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Catalysts, Volume 7, Issue 11 (November 2017) – 42 articles

Cover Story (view full-size image): Fine chemistry products such as agro-chemicals or pharmaceuticals require ketones and/or aldehydes as starting materials, which are obtained by alcohols oxidation. Nowadays it is imperative converting alcohols into the desired oxidized forms in a sustainable way. This paper is focused on the use of cheap EDTA functionalized magnetite type magnetic nanoparticles as reusable catalysts for the selective oxidation of alcohols to aldehydes or ketones in solvent-free medium and using the green alternative microwave energy source. Additional advantages of using these materials are their high accessible surface area and easy separation from the reaction medium by an external magnet. View Paper here.
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4337 KiB  
Article
Polyelectrolyte Complex Beads by Novel Two-Step Process for Improved Performance of Viable Whole-Cell Baeyer-Villiger Monoxygenase by Immobilization
by Tomáš Krajčovič, Marek Bučko, Alica Vikartovská, Igor Lacík, Lucia Uhelská, Dušan Chorvát, Vilém Neděla, Eva Tihlaříková, Martin Gericke, Thomas Heinze and Peter Gemeiner
Catalysts 2017, 7(11), 353; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110353 - 21 Nov 2017
Cited by 9 | Viewed by 5072
Abstract
A novel immobilization matrix for the entrapment of viable whole-cell Baeyer–Villiger monooxygenase was developed. Viable recombinant Escherichia coli cells overexpressing cyclohexanone monooxygenase were entrapped in polyelectrolyte complex beads prepared by a two-step reaction of oppositely-charged polymers including highly defined cellulose sulphate. Immobilized cells [...] Read more.
A novel immobilization matrix for the entrapment of viable whole-cell Baeyer–Villiger monooxygenase was developed. Viable recombinant Escherichia coli cells overexpressing cyclohexanone monooxygenase were entrapped in polyelectrolyte complex beads prepared by a two-step reaction of oppositely-charged polymers including highly defined cellulose sulphate. Immobilized cells exhibited higher operational stability than free cells during 10 repeated cycles of Baeyer–Villiger biooxidations of rac-bicyclo[3.2.0]hept-2-en-6-one to the corresponding lactones (1R,5S)-3-oxabicyclo-[3.3.0]oct-6-en-3-one and (1S,5R)-2-oxabicyclo-[3.3.0]oct-6-en-3-one. The morphology of polyelectrolyte complex beads was characterised by environmental scanning electron microscopy; the spatial distribution of polymers in the beads and cell viability were examined using confocal laser scanning microscopy, and the texture was characterised by the mechanical resistance measurements. Full article
(This article belongs to the Special Issue Immobilized Biocatalysts)
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3695 KiB  
Review
Advances in Base-Free Oxidation of Bio-Based Compounds on Supported Gold Catalysts
by Robert Wojcieszak, Camila P. Ferraz, Jin Sha, Sarah Houda, Liane M. Rossi and Sébastien Paul
Catalysts 2017, 7(11), 352; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110352 - 21 Nov 2017
Cited by 45 | Viewed by 6606
Abstract
The oxidation of bio-based molecules in general, and of carbohydrates and furanics in particular, is a highly attractive process. The catalytic conversion of renewable compounds is of high importance. Acids and other chemical intermediates issued from oxidation processes have many applications related, especially, [...] Read more.
The oxidation of bio-based molecules in general, and of carbohydrates and furanics in particular, is a highly attractive process. The catalytic conversion of renewable compounds is of high importance. Acids and other chemical intermediates issued from oxidation processes have many applications related, especially, to food and detergents, as well as to pharmaceutics, cosmetics, and the chemical industry. Until now, the oxidation of sugars, furfural, or 5-hydroxymethylfurfural has been mainly conducted through biochemical processes or with strong inorganic oxidants. The use of these processes very often presents many disadvantages, especially regarding products separation and selectivity control. Generally, the oxidation is performed in batch conditions using an appropriate catalyst and a basic aqueous solution (pH 7–9), while bubbling oxygen or air through the slurry. However, there is a renewed interest in working in base-free conditions to avoid the production of salts. Actually, this gives direct access to different acids or diacids without laborious product purification steps. This review focuses on processes applying gold-based catalysts, and on the catalytic properties of these systems in the base-free oxidation of important compounds: C5–C6 sugars, furfural, and 5-hydroxymethylfurfural. A better understanding of the chemical and physical properties of the catalysts and of the operating conditions applied in the oxidation reactions is essential. For this reason, in this review we put emphasis on these most impacting factors. Full article
(This article belongs to the Special Issue Catalytic Sustainable Processes in Biorefineries)
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14872 KiB  
Article
Facile One-Pot Synthesis of Amidoalkyl Naphthols and Benzopyrans Using Magnetic Nanoparticle-Supported Acidic Ionic Liquid as a Highly Efficient and Reusable Catalyst
by Qiang Zhang, Yin-Hong Gao, Shan-Lin Qin and Huai-Xin Wei
Catalysts 2017, 7(11), 351; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110351 - 21 Nov 2017
Cited by 35 | Viewed by 6125
Abstract
An efficient and eco-friendly procedure for the synthesis of 1-amidoalkyl-2-naphthol and tetrahydrobenzo[b]pyran derivatives has been developed through a one-pot three-component condensation of aldehydes with 2-naphthol and amides, or with malononitrile and dimedone in the presence of magnetic nanoparticle supported acidic ionic [...] Read more.
An efficient and eco-friendly procedure for the synthesis of 1-amidoalkyl-2-naphthol and tetrahydrobenzo[b]pyran derivatives has been developed through a one-pot three-component condensation of aldehydes with 2-naphthol and amides, or with malononitrile and dimedone in the presence of magnetic nanoparticle supported acidic ionic liquid (AIL@MNP) as a novel heterogeneous catalyst under solvent-free conditions. This new procedure offers several advantages such as short reaction time, excellent yields, operational simplicity and without any tedious work-up for catalyst recovery or product purification. Moreover, the catalyst could be simply separated by an external magnet and reused six times without significant loss of catalytic activity. Full article
(This article belongs to the Special Issue Organocatalysis in Ionic Liquids)
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1220 KiB  
Article
Characteristics of NixFe1−xOy Electrocatalyst on Hematite as Photoanode for Solar Hydrogen Production
by Chih-Ping Yen, Yan-Jin Li, Jyhpyng Wang, Szu-yuan Chen and Chung-Jen Tseng
Catalysts 2017, 7(11), 350; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110350 - 20 Nov 2017
Cited by 4 | Viewed by 4276
Abstract
The use of hematite as the photoanode for photoelectrochemical hydrogen production by solar energy has been actively studied due to its abundance, stability, and adequate optical properties. Deposition of an electrocatalyst overlayer on the hematite may increase kinetics and lower the onset potential [...] Read more.
The use of hematite as the photoanode for photoelectrochemical hydrogen production by solar energy has been actively studied due to its abundance, stability, and adequate optical properties. Deposition of an electrocatalyst overlayer on the hematite may increase kinetics and lower the onset potential for water splitting. NixFe1−xOy is one of the most effective electrocatalysts reported for this purpose. However, the condition and results of the previous reports vary significantly, and a comprehensive model for NixFe1−xOy/hematite is lacking. Here, we report a simple and novel chemical bath deposition method for depositing low-onset-potential NixFe1−xOy electrocatalyst on hematite. With a Ni percentage of 80% and an immersion time of 2 min, the as-prepared NixFe1−xOy overlayer raised the photovoltage from 0.2 V to 0.7 V, leading to a cathodic shift of the onset potential by 400 mV, while maintaining the same level of current density. The dependence of the electrochemical and photoelectrochemical characteristics of the photoanode on the condition of the electrocatalyst was studied systematically and explained based on energy level diagrams and kinetics. Full article
(This article belongs to the Special Issue Advances in Electrocatalysis)
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5634 KiB  
Article
Synergistic Enhancement in Catalytic Performance of Superparamagnetic Fe3O4@Bacilus subtilis as Recyclable Fenton-Like Catalyst
by Pei Zheng, Zhe Pan and Jun Zhang
Catalysts 2017, 7(11), 349; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110349 - 20 Nov 2017
Cited by 13 | Viewed by 4325
Abstract
Novel well-defined superparamagnetic Fe3O4@Bacilus subtilis composite (Fe3O4@B. subtilis SPMC) was synthesized through a facile electrostatic attraction method and used as a recyclable heterogeneous Fenton-like catalyst. With the presence of H2O2 [...] Read more.
Novel well-defined superparamagnetic Fe3O4@Bacilus subtilis composite (Fe3O4@B. subtilis SPMC) was synthesized through a facile electrostatic attraction method and used as a recyclable heterogeneous Fenton-like catalyst. With the presence of H2O2, Fe3O4@B. subtilis SPMC can remove nearly 87% of the doxycycline at the initial concentration of 50 mg L−1, exhibiting enhanced Fenton-like catalytic performance than pristine Fe3O4. The mechanism study demonstrates the synergistic effect between Bacilus subtilis adsorption and Fenton-like ability of Fe3O4 dominates the enhancement for Fenton-like catalytic efficiency of Fe3O4@B. subtilis SPMC. The obtained composite shows excellent recycling ability, reusability, and stability, which pave a new way for future design on highly efficient Fenton-like catalyst for degradation of organic pollutants. Full article
(This article belongs to the Special Issue Magnetic Nanocatalysts)
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2286 KiB  
Article
Dehydrogenation of Formic Acid over a Homogeneous Ru-TPPTS Catalyst: Unwanted CO Production and Its Successful Removal by PROX
by Vera Henricks, Igor Yuranov, Nordahl Autissier and Gábor Laurenczy
Catalysts 2017, 7(11), 348; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110348 - 20 Nov 2017
Cited by 12 | Viewed by 5879
Abstract
Formic acid (FA) is considered as a potential durable energy carrier. It contains ~4.4 wt % of hydrogen (or 53 g/L) which can be catalytically released and converted to electricity using a proton exchange membrane (PEM) fuel cell. Although various catalysts have been [...] Read more.
Formic acid (FA) is considered as a potential durable energy carrier. It contains ~4.4 wt % of hydrogen (or 53 g/L) which can be catalytically released and converted to electricity using a proton exchange membrane (PEM) fuel cell. Although various catalysts have been reported to be very selective towards FA dehydrogenation (resulting in H2 and CO2), a side-production of CO and H2O (FA dehydration) should also be considered, because most PEM hydrogen fuel cells are poisoned by CO. In this research, a highly active aqueous catalytic system containing Ru(III) chloride and meta-trisulfonated triphenylphosphine (mTPPTS) as a ligand was applied for FA dehydrogenation in a continuous mode. CO concentration (8–70 ppm) in the resulting H2 + CO2 gas stream was measured using a wide range of reactor operating conditions. The CO concentration was found to be independent on the reactor temperature but increased with increasing FA feed. It was concluded that unwanted CO concentration in the H2 + CO2 gas stream was dependent on the current FA concentration in the reactor which was in turn dependent on the reaction design. Next, preferential oxidation (PROX) on a Pt/Al2O3 catalyst was applied to remove CO traces from the H2 + CO2 stream. It was demonstrated that CO concentration in the stream could be reduced to a level tolerable for PEM fuel cells (~3 ppm). Full article
(This article belongs to the Special Issue Homogeneous Catalysis and Mechanisms in Water and Biphasic Media)
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4126 KiB  
Review
On the Structure of Chiral Dirhodium(II) Carboxylate Catalysts: Stereoselectivity Relevance and Insights
by Frady G. Adly
Catalysts 2017, 7(11), 347; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110347 - 20 Nov 2017
Cited by 30 | Viewed by 6082
Abstract
Modern experiments have offered alternative interpretations on the symmetry of chiral dirhodium(II) carboxylate complexes and its relationship to their level of enantioselectivity. So, this contribution is to provide an insight on how the knowledge around the structure of these catalysts has evolved with [...] Read more.
Modern experiments have offered alternative interpretations on the symmetry of chiral dirhodium(II) carboxylate complexes and its relationship to their level of enantioselectivity. So, this contribution is to provide an insight on how the knowledge around the structure of these catalysts has evolved with a particular emphasis on the impact of this knowledge on enantioselectivity prediction and catalyst design. Full article
(This article belongs to the Special Issue Asymmetric Catalysis in Organic Synthesis)
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7766 KiB  
Article
Efficient Degradation of Refractory Organics Using Sulfate Radicals Generated Directly from WO3 Photoelectrode and the Catalytic Reaction of Sulfate
by Jingyuan Zheng, Jinhua Li, Jing Bai, Xiaohan Tan, Qingyi Zeng, Linsen Li and Baoxue Zhou
Catalysts 2017, 7(11), 346; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110346 - 17 Nov 2017
Cited by 14 | Viewed by 5051
Abstract
An environment-friendly method of efficiently degrading refractory organics using SO4• generated directly from a WO3 photoelectrode and a catalytic reaction of sulfate was proposed, in which the cycling process of SO42− → SO4• → [...] Read more.
An environment-friendly method of efficiently degrading refractory organics using SO4• generated directly from a WO3 photoelectrode and a catalytic reaction of sulfate was proposed, in which the cycling process of SO42− → SO4• → SO42− was achieved in the treatment of organic pollutants without any other activator and without the continuous addition of sulfate. The results show that the removal efficiency for a typical refractory organics of methyl orange (MO) with 5 mg/L was up to 95% within 80 min, and merely 3% by photolysis and 19% by photocatalysis, respectively, under similar conditions. The rate constant for the disposal of MO at pH 2, in which SO4• instead of HO• is the main oxidizer confirmed by radical scavenger experiment, is up to 5.21 × 10−4 s−1, which was ~6.6 times that (7.89 × 10−5 s−1) under neutral condition, in which HO• is the main oxidizer. The concentration of active persulfate (S2O82−, SO52−, and SO4•) species at pH 2 was up to 0.38 mM, which was ~16-fold as much as that (0.023 mM) in neutral conditions. The method provides a new approach for the treatment and resource utilization of sulfate wastewater. Full article
(This article belongs to the Special Issue Advances in Electrocatalysis)
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7487 KiB  
Review
Base Catalysis by Mono- and Polyoxometalates
by Keigo Kamata and Kosei Sugahara
Catalysts 2017, 7(11), 345; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110345 - 16 Nov 2017
Cited by 45 | Viewed by 8957
Abstract
In sharp contrast with acid-, photo-, and oxidation-catalysis by polyoxometalates, base catalysis by polyoxometalates has scarcely been investigated. The use of polyoxometalates as base catalysts have very recently received much attention and has been extensively investigated. Numerous mono- and polyoxometalate base catalyst systems [...] Read more.
In sharp contrast with acid-, photo-, and oxidation-catalysis by polyoxometalates, base catalysis by polyoxometalates has scarcely been investigated. The use of polyoxometalates as base catalysts have very recently received much attention and has been extensively investigated. Numerous mono- and polyoxometalate base catalyst systems effective for the chemical fixation of CO2, cyanosilylation of carbonyl compounds, and C–C bond forming reactions have been developed. Mono- and polyoxometalate base catalysts are classified into four main groups with respect to their structures: (a) monomeric metalates; (b) isopolyoxometalates; (c) heteropolyoxometalates; and (d) transition-metal-substituted polyoxometalates. This review article focuses on the relationship among the molecular structures, the basic properties, and the unique base catalysis of polyoxometalates on the basis of groups (a)–(d). In addition, reaction mechanisms including the specific activation of substrates and/or reagents such as the abstraction of protons, nucleophilic action toward substrates, and bifunctional action in combination with metal catalysts are comprehensively summarized. Full article
(This article belongs to the Special Issue Recent Advances in Polyoxometalate-Catalyzed Reactions)
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8212 KiB  
Review
Ultrasonic Monitoring of Biocatalysis in Solutions and Complex Dispersions
by Vitaly Buckin and Margarida Caras Altas
Catalysts 2017, 7(11), 336; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110336 - 15 Nov 2017
Cited by 21 | Viewed by 5102
Abstract
The rapidly growing field of chemical catalysis is dependent on analytical methods for non-destructive real-time monitoring of chemical reactions in complex systems such as emulsions, suspensions and gels, where most analytical techniques are limited in their applicability, especially if the media is opaque, [...] Read more.
The rapidly growing field of chemical catalysis is dependent on analytical methods for non-destructive real-time monitoring of chemical reactions in complex systems such as emulsions, suspensions and gels, where most analytical techniques are limited in their applicability, especially if the media is opaque, or if the reactants/products do not possess optical activity. High-resolution ultrasonic spectroscopy is one of the novel technologies based on measurements of parameters of ultrasonic waves propagating through analyzed samples, which can be utilized for real-time non-invasive monitoring of chemical reactions. It does not require optical transparency, optical markers and is applicable for monitoring of reactions in continuous media and in micro/nano bioreactors (e.g., nanodroplets of microemulsions). The technology enables measurements of concentrations of substrates and products over the whole course of reaction, analysis of time profiles of the degree of polymerization and molar mass of polymers and oligomers, evolutions of reaction rates, evaluation of kinetic mechanisms, measurements of kinetic and equilibrium constants and reaction Gibbs energy. It also provides tools for assessments of various aspects of performance of catalysts/enzymes including inhibition effects, reversible and irreversible thermal deactivation. In addition, ultrasonic scattering effects in dispersions allow real-time monitoring of structural changes in the medium accompanying chemical reactions. Full article
(This article belongs to the Special Issue Homogeneous Catalysis and Mechanisms in Water and Biphasic Media)
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2932 KiB  
Article
Fe-Doped TiO2 Supported on HY Zeolite for Solar Photocatalytic Treatment of Dye Pollutants
by Ghania Foura, Nawel Chouchou, Ahcène Soualah, Kahina Kouachi, Matteo Guidotti and Didier Robert
Catalysts 2017, 7(11), 344; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110344 - 14 Nov 2017
Cited by 28 | Viewed by 7657
Abstract
Zeolite-supported TiO2 and Fe-doped TiO2/zeolite photocatalysts were synthesized, aiming at improving the adsorption properties of the microporous support towards polluting dyes and the photocatalytic performance of TiO2 in the treatment of the adsorbed organics. The TiO2/HY zeolite [...] Read more.
Zeolite-supported TiO2 and Fe-doped TiO2/zeolite photocatalysts were synthesized, aiming at improving the adsorption properties of the microporous support towards polluting dyes and the photocatalytic performance of TiO2 in the treatment of the adsorbed organics. The TiO2/HY zeolite catalyst exhibited the best performance in the photocatalytic degradation of methylene blue, MB, over 10 wt% TiO2/HY under UV light at 254 nm. The addition of Fe species in the synthesis mixture led to Fe-TiO2/HY catalyst. The combination of adequate zeolite, good titanium dioxide dispersion, and Fe doping led to a remarkable performance in the degradation of the model dye. Over a 10 wt% Fe-doped TiO2/HY catalyst a total removal of MB (>98%) was achieved after 60 min under very mild conditions and simple visible light irradiation. Full article
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12708 KiB  
Article
Fine-Tuning Synthesis and Characterization of Mono-Sized H-Beta Zeolite-Supported Palladium-Iridium Nanoparticles and Application in the Selective Hydrogenation of Acetylene
by Masood Sahooli, Mohammad Reza Rahimpour and Mohammad Khorram
Catalysts 2017, 7(11), 343; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110343 - 13 Nov 2017
Cited by 5 | Viewed by 5309
Abstract
In this research, a mono-sized Beta zeolite support synthesized by the solvothermal method was used in the selective acetylene to ethylene hydrogenation reaction with minimum coke build up on the catalyst surface. Tetrapropylammonium hydroxide (TPAOH), tetrapropylammonium bromide (TPABr), n-butylamine, and morpholine were [...] Read more.
In this research, a mono-sized Beta zeolite support synthesized by the solvothermal method was used in the selective acetylene to ethylene hydrogenation reaction with minimum coke build up on the catalyst surface. Tetrapropylammonium hydroxide (TPAOH), tetrapropylammonium bromide (TPABr), n-butylamine, and morpholine were used as structure direct agents (SDA) in the support to obtain various shapes. The characterization results show that although the Si/(Al+SDA) ratio has no effect on the phase purity of support, it has a remarkable effect on porosity, crystal size, shape, and structure of micropores. After comparing characterization results, the developed support, based on TPAOH, was selected and modified by different metals (Ce, Ir, Ag, and Pd) using the incipient wetness co-impregnation method. Since there is an interaction between selectivity and conversion, the optimum metal content in the synthesized catalysts and reaction condition were determined to achieve the desired acetylene conversion and ethylene selectivity. The physicochemical transformation of the developed optimum catalysts was determined using different techniques. Based on the characterization and cata-test results, the catalyst which contains 0.29% Ir and 0.08% Pd presents a better performance and higher stability compared to the other catalysts due to the moderate size and mono layer dispersion of the metals on the support. The experimental results show that acetylene conversion and ethylene selectivity approach 97% and 92% at 55 °C, respectively. Full article
(This article belongs to the Special Issue Zeolites and Catalysis)
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2633 KiB  
Article
Green Synthesis of Ultraviolet Absorber 2-Ethylhexyl Salicylate: Experimental Design and Artificial Neural Network Modeling
by Shang-Ming Huang, Tzu-Hsiang Hung, Yung-Chuan Liu, Chia-Hung Kuo and Chwen-Jen Shieh
Catalysts 2017, 7(11), 342; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110342 - 13 Nov 2017
Cited by 7 | Viewed by 5911
Abstract
2-Ethylhexyl salicylate, an ultraviolet filter, is widely used to protect skin against sunlight-induced harmful effects in the cosmetic industry. In this study, the green synthesis of 2-ethylhexyl salicylate using immobilized lipase through a solvent-free and reduced pressure evaporation system was investigated. A Box–Behnken [...] Read more.
2-Ethylhexyl salicylate, an ultraviolet filter, is widely used to protect skin against sunlight-induced harmful effects in the cosmetic industry. In this study, the green synthesis of 2-ethylhexyl salicylate using immobilized lipase through a solvent-free and reduced pressure evaporation system was investigated. A Box–Behnken design was employed to develop an artificial neural network (ANN) model. The parameters for an optimal architecture of an ANN were set out: a quick propagation algorithm, a hyperbolic tangent transfer function, 10,000 iterations, and six nodes within the hidden layer. The best-fitting performance of the ANN was determined by the coefficient of determination and the root-mean-square error between the correlation of predicted and experimental data, indicating that the ANN displayed excellent data-fitting properties. Finally, the experimental conditions of synthesis were well established with the optimal parameters to obtain a high conversion of 2-ethylhexyl salicylate. In conclusion, this study efficiently replaces the traditional solvents with a green process for the synthesis of 2-ethylhexyl salicylate to avoid environmental contamination, and this process is well-modeled by a methodological ANN for optimization, which might be a benefit for industrial production. Full article
(This article belongs to the Special Issue Biocatalysis and Biotransformations)
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4487 KiB  
Review
Heterogeneous Catalysis on Metal Oxides
by Jacques C. Védrine
Catalysts 2017, 7(11), 341; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110341 - 10 Nov 2017
Cited by 339 | Viewed by 32131
Abstract
This review article contains a reminder of the fundamentals of heterogeneous catalysis and a description of the main domains of heterogeneous catalysis and main families of metal oxide catalysts, which cover acid-base reactions, selective partial oxidation reactions, total oxidation reactions, depollution, biomass conversion, [...] Read more.
This review article contains a reminder of the fundamentals of heterogeneous catalysis and a description of the main domains of heterogeneous catalysis and main families of metal oxide catalysts, which cover acid-base reactions, selective partial oxidation reactions, total oxidation reactions, depollution, biomass conversion, green chemistry and photocatalysis. Metal oxide catalysts are essential components in most refining and petrochemical processes. These catalysts are also critical to improving environmental quality. This paper attempts to review the major current industrial applications of supported and unsupported metal oxide catalysts. Viewpoints for understanding the catalysts’ action are given, while applications and several case studies from academia and industry are given. Emphases are on catalyst description from synthesis to reaction conditions, on main industrial applications in the different domains and on views for the future, mainly regulated by environmental issues. Following a review of the major types of metal oxide catalysts and the processes that use these catalysts, this paper considers current and prospective major applications, where recent advances in the science of metal oxide catalysts have major economic and environmental impacts. Full article
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6277 KiB  
Article
YCl3-Catalyzed Highly Selective Ring Opening of Epoxides by Amines at Room Temperature and under Solvent-Free Conditions
by Wuttichai Natongchai, Rais Ahmad Khan, Ali Alsalme and Rafik Rajjak Shaikh
Catalysts 2017, 7(11), 340; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110340 - 10 Nov 2017
Cited by 5 | Viewed by 7080
Abstract
A simple, efficient, and environmentally benign approach for the synthesis of β-amino alcohols is herein described. YCl3 efficiently carried out the ring opening of epoxides by amines to produce β-amino alcohols under solvent-free conditions at room temperature. This catalytic approach is very [...] Read more.
A simple, efficient, and environmentally benign approach for the synthesis of β-amino alcohols is herein described. YCl3 efficiently carried out the ring opening of epoxides by amines to produce β-amino alcohols under solvent-free conditions at room temperature. This catalytic approach is very effective, with several aromatic and aliphatic oxiranes and amines. A mere 1 mol % concentration of YCl3 is enough to deliver β-amino alcohols in good to excellent yields with high regioselectivity. Full article
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2325 KiB  
Article
Intrinsic Activity of MnOx-CeO2 Catalysts in Ethanol Oxidation
by Dimitrios Delimaris and Theophilos Ioannides
Catalysts 2017, 7(11), 339; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110339 - 10 Nov 2017
Cited by 8 | Viewed by 4715
Abstract
MnOx-CeO2 mixed oxides are considered efficient oxidation catalysts superior to the corresponding single oxides. Although these oxides have been the subject of numerous studies, their fundamental performance indicators, such as turnover frequency (TOF) or specific activity, are scarcely reported. The [...] Read more.
MnOx-CeO2 mixed oxides are considered efficient oxidation catalysts superior to the corresponding single oxides. Although these oxides have been the subject of numerous studies, their fundamental performance indicators, such as turnover frequency (TOF) or specific activity, are scarcely reported. The purpose of the present work is to investigate the effect of catalyst composition on the concentration of active sites and intrinsic activity in ethanol oxidation by the employment of temperature-programmed desorption and oxidation of isotopically-labelled ethanol, 12CH313CH2OH. The transformation pathways of preadsorbed ethanol in the absence of gaseous oxygen refer to dehydrogenation to acetaldehyde followed by its dissociation combined with oxidation by lattice oxygen. In the presence of gaseous oxygen, lattice oxygen is rapidly restored and the main products are acetaldehyde, CO2, and water. CO2 forms less easily on mixed oxides than on pure MnOx. The TOF of ethanol oxidation has been calculated assuming that the amount of adsorbed ethanol and CO2 produced during temperature-programmed oxidation (TPO) is a reliable indicator of the concentration of the active sites. Full article
(This article belongs to the Special Issue Ceria-based Catalysts)
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3500 KiB  
Article
Terpyridine-Containing Imine-Rich Graphene for the Oxygen Reduction Reaction
by Min Seok Lee, Mun Ho Yang, Jong S. Park and Dong Wook Chang
Catalysts 2017, 7(11), 338; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110338 - 10 Nov 2017
Cited by 5 | Viewed by 5185
Abstract
We report a facile synthetic method for the preparation of a terpyridine-containing imine-rich graphene (IrGO-Tpy) using an acid-catalyzed dehydration reaction between graphene oxide (GO) and 4′-(aminophenyl)-2,2′:6′2″-terpyridine. Owing to the presence of terpyridine ligands, cobalt ions (Co2+) were readily incorporated into the [...] Read more.
We report a facile synthetic method for the preparation of a terpyridine-containing imine-rich graphene (IrGO-Tpy) using an acid-catalyzed dehydration reaction between graphene oxide (GO) and 4′-(aminophenyl)-2,2′:6′2″-terpyridine. Owing to the presence of terpyridine ligands, cobalt ions (Co2+) were readily incorporated into the IrGO-Tpy structures, affording a metal complex, denoted IrGo-Tpy-Co. Cyclic voltammetry and linear sweep voltammetry measurements confirm the noticeable oxygen reduction reaction (ORR) activities of the IrGo-Tpy and IrGo-Tpy-Co electroacatalysts in alkaline electrolytes, along with the additional merits of high selectivity, excellent long-term durability, and good resistance to methanol crossover. In addition, a remarkable improvement in the ORR performance was observed for IrGO-Tpy-Co compared with that of IrGo-Tpy, arising from the significant contribution of the cobalt-terpyridine complex in facilitating the ORR process. Full article
(This article belongs to the Special Issue Advances in Electrocatalysis)
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1071 KiB  
Article
Visible-Light Photocatalytic E to Z Isomerization of Activated Olefins and Its Application for the Syntheses of Coumarins
by Kun Zhan and Yi Li
Catalysts 2017, 7(11), 337; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110337 - 09 Nov 2017
Cited by 42 | Viewed by 8762
Abstract
Photocatalytic isomerization of thermodynamically stable E-alkene to less stable Z-alkene has been the subject of numerous studies, being successfully achieved mainly under UV irradiation. Recent development of visible light photoredox catalysis has witnessed it emerging as a powerful tool for the [...] Read more.
Photocatalytic isomerization of thermodynamically stable E-alkene to less stable Z-alkene has been the subject of numerous studies, being successfully achieved mainly under UV irradiation. Recent development of visible light photoredox catalysis has witnessed it emerging as a powerful tool for the access of new structural complexity and many challenging targets. Herein, we report a visible light-promoted E to Z isomerization of cinnamates. When E-isomer of cinnamates was irradiated with blue light in the presence of an organo-photocatalyst, fac-Ir(ppy)3, Z-isomer was exclusively obtained in high yields and with good selectivity. The mild, convenient reaction condition has made this protocol an effective synthetic methodology, which was subsequently implemented in an efficient synthesis of coumarins. Full article
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17704 KiB  
Article
First-Row-Transition Ion Metals(II)-EDTA Functionalized Magnetic Nanoparticles as Catalysts for Solvent-Free Microwave-Induced Oxidation of Alcohols
by Nuno M. R. Martins, Luísa M. D. R. S. Martins, Carlos O. Amorim, Vitor S. Amaral and Armando J. L. Pombeiro
Catalysts 2017, 7(11), 335; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110335 - 09 Nov 2017
Cited by 6 | Viewed by 6015
Abstract
A series of first-row transition-metals combined with ethylenediamine tetraacetic acid (EDTA), as metal-based N,O-chelating ligands, at the surface of ferrite magnetic nanoparticles (MNPs) was prepared by a co-precipitation method. Those EDTA functionalized MNPs with general formula Fe3O4 [...] Read more.
A series of first-row transition-metals combined with ethylenediamine tetraacetic acid (EDTA), as metal-based N,O-chelating ligands, at the surface of ferrite magnetic nanoparticles (MNPs) was prepared by a co-precipitation method. Those EDTA functionalized MNPs with general formula Fe3O4@EDTA-M2+ [M = Mn2+ (1), Fe2+ (2), Co2+ (3), Ni2+ (4), Cu2+ (5) or Zn2+ (6)] were characterized by FTIR (Fourier Transform Infrared) spectroscopy, powder XRD (X-ray Diffraction), SEM (Scanning Electron Microscope), EDS (Energy Dispersive Spectrometer), VSM (Vibrating Sample Magnetometer) and TGA (Thermal Gravity Analysis). The application of the magnetic NPs towards the microwave-assisted oxidation of several alcohol substrates in a solvent-free medium was evaluated. The influence of reaction parameters such as temperature, time, type of oxidant, and presence of organic radicals was investigated. This study demonstrates that these MNPs can act as efficient catalysts for the conversion of alcohols to the corresponding ketones or aldehydes with high selectivity and yields up to 99% after 2 h of reaction at 110 °C using t-BuOOH as oxidant. Moreover, they have the advantage of being magnetically recoverable catalysts that can be easily recycled in following runs. Full article
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161 KiB  
Editorial
Reforming Catalysts
by Simon Penner
Catalysts 2017, 7(11), 334; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110334 - 09 Nov 2017
Cited by 2 | Viewed by 2749
Abstract
Steam and dry reforming of hydrocarbons (e.g., methane, ethane or propane), alcohols (e.g., methanol, ethanol or glycerol) or bio-compounds is one of the most promising and effective routes to enhanced hydrogen production and for the production of synthesis gas likewise.[...] Full article
(This article belongs to the Special Issue Reforming Catalysts)
3836 KiB  
Article
Catalytic Deoxygenation of Hexadecyl Palmitate as a Model Compound of Euglena Oil in H2 and N2 Atmospheres
by Yanyong Liu, Megumu Inaba and Koichi Matsuoka
Catalysts 2017, 7(11), 333; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110333 - 09 Nov 2017
Cited by 8 | Viewed by 4120
Abstract
Hexadecyl palmitate (C15H31COOC16H33, used as a model compound for Euglena oil) was deoxygenated to hydrocarbons over various solid catalysts in autoclave reactors. In a H2 atmosphere, 1 wt.% of Pd/Mg(Al)O catalyst, derived from a [...] Read more.
Hexadecyl palmitate (C15H31COOC16H33, used as a model compound for Euglena oil) was deoxygenated to hydrocarbons over various solid catalysts in autoclave reactors. In a H2 atmosphere, 1 wt.% of Pd/Mg(Al)O catalyst, derived from a hydrotalcite precursor, yielded a C15H31COOC16H33 conversion close to 100%, and a C10‒C16 (aviation fuel range) hydrocarbon yield of 90.2% for the deoxygenation of C15H31COOC16H33 at 300 °C for 2 h. In a N2 atmosphere, 1 wt.% of Pd/Mg(Al)O catalyst yielded a C10‒C16 hydrocarbon yield of 63.5%, which was much higher than those obtained with Mg(Al)O (15.1%), H-ZSM-5 (8.3%), and 1 wt.% Pd/C (26.2%) for the deoxygenation of C15H31COOC16H33 at 300 °C for 2 h. The Pd metal site and the solid base site in Mg(Al)O had a synergetic effect on the deoxygenation of C15H31COOC16H33 in N2 atmosphere over the Pd/Mg(Al)O catalyst. By prolonging the reaction time to 5 h for reaction at 300 °C in N2 atmosphere, the yield of C10‒C16 hydrocarbons increased to 80.4% with a C15H31COOC16H33 conversion of 99.1% over the 1 wt.% Pd/Mg(Al)O catalyst. Full article
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6321 KiB  
Article
Development of an Efficient Methanol Production Process for Direct CO2 Hydrogenation over a Cu/ZnO/Al2O3 Catalyst
by Fereshteh Samimi, Mohammad Reza Rahimpour and Ali Shariati
Catalysts 2017, 7(11), 332; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110332 - 08 Nov 2017
Cited by 45 | Viewed by 13919
Abstract
Carbon capture and utilization as a raw material for methanol production are options for addressing energy problems and global warming. However, the commercial methanol synthesis catalyst offers a poor efficiency in CO2 feedstock because of a low conversion of CO2 and [...] Read more.
Carbon capture and utilization as a raw material for methanol production are options for addressing energy problems and global warming. However, the commercial methanol synthesis catalyst offers a poor efficiency in CO2 feedstock because of a low conversion of CO2 and its deactivation resulting from high water production during the process. To overcome these barriers, an efficient process consisting of three stage heat exchanger reactors was proposed for CO2 hydrogenation. The catalyst volume in the conventional methanol reactor (CR) is divided into three sections to load reactors. The product stream of each reactor is conveyed to a flash drum to remove methanol and water from the unreacted gases (H2, CO and CO2). Then, the gaseous stream enters the top of the next reactor as the inlet feed. This novel configuration increases CO2 conversion almost twice compared to one stage reactor. Also to reduce water production, a water permselective membrane was assisted in each reactor to remove water from the reaction side. The proposed process was compared with one stage reactor and CR from coal and natural gas. Methanol is produced 288, 305, 586 and 569 ton/day in CR, one-stage, three-stage and three-stage membrane reactors (MR), respectively. Although methanol production rate in three-stage MR is a bit lower than three stage reactors, the produced water, as the cause of catalyst poisoning, is notably reduced in this configuration. Results show that the proposed process is a strongly feasible way to produce methanol that can competitive with a traditional synthesis process. Full article
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3198 KiB  
Article
Novel Ni-Ce-Zr/Al2O3 Cellular Structure for the Oxidative Dehydrogenation of Ethane
by Juan Pablo Bortolozzi, Raquel Portela, Pedro Ávila, Viviana Milt and Eduardo Miró
Catalysts 2017, 7(11), 331; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110331 - 08 Nov 2017
Cited by 7 | Viewed by 5057
Abstract
A novel γ-alumina-supported Ni-Ce-Zr catalyst with cellular structure was developed for oxidative dehydrogenation of ethane (ODHE). First, powdered samples were synthesized to study the effect of both the total metal content and the Ce/Zr ratio on the physicochemical properties and performance of these [...] Read more.
A novel γ-alumina-supported Ni-Ce-Zr catalyst with cellular structure was developed for oxidative dehydrogenation of ethane (ODHE). First, powdered samples were synthesized to study the effect of both the total metal content and the Ce/Zr ratio on the physicochemical properties and performance of these catalysts. All synthesized powdered samples were highly active and selective for ODHE with a maximum ethylene productivity of 6.94 µmolethylene gact cat−1 s−1. According to the results, cerium addition increased the most reducible nickel species population, which would benefit ethane conversion, whereas zirconium incorporation would enhance ethylene selectivity through the generation of higher amounts of the least reducible nickel species. Therefore, the modification of active site properties by addition of both promoters synergistically increases the productivity of the Ni-based catalysts. The most efficient formulation, in terms of ethylene productivity per active phase amount, contained 15 wt% of the mixed oxide with Ni0.85Ce0.075Zr0.075 composition. This formulation was selected to synthesize a Ni-Ce-Zr/Al2O3 structured body by deposition of the active phase onto a homemade γ-alumina monolith. The structured support was manufactured by extrusion of boehmite-containing dough. The main properties of the Ni0.85Ce0.075Zr0.075 powder were successfully preserved after the shaping procedure. In addition, the catalytic performance of the monolithic sample was comparable in terms of ethylene productivity to that of the powdered counterpart. Full article
(This article belongs to the Special Issue Structured and Micro-Structured Catalysts and Reactors)
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6448 KiB  
Article
A Non-Precious Metal Promoting the Synthesis of 5-Hydroxymethylfurfural
by Xinyuan Lu, Hongjie Zhao, Wei Feng and Peijun Ji
Catalysts 2017, 7(11), 330; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110330 - 06 Nov 2017
Cited by 5 | Viewed by 3625
Abstract
In this work, a new kind of catalyst was prepared for synthesis of 5-hydroxymethylfurfural. Copper ions were incorporated into manganese oxide octahedral molecular sieves (K-OMS-2). The catalysts Cu-K-OMS-2 were characterized by measuring FTIR spectra, scanning electron microscope images, X-ray diffraction patterns, and temperature-programmed [...] Read more.
In this work, a new kind of catalyst was prepared for synthesis of 5-hydroxymethylfurfural. Copper ions were incorporated into manganese oxide octahedral molecular sieves (K-OMS-2). The catalysts Cu-K-OMS-2 were characterized by measuring FTIR spectra, scanning electron microscope images, X-ray diffraction patterns, and temperature-programmed desorption (TPD) and temperature-programmed reduction (TPR) profiles. Thermogravimetric analysis (TGA) demonstrated that the stability of Cu-K-OMS-2 is almost the same as that of K-OMS-2. XRD patterns showed that introducing copper ions did not change the structure of K-OMS-2, but copper ions had an effect on the morphology of K-OMS-2 as illustrated by SEM images. TPD profiles demonstrated that both K-OMS-2 and Cu-K-OMS-2 possess basic and acidic sites, and Cu-K-OMS-2 has weak acidic sites. One-pot synthesis of 2,5-diformylfuran (DFF) from fructose was investigated under the catalysis of Cu-K-OMS-2 together with a commercial catalyst Amberlyst 15. The effect of reaction time and temperature on the DFF yield was investigated, and reaction temperature had an effect on the DFF yield. The effect of atomic ratio of Cu to Mn of Cu-K-OMS-2 on the DFF yield was also investigated. The DFF yield was improved 34.7% by Cu-K-OMS-2 in comparison to K-OMS-2, indicating the promotion effect of copper on the DFF yield. Consecutive use of Cu-K-OMS-2 demonstrated that after 6 cycles, the loss of DFF yield was 6.3%, indicating a good reusability of Cu-K-OMS-2. Full article
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3543 KiB  
Article
Synergetic Effect of Ni2P/SiO2 and γ-Al2O3 Physical Mixture in Hydrodeoxygenation of Methyl Palmitate
by Ivan V. Shamanaev, Irina V. Deliy, Evgeny Yu. Gerasimov, Vera P. Pakharukova, Evgeny G. Kodenev, Pavel V. Aleksandrov and Galina A. Bukhtiyarova
Catalysts 2017, 7(11), 329; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110329 - 06 Nov 2017
Cited by 24 | Viewed by 6072
Abstract
The Ni2P/SiO2 catalyst, which was prepared by in situ temperature-programmed reduction and in the mixture with the inert (SiC, SiO2) or acidic (γ-Al2O3) material was studied in methyl palmitate hydrodeoxygenation (HDO). Methyl palmitate HDO [...] Read more.
The Ni2P/SiO2 catalyst, which was prepared by in situ temperature-programmed reduction and in the mixture with the inert (SiC, SiO2) or acidic (γ-Al2O3) material was studied in methyl palmitate hydrodeoxygenation (HDO). Methyl palmitate HDO was carried out at temperatures of 270–330 °C, H2/feed volume ratio of 600 Nm3/m3, and H2 pressure of 3.0 MPa. Ni2P/SiO2 catalyst, diluted with γ-Al2O3 showed a higher activity than Ni2P/SiO2 catalyst diluted with SiC or SiO2. The conversion of methyl palmitate increased significantly in the presence of γ-Al2O3 most probably due to the acceleration of the acid-catalyzed reaction of ester hydrolysis. The synergism of Ni2P/SiO2 and γ-Al2O3 in methyl palmitate HDO can be explained by the cooperation of the metal sites of Ni2P/SiO2 and the acid sites of γ-Al2O3 in consecutive metal-catalyzed and acid-catalyzed reactions of HDO. The obtained results let us conclude that the balancing of metal and acid sites plays an important role in the development of the efficient catalyst for the HDO of fatty acid esters over supported phosphide catalysts. Full article
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6436 KiB  
Review
Metal-Catalyzed Intra- and Intermolecular Addition of Carboxylic Acids to Alkynes in Aqueous Media: A Review
by Javier Francos and Victorio Cadierno
Catalysts 2017, 7(11), 328; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110328 - 06 Nov 2017
Cited by 31 | Viewed by 6172
Abstract
The metal-catalyzed addition of carboxylic acids to alkynes is a very effective tool for the synthesis of carboxylate-functionalized olefinic compounds in an atom-economical manner. Thus, a large variety of synthetically useful lactones and enol-esters can be accessed through the intra- or intermolecular versions [...] Read more.
The metal-catalyzed addition of carboxylic acids to alkynes is a very effective tool for the synthesis of carboxylate-functionalized olefinic compounds in an atom-economical manner. Thus, a large variety of synthetically useful lactones and enol-esters can be accessed through the intra- or intermolecular versions of this process. In order to reduce the environmental impact of these reactions, considerable efforts have been devoted in recent years to the development of catalytic systems able to operate in aqueous media, which represent a real challenge taking into account the tendency of alkynes to undergo hydration in the presence of transition metals. Despite this, different Pd, Pt, Au, Cu and Ru catalysts capable of promoting the intra- and intermolecular addition of carboxylic acids to alkynes in a selective manner in aqueous environments have appeared in the literature. In this review article, an overview of this chemistry is provided. The synthesis of β-oxo esters by catalytic addition of carboxylic acids to terminal propargylic alcohols in water is also discussed. Full article
(This article belongs to the Special Issue Homogeneous Catalysis and Mechanisms in Water and Biphasic Media)
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3181 KiB  
Communication
In-Situ Self-Assembly of Zinc/Adenine Hybrid Nanomaterials for Enzyme Immobilization
by Hao Liang, Shanshan Sun, Yan Zhou and Yanhui Liu
Catalysts 2017, 7(11), 327; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110327 - 03 Nov 2017
Cited by 17 | Viewed by 6234
Abstract
In this study, a one-step and facile immobilization of enzymes by self-assembly of zinc ions and adenine in aqueous solution with mild conditions was reported. Enzymes, such as glucose oxidase (GOx) and horseradish peroxidase (HRP), could be efficiently encapsulated in Zn/adenine coordination polymers [...] Read more.
In this study, a one-step and facile immobilization of enzymes by self-assembly of zinc ions and adenine in aqueous solution with mild conditions was reported. Enzymes, such as glucose oxidase (GOx) and horseradish peroxidase (HRP), could be efficiently encapsulated in Zn/adenine coordination polymers (CPs) with high loading capacity over 90%. When the enzyme was immobilized by CPs, it displayed high catalytic efficiency, high selectivity and enhanced stability due to the protecting effect of the rigid framework. As a result, the relative activity of Zn/adenine nano-CP-immobilized GOx increased by 1.5-fold at pH 3 and 4-fold at 70 to 90 °C, compared to free GOx. The immobilized GOx had excellent reusability (more than 90% relative activity after being reused eight times). Furthermore, the use of this system as a glucose biosensor was also demonstrated by co-immobilization of two enzymes, detecting glucose down to 1.84 µM with excellent selectivity. The above work indicated that in-situ self-assembly of Zn/adenine CPs could be a simple and efficient method for biocatalyst immobilization. Full article
(This article belongs to the Special Issue Immobilized Biocatalysts)
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2742 KiB  
Article
Synthesis of Phase Pure Hexagonal YFeO3 Perovskite as Efficient Visible Light Active Photocatalyst
by Mohammed Ismael, Engy Elhaddad, Dereje H. Taffa and Michael Wark
Catalysts 2017, 7(11), 326; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110326 - 03 Nov 2017
Cited by 55 | Viewed by 7937
Abstract
Hexagonal perovskite YFeO3 was synthesized by a complex-assisted sol-gel technique allowing crystallization at calcination temperatures below 700 °C. As determined by diffuse reflectance spectroscopy (DRS) and Tauc plots, the hexagonal YFeO3 exhibits a lower optical band gap (1.81 eV) than the [...] Read more.
Hexagonal perovskite YFeO3 was synthesized by a complex-assisted sol-gel technique allowing crystallization at calcination temperatures below 700 °C. As determined by diffuse reflectance spectroscopy (DRS) and Tauc plots, the hexagonal YFeO3 exhibits a lower optical band gap (1.81 eV) than the orthorhombic structure (about 2.1 eV or even higher) being typically obtained at elevated temperatures (>700 °C), and thus enables higher visible light photocatalysis activity. Structure and morphology of the synthesized YFeO3 perovskites were analyzed by powder X-ray diffraction (XRD) and nitrogen adsorption, proving that significantly smaller crystallite sizes and higher surface areas are obtained for YFeO3 with a hexagonal phase. The photocatalytic activity of the different YFeO3 phases was deduced via the degradation of the model pollutants methyl orange and 4-chlorophenol. Experiments under illumination with light of different wavelengths, in the presence of different trapping elements, as well as photoelectrochemical tests allow conclusions regarding band positions of YFeO3 and the photocatalytic degradation mechanism. X-ray photoelectron spectroscopy indicates that a very thin layer of Y2O3 might support the photocatalysis by improving the separation of photogenerated charge carriers. Full article
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4450 KiB  
Article
Consideration of the Role of Plasma in a Plasma-Coupled Selective Catalytic Reduction of Nitrogen Oxides with a Hydrocarbon Reducing Agent
by Byeong Ju Lee, Ho-Chul Kang, Jin Oh Jo and Young Sun Mok
Catalysts 2017, 7(11), 325; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110325 - 31 Oct 2017
Cited by 12 | Viewed by 4832
Abstract
The purpose of this study is to explain how plasma improves the performance of selective catalytic reduction (SCR) of nitrogen oxides (NOx) with a hydrocarbon reducing agent. In the plasma-coupled SCR process, NOx reduction was performed with n-heptane as a [...] Read more.
The purpose of this study is to explain how plasma improves the performance of selective catalytic reduction (SCR) of nitrogen oxides (NOx) with a hydrocarbon reducing agent. In the plasma-coupled SCR process, NOx reduction was performed with n-heptane as a reducing agent over Ag/γ-Al2O3 as a catalyst. We found that the plasma decomposes n-heptane into several oxygen-containing products such as acetaldehyde, propionaldehyde and butyraldehyde, which are more reactive than the parent molecule n-heptane in the SCR process. Separate sets of experiments using acetaldehyde, propionaldehyde and butyraldehyde, one by one, as a reductant in the absence of plasma, have clearly shown that the presence of these partially oxidized compounds greatly enhanced the NOx conversion. The higher the discharge voltage, the more the amounts of such partially oxidized products. The oxidative species produced by the plasma easily converted NO into NO2, but the increase of the NO2 fraction was found to decrease the NOx conversion. Consequently, it can be concluded that the main role of plasma in the SCR process is to produce partially oxidized compounds (aldehydes), having better reducing power. The catalyst-alone NOx removal efficiency with n-heptane at 250 °C was measured to be less than 8%, but it increased to 99% in the presence of acetaldehyde at the same temperature. The NOx removal efficiency with the aldehyde reducing agent was higher as the number of carbons in the aldehyde was more; for example, the NOx removal efficiencies at 200 °C with butyraldehyde, propionaldehyde and acetaldehyde were measured to be 83.5%, 58.0% and 61.5%, respectively, which were far above the value (3%) obtained with n-heptane. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction of NOx)
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4035 KiB  
Article
Hydrogen Production via Water Dissociation Using Pt–TiO2 Photocatalysts: An Oxidation–Reduction Network
by J. F. Guayaquil-Sosa, Alan Calzada, Benito Serrano, Salvador Escobedo and Hugo De Lasa
Catalysts 2017, 7(11), 324; https://0-doi-org.brum.beds.ac.uk/10.3390/catal7110324 - 30 Oct 2017
Cited by 26 | Viewed by 8410
Abstract
Several TiO2 based semiconductors with different Pt loadings are prepared using incipient impregnation, wet impregnation and the sol-gel method. These photocatalysts are evaluated in the Photo-CREC-Water II Photoreactor for hydrogen production via water dissociation, using an organic renewable scavenger (ethanol). Results obtained [...] Read more.
Several TiO2 based semiconductors with different Pt loadings are prepared using incipient impregnation, wet impregnation and the sol-gel method. These photocatalysts are evaluated in the Photo-CREC-Water II Photoreactor for hydrogen production via water dissociation, using an organic renewable scavenger (ethanol). Results obtained show the influence of the photocatalyst preparation in the production of hydrogen and in the observed quantum yields. Furthermore, it is established that the reaction networks leading to hydrogen production, using various photocatalysts, share common features. This analysis is developed by both identifying and quantifying different chemical species and their changes with irradiation time. Key species in this oxidation–reduction network are hydrogen, hydrogen peroxide, ethanol, methane, ethane, acetaldehyde and carbon dioxide. On this basis, it is shown that under an inert gas atmosphere, ethanol consumption is sub-stoichiometric. This points towards simultaneous ethanol consumption and the formation of the ethanol scavenger. Full article
(This article belongs to the Special Issue Photocatalytic Water Splitting)
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