Co-immobilization of Laccase and TEMPO in the Compartments of Mesoporous Silica for a Green and One-pot Cascade Synthesis of Coumarins via Knoevenagel Condensation ChemCatChem (IF 4.803) Pub Date : 2018-01-16 Mehdi Mogharabi-Manzari, Mohsen Amini, Mohammad Abdollahi, Mehdi Khoobi, Ghodsieh Bagherzadeh, Mohammad Ali Faramarzi
Co-immobilization of bio- and chemo-catalysts produces sustainable, recyclable hybrid systems that open new horizons for green cascade approaches in organic synthesis. Here, a co-immobilization of laccase and TEMPO in mesoporous silica was used for one-pot synthesis of 30 coumarin-3-carboxylate derivatives in aqueous medium under mild conditions via condensation of in situ oxidized 2-hydroxybenzyl alcohols and malonate derivatives. A maximal yield was obtained after 24-h incubation at pH 6.0 and 45 °C. An efficient organic synthesis was catalyzed by the hybrid catalyst in 10% organic solvent. More than 95 % of the initial enzyme activity was preserved after 10 cycles, and no significant catalyst deactivation occurred after 10 runs. This new system efficiently catalyzed in situ aerobic oxidation of salicyl alcohols, followed by Knoevenagel condensation, confirming the possibility of producing efficient hybrid catalysts by co-immobilization of catalytic species in mesoporous materials.
The role of Copper in the upgrading of Bio-alcohols ChemCatChem (IF 4.803) Pub Date : 2018-01-16 Federica Zaccheria, Nicola Scotti, Nicoletta Ravasio
Some recent results on Guerbet reactions and a short review on dehydrogenative coupling of alcohols (DHC) have been reported. The focus is on the role of acidic and basic sites and in particular on the role of Cu when present in the catalyst, taking into account that the two processes share the first step namely alcohol dehydrogenation while the second one is determining in driving selectivity towards self-coupling or symmetrical ester formation. The main type of catalysts for the Guerbet reaction are based on hydrotalcites, hydroxyapatite and supported metal systems, whereas the catalysts for DHC are copper catalysts on different supports. The role of acidic and basic sites in determining activity and selectivity to Guerbet alcohols has been investigated putting in light quite stringent requirements as far as selectivity is concerned. In DHC focus has been set on the role of interaction of copper with the support in turn influencing the distribution of acidic and basic sites. The morphology of the metallic phase has been suggested as distinctive factor for Cu containing catalysts in promoting C-C coupling or C-O coupling in the second step.
Reduced graphene oxide-CdS nanorods decorated with Ag nanoparticles for efficient photocatalytic reduction CO2 under visible light ChemCatChem (IF 4.803) Pub Date : 2018-01-14 Zezhou Zhu, Ying Han, Caiping Chen, Zhengxin Ding, Jinlin Long, Yidong Hou
Photocatalytic CO2 reduction is an attractive approach for the direct conversion of solar energy into chemical fuels. In this study, we synthesized a composite material consisting of Ag, reduced graphene oxide (RGO) and CdS nanorods as the novel photocatalyst for CO2 reduction. The morphological, structural, optical and electrochemical properties of the resultant nanocomposite (Ag-RGO-CdS) were investigated by various physical techniques (e.g., XRD, SEM, TEM, XPS, DRS and EIS). These results indicate that Ag-RGO-CdS nanocomposites exhibit an enhanced photocatalytic activity for the conversion of CO2 into CO, and the optimum activity is achieved over 1.0 wt.%Ag-3.0 wt.%RGO-CdS. This enhanced performance can be ascribed to the multifunctional promoting effects of RGO and Ag in the composite. On one hand, RGO and Ag can act as electron acceptors, thus enhance the separation efficiency of photogenerated carriers. On the other hand, the incorporation of RGO and Ag can improve the adsorption and activation of CO2, which results in the enhancement of the photocatalytic reduction of CO2 to CO. Furthermore, the possible mechanism for photocatalytic CO2 reduction over Ag-RGO-CdS nanocomposites was proposed. This study demonstrates a semiconductor-based hybrid for efficient photocatalytic CO2 reduction by virtue of the combinational effect of dual cocatalysts.
Engineered sulphur resistant catalyst system with an assisted regeneration strategy for lean-burn methane combustion ChemCatChem (IF 4.803) Pub Date : 2018-01-12 Niko M Kinnunen, Matthew Keenan, Kauko Kallinen, Teuvo Maunula, Mika Suvanto
Catalytic combustion of methane, the main component of natural gas, is a challenge under lean-burn conditions and at low temperature, due sulphur poisoning of the Pd rich catalyst. The paper introduces a more sulphur resistant catalyst system which can be regenerated in operation. The developed catalyst system lowers the barrier that has restrained the use of liquefied natural gas as a fuel in energy production.
Selective decomposition of cyclohexyl hydroperoxide using homogeneous and heterogeneous Cr(VI) catalysts: Optimizing the reaction by evaluating the reaction mechanism ChemCatChem (IF 4.803) Pub Date : 2018-01-11 Jessica Nadine Hamann, Marko Hermsen, Anna-Corina Schmidt, Saskia Krieg, Jasmin Schießl, Dominic Riedel, Joaquim Henrique Teles, Ansgar Schäfer, Peter Comba, A. Stephen K. Hashmi, Thomas Schaub
In this study, known homogeneous and heterogeneous chromium(VI) catalyst systems were investigated with respect to the favored formation of cyclohexanone during the decomposition of cyclohexyl hydroperoxide (CHHP). The focus was on mechanistic studies using different spectroscopic methods as well as DFT calculations to further optimize the reaction conditions. As in previous decomposition studies, a mechanism via the formation of a metal alkylperoxido intermediate is probable. In situ spectroscopic studies revealed that in case of both the soluble and insoluble catalyst, the selective decomposition happens via a non-radical, non-redox mechanism at the Cr(VI) stage through the formation of a cyclohexylperoxychromium(VI)¬ complex. The proposed mechanism is supported by thorough DFT calculations.
Methanation of CO2 over Zeolite-Encapsulated Nickel Nanoparticles ChemCatChem (IF 4.803) Pub Date : 2018-01-11 Farnoosh Goodarzi, Liqun Kang, Feng Ryan Wang, Finn Joensen, Søren Kegnæs, Jerrik Mielby
Here we present a simple and effective method to encapsulate Ni nanoparticles in zeolite silicalite-1. In this method, the zeolite is modified by selective desilication, which creates intra-particle voids and mesopores that facilitate the formation of small and well-dispersed nanoparticles upon impregnation and reduction. TEM and XPS analysis confirm that a significant part of the Ni nanoparticles are situated inside the zeolite rather than on the outer surface. The encapsulation results in an increased metal dispersion and, consequently, a high catalytic activity for CO2 methanation. With a gas hourly space velocity of 60000 ml/g catalyst h-1 and H2/CO2=4, the zeolite-encapsulated Ni nanoparticles result in 60% conversion at 450°C, which corresponds to a site-time yield of around 304 mol CH4/mol Ni h-1. The encapsulated Ni nanoparticles show no change in activity or selectivity after 50 h of operation, although post-catalysis characterisation reveals some particle migration.
Hydrogenation and Reductive Amination of Aldehydes using Triphos Ruthenium Catalysts ChemCatChem (IF 4.803) Pub Date : 2018-01-11 Francesca Christie, Antonio Zanotti-Gerosa, Damian Grainger
Air-stable Ru(II)-NNN Pincer Complexes for Efficient Coupling of Aromatic Diamines and Alcohols to 1H-benzo[d]imidazoles with liberation of H2 ChemCatChem (IF 4.803) Pub Date : 2018-01-10 Lin Li, Qi Luo, Huahua Cui, Renjie Li, Jing Zhang, Tianyou Peng
Abstract: Two new phosphine-free Ru(II)-NNN pincer complexes ([RuCl(L1)(CH3CN)2]Cl (1) and [RuCl(L2)(CH3CN)2]Cl (2), L1 = 2,6-bis(1H-imidazole-2-yl)pyridine, L2 = 2,6-bis(1-hexyl-1H-imidazole-2-yl)pyridine) were synthesized for homogeneously catalyzing the condensation of benzyl alcohol and benzene-1,2-diamine to 2-pheny-1H-benzo[d]imidazole and H2. It was found that the reactivity with an order of 1 > 2 is lower than that of the phosphine-containing Ru(II)-NNN pincer complex [RuCl2(L1)(PPh3)3] (3), and thus a homogeneous system containing complex 1, 1 equiv. of 1,2-bis(diphenyl-phosphanyl)ethane (dppe), and 10 equiv. of NaBPh4 was developed to improve the catalytic efficiency for the condensation of primary alcohols and benzene-1,2-diamine (or its derivatives) to 2-substituted 1H-benzo[d]imidazoles in excellent yields (up to 97%) and turnover number (TONs ~ 388). The present system realizes facile one-step synthesis of 1H-benzo[d]imidazole derivatives from alcohols without using the oxidant and/or the stoichiometric amount of inorganic bases that is usually necessary in homogeneous systems reported previously.
Fabrication of Single-atom Pt Catalyst for Hydrogen Evolution Reaction: A New Protocol by Utilization of HxMoO3-x with Plasmon Resonance ChemCatChem (IF 4.803) Pub Date : 2018-01-10 Wei Liu, Qun Xu, Pengfei Yan, Jun Chen, Yi Du, Shengqi Chu, Jiaou Wang
Single-atom catalysts (SACs) play a key role in many chemical processes owing to the highly desirable atom efficiency, but the challenging synthesis of the catalysts limits their commercialization or application on a large scale. Here we report a facile strategy to integrate atomically Pt into richly-deficient MoO3-x. The core of the experimental strategy is the fabrication and utilization of HxMoO3-x with plasmon resonance that contains intercalated H+. The obtained catalyst possesses the remarkable electrocatalytic activity toward the hydrogen evolution reaction, which is even comparable with that of the commercial Pt/C. While the application amount of Pt is reduced greatly and it is only 10 percent of the commercial Pt/C. Therefore this work not only supplies a new synthesis route to SACs, but also it reveals the potential relation between plasmon resonance materials and fabrication of single- atom catalyst at the same time.
Hydrogen Peroxide Production on Carbon Nitride-Boron Nitride-Reduced Graphene Oxide Hybrid Photocatalyst under Visible Light ChemCatChem (IF 4.803) Pub Date : 2018-01-09 Yusuke Kofuji, Yuki Isobe, Yasuhiro Shiraishi, Hirokatsu Sakamoto, Satoshi Ichikawa, Shunsuke Tanaka, Takayuki Hirai
Photocatalytic production of hydrogen peroxide (H2O2) from earth-abundant water and O2 is one desirable artificial photosynthesis for solar fuel production. We prepared a metal-free hybrid photocatalyst consisting of pyromellitic diimide-doped carbon nitride (g-C3N4/PDI), boron nitride (BN), and reduced graphene oxide (rGO). The g-C3N4/PDI-BN-rGO catalyst, when photoirradiated in water with O2 by visible light at room temperature, efficiently produces H2O2. The photoexcited g-C3N4/PDI moiety transfers the conduction band electrons to rGO, leading to selective production of H2O2 via two-electron reduction of O2 on the rGO surface. In contrast, the valence band holes photoformed on the g-C3N4/PDI moieties are transferred to BN, leading to efficient oxidation of water. The electron-hole separation enhanced by the incorporation of rGO and BN significantly suppresses the charge recombination and exhibits high photocatalytic activity. The solar-to-chemical conversion (SCC) efficiency for H2O2 production on the hybrid catalyst is 0.27 %, which is higher than the highest efficiencies obtained by overall water splitting on powdered catalysts.
Asymmetric synthesis of chiral halogenated amines using amine transaminases ChemCatChem (IF 4.803) Pub Date : 2018-01-09 Ayad Dawood, Rodrigo de Souza, Uwe Bornscheuer
Amine transaminases (ATA) are versatile and industrially relevant biocatalysts, catalyzing the transfer of an amine group from a donor to an acceptor molecule. Asymmetric synthesis from a prochiral ketone is the most preferred route to the desired amine product, since it is obtainable at a theoretical yield of 100 %. In addition to the requirement of active and enantioselective ATAs, also the choice of a suitable amine donor is important to save costs and to avoid additional enzymes for shifting the equilibrium and/or recycling of cofactors. In this work, we identified suitable (R)- and (S)-ATAs from Aspergillus fumigatus and Silicibacter pomeroyi, respectively to afford a set of halogen-substituted derivatives of brominated or chlorinated 1-phenyl-2-propanamine, 4-phenylbutan-2-amine and 1-(3-pyridinyl)ethanamine. Optimization of the donor-acceptor-ratio enabled the application of isopropylamine as amine donor resulting in high conversion and amines with 73-99 %ee.
Cu-Co-Ce Ternary Oxide as an additive to conventional PGM catalyst for automotive exhaust catalysis ChemCatChem (IF 4.803) Pub Date : 2018-01-08 Andrew Justin Binder, Todd J. Toops, James E. Parks II
Recently we reported on a ternary mixed oxide catalyst which showed low temperature CO oxidation activity in lean exhaust conditions without inhibition by hydrocarbons such as propene. However, this Cu-Co-Ce catalyst's (CCC) hydrocarbon oxidation activity cannot be considered as a stand-alone solution to low temperature automotive exhaust catalysis. To achieve both low temperature oxidation of pollutants and a reduction of total PGM content we have examined a 50% physical mixture of traditional Pt/Al2O3 and our CCC catalyst in two simulated exhaust protocols. Using this physical mixture, we are able to obtain equivalent or better hydrocarbon activity to the baseline Pt/Al2O3 catalyst with half of the total PGM content as well as an increased sulfur tolerance for the CCC component of the mixture. DRIFTS data confirms that despite exposure of sulfur-sensitive CCC to SO2, Cu+-carbonyl binding sites can still be seen when the catalyst is mixed with Pt/Al2O3.
Biocatalytic Racemization Employing TeSADH: Substrate Scope and Organic Solvent Compatibility for Dynamic Kinetic Resolution ChemCatChem (IF 4.803) Pub Date : 2018-01-09 Jarosław Popłoński, Tamara Reiter, Wolfgang Kroutil
Front Cover: Mechanism of Carbon Monoxide Dissociation on a Cobalt Fischer–Tropsch Catalyst (ChemCatChem 1/2018) ChemCatChem (IF 4.803) Pub Date : 2018-01-09 Wei Chen, Bart Zijlstra, Ivo A. W. Filot, Robert Pestman, Emiel J. M. Hensen
Cover Feature: Confining Gold Nanoclusters in Highly Defective Graphitic Layers To Enhance the Methanol Electrooxidation Reaction (ChemCatChem 1/2018) ChemCatChem (IF 4.803) Pub Date : 2018-01-09 Zhe Mao, Haihua Hu, Rui Su, Peizhi Liu, Yixing Li, Wenting Zhang, Xiaoning Zhao, Junjie Guo, Pengfei Guan, Gaowu Qin, Xuefeng Zhang
Cover Feature: Switching the Cofactor Specificity of an Imine Reductase (ChemCatChem 1/2018) ChemCatChem (IF 4.803) Pub Date : 2018-01-09 Niels Borlinghaus, Bettina M. Nestl
Cover Feature: Modular Polyoxometalate–Layered Double Hydroxides as Efficient Heterogeneous Sulfoxidation and Epoxidation Catalysts (ChemCatChem 1/2018) ChemCatChem (IF 4.803) Pub Date : 2018-01-09 Tengfei Li, Wei Zhang, Wei Chen, Haralampos N. Miras, Yu-Fei Song
Mechanism of Carbon Monoxide Dissociation on a Cobalt Fischer–Tropsch Catalyst ChemCatChem (IF 4.803) Pub Date : 2018-01-09 Wei Chen, Bart Zijlstra, Ivo A. W. Filot, Robert Pestman, Emiel J. M. Hensen
Ring-Expanded N-Heterocyclic Carbenes for Copper-Mediated Azide-Alkyne Click Cycloaddition Reactions ChemCatChem (IF 4.803) Pub Date : 2018-01-05 Filip Sebest, Jay J Dunsford, Matthew Adams, Jeremy Pivot, Paul D Newman, Silvia Díez-González
A series of well-defined copper(I) complexes bearing ring expanded N-heterocyclic carbene (NHC) ligands has been applied to the azide-alkyne cycloaddition reaction. The obtained results notably showed that the six membered NHC ligands outperform well-established five-membered ones. [CuI(Mes-6)] displayed a remarkable catalytic activity while respecting the strict criteria for Click reactions.
10 Volumes of ChemCatChem, a Cross Section of Catalysis Research from ChemPubSoc Europe ChemCatChem (IF 4.803) Pub Date : 2018-01-05 Michael A. Rowan
Continuous-flow Pd-catalyzed synthesis of cyclohexanones from phenols using sodium formate as a safe hydrogen source ChemCatChem (IF 4.803) Pub Date : 2018-01-04 Luigi Vaccaro, Federica Valentini, Niccolò Santillo, Chiara Petrucci, Daniela Lanari, Elena Petricci, Maurizio Taddei
We report a procedure for the continuous flow production of cyclohexanone from phenol, based on the use of sodium formate as a biomass derived source of hydrogen and on Pd/C as an easily accessible catalytic system. The reaction works in water at pH = 12.0 and at 90 °C. by setting a packed reactor charged with the catalyst Pd/C (10 wt%) at a flow rate of 0.5 mL min-1 we achieved a continuous flow production of cyclohexanone with high yields, selectivity and productivity.
Porous Organic Polymers Constructed from Tröger's Base as Efficient Carbon Dioxide Adsorbents and Heterogeneous Catalysts ChemCatChem (IF 4.803) Pub Date : 2018-01-04 Zhifeng Dai, Yongquan Tang, Qi Sun, Xiaolong Liu, Xiangju Meng, Feng Deng, Feng-Shou Xiao
Commercial gold(I) and gold(III) compounds supported on carbon materials as greener catalysts for the oxidation of alkanes and alcohols ChemCatChem (IF 4.803) Pub Date : 2018-01-03 Sonia A. C. Carabineiro, Luísa M.D.R.S. Martins, Armando J.L. Pombeiro, José L Figueiredo
The present paper reports strategies for oxidative functionalization of cyclohexane and alcohols, under mild conditions, catalysed by Au(I) or Au(III) compounds, namely, dichloro(2-pyridinecarboxylato)gold(III) (1), tetrabutylammonium tetrachloroaurato(III) (2), chlorotrimethylphosphinegold(I) (3), chlorotriphenylphosphinegold(I) (4) and 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidenegold(I) chloride (5) supported on different carbon materials: activated carbon (AC), multi-walled carbon nanotubes (CNT) and carbon xerogel (CX), with three different surface treatments: original, as purchased/prepared, oxidized with nitric acid (-ox), and oxidized with nitric acid and subsequently treated with NaOH (-ox-Na). The obtained materials were tested for the oxidation of cyclohexane. All materials were very selective to the production of cyclohexanol and cyclohexanone with no trace of by-products detected. The same catalysts were tested in the selective oxidation of methyl benzyl alcohol, cyclohexanol and 2-octanol, to the corresponding aldehydes or ketones. It was found that better results were obtained for the heterogenised complexes and that the most efficient support is CNT-ox-Na. The best result for cyclohexane oxidation was obtained for 5/CNT-ox-Na, which showed recyclability up to 5 cycles without decrease of activity. The highest activity for methyl benzyl alcohol oxidation was found for the 3/CNT-ox-Na material, which could be recycled to 7 cycles without loss of activity.
A seed-mediated approach for the preparation of modified heterogeneous catalysts ChemCatChem (IF 4.803) Pub Date : 2018-01-03 Katerina Soulantica, Justine Harmel, Adrien Berliet, Kassiogé Dembélé, Cécile Marcelot, Anne-Sophie Gay, Ovidiu Ersen, Sylvie Maury, Antoine Fécant, Bruno Chaudret, Philippe Serp
Abstract: Colloidal chemistry is very efficient in providing nanocrystals of well controlled structural characteristics. While nanoparticles are essential components of heterogeneous catalysts, colloidal methods are rarely employed for their preparation. We have employed a seed mediated growth approach for modifying the structural characteristics of a conventional cobalt-based Fischer-Tropsch catalyst. The Co particles of this catalyst can play the role of seeds for the overgrowth of shape and structure controlled cobalt nanostructures using a simple wet chemical method involving a molecular cobalt precursor and stabilizing agents. Thus, cobalt nanorods exhibiting the hexagonal compact structure were selectively grown on the immobilized Co particles of a reference Co/Al2O3-SiO2 catalyst. The as obtained catalyst shows a better stability than a reference catalyst for the Fischer-Tropsch reaction. The removal of most of the ligands from the nanorod catalyst allows improving the catalyst activity while maintaining its stability. This is a proof of concept concerning the implementation of wet chemistry nanoparticle synthesis for the modification of heterogeneous catalysts.
Structure Sensitive Scaling Relations: Adsorption Energies from Surface Site Stability ChemCatChem (IF 4.803) Pub Date : 2017-12-31 Luke T Roling, Frank Abild-Pedersen
The design of heterogeneous catalysts is accelerated by the identification of thermochemical reactivity descriptors, which enable the prediction of promising materials through efficient screening. Motivated by previous discoveries of linear scaling relations between the adsorption energies of related atoms and molecules, we present a new scaling between the adsorption energies of metal atoms and metal-adsorbate complexes, which can be used to directly predict catalytically relevant molecular adsorption energies. In contrast to existing models based on the coordination number of surface atoms alone, our model can predict adsorption energies with site-by-site resolution considering local structural effects and also has potential extensions to include contributions of neighboring metal identity in alloy systems. Integration of this scaling with a previously identified model for metal-metal interactions enables the accurate prediction of molecular adsorption energies on nanoparticles by performing only a small set of slab-based calculations.
Photoelectrocatalytic synthesis of Hydrogen Peroxide by Molecular Copper-Porphyrin Supported on Titanium Dioxide Nanotubes ChemCatChem (IF 4.803) Pub Date : 2017-12-29 Dogukan Apaydin, Hathaichanok Seelajaroen, Orathip Pengsakul, Patchanita Thamyongkit, Niyazi Serdar Sariciftci, Julia Kunze-Liebhäuser, Engelbert Portenkirchner
We report on a self-assembled system comprising a molecular copper-porphyrin photoelectrocatalyst, 5-(4-carboxy-phenyl)-10,15,20-triphenylporphyrinatocopper(II) (CuTPP-COOH), covalently bound to self-organized, anodic titania nanotube arrays (TiO2 NTs) for photoelectrochemical reduction of oxygen. Visible light irradiation of the porphyrin-covered TiO2 NTs under cathodic polarization up to -0.3 V vs. Normal Hydrogen Electrode (NHE) photocatalytically produces H2O2 in pH neutral electrolyte, at room temperature and without need of sacrificial electron donors. The formation of H2O2 upon irradiation is proven and quantified by direct colorimetric detection using 4-nitrophenyl boronic acid (p-NPBA) as a reactant. This simple approach for the attachment of a small molecular catalyst to TiO2 NTs may ultimately allow for the preparation of a low-cost H2O2 evolving cathode for efficient photoelectrochemical energy storage under ambient conditions.
Iron(III) Amine Bis(phenolate) Complex Immobilized on Silica-Coated Magnetic Nanoparticles: A Highly Efficient Catalyst for the Oxidation of Alcohols and Sulfides ChemCatChem (IF 4.803) Pub Date : 2017-12-29 Touraj Karimpour, Elham Safaei, Babak Karimi, Yong-Ill Lee
TiO2-carbon materials derived from hydrothermal carbonization of waste biomass: A highly efficient, low cost visible-light-driven photocatalyst. ChemCatChem (IF 4.803) Pub Date : 2017-12-27 Yusuf Osman Donar, Selva Bilge, Ali Sinag, Oleksii Pliekhov
In this paper, we present a green, low cost carbon material derived from waste biomass (hazelnut shell and olive residue) to fabricate a binary TiO2/carbon composite for improving the photocatalytic performance of TiO2 under visible light. Synthesis, characterization and photocatalytic applications of TiO2/carbon composite were performed. Hydrothermal carbonization was used to obtain carbon support materials. A series of TiO2/carbon composite materials from waste biomass based hydrochar, fullerene and carbon nanotube has been prepared for the comparison purposes. Photocatalytic performances of all composites were measured by comparing Methylene Blue (MB) removal rates. The results show that waste biomass based hydrochar/TiO2 composites possessed superior visible light photocatalytic activity comparing with high technology carbons/TiO2 composites such as fullerene and carbon nanotube. The enhanced photodegradation capacity could be ascribed to the delocalized furanic conjugated system and functional groups of HS-TiO2 and OR-TiO2 composites.
Highly Dispersed Ultrafine Palladium Nanoparticles Enabled by Functionalized Porous Organic Polymer for Additive-free Dehydrogenation of Formic Acid ChemCatChem (IF 4.803) Pub Date : 2017-12-23 Caiyan Cui, Yujiao Tang, Muhammad Asad Ziaee, Ruihu Wang, Dongxu Tian
Formic acid (FA) is one of the most favorable chemical hydrogen storage materials for renewable energy transformation, the development of efﬁcient heterogeneous catalysts for ultraclean H2 generation from FA in the absence of any alkalis or additives under mild conditions remains a major challenge. Here, we present a porous organic polymer containing triphenylamine (TPA) and 2,6-bis(1,2,3-triazol-4-yl)pyridyl (BTP) units (TB-POP). The ultrafine palladium nanoparticles (NPs) with an average size of 1.5±0.6 nm can be facilely generated using convenient methods, and are uniformly dispersed over TB-POP support. TPA and BTP units are homogeneously arranged in the host framework of TB-POP, they serve as effective alternatives of basic sites to deprotonate FA into formate intermediates. Pd@TB-POP has demonstrated remarkable catalytic activity and high selectivity in additive-free dehydrogenation of aqueous FA solution. The value of initial turnover frequency (TOF) at 50 oC is as high as 1344 h-1. In sharp contrast, the use of sodium formate as an additive in the catalytic system results in the decrement of catalytic activity. The ultrafine palladium NPs are eﬀectively immobilized during dehydrogenation of FA, and no obvious aggregation of palladium NPs is observed after consecutive catalytic runs.
Homocoupling of Phenylboronic Acid using Atomically Dispersed Gold on Carbon Catalysts: Catalyst Evolution Before Reaction ChemCatChem (IF 4.803) Pub Date : 2017-12-21 Tanja Parmentier, Simon R Dawson, Grazia Malta, Li Lu, Thomas E Davies, Simon A. Kondrat, Simon J Freakley, Christopher J Kiely, Graham John Hutchings
Coupling reactions to form new C-C bonds are extensively used in industrial synthetic processes. Gold has been shown to be an active catalyst for such reactions however, conflicting reports exist as to whether cationic Au or metallic Au is acting as the active species. We prepared a heterogeneous catalyst consisting of atomically dispersed Au-Clx supported on carbon and showed this to be active in the homocoupling of phenylboronic acid to biphenyl. However; characterisation of the catalyst materials, even after just a short exposure time to the reactants, revealed rapid reduction and sintering of the Au species into larger metallic nanoparticles which we propose to be the true active species in this instance. This study suggests that if cationic Au is an active catalyst, it must be stabilised against reduction and agglomeration by either forming complexes which are more stable than common chlorides or by strongly anchoring them firmly onto alternative support materials; as in this case the carbon supported Au-Cl species were easily reduced.
Colloidal Au catalyst preparation: selective removal of polyvinylpyrrolidone from active Au sites ChemCatChem (IF 4.803) Pub Date : 2017-12-21 Baira Donoeva, Petra E. de Jongh
Colloids with controlled dimensions, morphology and composition can be used to obtain supported metal catalysts with desired characteristics. Yet, removal of capping agents which block active metal sites in such catalysts can be challenging: mild methods often result in incomplete removal of capping agents, while harsher methods can cause change in particle size or morphology or cause metal segregation for bimetallic particles. Here we provide evidence that polyvinylpyrrolidone used as a stabilizing agent for gold colloids is present both on the metal and the support surface after colloid deposition on the TiO2 support. The polymer adsorbed on Au sites blocks their catalytic activity when it cannot be desorbed/decomposed under reaction conditions. Polyvinylpyrrolidone can be removed completely from the active gold surface of Au/TiO2 without particle growth using a number of mild treatment methods described in this work, despite only partial removal (~45%) of the stabilizer from the bulk of Au/TiO2. The remaining >50% of polyvinylpyrrolidone resides exclusively on the TiO2 support and has no effect on the optical properties and catalytic activity of gold nanoparticles. The treated catalysts demonstrate catalytic activity and selectivity similar to those of a catalyst prepared by impregnation. These findings are important for further advancing the preparation of well-defined supported catalysts using metal colloids.
Porous Carbon Nanosheet-Supported Chiral Squaramide for Highly Enantioselective Friedel-Crafts Reaction ChemCatChem (IF 4.803) Pub Date : 2017-12-21 Liyuan Zhao, Xiaoze Bao, Qingtao Hu, Baomin Wang, An-Hui Lu
Porous carbon nanosheet (PCN) was used for the first time as a support to immobilize quinine-squramide catalyst for the asymmetric Friedel-Crafts addition of pyrazolones to isatin ketimines. Relying on its open structure with macroporous network as well as hydrophobicity, the PCN-supported catalyst presents comparable catalytic performance to its homogeneous catalyst, providing products with high yields and ee values of up to 90% and 99%, respectively. Recycling batch reactions together with a continuous flow process confirmed the stable activity of the catalyst.
Understanding the Hydro-metathesis Reaction of 1-decene by Using Well-defined Silica Supported W, Mo, Ta Carbene/Carbyne Complexes ChemCatChem (IF 4.803) Pub Date : 2017-12-21 Aya Saidi, Manoja Samantaray, Mykyta Tretiakov, Santosh Kavitake, Jean-Marie Basset
Direct conversion of 1-decene to petroleum range alkanes was obtained using hydro-metathesis reaction. To understand this reaction we employed three different well-defined single site catalysts precursors; [(≡Si-O-)W(CH3)5] 1, [(≡Si-O-)Mo(≡CtBu)(CH2tBu)2] 2 and [(≡Si-O)Ta(=CHtBu)(CH2tBu)2] 3. We witnessed that in our conditions olefin metathesis/isomerization of 1-decene occurs much faster followed by reduction of the newly formed olefins rather than reduction of the 1-decene to decane, followed by metathesis of decane. We found that Mo-based catalyst favors 2+2 cycloaddition of 1-decene forming metallocarbene, followed by reduction of the newly formed olefins to alkanes. However, in the case of W and Ta-based catalysts, a rapid isomerization (migration) of the double bond followed by olefin metathesis and reduction of the newly formed olefins were observed. We witnessed that silica supported W catalyst precursor 1 and Mo catalyst precursor 2 are better catalysts for hydro-metathesis reaction with TONs of 818 and 808 than Ta-based catalyst 3 (TON of 334). This comparison of the catalysts provides us a better understanding that, if a catalyst is efficient in olefin metathesis reaction it would be a better catalyst for hydro-metathesis reaction.
Mechanistic Aspects of Acrylic Acid Formation from CO2-Ethylene Coupling over Pd- and Ni-based Catalysts ChemCatChem (IF 4.803) Pub Date : 2017-12-20 Yuanhui Li, Zhen Liu, Ruihua Cheng, Boping Liu
The mechanism of catalytic conversion of CO2 and ethylene to acrylic acid has been investigated through DFT and DLPNO-CCSD(T) calculations. Four bidentate ligands (dmpe,dcpe,dtbpe and tmeda) were systematically studied in order to understand the different catalytic behavior of the Pd-based catalyst and the well-known Ni-based catalyst. The energy barrier of Pd-/Ni-catalyzed C-C coupling appears to increase with a larger steric hindrance of the ligand, while the barrier of the corresponding β-H elimination shows an opposite tendency. The barrier of C-C coupling is likely higher than the associated barrier of β-H elimination in both catalytic systems provided that the coordinated ligand is bulky enough. The palladium catalytic center is more effective than the nickel center during the C-C coupling and β-H elimination stages when bulky ligand is involved, while the nickel catalyst in turn performs better with small ligands. The palladium catalyst tends to be always superior to the nickel catalyst during the following hydrogen transfer to the O atom. In general, the diamine ligand (tmeda) is less efficient than the diphosphine ligands for both systems. In the absence of the auxiliaries, a novel chelating carbene ligand was proposed to be quite efficient for Pd-catalyzed C-C coupling with the lowest energy barrier. Two ligands (dcpm, dtbpm) showed relatively better performance towards the palladium-catalyzed acrylic acid formation reaction among all the investigated ligands.
Front Cover: Intramolecular Hydroamination by a Primary Amine of an Unactivated Alkene on Gold Nanoclusters: A DFT Study (ChemCatChem 24/2017) ChemCatChem (IF 4.803) Pub Date : 2017-12-20 Karan Bobuatong, Hidehiro Sakurai, Masahiro Ehara
Cover Feature: Distinct Promotive Effects of 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) on Polymer Supports in Copper-Catalyzed Hydrogenation of C=O Bonds (ChemCatChem 24/2017) ChemCatChem (IF 4.803) Pub Date : 2017-12-20 Ryo Watari, Norio Matsumoto, Shigeki Kuwata, Yoshihito Kayaki
In-situ synthesis of Bi2O3 nanoparticles on ZnMeLDHs (Me:Al/Cr) frameworks for the photocatalytic O2 evolutions from water under solar-light activation ChemCatChem (IF 4.803) Pub Date : 2017-12-19 Gabriela Carja, Diana Gilea, Pegie Cool, Elena M. Seftel
A key target to boost solar-to-chemical conversion processes is to fabricate an efficient solar-light responsive photocatalyst. Herein, we report the in-situ synthesis of nanoparticles (NPs) of Bi2O3 directly on Zn-based layered double hydroxides (LDHs) framework. The in-situ synthesis of Bi2O3NPs is done at room temperature, is ligand-free and explores the ability of ZnMeLDHs to reconstruct its layered structure after calcination in Bi(NO3)3 aqueous solution. The in-situ formation of Bi2O3NPs on ZnMeLDHs is assessed by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), and UV-Vis analysis (UV-Vis) and compared with the features of a corresponding Bi2O3/LDH prepared by conventional impregnation route. The rapid photocatalytic response of the Bi2O3NPs/ZnMeLDHs (Me:Al/Cr)heterostructures is confirmed in O2 generation from water under solar-light irradiation. The O2 rate increased by a factor of ~ 2 for the ZnCrLDH based catalysts as compared to that of the family of ZnAlLDH catalysts. Further, the presence of the bismuth phase and its nano-dimension leads to an increased efficiency for the in-situ prepared Bi2O3NPs/LDHs as compared to that of impregnated Bi2O3/LDH and the pristine LDHs.
Using Mg-Al mixed oxide and reconstructed hydrotalcite as basic catalysts for aldol condensation of furfural and cyclohexanone ChemCatChem (IF 4.803) Pub Date : 2017-12-19 Oleg Kikhtyanin, David Kadlec, Romana Velvarská, David Kubička
This study presents results on aldol condensation of furfural and cyclohexanone in presence of Mg-Al hydrotalcite-derived materials as solid basic catalysts at reaction temperature from 25 to 90 °C and cyclohexanone to furfural molar ratio of 1-10. Mg-Al mixed oxide exhibited reasonable activity with furfural conversion of ca. 50% after 180 min of the reaction at T=90 °C. The activity of reconstructed hydrotalcite was much higher with furfural conversion close to 100% at short reaction times. In comparison with Mg-Al mixed oxide, the initial reaction rate has increased 30-50 times. At similar reaction conditions cyclohexanone self-condensation on HTC-derived catalysts could not compete with aldol condensation because the former reaction was inhibited by produced water. The change in CH/F molar ratio influenced both furfural conversion and product selectivity, higher furfural content in the reaction mixture favoured the second condensation step.
Green synthesis of rhodium nanoparticles, catalytically active in benzene hydrogenation and 1-hexene hydroformylation ChemCatChem (IF 4.803) Pub Date : 2017-12-19 Waleed Alsalahi, Wlodzimierz Tylus, Anna Trzeciak
Rhodium nanoparticles (Rh NPs) were prepared according to a novel green methodology based on the reduction of Rh(acac)(CO)2 in water at 80 °C. The nanoparticles, obtained without the addition of a reducing agent, were stabilized by polyvinylpyrrolidone (PVP) or polyvinyl alcohol (PVA) polymers and characterized by TEM (transmission electron microscopy), XPS (X-ray photoelectron spectroscopy), and XRD (X-ray powder diffraction) methods. The excellent catalytic activity of these Rh NPs was evidenced in the hydrogenation of benzene to cyclohexane. In the presence of PPh3, Rh NPs formed a highly active system in the hydroformylation of 1-hexene. In this system, they acted as a source of soluble rhodium species. Rh NPs were also synthesized in water using Rh2(OAc)4 and RhCl3 as rhodium sources, and their catalytic activity was compared with that of the rhodium precursors.
An overview on the recent strategies for the enantioselective synthesis of 1,1-diarylalkanes, triarylmethanes and related molecules containing the diarylmethine stereocenter ChemCatChem (IF 4.803) Pub Date : 2017-12-19 Gautam Panda, Sankalan Mondal, Deblina Roy
Of late there has been an increase in the active pharmaceutical agents and various other molecules containing the 1, 1-diaryl stereocenter. This has led to the increase in the development of novel synthetic strategies for accessing molecules having this structural moiety. The current review describes the various synthetic methodologies for the enantioselective synthesis of 1,1-diarylethanes, triarylmethanes and related molecules having 1,1-diaryl stereogenic center that came up during 1995-2017. The prime focus of the review is on the formation of the 1,1-diarylmethine stereocenter either through the use of various enantioselective processes using chiral catalysts (the asymmetric catalytic approach) or through the use of chiral substrates and achiral catalysts. Resolution of racemic substrates is also followed for the synthesis of this chiral molecule but this approach is not covered in this review. Moreover, comparative discussions on the future aspects of the synthesis of these molecules with a short comparison of the different routes and possible areas of development are also dealt with.
Conventional and New Materials for SCR NOx Catalytic Reduction ChemCatChem (IF 4.803) Pub Date : 2017-12-19 Yu Liu, Jong-Min Lee
It is important to minimize NOx pollutant released into the atmosphere due to the harmful environmental and health effects brought by NOx emission. Many techniques are available to reduce NOx emission, among of them, Selective Catalytic Reduction (SCR) is one of the most efficient techniques. Conventional SCR systems involve ammonia (NH3) or urea (CO(NH2)2) as a reducing reagent to reduce NOx to N2 and H2O at high temperatures 300-400 °C. Research on developing novel low-temperature catalysts (LTC) for SCR of NOx still remains of interest. This work reviewed and compared conventional SCR catalysts with newly emerging Metal-Organic-Frame (MOFs) materials as potential alternatives for SCR catalysts.
Intramolecular Hydroamination by a Primary Amine of an Unactivated Alkene on Gold Nanoclusters: A DFT Study ChemCatChem (IF 4.803) Pub Date : 2017-12-19 Karan Bobuatong, Hidehiro Sakurai, Masahiro Ehara
Graphene Quantum Dots Modified Hexagonal Tubular Carbon Nitride for Visible-light Photocatalytic Hydrogen Evolution ChemCatChem (IF 4.803) Pub Date : 2017-12-18 baojiang jiang, yanting gao, feng hou, shan hu, baogang wu, ying wang, haiqiu zhang, honggang fu
Herein, graphene quantum dots were modified on hexagonal tubular carbon nitride to form a composite photocatalyst by freeze-dry technology. The composite material with typical porous structure and enhanced surface area exhibits an improved visible-light photocatalytic performance for hydrogen evolution. With an optimum loading amount of 0.15 wt.% GQDs, the efficiency of composite photocatalyst for hydrogen evolution is 112.1 μmol h-1, which is about 9 times higher than that of bulk carbon nitride. During the photocatalytic reaction, graphene quantum dots play a photosensitizer role, which can expand the visible-light respond of photocatalyst, and decrease its band gap. Meanwhile, graphene quantum dots also act as an electron reservoir to improve the separation efficiency of photoinduced electron-hole pairs. It is important the graphene quantum dots can also absorb the long wave light based on its upper transfer luminescence property, which also contribute to the utilization of visible-light. This finding demonstrates that the graphene quantum dot modification is a promising method to improve visible-light photocatalytic activities for traditional photocatalysts.
Nanosheets/Mesopore Structured Co3O4@CMK-3 Composite as Electrocatalyst for Oxygen Reduction Reaction ChemCatChem (IF 4.803) Pub Date : 2017-12-18 Lang Gan, Mengran Wang, Langtao Hu, Jing Fang, Yanqing Lai, Jie Li
Exploring highly effective and low-cost non-noble metal electrocatalysts for oxygen reduction reactions (ORR) will have a significance impact on the area of fuel cells and metal-air batteries. In this manuscript, we report a facile, efficient and environmental friendly method to deposit transition metal oxide nanosheets (NSs) on the backbone of ordered mesoporous carbon (CMK-3) via pyrolysis of the metal-precursor@CMK-3. The optimized CMK-3 catalyst with a coating of Co3O4 NS possesses a high surface area of 2396 m2 g-1 and demonstrates an excellent electrocatalytic activity towards ORR in alkaline media, which is much better than other transition metal oxide@CMK-3 catalysts and other carbon material-based catalysts (such as carbon nanotubes). In addition, the as-prepared catalyst possesses comparable electrochemical performances, and even superior durability and higher tolerance to methanol compared with commercially available Pt/C, which can be ascribed to the distinctive structure of nanosheets/mesopore (NSs/MP), indicative of great potential in the application of metal-air batteries.
Silica-Grafted Neodymium Catalysts for the Production of Ultra-High Molecular Weight 1,4-cis-Polyisoprene ChemCatChem (IF 4.803) Pub Date : 2017-12-18 Reiner Anwander, Erwan Le Roux, Yucang Liang
Supported neodymium-based Ziegler-type catalysts are obtained by grafting homoleptic methylaluminate Nd(AlMe4)3 onto high-surface silicas including periodic mesoporous silica MCM-41, SBA-15, and KIT-6. Low [Et2AlCl]-cocatalyst contents allow for the fabrication of polyisoprenes with ultra-high molecular weight (UHMWPI). The synthetic rubbers display molecular weights as high as 3×106 g mol-1, polydispersity indices (PDIs) as low as 1.2, and microstructures with 99% cis-stereospecificity. Combined analysis of the organolanthanide/silica hybrid materials by nitrogen physisorption, FTIR and MAS-NMR spectroscopy, as well as elemental(metal) analysis, assist in elucidating the intra-pore surface organometallic chemistry, and suggest the formation of unprecedented organolanthanide species.
NMR Isotope Tracking Reveals Cascade Steps in Carbohydrate Conversion by Sn-Beta ChemCatChem (IF 4.803) Pub Date : 2017-12-18 Samuel G Elliot, Esben Taarning, Robert Madsen, Sebastian Meier
Quantitative isotope tracking studies were used to investigate the reaction pathways occurring for Sn-Beta catalyzed carbohydrate conversion to various alpha-hydroxy esters. Experimental insight into the conversion of pentoses was sought (i) by identifying pathways based on isotope patterns in the reaction products and (ii) through probing asymmetric isotope incorporation into products. The results indicate that reaction intermediates remain coordinated to the active site throughout the reaction cascades, regardless of the reaction pathway. A predominant transformation of the C1 carbohydrate position to the C3 position of methyl lactate resembles enzymatic glycolysis. Likewise, the majority of retro-aldol cleavage occurs from the carbohydrate in the ketose form, again resembling biological glycolysis. In addition, various side-activities are detected in Sn-Beta catalyzed carbohydrate conversion, including 5,1-hydride and 1,2-carbon shift reaction of the carbohydrates.
Sol-Gel Entrapped Nitroxyl Radicals: Catalysts of Broad Scope ChemCatChem (IF 4.803) Pub Date : 2017-12-18 Rosaria Ciriminna, Valerica Pandarus, Francois Béland, Mario Pagliaro
Sol-gel entrapped TEMPO-like radicals, excellent supported molecular catalysts for the selective and clean alcohol oxidation, including the primary hydroxyl functions of cellulose. Could these materials reach widespread utilization for the synthesis of fine chemicals, bio-based building blocks and even carboxyl cellulose nanofibrils? This study offers a critical perspective.
The strongBeta-CF3 shielding effect in HFIP and 100 other organic solvents revisited with 17O NMR ChemCatChem (IF 4.803) Pub Date : 2017-12-15 Annika Bernhardt, Harald Kelm, Frederic William Patureau
An 17O NMR survey of more than one hundred ubiquitous organic solvents and compounds is presented with D2O as reference, including some typical oxofluorinated solvents such as HFIP, TFE, TFA and others. A strong alternating alfa, beta-CF3-substituent chemical shifts effect was thus observed. This alternating deshielding-shielding effect is suspected of having a role in the exceptional properties of these oxofluorinated solvents, notably in oxidative cross-coupling reactions.
Operando Spectroscopic Study of Dynamic Structure of Iron Oxide Catalysts during CO₂ Hydrogenation ChemCatChem (IF 4.803) Pub Date : 2017-12-15 Yulong Zhang, Donglong Fu, Xianglin Liu, Zhengpai Zhang, Chao Zhang, Bianfang Shi, Jing Xu, Yi-Fan Han
Understanding of dynamic structure of active sites is of paramount importance for rational design of industrial catalysts. This work revealed the structure evolution of iron active phases for CO₂ hydrogenation over iron-based catalysts. With a combination of operando Raman spectroscopy and X-ray Diffraction coupled with online gas chromatography, the panoramic structure evolution of iron oxides (α-Fe₂O₃ and γ-Fe₂O₃) during activation and CO₂ hydrogenation were elaborated, i.e. α-Fe₂O₃ (γ-Fe₂O₃)α-Fe₃O₄ (γ-Fe₃O₄)α-Fe (γ-Fe)χ-Fe₅C₂ (θ-Fe₃C). Both iron carbides showed high catalytic activities while χ-Fe₅C₂ exhibited higher selectivity to lower olefins but weaker chain growth probability than θ-Fe₃C.
In Situ Prepared Flexible 3D Polymer Film Photocatalyst for Highly Selective Solar Fuel Production from CO2 ChemCatChem (IF 4.803) Pub Date : 2017-12-15 Rajesh Kumar Yadav, Abhishek Kumar, Dolly Yadav, No-Joong Park, Jae Young Kim, Jin-Ook Baeg
The conversion of CO2 to valuable solar fuels by means of solar energy using metal-free flexible film photocatalysts is an appealing strategy. Here we demonstrate a three dimensional aromatic polymer (3DAP) derived from triptycene (TC) as a metal free, stable and highly efficient visible light responsive flexible film photocatalyst for selective solar fuel production from CO2. For this research work, the polymerization of TC by the Diels-Alder reaction is exploited for the first time as a new synthetic approach for the construction of three dimensional aromatic polymer photocatalyst. The visible-light harvesting ability, band gap suitability, high Brunauer-Emmett-Teller (BET) surface area and electron transfer capability via interconnecting 3D chain of 3DAP contribute to the excellent performance of the film photocatalyst compared to the corresponding TC ligand. This work provides important insights into the design of flexible polymer film photocatalyst for selective solar fuel formation from CO2 and is expected to trigger further interest in sustainable solar energy conversion applications such as tailorable and wearable devices.
Conductive Porous Network of Metal Organic Frameworks Derived Cobalt-Nitrogen-doped Carbon with the Assistance of Carbon Nanohorns as Electrocatalyst for Zinc-Air Battery ChemCatChem (IF 4.803) Pub Date : 2017-12-13 Jianshuo Zhang, Chuxin Wu, Meihua Huang, Yi Zhao, Jiaxin Li, Lunhui Guan
Herein, we report a new electrocatalyst for oxygen reduction reaction derived from bimetallic metal organic framework and single-walled carbon nanohorns. Due to the 3-D conductive network offered by the nanohorns, this type of catalysts exhibit comparable performance with the commercial 20% Pt/C catalyst as well as excellent durability and methanol tolerance at the half-cell test in an alkaline medium. Moreover, the new electrocatalyst shows higher peak power density (185 mW cm-2) than that of Pt/C catalyst (160 mW cm-2) in addition to a comparable stability in the real Zn-air battery test. A correlation between the value of the peak power densities and pore structures of some paralleled samples is studied in details.
Photothermally Enhanced Plasmon-Driven Catalysis on Fe5C2@Au Core-Shell Nanostructures ChemCatChem (IF 4.803) Pub Date : 2017-12-13 Peng Miao, Wei Huang, Mansha Gao, Jiayu Chu, Bo Song, Ping Xu
Plasmon-driven catalysis has attracted great attention in recent years, while the reaction efficiency remains to be improved. Here, we demonstrate the fabrication of novel photothermal Fe5C2@Au core-shell nanostructures through a self-assembly process of Fe5C2 and Au nanoparticles (NPs) with the assistance of hexanethiol, which can be highly efficient surface enhanced Raman spectroscopy (SERS) platforms for the study of plasmon-driven dimerization of 4-aminothiophenol (4-ATP) and 4-nitrothiophenol (4-NTP). As compared to bare Au NPs, much accelerated reaction kinetics can be achieved on the Fe5C2@Au core-shell nanostructures by quantitatively determining the Raman intensity of the ν(N=N) band in the generated 4,4'-dimercaptobenzene (DMAB). The photothermal effect from the Fe5C2 NPs may lower the energy barrier and generate more "hot electrons" for the plasmon-driven catalysis. This photothermal route may open up new avenues for enhancing the reaction rate and broadening the research area of the plasmon-driven catalysis.
The role of metallic copper in the selective hydrodeoxygenation of glycerol to 1,2-propanediol over Cu/ZrO2 ChemCatChem (IF 4.803) Pub Date : 2017-12-13 Thomas Gabrysch, Baoxiang Peng, Sorin Bunea, Gerald Dyker, Martin Muhler
A series of Cu/ZrO2 catalysts with nominal CuO loadings of 5, 10, 18 and 31 wt.% was synthesized by co-precipitation, characterized and applied in the hydrodeoxygenation of glycerol under mild reaction conditions (200 °C, 25 bar H2). These catalysts were highly selective for the cleavage of C-O bonds while preserving C-C bonds leading to 95% selectivity to 1,2-propanediol. The conversion of glycerol was observed to be linearly correlated with the specific copper surface area derived from N2O frontal chromatography. The reaction was found to occur through the dehydration of glycerol to acetol followed by its hydrogenation to 1,2-propanediol. Metallic copper was identified as the active site for both reactions suggesting the acid ZrO2 sites to be blocked by water. Reusability studies showed that the catalyst was relatively stable and the conversion decreased by only 18% after three cycles.
Improving the Thermodynamic Profiles of Potential Suzuki-Miyaura Cross-Coupling Catalysts by Altering the Electrophilic Coupling Component ChemCatChem (IF 4.803) Pub Date : 2017-12-13 Michael Busch, Matthew Davisson Wodrich, Clemence Corminboeuf
As a heavily used technique for forming new C-C bonds, developing new catalysts and reaction conditions for Suzuki-Miyaura cross-coupling reactions is highly desirable. Here, using molecular volcano plots, the influence of the electrophilic coupling component in catalytic cycle thermodynamics is revealed. Less reactive electrophiles, such as iodine, broaden the volcano plateau leading to a larger selection of catalysts having appealing thermodynamic profiles. On the other hand, fluorine and other more reactive electrophiles compress the volcano plateau, which shrinks the pool of catalysts having good thermodynamic profiles. As a result, judicious selection of the electrophile employed in a reaction may represent an appealing strategy for further tuning the thermodynamics of cross-coupling reactions.
Engineering Surface Structure of Binary/Ternary Ferrite Nanoparticles as High-Performance Electrocatalysts for Oxygen Evolution Reaction ChemCatChem (IF 4.803) Pub Date : 2017-12-12 Zhi-Ming Zhang, Pathik Pathik Sahoo, Jing-Bo Tan, Tong-Bu Lu, Shiva Kumar Singh
Cost-effective production of efficient and robust oxygen evolution electrocatalysts is primary importance in developing renewable energy technologies. Herein, we develop a simple and efficient method for exploring high-performance oxygen evolution reaction (OER) electrocatalysts by engineering the surface structure of ferrite nanoparticles on the carbon nanotube support via a reduction-engraved strategy. After the reduction treatment, abundant oxygen vacancies localized on the surface of the ultrafine ferrite nanoparticles favorably affect their electronic structure, assuring a rapid charge transfer, and expose more active sites. In 1.0 M KOH solution, the reduced composites exhibit superior OER electrocatalytic activity to IrO2, affording a current density of 10 mA cm−2 at overpotentials of merely 214 mV for Co0.5Ni0.5Fe2O4@o-MWCNT (r-CNFc), 221 mV for CoFe2O4@o-MWCNT (r-CFc) and 216 mV for NiFe2O4@o-MWCNT (r-NFc). It is worth mentioning that the r-CNFc could afford a current density of 100 mAcm−2 at an overpotential of 256 mV, which is ca.10 times higher than that of CNFc at the same overpotential(10.6 mA cm−2). These catalysts also exhibit long-term stability evaluated by controlled-current electrolysis at least for 120 h. These results demonstrate an efficient method for constructing high-performance and durable OER electrocatalysts by reducing mixed metal spinel oxides on the conductive support.
Development of visible light response of CeO2-x with the high content of Ce3+ and its photocatalytic property ChemCatChem (IF 4.803) Pub Date : 2017-12-11 Sàisài Yuán, Bin Xu, Qitao Zhang, Sixiao Liu, Ju Xie, Ming Zhang, Teruhisa Ohno
Photocatalysts that are responsive to visible light are necessary to utilize solar. We prepared a reduced CeO2-x with absorption in the visible region by a simple solvothermal method. A new absorption peak appeared around 500 nm (SPR), which is the origin of Ce3+. To elucidate the relationship between the Ce3+ and activity, decomposition of isopropyl alcohol (IPA) to generate acetone has been carried out under visible light irradiation. CeO2-x showed superior activity than that of pure CeO2. Ce3+ can induce oxygen vacancies in the lattice of CeO2-x, resulting in improvement of activity. In addition, the introduction of Ce3+ resulted in improvement of absorption of CeO2-x in the visible light region. Also, the appearance of small tentacles (Confeito-like) on the surface of CeO2-x not only provided more active sites but also prevented aggregation. Owing to its visible light responsiveness and its unique morphology, the performance of the material has been significantly improved.
Catalytic Transfer Hydrogenation of Furfural to Furfuryl Alcohol with Recyclable Al–Zr@Fe Mixed Oxides ChemCatChem (IF 4.803) Pub Date : 2017-12-12 Jian He, Hu Li, Anders Riisager, Song Yang
Oxygen Reduction Reaction on Ag(111) in Alkaline Solution: A Combined Density Functional Theory and Kinetic Monte Carlo Study ChemCatChem (IF 4.803) Pub Date : 2017-12-11 Shizhong Liu, Michael G. White, Ping Liu
We reported a detailed mechanistic study of the oxygen reduction reaction (ORR) on the model Ag(111) surface in alkaline solution by using density functional theory (DFT) and Kinetic Monte Carlo (KMC) simulations, where multiple pathways via either 2e- or 4e- mechanisms were included. The theoretical modelling presented is able to reproduce the experimentally measured polarization curves in both low and high potential regions. An electrochemical 4e- network including both chemisorbed water (*H2O)-mediated 4e- associative pathway and the conventional associative pathway was identified to dominate the ORR mechanism. On the basis of the mechanistic understanding derived from these calculations, the ways to promote the ORR on Ag(111) were provided, including facilitating *OH removal, **O2 reduction by *H2O, and suppressing **O2 desorption. Finally, the origin of different ORR behaviors between Ag(111) and Pt(111) was also discussed in detail.
Solid Molecular Frustrated Lewis Pairs in a Polyamine Organic Framework for the Catalytic Metal-free Hydrogenation of Alkenes ChemCatChem (IF 4.803) Pub Date : 2017-12-11 Marcus Rose, Andrea Willms, Hannah Schumacher, Tarnuma Tabassum, Long Qi, Susannah L. Scott, Peter J. C. Hausoul
We report for the first time a metal-free heterogeneously catalyzed hydrogenation using a semi-solid frustrated Lewis pair (FLP). The catalyst consists of a solid polyamine organic framework and molecular tris(pentafluorophenyl)borane (BCF) that form a semi-immobilized FLP in situ in the catalytic hydrogenation of diethyl benzylidenemalonate. 11B NMR spectroscopy proves the successful hydrogen activation by the FLP. Furthermore, the B N interactions between the polyamine and BCF are investigated by IR and solid state NMR spectroscopy. The FLP 1,4-diazabicyclo[2.2.2]octane (DABCO)/BCF, which combines the features of a FLP and a classical Lewis adduct, functions as molecular reference in both, catalysis and characterization. Furthermore, computational studies enable a better insight into the hydrogen activation through DABCO/BCF and polyamine/BCF.
Gold(I)-Catalyzed Conia-ene Cyclization of Internal ϵ-Acetylenic β-Ketoesters under High Pressure. ChemCatChem (IF 4.803) Pub Date : 2017-12-08 Wojciech Chaładaj, Agata Kołodziejczyk, Sylwester Domański
The influence of pressure on the gold(I)-catalyzed Conia-ene cyclization of ϵ-acetylenic-β-ketoesters bearing an internal alkyne moiety was investigated for the first time. The reaction catalyzed by commercially available PPh3AuNTf2 complex, which is sluggish at ambient pressure owing to steric reasons, proceeds smoothly under high-pressure conditions (6 kbar). Mechanistic aspects of the reaction proceeding via 5-exo-dig and 6-endo-dig cyclization pathways were also studied employing DFT methods. Differences in the reactivity of substrates containing terminal and internal alkynes is discussed. Under pressure: High pressure enables effective Au-catalyzed cyclization of internal ϵ-acetylenic β-ketoesters, otherwise hampered by sterics. DFT studies of the 5-exo-dig and 6-endo-dig cyclization modes illustrate the difference in reactivity of terminal and internal alkynes.
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