2(111) surface during reaction conditions. Single Pd atoms stabilized in the form of PdO and PdO2 in a CO/O2 atmosphere participate in a catalytic cycle involving very low activation barriers for CO oxidation...
October 6, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/29034120/modulating-the-external-facets-of-functional-nanocrystals-enabled-by-two-dimensional-oxide-crystal-templates
#13
Huiyu Yuan, Kai Han, David Dubbink, Guido Mul, Johan E Ten Elshof
The nature of the external crystal facets is critical to control the (photo)catalytic properties. Two-dimensional materials can expose only one type of crystal facet among zero-dimensional (0D), one-dimensional (1D), and two-dimensional (2D) materials. Controllable tuning of the nature of the external crystal facets of 2D materials is highly desirable but very challenging. Here, we show that 2D particles with the desirable crystal facet for high-performance photocatalytic H2 generation can be obtained by using 2D metal oxide materials (i...
October 6, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/29034119/chloride-tolerant-gold-i-catalyzed-regioselective-hydrochlorination-of-alkynes
#14
Rene Ebule, Shengzong Liang, Gerald B Hammond, Bo Xu
We have developed a highly regioselective homogeneous gold(I)-catalyzed anti-hydrochlorination of unactivated alkynes at room temperature. We have overcome the incompatibility between conventional cationic gold catalysts and chloride by using a hydrogen-bonding activation of the Au-Cl bond. This approach is scalable, exhibits excellent functional group tolerance, and can be conducted in open air.
October 6, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/29308295/mechanistic-insights-into-dye-decolorizing-peroxidase-revealed-by-solvent-isotope-and-viscosity-effects
#15
Ruben Shrestha, Gaochao Huang, David A Meekins, Brian V Geisbrecht, Ping Li
Dye-decolorizing peroxidases (DyPs) are a family of H2O2-dependent heme peroxidases, which have shown potential applications in lignin degradation and valorization. However, the DyP kinetic mechanism remains underexplored. Using structural biology and solvent isotope (sKIE) and viscosity effects, many mechanistic characteristics have been uncovered for the B-class ElDyP from Enterobacter lignolyticus. Its structure revealed that a water molecule acts as the sixth axial ligand with two channels at diameters of ~3...
September 1, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/29291138/shuffling-active-site-substate-populations-affects-catalytic-activity-the-case-of-glucose-oxidase
#16
Dušan Petrović, David Frank, Shina Caroline Lynn Kamerlin, Kurt Hoffmann, Birgit Strodel
Glucose oxidase has wide applications in the pharmaceutical, chemical, and food industries. Many recent studies have enhanced key properties of this enzyme using directed evolution, yet without being able to reveal why these mutations are actually beneficial. This work presents a synergistic combination of experimental and computational methods, indicating how mutations, even when distant from the active site, positively affect glucose oxidase catalysis. We have determined the crystal structures of glucose oxidase mutants containing molecular oxygen in the active site...
September 1, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/28966841/s-o-ligand-promoted-palladium-catalyzed-c-h-functionalization-reactions-of-nondirected-arenes
#17
Kananat Naksomboon, Carolina Valderas, Melania Gómez-Martínez, Yolanda Álvarez-Casao, M Ángeles Fernández-Ibáñez
Pd(II)-catalyzed C-H functionalization of nondirected arenes has been realized using an inexpensive and easily accessible type of bidentate S,O-ligand. The catalytic system shows high efficiency in the C-H olefination reaction of electron-rich and electron-poor arenes. This methodology is operationally simple, scalable, and can be used in late-stage functionalization of complex molecules. The broad applicability of this catalyst has been showcased in other transformations such as Pd(II)-catalyzed C-H acetoxylation and allylation reactions...
September 1, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/28966840/structural-basis-of-catalysis-in-the-bacterial-monoterpene-synthases-linalool-synthase-and-1-8-cineole-synthase
#18
Vijaykumar Karuppiah, Kara E Ranaghan, Nicole G H Leferink, Linus O Johannissen, Muralidharan Shanmugam, Aisling Ní Cheallaigh, Nathan J Bennett, Lewis J Kearsey, Eriko Takano, John M Gardiner, Marc W van der Kamp, Sam Hay, Adrian J Mulholland, David Leys, Nigel S Scrutton
Terpenoids form the largest and stereochemically most diverse class of natural products, and there is considerable interest in producing these by biocatalysis with whole cells or purified enzymes, and by metabolic engineering. The monoterpenes are an important class of terpenes and are industrially important as flavors and fragrances. We report here structures for the recently discovered Streptomyces clavuligerus monoterpene synthases linalool synthase (bLinS) and 1,8-cineole synthase (bCinS), and we show that these are active biocatalysts for monoterpene production using biocatalysis and metabolic engineering platforms...
September 1, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/28966839/catalyzed-bimolecular-reactions-in-responsive-nanoreactors
#19
Rafael Roa, Won Kyu Kim, Matej Kanduč, Joachim Dzubiella, Stefano Angioletti-Uberti
We describe a general theory for surface-catalyzed bimolecular reactions in responsive nanoreactors, catalytically active nanoparticles coated by a stimuli-responsive "gating" shell, whose permeability controls the activity of the process. We address two archetypal scenarios encountered in this system: the first, where two species diffusing from a bulk solution react at the catalyst's surface, and the second, where only one of the reactants diffuses from the bulk while the other is produced at the nanoparticle surface, e...
September 1, 2017: ACS Catalysis
https://www.readbyqxmd.com/read/28944089/superior-stability-of-au-sio2-compared-to-au-tio2-catalysts-for-the-selective-hydrogenation-of-butadiene
#20
Nazila Masoud, Laurent Delannoy, Herrick Schaink, Ad van der Eerden, Jan Willem de Rijk, Tiago A G Silva, Dipanjan Banerjee, Johannes D Meeldijk, Krijn P de Jong, Catherine Louis, Petra E de Jongh
Supported gold nanoparticles are highly selective catalysts for a range of both liquid-phase and gas-phase hydrogenation reactions. However, little is known about their stability during gas-phase catalysis and the influence of the support thereon. We report on the activity, selectivity, and stability of 2-4 nm Au nanoparticulate catalysts, supported on either TiO2 or SiO2, for the hydrogenation of 0.3% butadiene in the presence of 30% propene. Direct comparison of the stability of the Au catalysts was possible as they were prepared via the same method but on different supports...
September 1, 2017: ACS Catalysis
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