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ACS Catalysis

Tom W van Deelen, Jelle J Nijhuis, Nynke A Krans, Jovana Zečević, Krijn P de Jong
Colloidal synthesis of nanocrystals (NC) followed by their attachment to a support and activation is a promising route to prepare model catalysts for research on structure-performance relationships. Here, we investigated the suitability of this method to prepare well-defined Co/TiO2 and Co/SiO2 catalysts for the Fischer-Tropsch (FT) synthesis with high control over the cobalt particle size. To this end, Co-NC of 3, 6, 9, and 12 nm with narrow size distributions were synthesized and attached uniformly on either TiO2 or SiO2 supports with comparable morphology and Co loadings of 2-10 wt %...
November 2, 2018: ACS Catalysis
John A Gurak, Keary M Engle
The hydroarylation of alkenes is an attractive approach to construct carbon-carbon (C-C) bonds from abundant and structurally diverse starting materials. Herein we report a palladiumcatalyzed reductive Heck hydroarylation of unactivated and heteroatom-substituted terminal alkenes with an array of (hetero)aryl iodides. The reaction is anti-Markovnikov selective and tolerates a wide variety of functional groups on both the alkene and (hetero)aryl coupling partners. Additionally, applications of this method to complex molecule diversifications were demonstrated...
October 5, 2018: ACS Catalysis
Juan Chen, Apparao Draksharapu, Davide Angelone, Duenpen Unjaroen, Sandeep K Padamati, Ronald Hage, Marcel Swart, Carole Duboc, Wesley R Browne
The oxidation of the C-H and C=C bonds of hydrocarbons with H2 O2 catalyzed by non-heme iron complexes with pentadentate ligands is widely accepted as involving a reactive FeIV =O species such as [(N4Py)FeIV =O]2+ formed by homolytic cleavage of the O-O bond of an FeIII -OOH intermediate (where N4Py is 1,1-bis(pyridin-2-yl)- N , N -bis(pyridin-2-ylmethyl)methanamine). We show here that at low H2 O2 concentrations the FeIV =O species formed is detectable in methanol. Furthermore, we show that the decomposition of H2 O2 to water and O2 is an important competing pathway that limits efficiency in the terminal oxidant and indeed dominates reactivity except where only sub-/near-stoichiometric amounts of H2 O2 are present...
October 5, 2018: ACS Catalysis
Pieter Cnudde, Kristof De Wispelaere, Louis Vanduyfhuys, Ruben Demuynck, Jeroen Van der Mynsbrugge, Michel Waroquier, Veronique Van Speybroeck
Catalytic alkene cracking on H-ZSM-5 involves a complex reaction network with many possible reaction routes and often elusive intermediates. Herein, advanced molecular dynamics simulations at 773 K, a typical cracking temperature, are performed to clarify the nature of the intermediates and to elucidate dominant cracking pathways at operating conditions. A series of C4 -C8 alkene intermediates are investigated to evaluate the influence of chain length and degree of branching on their stability. Our simulations reveal that linear, secondary carbenium ions are relatively unstable, although their lifetime increases with carbon number...
October 5, 2018: ACS Catalysis
Amanda C Garcia, Marc T M Koper
No abstract text is available yet for this article.
October 5, 2018: ACS Catalysis
Bastian Mei, Kai Han, Guido Mul
Materials used for photocatalytic overall water splitting (POWS) are typically composed of light-absorbing semiconductor crystals, functionalized with so-called cocatalytic nanoparticles to improve the kinetics of the hydrogen and/or oxygen evolution reactions. While function, quantity, and protection of such metal(oxide) nanoparticles have been addressed in the literature of photocatalysis, the stability and transients in the active oxidation-state upon illumination have received relatively little attention...
October 5, 2018: ACS Catalysis
Aditya Sengar, Rutger A van Santen, Erik Steur, Johannes A M Kuipers, Johan Padding
Differences in catalyst deactivation kinetics in solid acid catalysis are studied with catalyst models that allow for lateral interaction between protons. Deactivation of a solid acid catalyst with laterally interacting protons induces inhomogeneity of proton reactivity that develops with time. As a consequence, product selectivity changes and deactivation will accelerate. This is demonstrated by simulations of the deactivation kinetics of the alkylation reaction of propylene with isobutane. The effect of lateral interactions between protons arises because initial catalyst deactivation is not caused by pore blocking or coke deposition but by a molecular mechanism where protons are consumed due to the formation of stable nonreactive carbenium ions...
October 5, 2018: ACS Catalysis
Karl J Koebke, Vincent L Pecoraro
The development of redox-active metalloprotein catalysts is a challenging objective of de novo protein design. Within this Perspective we detail our efforts to create a redox-active Cu nitrite reductase (NiR) by incorporating Cu into the hydrophobic interior of well-defined three-stranded coiled coils (3SCCs). The scaffold contains three histidine residues that provide a layer of three nitrogen donors that mimic the type 2 catalytic site of NiR. We have found that this strategy successfully produces an active and stable CuNiR model that functions for over 1000 turnovers...
September 7, 2018: ACS Catalysis
Steven C Schmid, Ilia A Guzei, Israel Fernández, Jennifer M Schomaker
The synthesis of densely functionalized azetidinesin a highly stereocontrolled manner is challenging, but interest in the bioactivities of these small heterocycles has stimulated methods for their preparation. We recently reported a one-carbon ring expansion of bicyclic methylene aziridines under dirhodium catalysis capable of delivering enantioenriched azetidines. This work explores this ring expansion using computational and experimental studies. DFT computations indicate that the reaction proceeds through formation of an aziridinium ylide, which is precisely poised for concerted, asynchronous ring-opening/closing to deliver the azetidines in a [2,3]-Stevens-type rearrangement...
September 7, 2018: ACS Catalysis
Nikolay Kosinov, Evgeny A Uslamin, Ferdy J A G Coumans, Alexandra S G Wijpkema, Roderigh Y Rohling, Emiel J M Hensen
Surface carbon (coke, carbonaceous deposits) is an integral aspect of methane dehydroaromatization catalyzed by Mo/zeolites. We investigated the evolution of surface carbon species from the beginning of the induction period until the complete catalyst deactivation by the pulse reaction technique, TGA, 13 C NMR, TEM, and XPS. Isotope labeling was performed to confirm the catalytic role of confined carbon species during MDA. It was found that "hard" and "soft" coke distinction is mainly related to the location of coke species inside the pores and on the external surface, respectively...
September 7, 2018: ACS Catalysis
Raquel Roldán, Karel Hernandez, Jesús Joglar, Jordi Bujons, Teodor Parella, Israel Sánchez-Moreno, Virgil Hélaine, Marielle Lemaire, Christine Guérard-Hélaine, Wolf-Dieter Fessner, Pere Clapés
Asymmetric aldol addition of simple aldehydes and ketones to electrophiles is a cornerstone reaction for the synthesis of unusual sugars and chiral building blocks. We investigated d-fructose-6-phosphate aldolase from E. coli (FSA) D6X variants as catalysts for the aldol additions of ethanal and nonfunctionalized linear and cyclic aliphatic ketones as nucleophiles to nonphosphorylated hydroxyaldehydes. Thus, addition of propanone, cyclobutanone, cyclopentanone, or ethanal to 3-hydroxypropanal or ( S )- or ( R )-3-hydroxybutanal catalyzed by FSA D6H and D6Q variants furnished rare deoxysugars in 8-77% isolated yields with high stereoselectivity (97:3 dr and >95% ee )...
September 7, 2018: ACS Catalysis
Liliana Lukashuk, Nevzat Yigit, Raffael Rameshan, Elisabeth Kolar, Detre Teschner, Michael Hävecker, Axel Knop-Gericke, Robert Schlögl, Karin Föttinger, Günther Rupprechter
Cobalt oxide Co3 O4 has recently emerged as promising, noble metal-free catalyst for oxidation reactions but a better understanding of the active catalyst under working conditions is required for further development and potential commercialization. An operando approach has been applied, combining near ambient (atmospheric) pressure X-ray photoelectron spectroscopy (NAP-XPS), Fourier transform infrared spectroscopy (FTIR), or X-ray diffraction (XRD) with simultaneous catalytic tests of CO oxidation on Co3 O4 , enabling one to monitor surface and bulk states under various reaction conditions (steady-state and dynamic conditions switching between CO and O2 )...
September 7, 2018: ACS Catalysis
Caomhán Stewart, Emma K Gibson, Kevin Morgan, Giannantonio Cibin, Andrew J Dent, Christopher Hardacre, Evgenii V Kondratenko, Vita A Kondratenko, Colin McManus, Scott Rogers, Cristina E Stere, Sarayute Chansai, Yi-Chi Wang, Sarah J Haigh, Peter P Wells, Alexandre Goguet
The promotional effect of H2 on the oxidation of CO is of topical interest, and there is debate over whether this promotion is due to either thermal or chemical effects. As yet there is no definitive consensus in the literature. Combining spatially resolved mass spectrometry and X-ray absorption spectroscopy (XAS), we observe a specific environment of the active catalyst during CO oxidation, having the same specific local coordination of the Pd in both the absence and presence of H2 . In combination with Temporal Analysis of Products (TAP), performed under isothermal conditions, a mechanistic insight into the promotional effect of H2 was found, providing clear evidence of nonthermal effects in the hydrogen-promoted oxidation of carbon monoxide...
September 7, 2018: ACS Catalysis
Gui-Rong Zhang, Thomas Wolker, Daniel J S Sandbeck, Macarena Munoz, Karl J J Mayrhofer, Serhiy Cherevko, Bastian J M Etzold
Modifying Pt catalysts using hydrophobic ionic liquids (ILs) has been demonstrated to be a facile approach for boosting the performance of Pt catalysts for the oxygen reduction reaction (ORR). This work aims to deepen the understanding and initiate a rational molecular tuning of ILs for improved activity and stability. To this end, Pt/C catalysts were modified using a variety of 1-methyl-3-alkylimidazolium bis(trifluoromethanesulfonyl)imide ([C n C1 im][NTf2 ], n = 2-10) ILs with varying alkyl chain lengths in imidazolium cations, and the electrocatalytic properties (e...
September 7, 2018: ACS Catalysis
Ágnes Szécsényi, Guanna Li, Jorge Gascon, Evgeny A Pidko
Periodic density functional theory (DFT) calculations were carried out to investigate the mechanism of methane oxidation with H2 O2 over the defined Fe sites in Fe/ZSM-5 zeolite. The initial Fe site is modeled as a [(H2 O)2 -Fe(III)-(μO)2 -Fe(III)-(H2 O)2 ]2+ extraframework cluster deposited in the zeolite pore and charge-compensated by two anionic lattice sites. The activation of this cluster with H2 O2 gives rise to the formation of a variety of Fe(III)-oxo and Fe(IV)-oxo complexes potentially reactive toward methane dissociation...
September 7, 2018: ACS Catalysis
Vivek Sinha, Nitish Govindarajan, Bas de Bruin, Evert Jan Meijer
Insights into the mechanism of the catalytic cycle for methanol dehydrogenation catalyzed by a highly active PNP pincer ruthenium complex in methanol solvent are presented, using DFT-based molecular dynamics with an explicit description of the solvent, as well as static DFT calculations using microsolvation models. In contrast to previous results, we find the amido moiety of the catalyst to be permanently protonated under catalytic conditions. Solvent molecules actively participate in crucial reaction steps and significantly affect the reaction barriers when compared to pure gas-phase models, which is a direct result of the enhanced solvent stabilization of methoxide anion intermediates...
August 3, 2018: ACS Catalysis
Milton R Smith, Ranjana Bisht, Chabush Haldar, Gajanan Pandey, Jonathan E Dannatt, Behnaz Ghaffari, Robert E Maleczka, Buddhadeb Chattopadhyay
High ortho selectivity for Ir-catalyzed C-H borylations (CHBs) of anilines results when B2 eg2 (eg = ethylene glycolate) is used as the borylating reagent in lieu of B2 pin2 , which is known to give isomeric mixtures with anilines lacking a blocking group at the 4-position. With this modification, high selectivities and good yields are now possible for various anilines, including those with groups at the 2- and 3-positions. Experiments indicate that ArylN(H)Beg species are generated prior to CHB and support the improved ortho selectivity relative to B2 pin2 reactions arising from smaller Beg ligands on the Ir catalyst...
July 6, 2018: ACS Catalysis
Ya-Qiong Su, Jin-Xun Liu, Ivo A W Filot, Long Zhang, Emiel J M Hensen
Methane (CH4 ) combustion is an increasingly important reaction for environmental protection, for which Pd/CeO2 has emerged as the preferred catalyst. There is a lack of understanding of the nature of the active site in these catalysts. Here, we use density functional theory to understand the role of doping of Pd in the ceria surface for generating sites highly active toward the C-H bonds in CH4 . Specifically, we demonstrate that two Pd2+ ions can substitute one Ce4+ ion, resulting in a very stable structure containing a highly coordinated unsaturated Pd cation that can strongly adsorb CH4 and dissociate the first C-H bond with a low energy barrier...
July 6, 2018: ACS Catalysis
Miguel Martínez-Calvo, José R Couceiro, Paolo Destito, Jéssica Rodríguez, Jesús Mosquera, José L Mascareñas
Discrete palladium(II) complexes featuring purposely designed phosphine ligands can promote depropargylation and deallylation reactions in cell lysates. These complexes perform better than other palladium sources, which apparently are rapidly deactivated in such hostile complex media. This good balance between reactivity and stability allows the use of these discrete phosphine palladium complexes in living mammalian cells, whereby they can mediate similar transformations. The presence of a phosphine ligand in the coordination sphere of palladium also provides for the introduction of targeting groups, such as hydrophobic phosphonium moieties, which facilitate the accumulation of the complexes in mitochondria...
July 6, 2018: ACS Catalysis
Alex J Nett, Santiago Cañellas, Yuki Higuchi, Michael T Robo, Jeanne M Kochkodan, M Taylor Haynes, Jeff W Kampf, John Montgomery
The synthesis and catalytic activity of several classes of NHC-Ni(0) pre-catalysts stabilized by electron-withdrawing alkenes are described. Variations in the structure of fumarate and acrylate ligands modulate the reactivity and stability of the NHC-Ni(0) pre-catalysts and lead to practical and versatile catalysts for a variety of transformations. The catalytic activity and efficiency of representative members of this class of catalysts have been evaluated in reductive couplings of aldehydes and alkynes and in N -arylations of aryl chlorides...
June 6, 2018: ACS Catalysis
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