Read by QxMD icon Read


José G Moya-Cancino, Ari-Pekka Honkanen, Ad M J van der Eerden, Herrick Schaink, Lieven Folkertsma, Mahnaz Ghiasi, Alessandro Longo, Frank M F de Groot, Florian Meirer, Simo Huotari, Bert M Weckhuysen
An in-situ laboratory-based X-ray Absorption Near Edge Structure (XANES) Spectroscopy set-up is presented, which allows performing long-term experiments on a solid catalyst at relevant reaction conditions of temperature and pressure. Complementary to research performed at synchrotron radiation facilities the approach is showcased for a Co/TiO2 Fischer-Tropsch Synthesis (FTS) catalyst. Supported cobalt metal nanoparticles next to a (very small) fraction of cobalt(II) titanate, which is an inactive phase for FTS, were detected, with no signs of re-oxidation of the supported cobalt metal nanoparticles during FTS at 523 K, 5 bar and 200 h, indicating that cobalt metal is maintained as the main active phase during FTS...
February 6, 2019: ChemCatChem
Naresh Kumar, Sam Kalirai, Andrew J Wain, Bert M Weckhuysen
Determining the active site in real-life solid catalysts remains an intellectual challenge and is crucial for exploring the road towards their rational design. In recent years various micro-spectroscopic methods have revealed valuable structure-activity data at the level of a single catalyst particle, even under reaction conditions. Herein, we introduce Tip-Enhanced FLuorescence (TEFL) microscopy as a novel and versatile characterization tool for catalysis research. This has been achieved using a Fluid Catalytic Cracking (FCC) catalyst as showcase material...
January 9, 2019: ChemCatChem
Anne C H Jans, Xavier Caumes, Joost N H Reek
Gold catalysis has experienced a tremendous development over the past decades, and is nowadays widely used in organic synthesis to perform chemical transformations of π-bond-containing molecules. Catalyst development has been based mostly on ligand development and counter-ion strategies. More recently, the encapsulation of gold catalysts in (supra)molecular cages was explored as a new way to control selectivity and reactivity of gold catalysts. In this review, we describe the cages that have been employed as hosts for gold complexes, along with their impact on the catalytic performance...
January 9, 2019: ChemCatChem
Bei Zhang, Annelies Sels, Giovanni Salassa, Stephan Pollitt, Vera Truttmann, Christoph Rameshan, Jordi Llorca, Wojciech Olszewski, Günther Rupprechter, Thomas Bürgi, Noelia Barrabés
Thiolate protected metal clusters are valuable precursors for the design of tailored nanosized catalysts. Their performance can be tuned precisely at atomic level, e. g. by the configuration/type of ligands or by partial/complete removal of the ligand shell through controlled pre-treatment steps. However, the interaction between the ligand shell and the oxide support, as well as ligand removal by oxidative pre-treatment, are still poorly understood. Typically, it was assumed that the thiolate ligands are simply converted into SO2 , CO2 and H2 O...
December 7, 2018: ChemCatChem
Joelle E Romo, Nathan V Bollar, Coy J Zimmermann, Stephanie G Wettstein
Within the last decade, interest in using biphasic systems for producing furans from biomass has grown significantly. Biphasic systems continuously extract furans into the organic phase, which prevents degradation reactions and potentially allows for easier separations of the products. Several heterogeneous catalyst types, including zeolites, ion exchange resins, niobium-based, and others, have been used with various organic solvents to increase furan yields from sugar dehydration reactions. In this minireview, we summarized the use of heterogeneous catalysts in biphasic systems for furfural and 5-hydroxymethylfurfural production from the past five years, highlighting trends in chemical and physical properties that effect catalytic activity...
November 7, 2018: ChemCatChem
Federica Ruggieri, Luuk M van Langen, Derek T Logan, Björn Walse, Per Berglund
Dynamic kinetic resolution (DKR) reactions in which a stereoselective enzyme and a racemization step are coupled in one pot would represent powerful tools for the production of enantiopure amines through enantioconvergence of racemates. The exploitation of DKR strategies is currently hampered by the lack of effective, enzyme-compatible and scalable racemization strategies for amines. In the present work, the proof of concept of a fully biocatalytic method for amine racemization is presented. Both enantiomers of the model compound 1-methyl-3-phenylpropylamine could be racemized in water and at room temperature using a couple of wild-type, non-proprietary, enantiocomplementary amine transaminases and a minimum amount of pyruvate/alanine as a co-substrate couple...
November 7, 2018: ChemCatChem
Jing Li, Martin Lutz, Matthias Otte, Robertus J M Klein Gebbink
Trioxo-rhenium complexes are well known catalysts for the deoxydehydration (DODH) of vicinal diols (glycols). In this work, we report on the DODH of diols and biomass-derived polyols using Cptt ReO3 as a new catalyst (Cptt =1,3-di- tert -butylcyclopentadienyl). The DODH reaction was optimized using 2 mol % of Cptt ReO3 and 3-octanol as both reductant and solvent. The Cptt ReO3 catalyst exhibits an excellent activity for biomass-derived polyols. Specifically, glycerol is almost quantitatively converted to allyl alcohol and mucic acid gives 75 % of muconates at 91 % conversion...
October 23, 2018: ChemCatChem
Jessica M de Ruiter, Huub J M de Groot, Francesco Buda
When considering water oxidation catalysis theoretically, accounting for the transfer of protons and electrons from one catalytic intermediate to the next remains challenging: correction factors are usually employed to approximate the energetics of electron and proton transfer. Here these energetics were investigated using a closed system approach, which places the catalytic intermediate in a simulation box including proton and electron acceptors, as well as explicit solvent. As a proof of principle, the first two catalytic steps of the mononuclear ruthenium-based water oxidation catalyst [Ru(cy)(bpy)(H2 O)]2+ were examined using Car-Parrinello Molecular Dynamics...
October 23, 2018: ChemCatChem
Oriol Martínez-Ferraté, Christophe Werlé, Giancarlo Franciò, Walter Leitner
A catalytic system based on complexes comprising abundant and cheap manganese together with readily available aminotriazole ligands is reported. The new Mn(I) complexes are catalytically competent in transfer hydrogenation of ketones with 2-propanol as hydrogen source. The reaction proceeds under mild conditions at 80 °C for 20 h with 3 % of catalyst loading using either KO t Bu or NaOH as base. Good to excellent yields were obtained for a wide substrate scope with broad functional group tolerance. The obtained results by varying the substitution pattern of the ligand are consistent with an out-sphere mechanism for the H-transfer...
October 23, 2018: ChemCatChem
Emma V Sackville, Frank Marken, Ulrich Hintermair
We report the solution-phase electrochemistry of seven half-sandwich iridium(III) complexes with varying pyridine-alkoxide ligands to quantify electronic ligand effects that translate to their activity in catalytic water oxidation. Our results unify some previously reported electrochemical data of Cp*Ir complexes by showing how the solution speciation determines the electrochemical response: cationic complexes show over 1 V higher redox potentials that their neutral forms in a distinct demonstration of charge accumulation effects relevant to water oxidation...
October 9, 2018: ChemCatChem
Reza Vakili, Emma K Gibson, Sarayute Chansai, Shaojun Xu, Nadeen Al-Janabi, Peter P Wells, Christopher Hardacre, Alex Walton, Xiaolei Fan
Metal-organic frameworks (MOFs) are playing a key role in developing the next generation of heterogeneous catalysts. In this work, near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) is applied to study in operando the CO oxidation on Pt@MOFs (UiO-67) and Pt@ZrO2 catalysts, revealing the same Pt surface dynamics under the stoichiometric CO/O2 ambient at 3 mbar. Upon the ignition at ca . 200 °C, the signature Pt binding energy (BE) shift towards the lower BE (from 71.8 to 71.2 eV) is observed for all catalysts, confirming metallic Pt nanoparticles (NPs) as the active phase...
October 9, 2018: ChemCatChem
Stefan Weber, Julian Brünig, Veronika Zeindlhofer, Christian Schröder, Berthold Stöger, Andreas Limbeck, Karl Kirchner, Katharina Bica
A biphasic process for the hydrogenation of aldehydes was developed using a well-defined iron (II) PNP pincer complex as model system to investigate the performance of various ionic liquids. A number of suitable hydrophobic ionic liquids based on the N(Tf)2 - anion were identified, allowing to immobilize the iron (II) catalyst in the ionic liquid layer and to facilitate the separation of the desired alcohols. Further studies showed that targeted Brønsted basic ionic liquids can eliminate the need of an external base to activate the catalyst...
October 9, 2018: ChemCatChem
Koshiro Nakamura, Akihito Okuda, Kiyotaka Ohta, Hitoshi Matsubara, Kazu Okumura, Kana Yamamoto, Ryosuke Itagaki, Satoshi Suganuma, Etsushi Tsuji, Naonobu Katada
Cobalt-loaded MFI zeolite showed distinct activity for direct methylation of benzene with methane into toluene. High activity was found at around 0.6 of Co/Al molar ratio. Incorporation of carbon from methane into the methyl group of toluene was confirmed with isotope tracer experiments and mass spectroscopy. Ammonia infrared-mass spectroscopy temperature-programmed desorption, transmission electron microscopy, X-ray absorption near edge spectroscopy and extended X-ray absorption fine structure indicated that Lewis acidic divalent (+II of oxidation state) Co species mono-atomically dispersed on the ion exchange site of MFI zeolite was the active species...
September 7, 2018: ChemCatChem
Godwin A Aleku, Christoph Prause, Ruth T Bradshaw-Allen, Katharina Plasch, Silvia M Glueck, Samuel S Bailey, Karl A P Payne, David A Parker, Kurt Faber, David Leys
Fungal ferulic acid decarboxylases (FDCs) belong to the UbiD-family of enzymes and catalyse the reversible (de)carboxylation of cinnamic acid derivatives through the use of a prenylated flavin cofactor. The latter is synthesised by the flavin prenyltransferase UbiX. Herein, we demonstrate the applicability of FDC/UbiX expressing cells for both isolated enzyme and whole-cell biocatalysis. FDCs exhibit high activity with total turnover numbers (TTN) of up to 55000 and turnover frequency (TOF) of up to 370 min-1 ...
September 7, 2018: ChemCatChem
Rolf Sybren Postma, Roger Brunet Espinosa, Leon Lefferts
Nitrite hydrogenation is studied in steady-state as well as transient operation using a Pd catalyst in a tubular membrane contactor reactor. A negative reaction order in hydrogen in steady state operation proofs that hydrogen and nitrite adsorb competitively. In transient operation, feeding nitrite to the Pd surface fully covered with hydrogen results initially in very low conversion of nitrite, speeding up once hydrogen is removed from part of the Pd surface. Additional proof for competitive adsorption between hydrogen and nitrite is provided by the observation that exposure of a nitrite-covered catalyst to hydrogen induces desorption of nitrite...
September 7, 2018: ChemCatChem
Julia Blesl, Melanie Trobe, Felix Anderl, Rolf Breinbauer, Gernot A Strohmeier, Kateryna Fesko
We report the synthesis of diverse β-hydroxy-α,α-dialkyl-α-amino acids with perfect stereoselectivity for the α-quaternary center through the action of l- and d-specific threonine aldolases. A wide variety of aliphatic and aromatic aldehydes were accepted by the enzymes and conversions up to >80 % were obtained. In the case of d-selective threonine aldolase from Pseudomonas sp., generally higher diastereoselectivities were observed. The applicability of the protocol was demonstrated by performing enzymatic reactions on preparative scale...
August 21, 2018: ChemCatChem
Kazuyuki Yasukawa, Fumihiro Motojima, Atsushi Ono, Yasuhisa Asano
Discovery and development of enzymes for the synthesis of chiral amines have been a hot topic for basic and applied aspects of biocatalysts. Based on our X-ray crystallographic analyses of porcine kidney D-amino acid oxidase (pkDAO) and its variants, we rationally designed a new variant that catalyzed the oxidation of ( S )-4-Cl-benzhydrylamine (CBHA) from pkDAO and obtained it by functional high-throughput screening with colorimetric assay. The variant I230A/R283G was constructed from the variant R283G which had completely lost the activity for D-amino acids, further gaining new activity toward ( S )-chiral amines with the bulky substituents...
August 21, 2018: ChemCatChem
Flóra Nagy, Gábor Tasnádi, Diána Balogh-Weiser, Evelin Bell, Mélanie Hall, Kurt Faber, László Poppe
An easy to use method combining the selectivity of metal chelate affinity binding with strong covalent linking was developed for immobilization of non-specific acid phosphatases bearing a His-tag from crude cell lysate. Silica nanoparticles were grafted with aminopropyl functions which were partially transformed further with EDTA dianhydride to chelators. The heterofunctionalized nanoparticles charged with Ni2+ as the most appropriate metal ion were applied as support. First, the His-tagged phosphatases were selectively bound to the metal-chelate functions of the support...
August 21, 2018: ChemCatChem
Stefan Velikogne, Verena Resch, Carina Dertnig, Joerg H Schrittwieser, Wolfgang Kroutil
Imine reductases (IREDs) have recently become a primary focus of research in biocatalysis, complementing other classes of amine-forming enzymes such as transaminases and amine dehydrogenases. Following in the footsteps of other research groups, we have established a set of IRED biocatalysts by sequence-based in silico enzyme discovery. In this study, we present basic characterisation data for these novel IREDs and explore their activity and stereoselectivity using a panel of structurally diverse cyclic imines as substrates...
August 13, 2018: ChemCatChem
Beibei Guo, Douwe S Zijlstra, Johannes G de Vries, Edwin Otten
Water addition to α,β-unsaturated nitriles would give facile access to the β-hydroxy-nitriles, which in turn can be hydrogenated to the γ-amino alcohols. We have previously shown that alcohols readily add in 1,4-fashion to these substrates using Milstein's Ru(PNN) pincer complex as catalyst. However, attempted water addition to α,β-unsaturated nitriles gave the 3-hydroxynitriles in mediocre yields. On the other hand, addition of benzyl alcohol proceeded in excellent yields for a variety of β-substituted unsaturated nitriles...
July 9, 2018: ChemCatChem
Fetch more papers »
Fetching more papers... Fetching...
Read by QxMD. Sign in or create an account to discover new knowledge that matter to you.
Remove bar
Read by QxMD icon Read

Search Tips

Use Boolean operators: AND/OR

diabetic AND foot
diabetes OR diabetic

Exclude a word using the 'minus' sign

Virchow -triad

Use Parentheses

water AND (cup OR glass)

Add an asterisk (*) at end of a word to include word stems

Neuro* will search for Neurology, Neuroscientist, Neurological, and so on

Use quotes to search for an exact phrase

"primary prevention of cancer"
(heart or cardiac or cardio*) AND arrest -"American Heart Association"