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Catalysts, Volume 8, Issue 7 (July 2018)

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Cover Story (view full-size image) The temperature for the catalytic combustion of benzene decreases by using bimetallic Pd–Au [...] Read more.
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Open AccessFeature PaperArticle Molecular Rh(III) and Ir(III) Catalysts Immobilized on Bipyridine-Based Covalent Triazine Frameworks for the Hydrogenation of CO2 to Formate
Catalysts 2018, 8(7), 295; https://doi.org/10.3390/catal8070295
Received: 22 June 2018 / Revised: 20 July 2018 / Accepted: 20 July 2018 / Published: 22 July 2018
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Abstract
The catalytic reactivity of molecular Rh(III)/Ir(III) catalysts immobilized on two- and three-dimensional Bipyridine-based Covalent Triazine Frameworks (bpy-CTF) for the hydrogenation of CO2 to formate has been described. The heterogenized Ir complex demonstrated superior catalytic efficiency over its Rh counterpart. The Ir catalyst
[...] Read more.
The catalytic reactivity of molecular Rh(III)/Ir(III) catalysts immobilized on two- and three-dimensional Bipyridine-based Covalent Triazine Frameworks (bpy-CTF) for the hydrogenation of CO2 to formate has been described. The heterogenized Ir complex demonstrated superior catalytic efficiency over its Rh counterpart. The Ir catalyst immobilized on two-dimensional bpy-CTF showed an improved turnover frequency and turnover number compared to its three-dimensional counterpart. The two-dimensional Ir catalyst produced a maximum formate concentration of 1.8 M and maintained its catalytic efficiency over five consecutive runs with an average of 92% in each cycle. The reduced activity after recycling was studied by density functional theory calculations, and a plausible leaching pathway along with a rational catalyst design guidance have been proposed. Full article
(This article belongs to the Special Issue Catalysis and Catalytic Processes for CO2 Conversion)
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Open AccessArticle Influence of Transition Metal on the Hydrogen Evolution Reaction over Nano-Molybdenum-Carbide Catalyst
Catalysts 2018, 8(7), 294; https://doi.org/10.3390/catal8070294
Received: 29 June 2018 / Revised: 18 July 2018 / Accepted: 20 July 2018 / Published: 22 July 2018
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Abstract
The highly efficient electrochemical hydrogen evolution reaction (HER) provides a promising way to solve energy and environment problems. In this work, various transition metals (Fe, Co, Ni, Cu, Ag, and Pt) were selected to support on molybdenum carbides by a simple organic-inorganic precursor
[...] Read more.
The highly efficient electrochemical hydrogen evolution reaction (HER) provides a promising way to solve energy and environment problems. In this work, various transition metals (Fe, Co, Ni, Cu, Ag, and Pt) were selected to support on molybdenum carbides by a simple organic-inorganic precursor carburization process. X-ray diffraction (XRD) analysis results indicated that the β-Mo2C phase was formed in all metal-doped samples. X-ray photoelectron spectroscopy analysis indicated that the binding energy of Mo2+ species (Mo2C) shifted to a lower value after metal was doped on the molybdenum carbide surface. Comparing with pure β-Mo2C, the electrocatalytic activity for HER was improved by transition metal doping on the surface. Remarkably, the catalytic activity improvement was more obvious when Pt was doped on molybdenum carbide (2% Pt-Mo2C). The 2% Pt-Mo2C required a η10 of 79 mV, and outperformed that of pure β-Mo2C (η10 = 410 mV) and other transition metal doped molybdenum carbides, with a small Tafel slope (55 mV/dec) and a low onset overpotential (32 mV) in 0.5 M H2SO4. Also, the 2% Pt-Mo2C catalyst demonstrated a high stability for the HER in 0.5 M H2SO4. This work highlights a feasible strategy to explore efficient electrocatalysts with low cost via engineering on the composition and nanostructure. Full article
(This article belongs to the Special Issue Catalysts for Oxygen Reduction Reaction)
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Open AccessArticle Clarification of Active Sites at Interfaces between Silica Support and Nickel Active Components for Carbon Monoxide Methanation
Catalysts 2018, 8(7), 293; https://doi.org/10.3390/catal8070293
Received: 13 June 2018 / Revised: 15 July 2018 / Accepted: 16 July 2018 / Published: 20 July 2018
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Abstract
Identification of active site is critical for developing advanced heterogeneous catalysis. Here, a nickel/silica (Ni/SiO2) catalyst was prepared through an ammonia-evaporation method for CO methanation. The as-obtained Ni/SiO2 catalyst shows a CO conversion of 96.74% and a methane selectivity of
[...] Read more.
Identification of active site is critical for developing advanced heterogeneous catalysis. Here, a nickel/silica (Ni/SiO2) catalyst was prepared through an ammonia-evaporation method for CO methanation. The as-obtained Ni/SiO2 catalyst shows a CO conversion of 96.74% and a methane selectivity of 93.58% at 623 K with a weight hourly space velocity of 25,000 mL·g−1·h−1. After 150 h of continuous testing, the CO conversion still retains 96%, which indicates a high catalyst stability and long life. An in situ vacuum transmission infrared spectrum demonstrates that the main active sites locate at the interface between the metal Ni and the SiO2 at a wave number at 2060 cm−1 for the first time. The interesting discovery of the active site may offer a new insight for design and synthesis of methanation catalysts. Full article
(This article belongs to the Special Issue Active Sites in Catalytic Reaction)
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Open AccessArticle A Characterization Study of Reactive Sites in ALD-Synthesized WOx/ZrO2 Catalysts
Catalysts 2018, 8(7), 292; https://doi.org/10.3390/catal8070292
Received: 20 June 2018 / Revised: 11 July 2018 / Accepted: 17 July 2018 / Published: 19 July 2018
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Abstract
A series of ZrO2-supported WOx catalysts were prepared using atomic layer deposition (ALD) with W(CO)6, and were then compared to a WOx/ZrO2 catalyst prepared via conventional impregnation. The types of sites present in these samples
[...] Read more.
A series of ZrO2-supported WOx catalysts were prepared using atomic layer deposition (ALD) with W(CO)6, and were then compared to a WOx/ZrO2 catalyst prepared via conventional impregnation. The types of sites present in these samples were characterized using temperature-programmed desorption/thermogravimetric analysis (TPD-TGA) measurements with 2-propanol and 2-propanamine. Weight changes showed that the WOx catalysts grew at a rate of 8.8 × 1017 W atoms/m2 per cycle. Scanning transmission electron microscopy/energy-dispersive spectroscopy (STEM-EDS) indicated that WOx was deposited uniformly, as did the 2-propanol TPD-TGA results, which showed that ZrO2 was completely covered after five ALD cycles. Furthermore, 2-propanamine TPD-TGA demonstrated the presence of three types of catalytic sites, the concentrations of which changed with the number of ALD cycles: dehydrogenation sites associated with ZrO2, Brønsted-acid sites associated with monolayer WOx clusters, and oxidation sites associated with higher WOx coverages. The Brønsted sites were not formed via ALD of WOx on SiO2. The reaction rates for 2-propanol dehydration were correlated with the concentration of Brønsted sites. While TPD-TGA of 2-propanamine did not differentiate the strength of Brønsted-acid sites, H–D exchange between D2O and either toluene or chlorobenzene indicated that the Brønsted sites in tungstated zirconia were much weaker than those in H-ZSM-5 zeolites. Full article
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Open AccessArticle FeCrAlloy Monoliths Coated with Ni/Al2O3 Applied to the Low-Temperature Production of Ethylene
Catalysts 2018, 8(7), 291; https://doi.org/10.3390/catal8070291
Received: 24 May 2018 / Revised: 28 June 2018 / Accepted: 4 July 2018 / Published: 19 July 2018
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Abstract
This paper investigates the oxidative dehydrogenation of ethane to produce ethylene at low temperatures (500 °C) in metallic structured substrates. To check this point, the FeCrAlloy® monoliths with different channel sizes (289–2360 cpsi) were prepared. The monoliths were coated with a Ni/Al
[...] Read more.
This paper investigates the oxidative dehydrogenation of ethane to produce ethylene at low temperatures (500 °C) in metallic structured substrates. To check this point, the FeCrAlloy® monoliths with different channel sizes (289–2360 cpsi) were prepared. The monoliths were coated with a Ni/Al2O3 catalyst (by washcoating of alumina and the latter nickel impregnation) and characterized by Scanning Electron Microscopy and Energy-Dispersive X-ray analysis (SEM-EDX), Temperature-Programmed Reduction (TPR), X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). The catalytic results showed that all monoliths coated with ~300 mg of catalyst presented similar ethane conversion (15%) at 450 °C. However, the lowest selectivity to ethylene was found for the monolith with the lower channel size and the higher geometric surface area, where a heterogeneous catalyst layer with Ni enriched islands was generated. Therefore, it can be said that the selectivity to ethylene is linked to the distribution of Ni species on the support (alumina). Nevertheless, in all cases the selectivity was high (above 70%). On the other hand, the stability in reaction tests of one of the coated monoliths was done. This structured catalyst proved to be more stable under reaction conditions than the powder catalyst, with an initial slight drop in the first 8 h but after that, constant activity for the 152 h left. Full article
(This article belongs to the Special Issue Structured and Micro-Structured Catalysts and Reactors)
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Open AccessArticle Enantioselective Bioreduction of Prochiral Pyrimidine Base Derivatives by Boni Protect Fungicide Containing Live Cells of Aureobasidium pullulans
Catalysts 2018, 8(7), 290; https://doi.org/10.3390/catal8070290
Received: 22 June 2018 / Revised: 11 July 2018 / Accepted: 16 July 2018 / Published: 18 July 2018
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Abstract
The enzymatic enantioselective bioreduction of prochiral 1-substituted-5-methyl-3-(2-oxo-2-phenylethyl)pyrimidine-2,4(1H,3H)-diones to corresponding chiral alcohols by Boni Protect fungicide containing live cells of Aureobasidium pullulans was studied. The microbe-catalyzed reduction of bulky-bulky ketones provides enantiomerically pure products (96–99% ee). In the presence of
[...] Read more.
The enzymatic enantioselective bioreduction of prochiral 1-substituted-5-methyl-3-(2-oxo-2-phenylethyl)pyrimidine-2,4(1H,3H)-diones to corresponding chiral alcohols by Boni Protect fungicide containing live cells of Aureobasidium pullulans was studied. The microbe-catalyzed reduction of bulky-bulky ketones provides enantiomerically pure products (96–99% ee). In the presence of A. pullulans (Aureobasidium pullulans), one of the enantiotopic hydrides of the dihydropyridine ring coenzyme is selectively transferred to the si sides of the prochiral carbonyl group to give secondary alcohols with R configuration. The reactions were performed under various conditions in order to optimize the procedure with respect to time, solvent, and temperature. The present methodology demonstrates an alternative green way for the synthesis of chiral alcohols in a simple, economical, and eco-friendly biotransformation. Full article
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Open AccessArticle Optimization and in Silico Analysis of a Cold-Adapted Lipase from an Antarctic Pseudomonas sp. Strain AMS8 Reaction in Triton X-100 Reverse Micelles
Catalysts 2018, 8(7), 289; https://doi.org/10.3390/catal8070289
Received: 1 June 2018 / Revised: 7 July 2018 / Accepted: 11 July 2018 / Published: 18 July 2018
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Abstract
A moderate yield of a purified enzyme can be achieved by using the simple technique of reverse micellar extraction (RME). RME is a liquid–liquid extraction method that uses a surfactant and an organic solvent to extract biomolecules. Instead of traditional chromatographic purification methods,
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A moderate yield of a purified enzyme can be achieved by using the simple technique of reverse micellar extraction (RME). RME is a liquid–liquid extraction method that uses a surfactant and an organic solvent to extract biomolecules. Instead of traditional chromatographic purification methods, which are tedious and expensive, RME using the nonionic surfactant Triton X-100 and toluene is used as an alternative purification technique to purify a recombinant cold-adapted lipase, AMS8. Various process parameters were optimized to maximize the activity recovery of the AMS8 lipase. The optimal conditions were found to be 50 mM sodium phosphate buffer, pH 7, 0.125 M NaCl, and 0.07 M Triton X-100 in toluene at 10 °C. Approximately 56% of the lipase activity was successfully recovered. Structural analysis of the lipase in a reverse micelle (RM) was performed using an in silico approach. The predicted model of AMS8 lipase was simulated in the Triton X-100/toluene reverse micelles from 5 to 40 °C. The lid 2 was slightly opened at 10 °C. However, the secondary structure of AMS8 was most affected in the non-catalytic domain compared to the catalytic domain, with an increased coil conformation. These results suggest that an AMS8 lipase can be extracted using Triton X-100/water/toluene micelles at low temperature. This RME approach will be an important tool for the downstream processing of recombinant cold-adapted lipases. Full article
(This article belongs to the Special Issue Reactions in Water and in Micelles)
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Open AccessArticle Air Regeneration of Ethanol-Laden Pellet NaY-SiO2 and Pt/NaY-SiO2: Effects of Air Flow Rate on Pt Morphology and Regeneration Efficiency
Catalysts 2018, 8(7), 288; https://doi.org/10.3390/catal8070288
Received: 19 June 2018 / Revised: 10 July 2018 / Accepted: 12 July 2018 / Published: 17 July 2018
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Abstract
Regeneration process and adsorbent performance were investigated by a fixed-bed adsorber at 300 °C. Surface species, zeolite structure, and Pt morphology were characterized by FT-IR, XRPD and EXAFS, respectively. Performance test results indicated that ethanol adsorption capacity of Pt/NaY-SiO2 is about 2.5
[...] Read more.
Regeneration process and adsorbent performance were investigated by a fixed-bed adsorber at 300 °C. Surface species, zeolite structure, and Pt morphology were characterized by FT-IR, XRPD and EXAFS, respectively. Performance test results indicated that ethanol adsorption capacity of Pt/NaY-SiO2 is about 2.5 times that of NaY-SiO2. After regeneration, adsorption-capacity loss is 2.5 and 43%, respectively, for Pt/NaY-SiO2 regenerated at superficial velocity of 13.2 (PtR(HF)) and 5.3 cm/min (PtR(LF)); in contrast, it is 8 and 21%, respectively, for NaYR(HF) and NaYR(LF). The appearance of absorption bands in the CH stretching region (υCH) of the IR spectra characterizing the regenerated NaY-SiO2 suggested that the adsorption-capacity loss for NaY-SiO2 was mainly caused by the deposition of carbonaceous species formed in regeneration, which cannot be burned off readily at 300 °C. In contrast, no υCH bands have been observed for the IR spectra of PtR(HF) and PtR(LF), indicating that Pt helps to burn off carbonaceous species. However, Pt agglomeration was observed in TEM and EXAFS for Pt/NaY-SiO2(LF). The appearance of a υCO band at about 2085 cm−1 of the IR spectra characterizing PtR(LF) suggested that Pt agglomeration was induced by CO adsorption. The growth of Pt particles decreases the ethanol adsorbed on Pt together with the conversion of ethanol to ethoxides and aldehyde, leading to a decrease of adsorption capacity. Full article
(This article belongs to the Special Issue Catalysts for Oxidative Destruction of Volatile Organic Compounds)
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Open AccessArticle Immobilization of Prunus amygdalus Hydroxynitrile Lyase on Celite
Catalysts 2018, 8(7), 287; https://doi.org/10.3390/catal8070287
Received: 29 June 2018 / Revised: 12 July 2018 / Accepted: 13 July 2018 / Published: 17 July 2018
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Abstract
The hydroxynitrile lyase from Prunus amygdalus was immobilized on Celite R-633. The immobilized enzyme could successfully be utilized in buffer saturated MTBE and excellent conversions of benzaldehyde to R-mandelonitrile were observed. No leaching occurred. To achieve high enantioselectivities, the suppression of the
[...] Read more.
The hydroxynitrile lyase from Prunus amygdalus was immobilized on Celite R-633. The immobilized enzyme could successfully be utilized in buffer saturated MTBE and excellent conversions of benzaldehyde to R-mandelonitrile were observed. No leaching occurred. To achieve high enantioselectivities, the suppression of the undesired background reaction was essential. This could be achieved by high enzyme loadings and the tight packing of the immobilized enzymes. When the immobilized enzyme is loosely packed, both the enzyme catalysis and the background reaction accelerates and only a modest enantioselectivity is observed. The enzyme was recycled for up to ten times, with some loss of activity and also enantioselectivity after 5 cycles, independent of packing. Full article
(This article belongs to the Special Issue Immobilized Biocatalysts)
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Open AccessArticle An Improved Method to Encapsulate Laccase from Trametes versicolor with Enhanced Stability and Catalytic Activity
Catalysts 2018, 8(7), 286; https://doi.org/10.3390/catal8070286
Received: 14 June 2018 / Revised: 5 July 2018 / Accepted: 12 July 2018 / Published: 17 July 2018
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Abstract
In this work, laccase from Trametes versicolor pretreated with copper ion solution was entrapped in copper alginate beads. The presence of laccase in copper alginate beads was verified by Fourier transform infrared (FTIR) spectroscopy. The alginate concentration used was optimized based on the
[...] Read more.
In this work, laccase from Trametes versicolor pretreated with copper ion solution was entrapped in copper alginate beads. The presence of laccase in copper alginate beads was verified by Fourier transform infrared (FTIR) spectroscopy. The alginate concentration used was optimized based on the specific activity and immobilization yield. After entrapment, laccase presents perfect pH stability and thermal stability with 2,2′-azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) as the substrate. Moreover, laccase in copper alginate beads exhibits good reusability during continuous batch operation for removing 2,4-dichlorophenol. More importantly, owing to the coupled effect of copper ion activation and copper alginate entrapment, the entrapped laccase shows a 3.0-fold and a 2.4-fold increase in specific activity and 2,4-DCP degradation rate compared with that of free laccase, respectively. Full article
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Open AccessFeature PaperReview Ag/CeO2 Composites for Catalytic Abatement of CO, Soot and VOCs
Catalysts 2018, 8(7), 285; https://doi.org/10.3390/catal8070285
Received: 23 June 2018 / Revised: 10 July 2018 / Accepted: 11 July 2018 / Published: 16 July 2018
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Abstract
Nowadays catalytic technologies are widely used to purify indoor and outdoor air from harmful compounds. Recently, Ag–CeO2 composites have found various applications in catalysis due to distinctive physical-chemical properties and relatively low costs as compared to those based on other noble metals.
[...] Read more.
Nowadays catalytic technologies are widely used to purify indoor and outdoor air from harmful compounds. Recently, Ag–CeO2 composites have found various applications in catalysis due to distinctive physical-chemical properties and relatively low costs as compared to those based on other noble metals. Currently, metal–support interaction is considered the key factor that determines high catalytic performance of silver–ceria composites. Despite thorough investigations, several questions remain debating. Among such issues, there are (1) morphology and size effects of both Ag and CeO2 particles, including their defective structure, (2) chemical and charge state of silver, (3) charge transfer between silver and ceria, (4) role of oxygen vacancies, (5) reducibility of support and the catalyst on the basis thereof. In this review, we consider recent advances and trends on the role of silver–ceria interactions in catalytic performance of Ag/CeO2 composites in low-temperature CO oxidation, soot oxidation, and volatile organic compounds (VOCs) abatement. Promising photo- and electrocatalytic applications of Ag/CeO2 composites are also discussed. Full article
(This article belongs to the Special Issue New Concepts in Oxidation Processes)
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Open AccessArticle Photocatalytic Membrane Reactor (PMR) for Virus Removal in Drinking Water: Effect of Humic Acid
Catalysts 2018, 8(7), 284; https://doi.org/10.3390/catal8070284
Received: 13 June 2018 / Revised: 2 July 2018 / Accepted: 10 July 2018 / Published: 16 July 2018
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Abstract
In the actual water environment, the health risk of waterborne viruses is evaluated to be 101–104 times higher at a similar level of exposure compared with bacteria and has aroused strong concern in many countries in the world. Photocatalytic membrane
[...] Read more.
In the actual water environment, the health risk of waterborne viruses is evaluated to be 101–104 times higher at a similar level of exposure compared with bacteria and has aroused strong concern in many countries in the world. Photocatalytic membrane reactor (PMR), a new process for virus inactivation in water, has gradually become one of the main tools to inactivate pathogenic organisms in water. However, there is relatively little attention to the effect of natural organic matters (NOMs) on the PMR system, which actually exists in the water environment. In this paper, the TiO2-P25, a common type in sales and marketing, was selected as the photocatalyst, and humic acid was regarded as the representative substance of NOMs for investigating thoroughly the influence of humic acid on virus removal by the PMR system. It was found that competitive adsorption between the virus and humic acid occurred, which markedly reduced the amount of virus adsorbed on the surface of the photocatalyst. Moreover, with humic acid, the direct contact behavior between the virus and the photocatalyst was blocked to some extent, and the disinfection of phage f2 by the active free radicals produced by photocatalysis was furthermore badly affected. Meanwhile, the special structure of humic acid, which made humic acid be able to absorb light of 270–500 nm, led to the reduction of photocatalytic efficiency. Further experiments showed that when there was a certain concentration of humic acid in water, intermittent operation mode or higher membrane flux (>40 L/(m2·h)) was selected to partly alleviate the adverse effects of humic acid. Full article
(This article belongs to the Special Issue Photocatalytic Membrane Reactors)
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Open AccessArticle Effect of Y Modified Ceria Support in Mono and Bimetallic Pd–Au Catalysts for Complete Benzene Oxidation
Catalysts 2018, 8(7), 283; https://doi.org/10.3390/catal8070283
Received: 21 June 2018 / Revised: 10 July 2018 / Accepted: 11 July 2018 / Published: 16 July 2018
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Abstract
Mono metallic and bimetallic Pd (1 wt. %)–Au (3 wt. %) catalysts were prepared using two ceria supports doped with 1 wt. % Y2O3. Yttrium was added by impregnation or co-precipitation. The catalyst synthesis was carried out by deposition–precipitation
[...] Read more.
Mono metallic and bimetallic Pd (1 wt. %)–Au (3 wt. %) catalysts were prepared using two ceria supports doped with 1 wt. % Y2O3. Yttrium was added by impregnation or co-precipitation. The catalyst synthesis was carried out by deposition–precipitation method, with sequential deposition–precipitation of palladium over previously loaded gold in the case of the bimetallic samples. The obtained materials, characterized by X-ray powder diffraction (XRD), High resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and temperature programmed reduction (TPR) techniques, were tested in the complete benzene oxidation (CBO). The results of the characterization analyses and the catalytic performance pointed to a close relationship between structural, redox, and catalytic properties of mono and bimetallic catalysts. Among the monometallic systems, Pd catalysts were more active as compared to the corresponding Au catalysts. The bimetallic systems exhibited the best combustion activity. In particular, over Pd–Au supported on Y-impregnated ceria, 100% of benzene conversion towards total oxidation at the temperature of 150 °C was obtained. Comparison of surface sensitive XPS results of fresh and spent catalysts ascertained the redox character of the reaction. Full article
(This article belongs to the Special Issue Structure–Activity Relationships in Catalysis)
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Open AccessReview Magnetic Microreactors with Immobilized Enzymes—From Assemblage to Contemporary Applications
Catalysts 2018, 8(7), 282; https://doi.org/10.3390/catal8070282
Received: 29 June 2018 / Revised: 11 July 2018 / Accepted: 12 July 2018 / Published: 14 July 2018
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Abstract
Microfluidics, as the technology for continuous flow processing in microscale, is being increasingly elaborated on in enzyme biotechnology and biocatalysis. Enzymatic microreactors are a precious tool for the investigation of catalytic properties and optimization of reaction parameters in a thriving and high-yielding way.
[...] Read more.
Microfluidics, as the technology for continuous flow processing in microscale, is being increasingly elaborated on in enzyme biotechnology and biocatalysis. Enzymatic microreactors are a precious tool for the investigation of catalytic properties and optimization of reaction parameters in a thriving and high-yielding way. The utilization of magnetic forces in the overall microfluidic system has reinforced enzymatic processes, paving the way for novel applications in a variety of research fields. In this review, we hold a discussion on how different magnetic particles combined with the appropriate biocatalyst under the proper system configuration may constitute a powerful microsystem and provide a highly explorable scope. Full article
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Open AccessArticle Production of Structured Phosphatidylcholine with High Content of Myristic Acid by Lipase-Catalyzed Acidolysis and Interesterification
Catalysts 2018, 8(7), 281; https://doi.org/10.3390/catal8070281
Received: 6 June 2018 / Revised: 4 July 2018 / Accepted: 12 July 2018 / Published: 14 July 2018
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Abstract
Synthesis of structured phosphatidylcholine (PC) enriched with myristic acid (MA) was conducted by acidolysis and interesterification reactions using immobilized lipases as catalysts and two acyl donors: trimyristin (TMA) isolated from ground nutmeg, and myristic acid obtained by saponification of TMA. Screening experiments indicated
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Synthesis of structured phosphatidylcholine (PC) enriched with myristic acid (MA) was conducted by acidolysis and interesterification reactions using immobilized lipases as catalysts and two acyl donors: trimyristin (TMA) isolated from ground nutmeg, and myristic acid obtained by saponification of TMA. Screening experiments indicated that the most effective biocatalyst for interesterification was Rhizomucor miehei lipase (RML), whereas for acidolysis, the most active were Thermomyces lanuginosus lipase (TLL) and RML. The effect of the molar ratio of substrates (egg-yolk PC/acyl donor), enzyme loading, and different solvent on the incorporation of MA into PC and on PC recovery was studied. The maximal incorporation of MA (44 wt%) was achieved after 48 h of RML-catalyzed interesterification in hexane using substrates molar ratio (PC/trimyristin) 1/5 and 30% enzyme load. Comparable results were obtained in toluene with 1/3 substrates molar ratio. Interesterification of PC with trimyristin resulted in significantly higher MA incorporation than acidolysis with myristic acid, particularly in the reactions catalyzed by RML. Full article
(This article belongs to the Special Issue Catalyzed Synthesis of Natural Products)
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Open AccessArticle PdO/ZnO@mSiO2 Hybrid Nanocatalyst for Reduction of Nitroarenes
Catalysts 2018, 8(7), 280; https://doi.org/10.3390/catal8070280
Received: 27 June 2018 / Revised: 11 July 2018 / Accepted: 11 July 2018 / Published: 14 July 2018
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Abstract
Development of a novel approach for synthesizing nanostructured catalysts and achieving further improvements in catalytic activity, effectiveness, and efficiency remains a major challenge. In this report, we describe the preparation of a nanostructured PdO/ZnO@mSiO2 hybrid nanocatalyst featuring well-dispersed PdO nanoparticles within hollow
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Development of a novel approach for synthesizing nanostructured catalysts and achieving further improvements in catalytic activity, effectiveness, and efficiency remains a major challenge. In this report, we describe the preparation of a nanostructured PdO/ZnO@mSiO2 hybrid nanocatalyst featuring well-dispersed PdO nanoparticles within hollow ZnO@mSiO2. The as-prepared PdO/ZnO@mSiO2 hybrid nanocatalyst exhibited good morphological features, derived from the controlled stepwise synthesis from Pd/PS@ZIF-8@mSiO2 (PS = polystyrene). The morphology, size, oxidation state, crystallinity, and thermal stability of the prepared PdO/ZnO@mSiO2 hybrid nanocatalyst were confirmed by a series of physicochemical techniques. The PdO/ZnO@mSiO2 hybrid nanocatalyst showed very high catalytic efficiency in the reduction of 4-nitrophenol and various nitroarenes under eco-friendly conditions. Therefore, the PdO/ZnO@mSiO2 hybrid nanocatalyst is a promising alternative catalyst for applications in environmental remediation. Full article
(This article belongs to the Special Issue Hybrid Catalysis)
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Open AccessArticle Highly Active TiO2 Microspheres Formation in the Presence of Ethylammonium Nitrate Ionic Liquid
Catalysts 2018, 8(7), 279; https://doi.org/10.3390/catal8070279
Received: 14 May 2018 / Revised: 13 June 2018 / Accepted: 13 June 2018 / Published: 11 July 2018
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Abstract
Spherical microparticles of TiO2 were synthesized by the ionic liquid-assisted solvothermal method at different reaction times (3, 6, 12, and 24 h). The properties of the prepared photocatalysts were investigated by means of UV-VIS diffuse-reflectance spectroscopy (DRS), Brunauer–Emmett–Teller (BET) surface area measurements,
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Spherical microparticles of TiO2 were synthesized by the ionic liquid-assisted solvothermal method at different reaction times (3, 6, 12, and 24 h). The properties of the prepared photocatalysts were investigated by means of UV-VIS diffuse-reflectance spectroscopy (DRS), Brunauer–Emmett–Teller (BET) surface area measurements, scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), and X-ray photoelectron spectroscopy (XPS). The results indicated that the efficiency of the phenol degradation was related to the time of the solvothermal synthesis, as determined for the TiO2_EAN(1:1)_24h sample. The microparticles of TiO2_EAN(1:1)_3h that formed during only 3 h of the synthesis time revealed a really high photoactivity under visible irradiation (75%). This value increased to 80% and 82% after 12 h and 24 h, respectively. The photoactivity increase was accompanied by the increase of the specific surface area, thus the poresize as well as the ability to absorb UV-VIS irradiation. The high efficiency of the phenol degradation of the ionic liquid (IL)–TiO2 photocatalysts was ascribed to the interaction between the surface of the TiO2 and ionic liquid components (carbon and nitrogen). Full article
(This article belongs to the Special Issue Nanomaterials for Environmental Purification and Energy Conversion)
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Open AccessArticle Immobilization of an Endo-β-N-acetylglucosaminidase for the Release of Bioactive N-glycans
Catalysts 2018, 8(7), 278; https://doi.org/10.3390/catal8070278
Received: 1 June 2018 / Revised: 4 July 2018 / Accepted: 5 July 2018 / Published: 10 July 2018
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Abstract
As more is learned about glycoproteins’ roles in human health and disease, the biological functionalities of N-linked glycans are becoming more relevant. Protein deglycosylation allows for the selective release of N-glycans and facilitates glycoproteomic investigation into their roles as prebiotics or
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As more is learned about glycoproteins’ roles in human health and disease, the biological functionalities of N-linked glycans are becoming more relevant. Protein deglycosylation allows for the selective release of N-glycans and facilitates glycoproteomic investigation into their roles as prebiotics or anti-pathogenic factors. To increase throughput and enzyme reusability, this work evaluated several immobilization methods for an endo-β-N-acetylglucosaminidase recently discovered from the commensal Bifidobacterium infantis. Ribonuclease B was used as a model glycoprotein to compare N-glycans released by the free and immobilized enzyme. Amino-based covalent method showed the highest enzyme immobilization. Relative abundance of N-glycans and enzyme activity were determined using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Kinetic evaluation demonstrated that upon immobilization, both Vmax and the Km decreased. Optimal pH values of 5 and 7 were identified for the free and immobilized enzyme, respectively. Although a higher temperature (65 vs. 45 °C) favored rapid glycan release, the immobilized enzyme retained over 50% of its original activity after seven use cycles at 45 °C. In view of future applications in the dairy industry, we investigated the ability of this enzyme to deglycosylate whey proteins. The immobilized enzyme released a higher abundance of neutral glycans from whey proteins, while the free enzyme released more sialylated glycans, determined by nano-LC Chip Q-ToF MS. Full article
(This article belongs to the Special Issue Immobilized Biocatalysts)
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Open AccessArticle Cascade Strategy for the Tunable Catalytic Valorization of Levulinic Acid and γ-Valerolactone to 2-Methyltetrahydrofuran and Alcohols
Catalysts 2018, 8(7), 277; https://doi.org/10.3390/catal8070277
Received: 6 June 2018 / Revised: 3 July 2018 / Accepted: 5 July 2018 / Published: 9 July 2018
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Abstract
A cascade strategy for the catalytic valorization of aqueous solutions of levulinic acid as well as of γ-valerolactone to 2-methyltetrahydrofuran or to monoalcohols, 2-butanol and 2-pentanol, has been studied and optimized. Only commercial catalytic systems have been employed, adopting sustainable reaction conditions. For
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A cascade strategy for the catalytic valorization of aqueous solutions of levulinic acid as well as of γ-valerolactone to 2-methyltetrahydrofuran or to monoalcohols, 2-butanol and 2-pentanol, has been studied and optimized. Only commercial catalytic systems have been employed, adopting sustainable reaction conditions. For the first time, the combined use of ruthenium and rhenium catalysts supported on carbon, with niobium phosphate as acid co-catalyst, has been claimed for the hydrogenation of γ-valerolactone and levulinic acid, addressing the selectivity to 2-methyltetrahydrofuran. On the other hand, the use of zeolite HY with commercial Ru/C catalyst favors the selective production of 2-butanol, starting again from γ-valerolactone and levulinic acid, with selectivities up to 80 and 70 mol %, respectively. Both levulinic acid and γ-valerolactone hydrogenation reactions have been optimized, investigating the effect of the main reaction parameters, to properly tune the catalytic performances towards the desired products. The proper choice of both the catalytic system and the reaction conditions can smartly switch the process towards the selective production of 2-methyltetrahydrofuran or monoalcohols. The catalytic system [Ru/C + zeolite HY] at 200 °C and 3 MPa H2 is able to completely convert both γ-valerolactone and levulinic acid, with overall yields to monoalcohols of 100 mol % and 88.8 mol %, respectively. Full article
(This article belongs to the Special Issue Catalytic Transformation of Lignocellulosic Platform Chemicals)
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Open AccessArticle Synthesis of Vinyl Chloride Monomer over Carbon-Supported Tris-(Triphenylphosphine) Ruthenium Dichloride Catalysts
Catalysts 2018, 8(7), 276; https://doi.org/10.3390/catal8070276
Received: 24 May 2018 / Revised: 5 July 2018 / Accepted: 5 July 2018 / Published: 9 July 2018
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Abstract
A series of catalysts, including Ru/AC, Ф-P-Ru/AC, Ф-P-Ru/AC-HCl, and Ф-P-Ru/AC-HNO3, were prepared and evaluated for the hydrochlorination reaction of acetylene. The test results reveal that the Ф-P-Ru/AC-HNO3 catalyst shows superior catalytic performance with an initial acetylene
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A series of catalysts, including Ru/AC, Ф-P-Ru/AC, Ф-P-Ru/AC-HCl, and Ф-P-Ru/AC-HNO3, were prepared and evaluated for the hydrochlorination reaction of acetylene. The test results reveal that the Ф-P-Ru/AC-HNO3 catalyst shows superior catalytic performance with an initial acetylene conversion of 97.2% and a relative increment of 87.0% within 48 h in comparison with that of the traditional RuCl3 catalyst. The substitution of inorganic RuCl3 precursor by organic Ф-P-Ru complex species in the catalysts results in more active species and tends to confine them in the micro-pores; the modification of carbon support by nitric acid in Ф-P-Ru catalyst may produce an interaction between the functional groups on modified support and Ru species, which is favorable to anchor and then reduce the loss of active species during the reaction, further increasing the amount of dominating Ru species, and greatly improving the reactants adsorption ability on the catalysts, thus enhancing the performance of the resultant catalysts. The as-prepared Ф-P-Ru catalysts are shown to be promising mercury-free candidates for the synthesis of vinyl chloride monomer. Full article
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Open AccessArticle Cobalt and Nitrogen Co-Doped Graphene-Carbon Nanotube Aerogel as an Efficient Bifunctional Electrocatalyst for Oxygen Reduction and Evolution Reactions
Catalysts 2018, 8(7), 275; https://doi.org/10.3390/catal8070275
Received: 13 June 2018 / Revised: 30 June 2018 / Accepted: 3 July 2018 / Published: 7 July 2018
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Abstract
In this study, a low-cost and environmentally friendly method is developed to synthesize cobalt and nitrogen co-doped graphene-carbon nanotube aerogel (Co-N-GCA) as a bifunctional electrocatalyst for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). The as-prepared Co-N-GCA has a hierarchical
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In this study, a low-cost and environmentally friendly method is developed to synthesize cobalt and nitrogen co-doped graphene-carbon nanotube aerogel (Co-N-GCA) as a bifunctional electrocatalyst for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). The as-prepared Co-N-GCA has a hierarchical meso- and macroporous structure with a high N doping level (8.92 at. %) and a large specific surface area (456 m2 g−1). In an alkaline medium, the catalyst exhibits superior ORR electrocatalytic activity with an onset potential 15 mV more positive than Pt/C, and its diffusion-limiting current density is 29% higher than that of commercial Pt/C. The obtained Co-N-GCA is also highly active toward the OER, with a small overpotential of 408 mV at a current density of 10 mA cm−2. Its overall oxygen electrode activity parameter (ΔE) is 0.821 V, which is comparable to most of the best nonprecious-metal catalysts reported previously. Furthermore, Co-N-GCA demonstrates superior durability in both the ORR and the OER, making it a promising noble-metal-free bifunctional catalyst in practical applications for energy conversion and storage. Full article
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Open AccessReview Biocatalytic Synthesis of Fungal β-Glucans
Catalysts 2018, 8(7), 274; https://doi.org/10.3390/catal8070274
Received: 4 May 2018 / Revised: 25 June 2018 / Accepted: 4 July 2018 / Published: 6 July 2018
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Abstract
Glucans are the dominant polysaccharide constituents of fungal cell walls. Remarkably, these major bioactive polysaccharides account for the beneficial effects that have been observed by many mushrooms of medicinal interest. Accordingly, the prevailing tendency is the use of bioactive mushroom β-glucans mainly
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Glucans are the dominant polysaccharide constituents of fungal cell walls. Remarkably, these major bioactive polysaccharides account for the beneficial effects that have been observed by many mushrooms of medicinal interest. Accordingly, the prevailing tendency is the use of bioactive mushroom β-glucans mainly in pharmaceutical industries or as food additives, since it seems that they can be involved in meeting the overall growing demand for food in the future, but also in medical and material sectors. β-(1,3)-Glucan synthase (GLS) is the responsible enzyme for the synthesis of these important polysaccharides, which is a member of the glycosyl transferase (GT) family. For optimizing the production of such natural polymers of great interest, the comprehension of the fungal synthetic mechanism, as well as the biochemical and molecular characteristics of the key enzyme GLS and its expression seem to be crucial. Overall, in this review article, the fungal β-glucans biosynthesis by GLS is summarized, while the in vitro synthesis of major polysaccharides is also discussed, catalyzed by glycoside hydrolases (GHs) and GTs. Possible future prospects of GLS in medicine and in developing other potential artificial composite materials with industrial applications are also summarized. Full article
(This article belongs to the Special Issue Biocatalysis for Industrial Applications)
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Open AccessArticle Highly Efficient Electrocatalytic Carboxylation of 1-Phenylethyl Chloride at Cu Foam Cathode
Catalysts 2018, 8(7), 273; https://doi.org/10.3390/catal8070273
Received: 11 June 2018 / Revised: 1 July 2018 / Accepted: 2 July 2018 / Published: 6 July 2018
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Abstract
A simple and efficient electrocatalytic carboxylation of benzyl chloride with CO2 is described. The reaction operates under 1 atm CO2 and room temperature in an undivided cell with Cu foam cathode and Mg sacrificial anode without any additional catalyst. For the
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A simple and efficient electrocatalytic carboxylation of benzyl chloride with CO2 is described. The reaction operates under 1 atm CO2 and room temperature in an undivided cell with Cu foam cathode and Mg sacrificial anode without any additional catalyst. For the model compound 1-phenylethyl chloride, the influence of cathode material, solvent, charge, current density and temperature were investigated. Under optimized conditions, 99% yield of 2-phenylpropionic acid could be obtained. Moreover, reasonable yields were also achieved with other benzyl chlorides. Full article
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Open AccessArticle The Roles of Graphene and Ag in the Hybrid Ag@Ag2O-Graphene for Sulfamethoxazole Degradation
Catalysts 2018, 8(7), 272; https://doi.org/10.3390/catal8070272
Received: 24 May 2018 / Revised: 2 July 2018 / Accepted: 2 July 2018 / Published: 4 July 2018
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Abstract
Ag@Ag2O-graphene (Ag@Ag2O-G) with different concentrations of graphene was synthesized using a facile in situ precipitation method. The photocatalysts were characterized by field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS),
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Ag@Ag2O-graphene (Ag@Ag2O-G) with different concentrations of graphene was synthesized using a facile in situ precipitation method. The photocatalysts were characterized by field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectra (DRS). The antibioticsulfamethoxazole (SMX) degradationunder simulated solar light and visible light irradiationwas investigated to evaluate photocatalytic performance. The composite photocatalyst Ag@Ag2O-G with 2.5 wt% graphene presented the highest activity among all the prepared composite photocatalysts. The coupling of graphene and Ag0 increased the photocatalyticactivity and stability of pure Ag2O. Under higher SMX concentrations, the adsorption, not the photocatalytic ability, playeda crucial role during the SMX removal process. On the basis of the characterization and reactive oxygen species (ROS) scavenging experiments, a separation and transfer mechanism of photogenerated carriers was proposed. In the photocatalytic degradation of SMX, the major active species wereidentified as photogenerated holes; photogenerated electrons in the conduction band (CB) of Ag2O could not transfer to graphene through Ag0due to the more negative reduction potential of graphene. This is an important result regardinggraphene and Ag0 roles which isdifferent from that for the photocatalytic degradation of dyes. This researchmay provide new insights into photocatalytic processes for the degradation of non-dye pollutants bycomposite materials to guidethe design of highly efficient reaction systems. Full article
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Open AccessArticle Organic Base-Catalyzed C–S Bond Construction from CO2: A New Route for the Synthesis of Benzothiazolones
Catalysts 2018, 8(7), 271; https://doi.org/10.3390/catal8070271
Received: 9 May 2018 / Revised: 27 June 2018 / Accepted: 27 June 2018 / Published: 30 June 2018
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Abstract
The synthesis of organosulfur compounds via the construction of C−S bonds using CO2 as a C1 resource is very interesting. Herein, a novel method of synthesizing benzothiazolones via the cyclocarbonylation of 2-aminothiophenols with CO2 was developed. A series of organic bases
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The synthesis of organosulfur compounds via the construction of C−S bonds using CO2 as a C1 resource is very interesting. Herein, a novel method of synthesizing benzothiazolones via the cyclocarbonylation of 2-aminothiophenols with CO2 was developed. A series of organic bases was investigated for the catalysis of cyclocarbonylation, and 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) displayed the best catalytic activity. Then, various reaction parameters such as CO2 pressure, temperature, amount of catalyst, and reaction time for the catalytic performance were studied. Finally, a series of benzothiazolones was synthesized under the optimal reaction conditions, and a possible catalytic mechanism was also proposed. Full article
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Open AccessArticle Oxidative Dehydrogenation of Liquefied Petroleum Gas on Copper, Zinc and Iron Oxide Impregnated on MFI Zeolite Assisted by Electric Power
Catalysts 2018, 8(7), 270; https://doi.org/10.3390/catal8070270
Received: 26 May 2018 / Revised: 21 June 2018 / Accepted: 22 June 2018 / Published: 30 June 2018
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Abstract
Olefin was produced with a non-conventional method using an electric field exerted on zeolites. The lattice oxygen mobility increases with a decrease in band gap, leading to an increase in olefin yield. By impregnating the transition metal, an increase in carrier concentration occurs.
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Olefin was produced with a non-conventional method using an electric field exerted on zeolites. The lattice oxygen mobility increases with a decrease in band gap, leading to an increase in olefin yield. By impregnating the transition metal, an increase in carrier concentration occurs. The external electric field changes the Fermi level. In this research, HZSM-5 was placed in an external DC electric field with strength appropriate for studying its catalytic performance. The Fermi level changed with the metal type and the external electric field. The increase in permittivity with temperature extracts higher energy from the external electric field. In catalytic reactions assisted by the external DC electric field, at 510 °C, the yield was approximately equal to the yield in a conventional reaction at 650 °C. With regard to TGA, in the catalytic reaction assisted by the external DC electric field, the produced coke declined. The results showed that the maximum yield value (50.54%) and conversion (92.81%) were be obtained at 650 °C with an input electrical current of 12 mA, a gap distance of 10 mm and a metal loading of 4 wt. % over FeHZSM-5. Full article
(This article belongs to the Special Issue Porous Materials in Catalysis)
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Open AccessArticle N,S Co-Doped Carbon Nanofibers Derived from Bacterial Cellulose/Poly(Methylene blue) Hybrids: Efficient Electrocatalyst for Oxygen Reduction Reaction
Catalysts 2018, 8(7), 269; https://doi.org/10.3390/catal8070269
Received: 26 May 2018 / Revised: 27 June 2018 / Accepted: 27 June 2018 / Published: 30 June 2018
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Abstract
Exploring inexpensive and highly efficient electrocatalyst to decrease the overpotential of oxygen reduction reaction (ORR) is one of the key issues for the commercialization of energy conversion and storage devices. Heteroatom-doped carbon materials have attracted increasing attention as promising electrocatalysts. Herein, we prepared
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Exploring inexpensive and highly efficient electrocatalyst to decrease the overpotential of oxygen reduction reaction (ORR) is one of the key issues for the commercialization of energy conversion and storage devices. Heteroatom-doped carbon materials have attracted increasing attention as promising electrocatalysts. Herein, we prepared a highly active electrocatalyst, nitrogen, sulfur co-doped carbon nanofibers (N/S-CNF), via in situ chemical oxidative polymerization of methylene blue on the bacterial cellulose nanofibers, followed by carbonization process. It was found that the type of nitrogen/sulfur source, methylene blue and poly(methylene blue), has significantly influence on the catalytic activity of the resultant carbon nanofibers. Benefiting from the porous structure and high surface area (729 m2/g) which favors mass transfer and exposing of active N and S atoms, the N/S-CNF displays high catalytic activity for the ORR in alkaline media with a half-wave potential of about 0.80 V, and better stability and stronger methanol tolerance than that of 20 wt % Pt/C, indicating great potential application in the field of alkaline fuel cell. Full article
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Open AccessArticle Chiral Dirhodium(II) Carboxylates: New Insights into the Effect of Ligand Stereo-Purity on Catalyst Structure and Enantioselectivity
Catalysts 2018, 8(7), 268; https://doi.org/10.3390/catal8070268
Received: 7 May 2018 / Revised: 19 June 2018 / Accepted: 27 June 2018 / Published: 30 June 2018
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Abstract
The current report contributes to the understanding of the stereoselectivity of chiral dirhodium(II) carboxylate catalysts carrying N-protected tert-leucine ligands. Investigating the possible effect of ligand stereo-purity on catalyst structure and enantioselectivity was carried out. This was justified through a new X-ray
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The current report contributes to the understanding of the stereoselectivity of chiral dirhodium(II) carboxylate catalysts carrying N-protected tert-leucine ligands. Investigating the possible effect of ligand stereo-purity on catalyst structure and enantioselectivity was carried out. This was justified through a new X-ray crystal structure for Rh2(S,S,S,R-PTTL)4 diastereomer. Full article
(This article belongs to the Special Issue Asymmetric Catalysis in Organic Synthesis)
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Open AccessArticle Removal of Methylene Blue from Water by BiFeO3/Carbon Fibre Nanocomposite and Its Photocatalytic Regeneration
Catalysts 2018, 8(7), 267; https://doi.org/10.3390/catal8070267
Received: 25 April 2018 / Revised: 20 June 2018 / Accepted: 26 June 2018 / Published: 29 June 2018
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Abstract
It is essential to prepare a highly efficient and reproducible adsorbent for purifying industrial dye wastewater. In this work, a novel and efficient BiFeO3/carbon fiber (CCT-BFO) nanocomposite adsorbent was prepared by the template method and through optimizing the preparation process. The
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It is essential to prepare a highly efficient and reproducible adsorbent for purifying industrial dye wastewater. In this work, a novel and efficient BiFeO3/carbon fiber (CCT-BFO) nanocomposite adsorbent was prepared by the template method and through optimizing the preparation process. The morphology, physicochemical properties, and specific surface characteristics of the CCT-BFO were characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) patterns, Fourier-transform infrared spectrometer (FTIR), and N2 adsorption-desorption isotherm. The CCT-BFO could efficiently remove the Methylene blue (MB) from aqueous solutions, and the adsorption performance is not easily influenced by the environment. The equilibrium adsorption data were fitted to the classical models very well; the maximum capacity of adsorption MB onto the CCT-BFO was higher than many other reported adsorbents and the data of the adsorption kinetics were described by a pseudo-second-order model. Furthermore, the CCT-BFO can be recycled by photocatalytic regeneration. And the constant adsorption capacity was almost retained after recycling five times. Full article
(This article belongs to the Special Issue Hybrid Catalysis)
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Open AccessFeature PaperArticle Low-Temperature Activity and PdO-PdOx Transition in Methane Combustion by a PdO-PdOx/γ-Al2O3 Catalyst
Catalysts 2018, 8(7), 266; https://doi.org/10.3390/catal8070266
Received: 21 May 2018 / Revised: 18 June 2018 / Accepted: 28 June 2018 / Published: 29 June 2018
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Abstract
The search to discover a suitable catalyst for complete combustion of methane at low temperature continues to be an active area of research. We prepared a 5 wt % PdO-PdOx/γ-Al2O3 catalyst by a modified Vortex-assisted Incipient Wetness Method.
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The search to discover a suitable catalyst for complete combustion of methane at low temperature continues to be an active area of research. We prepared a 5 wt % PdO-PdOx/γ-Al2O3 catalyst by a modified Vortex-assisted Incipient Wetness Method. X-ray Photoelectron Spectroscopy showed that the original catalyst contained PdO (38%) and PdOx (62%) on the surface and indicated that PdOx originated from the interaction of PdO with the support. Scanning Transmission Electron Microscopy confirmed the catalyst had an average particle size of 10 nm and was well-dispersed in the support. The catalyst exhibited exceptional low-temperature activities with 90–94% methane conversion at 300–320 °C. The catalyst was active and stable after several catalytic runs with no signs of deactivation by steam in this narrow temperature range. However, the conversion decreased in the temperature range 325–400 °C. The surface composition changed to some extent after the reaction at 325 °C. A tentative mechanism proposes PdOx (Pd native oxide) as the active phase and migration of oxide ions from the support to PdO and then to PdOx during the catalytic oxidation. The high methane conversion at low temperature is attributed to the vortex method providing better dispersion, and to catalyst–support interaction producing the active phase of PdOx. Full article
(This article belongs to the Special Issue Catalytic Oxidation of Methane)
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