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Catalysts, Volume 6, Issue 12 (December 2016)

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Open AccessArticle N2O Decomposition over Cu–Zn/γ–Al2O3 Catalysts
Catalysts 2016, 6(12), 200; doi:10.3390/catal6120200
Received: 20 November 2016 / Revised: 5 December 2016 / Accepted: 6 December 2016 / Published: 12 December 2016
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Abstract
Cu–Zn/γ–Al2O3 catalysts were prepared by the impregnation method. Catalytic activity was evaluated for N2O decomposition in a fixed bed reactor. The fresh and used catalysts were characterized by several techniques such as BET surface area, X-ray diffraction (XRD),
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Cu–Zn/γ–Al2O3 catalysts were prepared by the impregnation method. Catalytic activity was evaluated for N2O decomposition in a fixed bed reactor. The fresh and used catalysts were characterized by several techniques such as BET surface area, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The Cu–Zn/γ–Al2O3 catalysts exhibit high activity and stability for N2O decomposition in mixtures simulating real gas from adipic acid production, containing N2O, O2, NO, CO2, and CO. Over the Cu–Zn/γ–Al2O3 catalysts, 100% of N2O conversion was obtained at about 601 °C at a gas hourly space velocity (GHSV) of 7200 h−1. Cu–Zn/γ–Al2O3 catalysts also exhibited considerably good durability, and no obvious activity loss was observed in the 100 h stability test. The Cu–Zn/γ–Al2O3 catalysts are promising for the abatement of this powerful greenhouse gas in the chemical industry, particularly in adipic acid production. Full article
(This article belongs to the Special Issue Heterogeneous Catalysis for Environmental Remediation)
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Open AccessArticle Synthesis of PtNi Alloy Nanoparticles on Graphene-Based Polymer Nanohybrids for Electrocatalytic Oxidation of Methanol
Catalysts 2016, 6(12), 201; doi:10.3390/catal6120201
Received: 10 September 2016 / Revised: 26 November 2016 / Accepted: 6 December 2016 / Published: 11 December 2016
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Abstract
We have successfully produced bimetallic PtNi alloy nanoparticles on poly(diallyldimethylammonium chloride) (PDDA)-modified graphene nanosheets (PtNi/PDDA-G) by the “one-pot” hydrothermal method. The size of PtNi alloy nanoparticles is approximately 2–5 nm. The PDDA-modified graphene nanosheets (PDDA-G) provides an anchored site for metal precursors; hence,
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We have successfully produced bimetallic PtNi alloy nanoparticles on poly(diallyldimethylammonium chloride) (PDDA)-modified graphene nanosheets (PtNi/PDDA-G) by the “one-pot” hydrothermal method. The size of PtNi alloy nanoparticles is approximately 2–5 nm. The PDDA-modified graphene nanosheets (PDDA-G) provides an anchored site for metal precursors; hence, the PtNi nanoparticles could be easily bond on the PDDA-G substrate. PtNi alloy nanoparticles (2–5 nm) display a homogenous alloy phase embedded on the PDDA-G substrate, evaluated by Raman, X-ray diffractometer (XRD), thermal gravity analysis (TGA), electron surface chemical analysis (ESCA), and electron energy loss spectroscopy (EELS). The Pt/Ni ratio of PtNi alloy nanoparticles is ~1.7, examined by the energy dispersive spectroscopy (EDS) spectra of transmitting electron microscopy (EDS/TEM spectra) and mapping technique. The methanol electro-oxidation of PtNi/PDDA-G was evaluated by cyclic voltammetry (CV) in 0.5 M of H2SO4 and 0.5 M of CH3OH. Compared to Pt on carbon nanoparticles (Pt/C) and Pt on Graphene (Pt/G), the PtNi/PDDA-G exhibits the optimal electrochemical surface area (ECSA), methanol oxidation reaction (MOR) activity, and durability by chrono amperometry (CA) test, which can be a candidate for MOR in the electro-catalysis of direct methanol fuel cells (DMFC). Full article
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Open AccessArticle Photoassisted Oxidation of Sulfides Catalyzed by Artificial Metalloenzymes Using Water as an Oxygen Source
Catalysts 2016, 6(12), 202; doi:10.3390/catal6120202
Received: 19 October 2016 / Revised: 24 November 2016 / Accepted: 6 December 2016 / Published: 12 December 2016
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Abstract
The Mn(TpCPP)-Xln10A artificial metalloenzyme, obtained by non-covalent insertion of Mn(III)-meso-tetrakis(p-carboxyphenyl)porphyrin [Mn(TpCPP), 1-Mn] into xylanase 10A from Streptomyces lividans (Xln10A) as a host protein, was found able to catalyze the selective photo-induced oxidation of organic substrates in the presence of [Ru
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The Mn(TpCPP)-Xln10A artificial metalloenzyme, obtained by non-covalent insertion of Mn(III)-meso-tetrakis(p-carboxyphenyl)porphyrin [Mn(TpCPP), 1-Mn] into xylanase 10A from Streptomyces lividans (Xln10A) as a host protein, was found able to catalyze the selective photo-induced oxidation of organic substrates in the presence of [RuII(bpy)3]2+ as a photosensitizer and [CoIII(NH3)5Cl]2+ as a sacrificial electron acceptor, using water as oxygen atom source. Full article
(This article belongs to the Special Issue Asymmetric and Selective Biocatalysis)
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Open AccessArticle Spatial Concentration Profiles for the Catalytic Partial Oxidation of Jet Fuel Surrogates in a Rh/Al2O3 Coated Monolith
Catalysts 2016, 6(12), 207; doi:10.3390/catal6120207
Received: 28 September 2016 / Revised: 20 November 2016 / Accepted: 1 December 2016 / Published: 14 December 2016
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Abstract
The catalytic partial oxidation (CPOX) of several hydrocarbon mixtures, containing n-dodecane (DD), 1,2,4-trimethylbenzene (TMB), and benzothiophene (BT) as a sulfur compound was studied over a Rh/Al2O3 honeycomb catalyst. The in-situ sampling technique SpaciPro was used in this study to
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The catalytic partial oxidation (CPOX) of several hydrocarbon mixtures, containing n-dodecane (DD), 1,2,4-trimethylbenzene (TMB), and benzothiophene (BT) as a sulfur compound was studied over a Rh/Al2O3 honeycomb catalyst. The in-situ sampling technique SpaciPro was used in this study to investigate the complex reaction system which consisted of total and partial oxidation, steam reforming, and the water gas shift reaction. The mixtures of 83 vol % DD, 17 vol % TMB with and without addition of the sulfur compound BT, as well as the pure hydrocarbons were studied at a molar C/O-ratio of 0.75. The spatially resolved concentration and temperature profiles inside a central channel of the catalyst revealed three reaction zones: an oxidation zone, an oxy-reforming zone, and a reforming zone. Hydrogen formation starts in the oxy-reforming zone, not directly at the catalyst inlet, contrary to methane CPOX on Rh. In the reforming zone, in which steam reforming is the predominant reaction, even small amounts of sulfur (10 mg S in 1 kg fuel) block active sites. Full article
(This article belongs to the Special Issue In Situ and Operando Characterization in Catalysis)
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Open AccessArticle Hydrogen Evolution Reaction of γ-Mo0.5W0.5 C Achieved by High Pressure High Temperature Synthesis
Catalysts 2016, 6(12), 208; doi:10.3390/catal6120208
Received: 30 October 2016 / Revised: 2 December 2016 / Accepted: 5 December 2016 / Published: 17 December 2016
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Abstract
For the first time, the hydrogen evolution reaction (HER) electrocatalytic performances of incompressible γ-Mo0.5W0.5C, prepared by high-pressure, high-temperature (HPHT) synthesis, were investigated in the electrolyte. The polarization curve of the γ-Mo0.5W0.5C cathode exhibits the current
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For the first time, the hydrogen evolution reaction (HER) electrocatalytic performances of incompressible γ-Mo0.5W0.5C, prepared by high-pressure, high-temperature (HPHT) synthesis, were investigated in the electrolyte. The polarization curve of the γ-Mo0.5W0.5C cathode exhibits the current density of 50 mA∙cm−2 at an overpotential value of 320 mV. The corresponding Tafel slope of the incompressible γ-Mo0.5W0.5C is 74 mV∙dec−1. After a 1000-cycle test, and then exposure to the air for six months, the γ-Mo0.5W0.5C electrode performed a current density of 50 mA∙cm−2 at an overpotential of 354 mV, which was close to the initial one. Full article
(This article belongs to the Special Issue Heterogeneous Catalysis & Hydrogen Storage)
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Open AccessArticle Investigation of the Effect of Plasma Polymerized Siloxane Coating for Enzyme Immobilization and Microfluidic Device Conception
Catalysts 2016, 6(12), 209; doi:10.3390/catal6120209
Received: 14 October 2016 / Revised: 25 November 2016 / Accepted: 9 December 2016 / Published: 16 December 2016
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Abstract
This paper describes the impact of a physical immobilization methodology, using plasma polymerized 1,1,3,3, tetramethyldisiloxane, on the catalytic performance of β-galactosidase from Aspergillus oryzae in a microfluidic device. The β-galactosidase was immobilized by a polymer coating grown by Plasma Enhanced Chemical Vapor Deposition
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This paper describes the impact of a physical immobilization methodology, using plasma polymerized 1,1,3,3, tetramethyldisiloxane, on the catalytic performance of β-galactosidase from Aspergillus oryzae in a microfluidic device. The β-galactosidase was immobilized by a polymer coating grown by Plasma Enhanced Chemical Vapor Deposition (PEVCD). Combined with a microchannel patterned in the silicone, a microreactor was obtained with which the diffusion through the plasma polymerized layer and the hydrolysis of a synthetic substrate, the resorufin-β-d-galactopyranoside, were studied. A study of the efficiency of the immobilization procedure was investigated after several uses and kinetic parameters of immobilized β-galactosidase were calculated and compared with those of soluble enzyme. Simulation and a modelling approach were also initiated to understand phenomena that influenced enzyme behavior in the physical immobilization method. Thus, the catalytic performances of immobilized enzymes were directly influenced by immobilization conditions and particularly by the diffusion behavior and availability of substrate molecules in the enzyme microenvironment. Full article
(This article belongs to the Special Issue Immobilized Enzymes: Strategies for Enzyme Stabilization)
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Open AccessArticle A Microwave-Sensitive Solid Acid Catalyst Prepared from Sweet Potato via a Simple Method
Catalysts 2016, 6(12), 211; doi:10.3390/catal6120211
Received: 16 October 2016 / Revised: 8 December 2016 / Accepted: 12 December 2016 / Published: 17 December 2016
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Abstract
In this study, a microwave-sensitive solid acid catalyst was successfully synthesized from sweet potatoes via a simple process. The catalyst was proven to have superior microwave-sensitive and homogeneous properties. The physicochemical properties were characterized by Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), Fourier-transform infrared spectra
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In this study, a microwave-sensitive solid acid catalyst was successfully synthesized from sweet potatoes via a simple process. The catalyst was proven to have superior microwave-sensitive and homogeneous properties. The physicochemical properties were characterized by Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), Fourier-transform infrared spectra (FT-IR), thermogravimetric (TGA), scanning electron microscope (SEM) and elemental analysis (EA). Results showed that the total acid density and specific surface area for the catalyst were 6.35 mmol/g and 78.35 m2/g, respectively. The elemental sulfur content reached 7.449% after sulfonation and the catalytic activity could reach over 91% within 30 min with microwave power density of 1.0 W/mL. The catalytic reaction temperature should not exceed 200 °C, as shown in TGA curve, and the moisture content in the oil raw material should be within 1%–2%. The catalyst deactivated gradually to 64.38% after reutilization five times, but the catalytic activity could be simply regenerated by re-sulfonation, albeit slightly reduced (87.56%). The shift of diffraction peaks in the XRD patterns and new absorption peaks at 619.98 and 1190.49 cm−1 of FT-IR spectra demonstrated that the –SO3H group was effectively attached to the catalyst. The SEM images displayed a loose and porous amorphous structure in the end catalyst. Full article
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Open AccessArticle N-acetylglucosamine 2-Epimerase from Pedobacter heparinus: First Experimental Evidence of a Deprotonation/Reprotonation Mechanism
Catalysts 2016, 6(12), 212; doi:10.3390/catal6120212
Received: 26 November 2016 / Revised: 11 December 2016 / Accepted: 12 December 2016 / Published: 17 December 2016
Cited by 1 | PDF Full-text (2675 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The control of cellular N-acetylmannosamine (ManNAc) levels has been postulated to be an effective way to modulate the decoration of cell surfaces with sialic acid. N-acetylglucosamine 2-epimerase catalyzes the interconversion of N-acetylglucosamine (GlcNAc) and ManNAc. Herein, we describe the cloning,
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The control of cellular N-acetylmannosamine (ManNAc) levels has been postulated to be an effective way to modulate the decoration of cell surfaces with sialic acid. N-acetylglucosamine 2-epimerase catalyzes the interconversion of N-acetylglucosamine (GlcNAc) and ManNAc. Herein, we describe the cloning, expression, purification and biochemical characterization of an unstudied N-acetylglucosamine 2-epimerase from Pedobacter heparinus (PhGn2E). To further characterize the enzyme, several N-acylated glucosamine derivatives were chemically synthesized, and subsequently used to test the substrate specificity of PhGn2E. Furthermore, NMR studies of deuterium/hydrogen exchange at the anomeric hydroxy group and C-2 positions of the substrate in the reaction mixture confirmed for the first time the postulated epimerization reaction via ring-opening/enolate formation. Site-directed mutagenesis of key residues in the active site showed that Arg63 and Glu314 are directly involved in proton abstraction and re-incorporation onto the substrate. As all mechanistically relevant active site residues also occur in all mammalian isoforms, PhGn2E can serve as a model N-acetylglucosamine 2-epimerase for further elucidation of the active site mechanism in these enzymes. Full article
(This article belongs to the Special Issue Asymmetric and Selective Biocatalysis)
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Open AccessFeature PaperArticle P-Stereogenic Phosphines for the Stabilisation of Metal Nanoparticles. A Surface State Study
Catalysts 2016, 6(12), 213; doi:10.3390/catal6120213
Received: 9 November 2016 / Revised: 13 December 2016 / Accepted: 13 December 2016 / Published: 20 December 2016
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Abstract
Palladium and ruthenium nanoparticles have been prepared following the organometallic precursor decomposition methodology, under dihydrogen pressure and in the presence of borane protected P-stereogenic phosphines. NMR (Nuclear Magnetic Resonance) monitoring of the corresponding syntheses has permitted to determine the optimal metal/ligand ratio
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Palladium and ruthenium nanoparticles have been prepared following the organometallic precursor decomposition methodology, under dihydrogen pressure and in the presence of borane protected P-stereogenic phosphines. NMR (Nuclear Magnetic Resonance) monitoring of the corresponding syntheses has permitted to determine the optimal metal/ligand ratio for leading to small and well-dispersed nanoparticles. Exchange ligand reactions of the as-prepared materials have proven the strong interaction of the phosphines with the metal surface; only oxidative treatment using hydrogen peroxide could release the phosphine-based stabiliser from the metal surface. Pd and Ru nanoparticles have been evaluated in hydrogenation reactions, confirming the robustness of the stabilisers, which selectively permitted the hydrogenation of exocyclic C=C bonds, preventing the coordination of the aromatic rings and as a result, their hydrogenation. Full article
(This article belongs to the Special Issue Soluble Nanoparticles in Catalytic Applications)
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Open AccessArticle CuO Nanorods-Decorated Reduced Graphene Oxide Nanocatalysts for Catalytic Oxidation of CO
Catalysts 2016, 6(12), 214; doi:10.3390/catal6120214
Received: 18 November 2016 / Revised: 8 December 2016 / Accepted: 13 December 2016 / Published: 21 December 2016
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Abstract
Developing an efficient non-noble catalyst for CO oxidation with high catalytic activity remains a challenge for practical applications. In this work, CuO nanorods decorated reduced graphene oxide (RGO) nanocatalysts were prepared via a facile one-step hydrothermal method. The structure and morphology of the
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Developing an efficient non-noble catalyst for CO oxidation with high catalytic activity remains a challenge for practical applications. In this work, CuO nanorods decorated reduced graphene oxide (RGO) nanocatalysts were prepared via a facile one-step hydrothermal method. The structure and morphology of the as-prepared samples were characterized by XRD, Raman spectroscopy, SEM, TEM, and X-ray photoelectron spectroscopy (XPS). The analysis results show that CuO nanorods were successfully deposited on the surface of RGO sheets with the length of 250–500 nm. The catalytic properties of the as-prepared catalysts for CO oxidation were evaluated by using a microreactor-gas chromatograph (GC) system. The as-prepared RGO–CuO nanocatalysts exhibited high activity for CO oxidation, and the 10 wt % reduced graphene oxide content catalyst can achieve CO total oxidation at 165 °C. Full article
(This article belongs to the Special Issue Heterogeneous Catalysis for Environmental Remediation)
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Open AccessFeature PaperArticle Aqueous-Phase Catalytic Chemical Reduction of p-Nitrophenol Employing Soluble Gold Nanoparticles with Different Shapes
Catalysts 2016, 6(12), 215; doi:10.3390/catal6120215
Received: 3 November 2016 / Revised: 30 November 2016 / Accepted: 14 December 2016 / Published: 21 December 2016
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Abstract
Gold nanoparticles with different shapes were prepared and used as catalysts in the reduction of p-nitrophenol (PNP) in the aqueous phase and in the presence of sodium borohydride (NaBH4). Parameters such as the reaction temperature, substrate/NaBH4 molar ratio, and
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Gold nanoparticles with different shapes were prepared and used as catalysts in the reduction of p-nitrophenol (PNP) in the aqueous phase and in the presence of sodium borohydride (NaBH4). Parameters such as the reaction temperature, substrate/NaBH4 molar ratio, and substrate/gold molar ratio were tested and evaluated. In this paper, we compare the catalytic reactivities of gold nanorods (AuNRs) and gold nanospheres (AuNSs), both synthesized by the seed-mediated method in the presence of cetyltrimethyl ammonium bromide (CTAB). Physical-chemical parameters such as the apparent rate constant (kapp) and activation energy (Ea) of the reactions were obtained for both systems. We observed that the catalytic system based on AuNRs is the most active. These colloidal dispersions were investigated and fully characterized by ultraviolet-visible absorption spectroscopy (UV–Vis) and transmission electron microscopy (TEM). Full article
(This article belongs to the Special Issue Soluble Nanoparticles in Catalytic Applications)
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Open AccessArticle Microporous Zeolites as Catalysts for the Preparation of Decyl Glucoside from Glucose with 1-Decanol by Direct Glucosidation
Catalysts 2016, 6(12), 216; doi:10.3390/catal6120216
Received: 10 November 2016 / Revised: 15 December 2016 / Accepted: 15 December 2016 / Published: 21 December 2016
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Abstract
The catalytic properties of microporous zeolite catalysts were evaluated in the synthesis of decyl glucoside from glucose with 1-decanol by direct glucosidation. The effects of the acidic properties and pore structure of the zeolite catalysts on the glucose conversions and decyl glucoside yields
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The catalytic properties of microporous zeolite catalysts were evaluated in the synthesis of decyl glucoside from glucose with 1-decanol by direct glucosidation. The effects of the acidic properties and pore structure of the zeolite catalysts on the glucose conversions and decyl glucoside yields were investigated. The conversions of glucose on the H+ ion-exchanged FAU, MFI, and BEA zeolite catalysts were above 70%. The conversion increased with decreasing acid strength of the catalysts. The highest conversion and yield of decyl glucoside were exhibited on the H-FAU(3) zeolite catalyst. The catalytic activities were enhanced with increasing amounts of acid sites. The selectivity of decyl glucopyranoside increased with decreasing Si/Al values for the same zeolite catalysts. The pore structure of H-FAU zeolite would allow sufficient spatial restriction to produce decyl glucopyranoside through the isomerization of decyl glucofuranoside into decyl glucopyranoside in its extensive pore channels. The selectivities of the decyl glucoside isomers relied significantly on the restricted transition state to the primary products due to their pore topologies. Full article
(This article belongs to the Special Issue Heterogeneous Catalysis for Environmental Remediation)
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Open AccessArticle Preparation of Pd-Diimine@SBA-15 and Its Catalytic Performance for the Suzuki Coupling Reaction
Catalysts 2016, 6(12), 181; doi:10.3390/catal6120181
Received: 1 October 2016 / Revised: 17 November 2016 / Accepted: 17 November 2016 / Published: 24 November 2016
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Abstract
A highly efficient and stable Pd-diimine@SBA-15 catalyst was successfully prepared by immobilizing Pd onto diimine-functionalized mesoporous silica SBA-15. With the help of diimine functional groups grafted onto the SBA-15, Pd could be anchored on a support with high dispersion. Pd-diimine@SBA-15 catalyst exhibited excellent
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A highly efficient and stable Pd-diimine@SBA-15 catalyst was successfully prepared by immobilizing Pd onto diimine-functionalized mesoporous silica SBA-15. With the help of diimine functional groups grafted onto the SBA-15, Pd could be anchored on a support with high dispersion. Pd-diimine@SBA-15 catalyst exhibited excellent catalytic performance for the Suzuki coupling reaction of electronically diverse aryl halides and phenylboronic acid under mild conditions with an ultralow amount of Pd (0.05 mol % Pd). When the catalyst amount was increased, it could catalyze the coupling reaction of chlorinated aromatics with phenylboronic acid. Compared with the catalytic performances of Pd/SBA-15 and Pd-diimine@SiO2 catalysts, the Pd-diimine@SBA-15 catalyst exhibited higher hydrothermal stability and could be repeatedly used four times without a significant decrease of its catalytic activity. Full article
(This article belongs to the Special Issue Suzuki–Miyaura Cross-Coupling Reaction and Potential Applications)
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Open AccessArticle Different Performance of Two Isomeric Phosphinobiphenyl Amidosulfonates in Pd-Catalyzed Cyanation of Aryl Bromides
Catalysts 2016, 6(12), 182; doi:10.3390/catal6120182
Received: 21 October 2016 / Revised: 16 November 2016 / Accepted: 21 November 2016 / Published: 25 November 2016
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Abstract
A hydrophilic phosphinobiphenyl amidosulfonate, 2′-(dicyclohexylphosphino)-2- {[(sulfonatomethyl)amino]carbonyl}[1,1′-biphenyl], triethylammonium salt (L2), was prepared and, together with its isomer bearing the polar amido-sulfonate tag in the position 4 of the biphenyl scaffold (compound L1), evaluated as a supporting ligand in Pd-catalyzed cyanation of
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A hydrophilic phosphinobiphenyl amidosulfonate, 2′-(dicyclohexylphosphino)-2- {[(sulfonatomethyl)amino]carbonyl}[1,1′-biphenyl], triethylammonium salt (L2), was prepared and, together with its isomer bearing the polar amido-sulfonate tag in the position 4 of the biphenyl scaffold (compound L1), evaluated as a supporting ligand in Pd-catalyzed cyanation of aryl bromides using K4[Fe(CN)6] as the non-toxic cyanide source. The less sterically demanding ligand L1 was found to form more active catalysts than the newly prepared compound L2. A catalyst formed in situ from palladium(II) acetate and L1 efficiently mediated cyanation of aryl bromides bearing electron-donating substituents but failed in the analogous reactions with electron-poor substrates. Full article
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Open AccessFeature PaperArticle One-Pot Synthesis of (+)-Nootkatone via Dark Singlet Oxygenation of Valencene: The Triple Role of the Amphiphilic Molybdate Catalyst
Catalysts 2016, 6(12), 184; doi:10.3390/catal6120184
Received: 16 September 2016 / Revised: 7 November 2016 / Accepted: 18 November 2016 / Published: 26 November 2016
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Abstract
Efficient one-pot catalytic synthesis of (+)-nootkatone was performed from (+)-valencene using only hydrogen peroxide and amphiphilic molybdate ions. The process required no solvent and proceeded in three cascade reactions: (i) singlet oxygenation of valencene according to the ene reaction; (ii) Schenck rearrangement of
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Efficient one-pot catalytic synthesis of (+)-nootkatone was performed from (+)-valencene using only hydrogen peroxide and amphiphilic molybdate ions. The process required no solvent and proceeded in three cascade reactions: (i) singlet oxygenation of valencene according to the ene reaction; (ii) Schenck rearrangement of one hydroperoxide into the secondary β-hydroperoxide; and (iii) dehydration of the hydroperoxide into the desired (+)-nootkatone. The solvent effect on the hydroperoxide rearrangement is herein discussed. The amphiphilic dimethyldioctyl ammonium molybdate, which is also a balanced surfactant, played a triple role in this process, as molybdate ions catalyzed at both Step 1 and Step 3 and it allowed the rapid formation of a three-phase microemulsion system that highly facilitates product recovery. Preparative synthesis of the high added value (+)-nootkatone was thus performed at room temperature with an isolated yield of 46.5%. This is also the first example of a conversion of allylic hydroperoxides into ketones catalyzed by molybdate ions. Full article
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Open AccessArticle Chitosan Aerogel Catalyzed Asymmetric Aldol Reaction in Water: Highly Enantioselective Construction of 3-Substituted-3-hydroxy-2-oxindoles
Catalysts 2016, 6(12), 186; doi:10.3390/catal6120186
Received: 3 October 2016 / Revised: 10 November 2016 / Accepted: 21 November 2016 / Published: 28 November 2016
Cited by 1 | PDF Full-text (4797 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A chitosan aerogel catalyzed asymmetric aldol reaction of ketones with isatins in the presence of water is described. This protocol was found to be environmentally benign, because it proceeds smoothly in water and the corresponding aldol products were obtained in excellent yields with
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A chitosan aerogel catalyzed asymmetric aldol reaction of ketones with isatins in the presence of water is described. This protocol was found to be environmentally benign, because it proceeds smoothly in water and the corresponding aldol products were obtained in excellent yields with good enantioselectivities. Full article
(This article belongs to the Special Issue Homogeneous Catalysis and Mechanisms in Water and Biphasic Media)
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Open AccessArticle Composition, Structural Evolution and the Related Property Variations in Preparation of Mixed Cesium/Ammonium Acidic Salts of Heteropolyacids
Catalysts 2016, 6(12), 187; doi:10.3390/catal6120187
Received: 26 October 2016 / Revised: 21 November 2016 / Accepted: 23 November 2016 / Published: 29 November 2016
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Abstract
The composition, structural evolution and the related property variations of mixed cesium/ammonium acidic salts of heteropolyacids were investigated in detail by tracking and analyzing the initial precipitates, evaporation residues and the calcined products in their preparation process. Results show that V cannot completely
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The composition, structural evolution and the related property variations of mixed cesium/ammonium acidic salts of heteropolyacids were investigated in detail by tracking and analyzing the initial precipitates, evaporation residues and the calcined products in their preparation process. Results show that V cannot completely enter the heteropolyanions in the initial precipitates when the Cs+ added amount is low, and the increase in Cs+ adding amount improves the substitution of V for Mo in the heteropolyanions. Both the initial precipitates and the evaporation residues are mixtures of cesium and ammonium salts of heteropolyacids before calcination. Thermal treatment causes the decomposition of the ammonium salts and the formation of single-phase solid solutions from mechanical mixtures. The calcined products of the initial precipitates and the evaporation residues vary greatly in textural properties. The determinants of the catalytic performance for the oxidation of methacrolein to methacrylic acid are acidity and specific surface area of the compounds. The increase in specific surface area mainly improves the conversion of methacrolein, but not the selectivity of methacrylic acid. Insufficient acidity caused by high Cs+ content in the compounds is responsible for the low selectivity. Full article
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Open AccessArticle Continuous Packed Bed Reactor with Immobilized β-Galactosidase for Production of Galactooligosaccharides (GOS)
Catalysts 2016, 6(12), 189; doi:10.3390/catal6120189
Received: 24 October 2016 / Revised: 23 November 2016 / Accepted: 27 November 2016 / Published: 30 November 2016
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Abstract
The β-galactosidase from Bacillus circulans was covalently attached to aldehyde-activated (glyoxal) agarose beads and assayed for the continuous production of galactooligosaccharides (GOS) in a packed-bed reactor (PBR). The immobilization was fast (1 h) and the activity of the resulting biocatalyst was 97.4 U/g
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The β-galactosidase from Bacillus circulans was covalently attached to aldehyde-activated (glyoxal) agarose beads and assayed for the continuous production of galactooligosaccharides (GOS) in a packed-bed reactor (PBR). The immobilization was fast (1 h) and the activity of the resulting biocatalyst was 97.4 U/g measured with o-nitrophenyl-β-d-galactopyranoside (ONPG). The biocatalyst showed excellent operational stability in 14 successive 20 min reaction cycles at 45 °C in a batch reactor. A continuous process for GOS synthesis was operated for 213 h at 0.2 mL/min and 45 °C using 100 g/L of lactose as a feed solution. The efficiency of the PBR slightly decreased with time; however, the maximum GOS concentration (24.2 g/L) was obtained after 48 h of operation, which corresponded to 48.6% lactose conversion and thus to maximum transgalactosylation activity. HPAEC-PAD analysis showed that the two major GOS were the trisaccharide Gal-β(1→4)-Gal-β(1→4)-Glc and the tetrasaccharide Gal-β(1→4)-Gal-β(1→4)-Gal-β(1→4)-Glc. The PBR was also assessed in the production of GOS from milk as a feed solution. The stability of the bioreactor was satisfactory during the first 8 h of operation; after that, a decrease in the flow rate was observed, probably due to partial clogging of the column. This work represents a step forward in the continuous production of GOS employing fixed-bed reactors with immobilized β-galactosidases. Full article
(This article belongs to the Special Issue Immobilized Enzymes: Strategies for Enzyme Stabilization)
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Open AccessArticle Mechanistic and Structural Insight to an Evolved Benzoylformate Decarboxylase with Enhanced Pyruvate Decarboxylase Activity
Catalysts 2016, 6(12), 190; doi:10.3390/catal6120190
Received: 1 November 2016 / Revised: 25 November 2016 / Accepted: 28 November 2016 / Published: 30 November 2016
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Abstract
Benzoylformate decarboxylase (BFDC) and pyruvate decarboxylase (PDC) are thiamin diphosphate-dependent enzymes that share some structural and mechanistic similarities. Both enzymes catalyze the nonoxidative decarboxylation of 2-keto acids, yet differ considerably in their substrate specificity. In particular, the BFDC from P. putida exhibits very
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Benzoylformate decarboxylase (BFDC) and pyruvate decarboxylase (PDC) are thiamin diphosphate-dependent enzymes that share some structural and mechanistic similarities. Both enzymes catalyze the nonoxidative decarboxylation of 2-keto acids, yet differ considerably in their substrate specificity. In particular, the BFDC from P. putida exhibits very limited activity with pyruvate, whereas the PDCs from S. cerevisiae or from Z. mobilis show virtually no activity with benzoylformate (phenylglyoxylate). Previously, saturation mutagenesis was used to generate the BFDC T377L/A460Y variant, which exhibited a greater than 10,000-fold increase in pyruvate/benzoylformate substrate utilization ratio compared to that of wtBFDC. Much of this change could be attributed to an improvement in the Km value for pyruvate and, concomitantly, a decrease in the kcat value for benzoylformate. However, the steady-state data did not provide any details about changes in individual catalytic steps. To gain insight into the changes in conversion rates of pyruvate and benzoylformate to acetaldehyde and benzaldehyde, respectively, by the BFDC T377L/A460Y variant, reaction intermediates of both substrates were analyzed by NMR and microscopic rate constants for the elementary catalytic steps were calculated. Herein we also report the high resolution X-ray structure of the BFDC T377L/A460Y variant, which provides context for the observed changes in substrate specificity. Full article
(This article belongs to the Special Issue Asymmetric and Selective Biocatalysis)
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Open AccessFeature PaperArticle New Tailor-Made Alkyl-Aldehyde Bifunctional Supports for Lipase Immobilization
Catalysts 2016, 6(12), 191; doi:10.3390/catal6120191
Received: 28 October 2016 / Revised: 24 November 2016 / Accepted: 27 November 2016 / Published: 30 November 2016
Cited by 3 | PDF Full-text (1643 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Immobilized and stabilized lipases are important biocatalytic tools. In this paper, different tailor-made bifunctional supports were prepared for the immobilization of a new metagenomic lipase (LipC12). The new supports contained hydrophobic groups (different alkyl groups) to promote interfacial adsorption of the lipase and
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Immobilized and stabilized lipases are important biocatalytic tools. In this paper, different tailor-made bifunctional supports were prepared for the immobilization of a new metagenomic lipase (LipC12). The new supports contained hydrophobic groups (different alkyl groups) to promote interfacial adsorption of the lipase and aldehyde groups to react covalently with the amino groups of side chains of the adsorbed lipase. The best catalyst was 3.5-fold more active and 5000-fold more stable than the soluble enzyme. It was successfully used in the regioselective deacetylation of peracetylated d-glucal. The PEGylated immobilized lipase showed high regioselectivity, producing high yields of the C-3 monodeacetylated product at pH 5.0 and 4 °C. Full article
(This article belongs to the Special Issue Asymmetric and Selective Biocatalysis)
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Open AccessArticle The Preparation of Cu-g-C3N4/AC Catalyst for Acetylene Hydrochlorination
Catalysts 2016, 6(12), 193; doi:10.3390/catal6120193
Received: 29 September 2016 / Revised: 29 November 2016 / Accepted: 29 November 2016 / Published: 5 December 2016
Cited by 1 | PDF Full-text (4847 KB) | HTML Full-text | XML Full-text
Abstract
A novel catalyst based on g-C3N4/activated carbon was prepared by adding CuCl2. The catalytic performance of the as-prepared catalyst was investigated in the acetylene hydrochlorination reaction. X-ray photoelectron spectroscopy, temperature programmed desorption, low temperature N2 adsorption/desorption
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A novel catalyst based on g-C3N4/activated carbon was prepared by adding CuCl2. The catalytic performance of the as-prepared catalyst was investigated in the acetylene hydrochlorination reaction. X-ray photoelectron spectroscopy, temperature programmed desorption, low temperature N2 adsorption/desorption (Brunauer–Emmett–Teller), and thermal gravity analysis showed that Cu-g-C3N4/AC significantly enhanced the catalytic performance of the original catalyst by increasing the relative pyrrolic N content. Cu-g-C3N4/AC also affected the adsorption of hydrogen chloride and acetylene, as well as inhibited the coke deposition during acetylene hydrochlorination. Full article
(This article belongs to the Special Issue Heterogeneous Catalysis for Environmental Remediation)
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Open AccessArticle Facile Synthesis of MnPO4·H2O Nanowire/Graphene Oxide Composite Material and Its Application as Electrode Material for High Performance Supercapacitors
Catalysts 2016, 6(12), 198; doi:10.3390/catal6120198
Received: 31 October 2016 / Revised: 26 November 2016 / Accepted: 5 December 2016 / Published: 9 December 2016
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Abstract
In this work, we reported a facile one-pot hydrothermal method to synthesize MnPO4·H2O nanowire/graphene oxide composite material with coated graphene oxide. Transmission electron microscopy and scanning electron microscope were employed to study its morphology information, and X-ray diffraction was
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In this work, we reported a facile one-pot hydrothermal method to synthesize MnPO4·H2O nanowire/graphene oxide composite material with coated graphene oxide. Transmission electron microscopy and scanning electron microscope were employed to study its morphology information, and X-ray diffraction was used to study the phase and structure of the material. Additionally, X-ray photoelectron spectroscopy was used to study the elements information. To measure electrochemical performances of electrode materials and the symmetry cell, cyclic voltammetry, chronopotentiometry and electrochemical impedance spectrometry were conducted on electrochemical workstation using 3 M KOH electrolytes. Importantly, electrochemical results showed that the as-prepared MnPO4·H2O nanowire/graphene oxide composite material exhibited high specific capacitance (287.9 F·g−1 at 0.625 A·g−1) and specific power (1.5 × 105 W·kg−1 at 2.271 Wh·kg−1), which is expected to have promising applications as supercapacitor electrode material. Full article
(This article belongs to the Special Issue Graphene-Based Materials for Energy Conversion)
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Open AccessArticle Selective Hydrogenation of Concentrated Vinyl Acetylene Mixed C4 by Modified Pd Catalysts: Effect of Cu
Catalysts 2016, 6(12), 199; doi:10.3390/catal6120199
Received: 19 September 2016 / Revised: 2 December 2016 / Accepted: 5 December 2016 / Published: 9 December 2016
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Abstract
The Pd and Pd-Cu on alumina catalysts were tested for hydrogenation of vinyl acetylene in mixed C4 in a circulating tubular reactor. The results showed that adding proper amounts of Cu improved the reaction activity, but inhibited 1,3-butadiene selectivity. Moreover, the presence of
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The Pd and Pd-Cu on alumina catalysts were tested for hydrogenation of vinyl acetylene in mixed C4 in a circulating tubular reactor. The results showed that adding proper amounts of Cu improved the reaction activity, but inhibited 1,3-butadiene selectivity. Moreover, the presence of Cu retarded the carbon deposition on catalysts during the reaction. Temperature programmed oxidation (TPO), Temperature programmed reduction (TPR), H2 chemisorption, and X-ray photoelectron spectroscopy (XPS) were utilized to characterize the catalysts. The characterization suggested both geometric and electronic modifications. Full article
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Review

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Open AccessReview Recent Breakthroughs in the Conversion of Ethanol to Butadiene
Catalysts 2016, 6(12), 203; doi:10.3390/catal6120203
Received: 30 October 2016 / Revised: 5 December 2016 / Accepted: 6 December 2016 / Published: 13 December 2016
Cited by 1 | PDF Full-text (3778 KB) | HTML Full-text | XML Full-text
Abstract
1,3-Butadiene is traditionally produced as a byproduct of ethylene production from steam crackers. What is unusual is that the alternative production route for this important commodity chemical via ethanol was developed a long time ago, before World War II. Currently, there is a
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1,3-Butadiene is traditionally produced as a byproduct of ethylene production from steam crackers. What is unusual is that the alternative production route for this important commodity chemical via ethanol was developed a long time ago, before World War II. Currently, there is a renewed interest in the production of butadiene from biomass due to the general trend to replace oil in the chemical industry. This review describes the recent progress in the production of butadiene from ethanol (ETB) by one or two-step process through intermediate production of acetaldehyde with an emphasis on the new catalytic systems. The different catalysts for butadiene production are compared in terms of structure-catalytic performance relationship, highlighting the key issues and requirements for future developments. The main difficulty in this process is that basic, acid and redox properties have to be combined in one single catalyst for the reactions of condensation, dehydration and hydrogenation. Magnesium and zirconium-based catalysts in the form of oxides or recently proposed silicates and zeolites promoted by metals are prevailing for butadiene synthesis with the highest selectivity of 70% at high ethanol conversion. The major challenge for further application of the process is to increase the butadiene productivity and to enhance the catalyst lifetime by suppression of coke deposition with preservation of active sites. Full article
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Open AccessReview In Situ Spectroscopic Studies of Proton Transport in Zeolite Catalysts for NH3-SCR
Catalysts 2016, 6(12), 204; doi:10.3390/catal6120204
Received: 26 October 2016 / Revised: 8 December 2016 / Accepted: 9 December 2016 / Published: 14 December 2016
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Abstract
Proton transport is an elementary process in the selective catalytic reduction of nitrogen oxides by ammonia (DeNOx by NH3-SCR) using metal-exchanged zeolites as catalysts. This review summarizes recent advancements in the study of proton transport in zeolite catalysts using in
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Proton transport is an elementary process in the selective catalytic reduction of nitrogen oxides by ammonia (DeNOx by NH3-SCR) using metal-exchanged zeolites as catalysts. This review summarizes recent advancements in the study of proton transport in zeolite catalysts using in situ electrical impedance spectroscopy (IS) under NH3-SCR reaction conditions. Different factors, such as the metal cation type, metal exchange level, zeolite framework type, or formation of intermediates, were found to influence the proton transport properties of zeolite NH3-SCR catalysts. A combination of IS with diffuse reflection infrared Fourier transformation spectroscopy in situ (in situ IS-DRIFTS) allowed to achieve a molecular understanding of the proton transport processes. Several mechanistic aspects, such as the NH3-zeolite interaction, NO-zeolite interaction in the presence of adsorbed NH3, or formation of NH4+ intermediates, have been revealed. These achievements indicate that IS-based in situ methods as complementary tools for conventional techniques (e.g., in situ X-ray absorption spectroscopy) are able to provide new perspectives for the understanding of NH3-SCR on zeolite catalysts. Full article
(This article belongs to the Special Issue In Situ and Operando Characterization in Catalysis)
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Open AccessReview Nature Inspired Solutions for Polymers: Will Cutinase Enzymes Make Polyesters and Polyamides Greener?
Catalysts 2016, 6(12), 205; doi:10.3390/catal6120205
Received: 31 October 2016 / Revised: 26 November 2016 / Accepted: 7 December 2016 / Published: 13 December 2016
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Abstract
The polymer and plastic sectors are under the urge of mitigating their environmental impact. The need for novel and more benign catalysts for polyester synthesis or targeted functionalization led, in recent years, to an increasing interest towards cutinases due to their natural ability
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The polymer and plastic sectors are under the urge of mitigating their environmental impact. The need for novel and more benign catalysts for polyester synthesis or targeted functionalization led, in recent years, to an increasing interest towards cutinases due to their natural ability to hydrolyze ester bonds in cutin, a natural polymer. In this review, the most recent advances in the synthesis and hydrolysis of various classes of polyesters and polyamides are discussed with a critical focus on the actual perspectives of applying enzymatic technologies for practical industrial purposes. More specifically, cutinase enzymes are compared to lipases and, in particular, to lipase B from Candida antarctica, the biocatalyst most widely employed in polymer chemistry so far. Computational and bioinformatics studies suggest that the natural role of cutinases in attacking natural polymers confer some essential features for processing also synthetic polyesters and polyamides. Full article
(This article belongs to the Special Issue Enzyme Catalysis)
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Open AccessReview Catalysis-Based Cataluminescent and Conductometric Gas Sensors: Sensing Nanomaterials, Mechanism, Applications and Perspectives
Catalysts 2016, 6(12), 210; doi:10.3390/catal6120210
Received: 31 October 2016 / Revised: 9 December 2016 / Accepted: 13 December 2016 / Published: 17 December 2016
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Abstract
Gas environment detection has become more urgent and significant, for both industrial manufacturing and environment monitoring. Gas sensors based on a catalytically-sensing mechanism are one of the most important types of devices for gas detection, and have been of great interest during the
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Gas environment detection has become more urgent and significant, for both industrial manufacturing and environment monitoring. Gas sensors based on a catalytically-sensing mechanism are one of the most important types of devices for gas detection, and have been of great interest during the past decades. However, even though many efforts have contributed to this area, some great challenges still remain, such as the development of sensitively and selectively sensing catalysts. In this review, two representative catalysis-based gas sensors, cataluminescent and conductometric sensors, the basis of optical and electric signal acquisition, respectively, are summarized comprehensively. The current challenges have been presented. Recent research progress on the working mechanism, sensing nanomaterials, and applications reported by our group and some other researchers have been discussed systematically. The future trends and prospects of the catalysis-based gas sensors have also been presented. Full article
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Open AccessFeature PaperReview Micro/Mesoporous Zeolitic Composites: Recent Developments in Synthesis and Catalytic Applications
Catalysts 2016, 6(12), 183; doi:10.3390/catal6120183
Received: 27 October 2016 / Revised: 10 November 2016 / Accepted: 11 November 2016 / Published: 29 November 2016
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Abstract
Micro/mesoporous zeolitic composites (MZCs) represent an important class of hierarchical zeolitic materials that have attracted increasing attention in recent years. By introducing an additional mesoporous phase interconnected with the microporosity of zeolites, a hierarchical porous system of MZCs is formed which facilitates molecular
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Micro/mesoporous zeolitic composites (MZCs) represent an important class of hierarchical zeolitic materials that have attracted increasing attention in recent years. By introducing an additional mesoporous phase interconnected with the microporosity of zeolites, a hierarchical porous system of MZCs is formed which facilitates molecular transport while preserving the intrinsic catalytic properties of zeolites. Thus, these materials offer novel perspectives for catalytic applications. Over the years, numerous synthesis strategies toward the formation of MZCs have been realized and their catalytic applications have been reported. In this review, the three main synthesis routes, namely direct synthesis using zeolite precursors, recrystallization of zeolites, and zeolitization of preformed mesoporous materials are thoroughly discussed, with focus on prior works and the most recent developments along with prominent examples given from the literature. In addition, the significant improvement in the catalytic properties of MZCs in a wide range of industrially relevant reactions is presented through several representative cases. Some perspectives for the future development of MZCs are also given. Full article
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Open AccessFeature PaperReview Untangling the Role of the Capping Agent in Nanocatalysis: Recent Advances and Perspectives
Catalysts 2016, 6(12), 185; doi:10.3390/catal6120185
Received: 28 October 2016 / Revised: 18 November 2016 / Accepted: 23 November 2016 / Published: 27 November 2016
Cited by 3 | PDF Full-text (6065 KB) | HTML Full-text | XML Full-text
Abstract
Capping agents (organic ligands, polymers, surfactants, etc.) are a basic component in the synthesis of metal nanoparticles with controlled size and well-defined shape. However, their influence on the performances of nanoparticle-based catalysts is multifaceted and controversial. Indeed, capping agent can act as a
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Capping agents (organic ligands, polymers, surfactants, etc.) are a basic component in the synthesis of metal nanoparticles with controlled size and well-defined shape. However, their influence on the performances of nanoparticle-based catalysts is multifaceted and controversial. Indeed, capping agent can act as a “poison”, limiting the accessibility of active sites, as well as a “promoter”, producing improved yields and unpredicted selectivity control. These effects can be ascribed to the creation of a metal-ligand interphase, whose unique properties are responsible for the catalytic behavior. Therefore, understanding the structure of this interphase is of prime interest for the optimization of tailored nanocatalyst design. This review provides an overview of the interfacial key features affecting the catalytic performances and details a selection of related literature examples. Furthermore, we highlight critical points necessary for the design of highly selective and active catalysts with surface and interphase control. Full article
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Open AccessReview The Applications of Morphology Controlled ZnO in Catalysis
Catalysts 2016, 6(12), 188; doi:10.3390/catal6120188
Received: 29 July 2016 / Revised: 24 October 2016 / Accepted: 9 November 2016 / Published: 30 November 2016
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Abstract
Zinc oxide (ZnO), with the unique chemical and physical properties of high chemical stability, broad radiation absorption range, high electrochemical coupling coefficient, and high photo-stability, is an attractive multifunctional material which has promoted great interest in many fields. What is more, its properties
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Zinc oxide (ZnO), with the unique chemical and physical properties of high chemical stability, broad radiation absorption range, high electrochemical coupling coefficient, and high photo-stability, is an attractive multifunctional material which has promoted great interest in many fields. What is more, its properties can be tuned by controllable synthesized morphologies. Therefore, after the success of the abundant morphology controllable synthesis, both the morphology-dependent ZnO properties and their related applications have been extensively investigated. This review concentrates on the properties of morphology-dependent ZnO and their applications in catalysis, mainly involved reactions on green energy and environmental issues, such as CO2 hydrogenation to fuels, methanol steam reforming to generate H2, bio-diesel production, pollutant photo-degradation, etc. The impressive catalytic properties of ZnO are associated with morphology tuned specific microstructures, defects or abilities of electron transportation, etc. The main morphology-dependent promotion mechanisms are discussed and summarized. Full article
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Open AccessFeature PaperReview Tandem Reactions Combining Biocatalysts and Chemical Catalysts for Asymmetric Synthesis
Catalysts 2016, 6(12), 194; doi:10.3390/catal6120194
Received: 7 November 2016 / Revised: 28 November 2016 / Accepted: 29 November 2016 / Published: 5 December 2016
Cited by 2 | PDF Full-text (6342 KB) | HTML Full-text | XML Full-text
Abstract
The application of biocatalysts in the synthesis of fine chemicals and medicinal compounds has grown significantly in recent years. Particularly, there is a growing interest in the development of one-pot tandem catalytic systems combining the reactivity of a chemical catalyst with the selectivity
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The application of biocatalysts in the synthesis of fine chemicals and medicinal compounds has grown significantly in recent years. Particularly, there is a growing interest in the development of one-pot tandem catalytic systems combining the reactivity of a chemical catalyst with the selectivity engendered by the active site of an enzyme. Such tandem catalytic systems can achieve levels of chemo-, regio-, and stereo-selectivities that are unattainable with a small molecule catalyst. In addition, artificial metalloenzymes widen the range of reactivities and catalyzed reactions that are potentially employable. This review highlights some of the recent examples in the past three years that combined transition metal catalysis with enzymatic catalysis. This field is still in its infancy. However, with recent advances in protein engineering, catalyst synthesis, artificial metalloenzymes and supramolecular assembly, there is great potential to develop more sophisticated tandem chemoenzymatic processes for the synthesis of structurally complex chemicals. Full article
(This article belongs to the Special Issue Asymmetric and Selective Biocatalysis)
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Open AccessReview Application, Deactivation, and Regeneration of Heterogeneous Catalysts in Bio-Oil Upgrading
Catalysts 2016, 6(12), 195; doi:10.3390/catal6120195
Received: 31 October 2016 / Revised: 21 November 2016 / Accepted: 1 December 2016 / Published: 7 December 2016
Cited by 9 | PDF Full-text (682 KB) | HTML Full-text | XML Full-text
Abstract
The massive consumption of fossil fuels and associated environmental issues are leading to an increased interest in alternative resources such as biofuels. The renewable biofuels can be upgraded from bio-oils that are derived from biomass pyrolysis. Catalytic cracking and hydrodeoxygenation (HDO) are two
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The massive consumption of fossil fuels and associated environmental issues are leading to an increased interest in alternative resources such as biofuels. The renewable biofuels can be upgraded from bio-oils that are derived from biomass pyrolysis. Catalytic cracking and hydrodeoxygenation (HDO) are two of the most promising bio-oil upgrading processes for biofuel production. Heterogeneous catalysts are essential for upgrading bio-oil into hydrocarbon biofuel. Although advances have been achieved, the deactivation and regeneration of catalysts still remains a challenge. This review focuses on the current progress and challenges of heterogeneous catalyst application, deactivation, and regeneration. The technologies of catalysts deactivation, reduction, and regeneration for improving catalyst activity and stability are discussed. Some suggestions for future research including catalyst mechanism, catalyst development, process integration, and biomass modification for the production of hydrocarbon biofuels are provided. Full article
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Open AccessReview New Frontiers in the Catalytic Synthesis of Levulinic Acid: From Sugars to Raw and Waste Biomass as Starting Feedstock
Catalysts 2016, 6(12), 196; doi:10.3390/catal6120196
Received: 28 October 2016 / Revised: 18 November 2016 / Accepted: 1 December 2016 / Published: 6 December 2016
Cited by 7 | PDF Full-text (2803 KB) | HTML Full-text | XML Full-text
Abstract
Levulinic acid (LA) is one of the top bio-based platform molecules that can be converted into many valuable chemicals. It can be produced by acid catalysis from renewable resources, such as sugars, lignocellulosic biomass and waste materials, attractive candidates due to their abundance
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Levulinic acid (LA) is one of the top bio-based platform molecules that can be converted into many valuable chemicals. It can be produced by acid catalysis from renewable resources, such as sugars, lignocellulosic biomass and waste materials, attractive candidates due to their abundance and environmentally benign nature. The LA transition from niche product to mass-produced chemical, however, requires its production from sustainable biomass feedstocks at low costs, adopting environment-friendly techniques. This review is an up-to-date discussion of the literature on the several catalytic systems that have been developed to produce LA from the different substrates. Special attention has been paid to the recent advancements on starting materials, moving from simple sugars to raw and waste biomasses. This aspect is of paramount importance from a sustainability point of view, transforming wastes needing to be disposed into starting materials for value-added products. This review also discusses the strategies to exploit the solid residues always obtained in the LA production processes, in order to attain a circular economy approach. Full article
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Open AccessReview Proton Exchange Membrane Fuel Cell Reversal: A Review
Catalysts 2016, 6(12), 197; doi:10.3390/catal6120197
Received: 19 July 2016 / Revised: 9 September 2016 / Accepted: 10 September 2016 / Published: 8 December 2016
Cited by 1 | PDF Full-text (2385 KB) | HTML Full-text | XML Full-text
Abstract
The H2/air-fed proton exchange membrane fuel cell (PEMFC) has two major problems: cost and durability, which obstruct its pathway to commercialization. Cell reversal, which would create irreversible damage to the fuel cell and shorten its lifespan, is caused by reactant starvation,
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The H2/air-fed proton exchange membrane fuel cell (PEMFC) has two major problems: cost and durability, which obstruct its pathway to commercialization. Cell reversal, which would create irreversible damage to the fuel cell and shorten its lifespan, is caused by reactant starvation, load change, low catalyst performance, and so on. This paper will summarize the causes, consequences, and mitigation strategies of cell reversal of PEMFC in detail. A description of potential change in the anode and cathode and the differences between local starvation and overall starvation are reviewed, which gives a framework for comprehending the origins of cell reversal. According to the root factor of cell starvation, i.e., fuel cells do not satisfy the requirements of electrons and protons of normal anode and cathode chemical reactions, we will introduce specific methods to mitigate or prevent fuel cell damage caused by cell reversal in the view of system management strategies and component material modifications. Based on a comprehensive understanding of cell reversal, it is beneficial to operate a fuel cell stack and extend its lifetime. Full article
(This article belongs to the Special Issue Catalysis for Low Temperature Fuel Cells)
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Other

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Open AccessPerspective Hidden but Possibly Fatal Misconceptions in Photocatalysis Studies: A Short Critical Review
Catalysts 2016, 6(12), 192; doi:10.3390/catal6120192
Received: 31 October 2016 / Revised: 24 November 2016 / Accepted: 30 November 2016 / Published: 2 December 2016
PDF Full-text (1052 KB) | HTML Full-text | XML Full-text
Abstract
This short review paper shows some misconceptions hidden in the discussion on the mechanism of heterogeneous photocatalysis, which may lead to fatal errors in conclusions. Topics described in this review are semiconductor photocatalysis, control experiments for proof of photocatalysis, and converse-proposition pitfalls in
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This short review paper shows some misconceptions hidden in the discussion on the mechanism of heterogeneous photocatalysis, which may lead to fatal errors in conclusions. Topics described in this review are semiconductor photocatalysis, control experiments for proof of photocatalysis, and converse-proposition pitfalls in discussion. Full article
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