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Catalysts, Volume 8, Issue 6 (June 2018)

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Cover Story (view full-size image) The development of nanostructures active in Vis light range in process of bacteria inactivation and [...] Read more.
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Open AccessArticle Desilicated ZSM-5 Zeolites for the Production of Renewable p-Xylene via Diels–Alder Cycloaddition of Dimethylfuran and Ethylene
Catalysts 2018, 8(6), 253; https://doi.org/10.3390/catal8060253
Received: 30 April 2018 / Revised: 7 June 2018 / Accepted: 14 June 2018 / Published: 20 June 2018
Cited by 1 | Viewed by 877 | PDF Full-text (5594 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The selective production of p-xylene and other aromatics starting from sugars and bioderived ethylene offers great promise and can eliminate the need for separation of xylene isomers, as well as decreasing dependency on fossil resources and CO2 emissions. Although the reaction
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The selective production of p-xylene and other aromatics starting from sugars and bioderived ethylene offers great promise and can eliminate the need for separation of xylene isomers, as well as decreasing dependency on fossil resources and CO2 emissions. Although the reaction is known, the microporosity of traditional commercial zeolites appears to be a limiting factor. In this work, we demonstrate for the first time that simply desilication of microporous commercial zeolites by a simple NaOH treatment can greatly enhance conversion and selectivity. The [4 + 2] Diels–Alder cycloaddition of 2,5-dimethylfuran with ethylene in a pressurised reactor was investigated using a series of H-ZSM-5 catalysts with SiO2/Al2O3 ratios 30 and 80 with increasing pore size induced by desilication. X-ray diffraction, scanning electron microscopy, 27Al magic-angle spinning nuclear magnetic resonance, temperature programmed desorption of ammonia, and nitrogen physisorption measurements were used to characterise the catalysts. The enhancement of conversion was observed for all desilicated samples compared to the untreated zeolite, and increases in temperature and ethylene pressure significantly improved both dimethylfuran conversion and selectivity to p-xylene due to the easier desorption from the zeolite’s surface and the augmented cycloaddition rate, respectively. A compromise between acidity and mesoporosity was found to be the key to enhancing the activity and maximising the selectivity in the production of p-xylene from 2,5-dimethylfuran. Full article
(This article belongs to the Special Issue Catalytic Processes for The Valorisation of Biomass Derived Molecules)
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Open AccessArticle Ti-Doped Pd-Au Catalysts for One-Pot Hydrogenation and Ring Opening of Furfural
Catalysts 2018, 8(6), 252; https://doi.org/10.3390/catal8060252
Received: 23 May 2018 / Revised: 13 June 2018 / Accepted: 14 June 2018 / Published: 20 June 2018
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Abstract
Pd-Au bimetallic catalysts with different Pd/Au atomic ratios, supported on ordered structured silica (Hexagonal mesoporous silica—HMS, or Santa Barbara Amorphous-15—SBA-15) were evaluated for one-pot hydrogenation of furfural to 1,2-pentanediol. The surface and structural properties of the catalysts were deeply investigated by X-ray photoelectron
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Pd-Au bimetallic catalysts with different Pd/Au atomic ratios, supported on ordered structured silica (Hexagonal mesoporous silica—HMS, or Santa Barbara Amorphous-15—SBA-15) were evaluated for one-pot hydrogenation of furfural to 1,2-pentanediol. The surface and structural properties of the catalysts were deeply investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), N2 adsorption isotherms (BET), Infrared spectroscopy (IR), and acid capacity measurements. XPS studies revealed that Ti doped supports had higher dispersion of the active phase, particularly in the case of Pd-Au materials in which Ti played an important role in stabilizing the metallic species. Among the various process conditions studied, such as temperature (160 °C), catalyst amount (10% w/w), and reaction time (5 h), H2 pressure (500 psi) was found to improve the 1,2-pentanediol selectivity. The SBA silica bimetallic Ti-doped system showed the best performance in terms of stability and reusability, after multiple cycles. Under specific reaction conditions, the synergism between Pd-Au alloy and Ti doping of the support allowed the ring opening pathway towards the formation of 1,2-pentanediol in furfural hydrogenation. Full article
(This article belongs to the Special Issue Sustainable Applications in Surface Chemistry and Catalysis)
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Open AccessArticle An Efficient Photocatalyst for Fast Reduction of Cr(VI) by Ultra-Trace Silver Enhanced Titania in Aqueous Solution
Catalysts 2018, 8(6), 251; https://doi.org/10.3390/catal8060251
Received: 10 May 2018 / Revised: 12 June 2018 / Accepted: 14 June 2018 / Published: 19 June 2018
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Abstract
For the purpose of establishing a simple route to prepare a metal-semiconductor hybrid catalyst efficiently and reduce its cost through precise doping noble metals. In this study, ultra-trace silver doped TiO2 photocatalysts were fabricated via a “green” ultrasonic impregnation-assisted photoreduction strategy in
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For the purpose of establishing a simple route to prepare a metal-semiconductor hybrid catalyst efficiently and reduce its cost through precise doping noble metals. In this study, ultra-trace silver doped TiO2 photocatalysts were fabricated via a “green” ultrasonic impregnation-assisted photoreduction strategy in an ethanol system, and its photocatalytic performance was systematically investigated by utilizing Cr(VI) as the model contaminant. A schottky energy barrier was constructed in Ag@TiO2, which served as a recombination center and possessed superior photocatalytic activity for Cr(VI) reduction. The obtained catalysts exhibited a significant e/h+ separation efficiency which directly led to an obvious photocatalytic property enhancement. Then, the resultant Ag@TiO2 (0.06 wt %, 30 min irradiation) showed about 2.5 times the activity as that of commercial P25 NPs for Cr(VI) degradation. Moreover, after five cycles, it still maintained considerably high catalytic ability (62%). This work provides a deep insight into preparation techniques of metal-semiconductor photocatalyst and broadens their application prospect. Full article
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Open AccessArticle Diastereoselective Synthesis of 7,8-Carvone Epoxides
Catalysts 2018, 8(6), 250; https://doi.org/10.3390/catal8060250
Received: 4 June 2018 / Revised: 15 June 2018 / Accepted: 16 June 2018 / Published: 19 June 2018
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Abstract
The synthesis of the two 7,8-epoxides of carvone has been attained using organocatalysis in a two-step synthetic route through a bromoester intermediate. Among the different reaction conditions tested for the bromination reaction, moderate yields and diastereoselection are achieved using proline, quinidine, and diphenylprolinol,
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The synthesis of the two 7,8-epoxides of carvone has been attained using organocatalysis in a two-step synthetic route through a bromoester intermediate. Among the different reaction conditions tested for the bromination reaction, moderate yields and diastereoselection are achieved using proline, quinidine, and diphenylprolinol, yielding the corresponding bromoesters that were transformed separately into their epoxides, obtaining the enantiopure products. Full article
(This article belongs to the Special Issue Catalyzed Synthesis of Natural Products)
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Open AccessCommunication Enzymatic Synthesis of Thioesters from Thiols and Vinyl Esters in a Continuous-Flow Microreactor
Catalysts 2018, 8(6), 249; https://doi.org/10.3390/catal8060249
Received: 16 May 2018 / Revised: 6 June 2018 / Accepted: 14 June 2018 / Published: 16 June 2018
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Abstract
The preparation of thioesters through the lipase-catalysed transesterification reaction of thiols with vinyl carboxyl esters is described. The reactions were carried out by Lipase TL IM from Thermomyces lanuginosus as a catalyst and performed under a continuous flow microreactor. We first found that
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The preparation of thioesters through the lipase-catalysed transesterification reaction of thiols with vinyl carboxyl esters is described. The reactions were carried out by Lipase TL IM from Thermomyces lanuginosus as a catalyst and performed under a continuous flow microreactor. We first found that lipase TL IM can be used in the reaction of thioester synthesis with high efficiency. Various reaction parameters were investigated including substrate molar ratio, reaction time, and temperature. Maximum conversion (96%) was obtained under the optimal condition of a substrate molar ratio of 1:2 (4-methylbenzyl mercaptan:vinyl esters) at 50 °C for about 30 min. Compared with other methods, the salient features of this work include mild reaction conditions (50 °C), short reaction times (30 min), high yields, and environment-friendliness. Full article
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Open AccessArticle Mode Transition of Filaments in Packed-Bed Dielectric Barrier Discharges
Catalysts 2018, 8(6), 248; https://doi.org/10.3390/catal8060248
Received: 15 May 2018 / Revised: 12 June 2018 / Accepted: 13 June 2018 / Published: 15 June 2018
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Abstract
We investigated the mode transition from volume to surface discharge in a packed bed dielectric barrier discharge reactor by a two-dimensional particle-in-cell/Monte Carlo collision method. The calculations are performed at atmospheric pressure for various driving voltages and for gas mixtures with different N
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We investigated the mode transition from volume to surface discharge in a packed bed dielectric barrier discharge reactor by a two-dimensional particle-in-cell/Monte Carlo collision method. The calculations are performed at atmospheric pressure for various driving voltages and for gas mixtures with different N2 and O2 compositions. Our results reveal that both a change of the driving voltage and gas mixture can induce mode transition. Upon increasing voltage, a mode transition from hybrid (volume+surface) discharge to pure surface discharge occurs, because the charged species can escape much more easily to the beads and charge the bead surface due to the strong electric field at high driving voltage. This significant surface charging will further enhance the tangential component of the electric field along the dielectric bead surface, yielding surface ionization waves (SIWs). The SIWs will give rise to a high concentration of reactive species on the surface, and thus possibly enhance the surface activity of the beads, which might be of interest for plasma catalysis. Indeed, electron impact excitation and ionization mainly take place near the bead surface. In addition, the propagation speed of SIWs becomes faster with increasing N2 content in the gas mixture, and slower with increasing O2 content, due to the loss of electrons by attachment to O2 molecules. Indeed, the negative O2 ion density produced by electron impact attachment is much higher than the electron and positive O2+ ion density. The different ionization rates between N2 and O2 gases will create different amounts of electrons and ions on the dielectric bead surface, which might also have effects in plasma catalysis. Full article
(This article belongs to the Special Issue Plasma Catalysis)
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Open AccessFeature PaperArticle Simulating Real World Soot-Catalyst Contact Conditions for Lab-Scale Catalytic Soot Oxidation Studies
Catalysts 2018, 8(6), 247; https://doi.org/10.3390/catal8060247
Received: 1 June 2018 / Revised: 10 June 2018 / Accepted: 12 June 2018 / Published: 14 June 2018
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Abstract
In diesel soot oxidation studies, both well-defined model soot and a reliable means to simulate realistic contact conditions with catalysts are crucial. This study is the first attempt in the field to establish a lab-scale continuous flame soot deposition method in simulating the
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In diesel soot oxidation studies, both well-defined model soot and a reliable means to simulate realistic contact conditions with catalysts are crucial. This study is the first attempt in the field to establish a lab-scale continuous flame soot deposition method in simulating the “contact condition” of soot and a structured diesel particulate filter (DPF) catalyst. The properties of this flame soot were examined by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM) for structure analysis, Brunauer-Emmett-Teller (BET) for surface area analysis, and thermogravimetric analysis (TGA) for reactivity and kinetics analysis. For validation purposes, catalytic oxidation of Tiki® soot using the simulated contact condition was conducted to compare with the diesel particulates collected from a real diesel engine exhaust system. It was found that the flame soot is more uniform and controllable than similar samples of collected diesel particulates. The change in T50 due to the presence of the catalyst is very similar in both cases, implying that the flame deposit method is able to produce comparably realistic contact conditions to that resulting from the real exhaust system. Comparing against the expensive engine testing, this novel method allows researchers to quickly set up a procedure in the laboratory scale to reveal the catalytic soot oxidation properties in a comparable loose contact condition. Full article
(This article belongs to the Special Issue Catalytic Oxidation in Environmental Protection)
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Open AccessArticle Synthesis of Sulfur-Resistant TiO2-CeO2 Composite and Its Catalytic Performance in the Oxidation of a Soluble Organic Fraction from Diesel Exhaust
Catalysts 2018, 8(6), 246; https://doi.org/10.3390/catal8060246
Received: 13 May 2018 / Revised: 8 June 2018 / Accepted: 11 June 2018 / Published: 14 June 2018
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Abstract
Sulfur poisoning is one of the most important factors deteriorating the purification efficiency of diesel exhaust after-treatment system, thus improving the sulfur resistibility of catalysts is imperative. Herein, ceria oxygen storage material was introduced into a sulfur-resistant titania by a co-precipitation method, and
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Sulfur poisoning is one of the most important factors deteriorating the purification efficiency of diesel exhaust after-treatment system, thus improving the sulfur resistibility of catalysts is imperative. Herein, ceria oxygen storage material was introduced into a sulfur-resistant titania by a co-precipitation method, and the sulfur resistibility and catalytic activity of prepared TiO2-CeO2 composite in the oxidation of diesel soluble organic fraction (SOF) were studied. Catalytic performance testing results show that the CeO2 modification significantly improves the catalytic SOF purification efficiency of TiO2-CeO2 catalyst. SO2 uptake and energy-dispersive X-ray (EDX) results suggest that the ceria doping does not debase the excellent sulfur resistibility of bare TiO2, the prepared TiO2-CeO2 catalyst exhibits obviously better sulfur resistibility than the CeO2 and commercial CeO2-ZrO2-Al2O3. X-ray powder diffraction (XRD) and Raman spectra indicate that cerium ions can enter into the TiO2 lattice and not form complete CeO2 crystals. X-ray photoelectron spectroscopy (XPS), H2-temperature programmed reduction (H2-TPR) and oxygen storage capacity (OSC) testing results imply that the addition of CeO2 in TiO2-CeO2 catalyst can significantly enhance the surface oxygen concentration and oxygen storage capacity of TiO2-CeO2. Full article
(This article belongs to the Special Issue Emissions Control Catalysis)
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Open AccessArticle Carbon Supported Multi-Branch Nitrogen-Containing Polymers as Oxygen Reduction Catalysts
Catalysts 2018, 8(6), 245; https://doi.org/10.3390/catal8060245
Received: 13 May 2018 / Revised: 1 June 2018 / Accepted: 8 June 2018 / Published: 12 June 2018
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Abstract
A composite catalyst was obtained by covalently linking G4-NH2 dendrimers and 1,10-phenanthroline-5-carboxylic acid on the surface of carbon powder, and the composite was named as PMPhen/C. In order to improve the catalytic performance of the composite, copper ions (II) were introduced to
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A composite catalyst was obtained by covalently linking G4-NH2 dendrimers and 1,10-phenanthroline-5-carboxylic acid on the surface of carbon powder, and the composite was named as PMPhen/C. In order to improve the catalytic performance of the composite, copper ions (II) were introduced to PMPhen/C by complex to form the PMPhen-Cu/C catalyst. Scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) were applied to investigate the surface microstructure and elemental compositions of the catalysts. The results from electrochemical analysis show that PMPhen/C reduced oxygen to hydrogen peroxide (H2O2) through a two-electron transfer process. PMPhen-Cu/C could reduce oxygen to water through a four-electron pathway. Except the slightly lower initial reduction potential, PMPhen-Cu/C has a comparable oxygen reduction ability (ORR) to that of the commercially available Pt/C catalyst, which makes it a potential candidate as the cathodic catalyst in some fuel cells running in neutral medium, such as a microbial fuel cell. Full article
(This article belongs to the Special Issue Advances in Fuel Cell Catalyst)
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Open AccessArticle Theoretical Study of the Mechanism for CO2 Hydrogenation to Methanol Catalyzed by trans-RuH2(CO)(dpa)
Catalysts 2018, 8(6), 244; https://doi.org/10.3390/catal8060244
Received: 6 May 2018 / Revised: 30 May 2018 / Accepted: 8 June 2018 / Published: 11 June 2018
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Abstract
In this work, the reaction mechanism for the conversion of CO2 and H2 to methanol has been researched by density functional theory (DFT). The production of methanol from CO2 and H2 is catalyzed by a univocal bifunctional pincer-type complex
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In this work, the reaction mechanism for the conversion of CO2 and H2 to methanol has been researched by density functional theory (DFT). The production of methanol from CO2 and H2 is catalyzed by a univocal bifunctional pincer-type complex trans-RuH2(CO)(dpa) (dpa = bis-(2-diphenylphosphinoethyl)amine). The reaction mechanism includes three continuous catalytic processes: (1) CO2 is converted to formic acid; (2) formic acid is converted to formaldehyde and water; (3) formaldehyde is converted to methanol. By computing the catalytic processes, we have shown that the rate-limiting step in the whole process is the direct cleavage of H2. The calculated largest free energy barrier is 21.6 kcal/mol. However, with the help of water, the free energy barrier can be lowered to 12.7 kcal/mol, which suggests viability of trans-RuH2(CO)(dpa) as a catalyst for the direct conversion of CO2 and H2 to methanol. Full article
(This article belongs to the Special Issue Catalysis and Catalytic Processes for CO2 Conversion)
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Open AccessArticle An Iron-Based Catalyst with Multiple Active Components Synergetically Improved Electrochemical Performance for Oxygen Reduction Reaction
Catalysts 2018, 8(6), 243; https://doi.org/10.3390/catal8060243
Received: 18 May 2018 / Revised: 4 June 2018 / Accepted: 4 June 2018 / Published: 7 June 2018
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Abstract
Lack of highly active and stable non-precious metal catalysts (NPMCs) as an alternative to Pt for oxygen reduction reaction (ORR) in the application of zinc-air batteries and proton-exchange membrane fuel cells (PEMFCs) significantly hinders the commercialization of these energy devices. Herein, we synthesize
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Lack of highly active and stable non-precious metal catalysts (NPMCs) as an alternative to Pt for oxygen reduction reaction (ORR) in the application of zinc-air batteries and proton-exchange membrane fuel cells (PEMFCs) significantly hinders the commercialization of these energy devices. Herein, we synthesize a new type of catalyst composed of nitrogen-coordinated and carbon-embedded metal (Fe-N/Fe3C/Fe/C) by pyrolyzing a precursor at 800 °C under argon atmosphere, and the precursor is obtained by heating a mixture of the tri (dipyrido [3,2-a:2′,3′-c] phenazinyl) phenylene and FeSO4 at 160 °C in a Teflon-lined stainless autoclave. The resultant Fe-N/Fe3C/Fe/C-800 exhibits the highest activity for the ORR with onset and half-wave potentials of 1.00 and 0.82 V in 0.1 M KOH, respectively. Furthermore, it also shows a potential ORR activity in 0.1 M HClO4, which is promising for the application in commercial PEMFCs. Most importantly, Fe-N/Fe3C/Fe/C-800 exhibits a comparable electrochemical performance to Pt/C for the application in zinc-air battery. The specific capacity approaches 700 mAh·g−1, and the maximum power density is also comparable to that of Pt/C at the current density of 200 mA·cm−2. The work opens up a simple strategy to prepare ORR electrocatalyts for zinc-air battery and PEMFCs. Full article
(This article belongs to the Special Issue Catalysts for Oxygen Reduction Reaction)
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Open AccessArticle The Synthetic Potential of Fungal Feruloyl Esterases: A Correlation with Current Classification Systems and Predicted Structural Properties
Catalysts 2018, 8(6), 242; https://doi.org/10.3390/catal8060242
Received: 21 May 2018 / Revised: 31 May 2018 / Accepted: 1 June 2018 / Published: 7 June 2018
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Abstract
Twenty-eight fungal feruloyl esterases (FAEs) were evaluated for their synthetic abilities in a ternary system of n-hexane: t-butanol: 100 mM MOPS-NaOH pH 6.0 forming detergentless microemulsions. Five main derivatives were synthesized, namely prenyl ferulate, prenyl caffeate, butyl ferulate, glyceryl ferulate, and
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Twenty-eight fungal feruloyl esterases (FAEs) were evaluated for their synthetic abilities in a ternary system of n-hexane: t-butanol: 100 mM MOPS-NaOH pH 6.0 forming detergentless microemulsions. Five main derivatives were synthesized, namely prenyl ferulate, prenyl caffeate, butyl ferulate, glyceryl ferulate, and l-arabinose ferulate, offering, in general, higher yields when more hydrophilic alcohol substitutions were used. Acetyl xylan esterase-related FAEs belonging to phylogenetic subfamilies (SF) 5 and 6 showed increased synthetic yields among tested enzymes. In particular, it was shown that FAEs belonging to SF6 generally transesterified aliphatic alcohols more efficiently while SF5 members preferred bulkier l-arabinose. Predicted surface properties and structural characteristics were correlated with the synthetic potential of selected tannase-related, acetyl-xylan-related, and lipase-related FAEs (SF1-2, -6, -7 members) based on homology modeling and small molecular docking simulations. Full article
(This article belongs to the Special Issue Novel Enzyme and Whole-Cell Biocatalysis)
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Open AccessArticle The Promoting Effect of Ce on the Performance of Au/CexZr1−xO2 for γ-Valerolactone Production from Biomass-Based Levulinic Acid and Formic Acid
Catalysts 2018, 8(6), 241; https://doi.org/10.3390/catal8060241
Received: 28 April 2018 / Revised: 31 May 2018 / Accepted: 2 June 2018 / Published: 7 June 2018
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Abstract
The production of γ-valerolactone (GVL) directly from biomass-based levulinic acid (LA) and formic acid (FA) without extra hydrogen source is attractive but challenging, due to the requirement of a highly active and stable catalyst. In present work, Au/CexZr1−xO2
[...] Read more.
The production of γ-valerolactone (GVL) directly from biomass-based levulinic acid (LA) and formic acid (FA) without extra hydrogen source is attractive but challenging, due to the requirement of a highly active and stable catalyst. In present work, Au/CexZr1−xO2 with various Ce/Zr ratios were prepared as the catalyst for GVL production from LA with the equivalent molar FA, and characterized by XRD, Raman-spectra, BET, NH3-TPD, TEM and XPS. It was found that the doped Ce in Au/CexZr1−xO2 catalyst could improve the reduction of Au3+ to metallic Au0, and also promoted the dispersion of Au0, yielding uniform Au0 nanoparticles with a small average particle size of about 2.4 nm, thus enhancing both the decomposition of FA to CO-free H2 and the hydrogenation of LA. Meanwhile, a certain amount of doped Ce (x ≤ 0.4) could facilitate the formation of tetragonal phase (the most desired structure on LA conversion to GVL), and increase the amount of weak and medium-strength acidic sites of catalyst, thereby promoting the dehydration reaction of the intermediate derived from LA hydrogenation. Au/Ce0.4Zr0.6O2 catalyst exhibited the best catalytic activity, achieving 90.8% of LA conversion and 83.5% of GVL yield (TON = 2047.8), with good recyclability, and the activity showed no obvious change after 5 runs. Full article
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Open AccessFeature PaperArticle Synergistic Effect of Cu2O and Urea as Modifiers of TiO2 for Enhanced Visible Light Activity
Catalysts 2018, 8(6), 240; https://doi.org/10.3390/catal8060240
Received: 14 March 2018 / Revised: 1 June 2018 / Accepted: 1 June 2018 / Published: 6 June 2018
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Low cost compounds, i.e., Cu2O and urea, were used as TiO2 modifiers to introduce visible light activity. Simple and cheap methods were applied to synthesize an efficient and stable nanocomposite photocatalytic material. First, the core-shell structure TiO2–polytriazine derivatives
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Low cost compounds, i.e., Cu2O and urea, were used as TiO2 modifiers to introduce visible light activity. Simple and cheap methods were applied to synthesize an efficient and stable nanocomposite photocatalytic material. First, the core-shell structure TiO2–polytriazine derivatives were prepared. Thereafter, Cu2O was added as the second semiconductor to form a dual heterojunction system. Enhanced visible light activity was found for the above-mentioned nanocomposite, confirming a synergistic effect of Cu2O and urea (via polytriazine derivatives on titania surface). Two possible mechanisms of visible light activity of the considered material were proposed regarding the type II heterojunction and Z-scheme through the essential improvement of the charge separation effect. Full article
(This article belongs to the Special Issue Nanomaterials for Environmental Purification and Energy Conversion)
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Open AccessArticle A Novel High-Activity Zn-Co Catalyst for Acetylene Acetoxylation
Catalysts 2018, 8(6), 239; https://doi.org/10.3390/catal8060239
Received: 26 April 2018 / Revised: 24 May 2018 / Accepted: 1 June 2018 / Published: 6 June 2018
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In this paper, Zn(OAc)2/AC and Zn-Co/AC catalysts were prepared and applied in an acetylene acetoxylation reaction. Compared with monometallic Zn(OAc)2/AC catalyst, which is widely applied in industry, the Zn-Co catalysts exhibited excellent catalytic performance. Transmission electron microscopy results displayed
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In this paper, Zn(OAc)2/AC and Zn-Co/AC catalysts were prepared and applied in an acetylene acetoxylation reaction. Compared with monometallic Zn(OAc)2/AC catalyst, which is widely applied in industry, the Zn-Co catalysts exhibited excellent catalytic performance. Transmission electron microscopy results displayed that the addition of cobalt improved the dispersity of zinc acetate particles and inhibited catalyst sintering on the catalyst surface. X-ray photoelectron spectra suggested that the Co additive changed the electron density of zinc acetate probably because of the interaction between Zn and Co species. Temperature programmed desorption analysis demonstrated Co additive strengthened the adsorption of acetic acid and weakened the adsorption of acetylene. Full article
(This article belongs to the Special Issue Heterogeneous Acid Catalyst)
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Open AccessReview Industrial Applications of Enzymes: Recent Advances, Techniques, and Outlooks
Catalysts 2018, 8(6), 238; https://doi.org/10.3390/catal8060238
Received: 5 May 2018 / Revised: 25 May 2018 / Accepted: 30 May 2018 / Published: 5 June 2018
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Abstract
Enzymes as industrial biocatalysts offer numerous advantages over traditional chemical processes with respect to sustainability and process efficiency. Enzyme catalysis has been scaled up for commercial processes in the pharmaceutical, food and beverage industries, although further enhancements in stability and biocatalyst functionality are
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Enzymes as industrial biocatalysts offer numerous advantages over traditional chemical processes with respect to sustainability and process efficiency. Enzyme catalysis has been scaled up for commercial processes in the pharmaceutical, food and beverage industries, although further enhancements in stability and biocatalyst functionality are required for optimal biocatalytic processes in the energy sector for biofuel production and in natural gas conversion. The technical barriers associated with the implementation of immobilized enzymes suggest that a multidisciplinary approach is necessary for the development of immobilized biocatalysts applicable in such industrial-scale processes. Specifically, the overlap of technical expertise in enzyme immobilization, protein and process engineering will define the next generation of immobilized biocatalysts and the successful scale-up of their induced processes. This review discusses how biocatalysis has been successfully deployed, how enzyme immobilization can improve industrial processes, as well as focuses on the analysis tools critical for the multi-scale implementation of enzyme immobilization for increased product yield at maximum market profitability and minimum logistical burden on the environment and user. Full article
(This article belongs to the Special Issue Immobilized Biocatalysts) Printed Edition available
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Open AccessArticle Electrochemically Obtained TiO2/CuxOy Nanotube Arrays Presenting a Photocatalytic Response in Processes of Pollutants Degradation and Bacteria Inactivation in Aqueous Phase
Catalysts 2018, 8(6), 237; https://doi.org/10.3390/catal8060237
Received: 15 May 2018 / Revised: 1 June 2018 / Accepted: 2 June 2018 / Published: 5 June 2018
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TiO2/CuxOy nanotube (NT) arrays were synthesized using the anodization method in the presence of ethylene glycol and different parameters applied. The presence, morphology, and chemical character of the obtained structures was characterized using a variety of methods—SEM (scanning
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TiO2/CuxOy nanotube (NT) arrays were synthesized using the anodization method in the presence of ethylene glycol and different parameters applied. The presence, morphology, and chemical character of the obtained structures was characterized using a variety of methods—SEM (scanning electron microscopy), XPS (X-ray photoelectron spectroscopy), XRD (X-ray crystallography), PL (photoluminescence), and EDX (energy-dispersive X-ray spectroscopy). A p-n mixed oxide heterojunction of Ti-Cu was created with a proved response to the visible light range and the stable form that were in contact with Ti. TiO2/CuxOy NTs presented the appearance of both Cu2O (mainly) and CuO components influencing the dimensions of the NTs (1.1–1.3 µm). Additionally, changes in voltage have been proven to affect the NTs’ length, which reached a value of 3.5 µm for Ti90Cu10_50V. Degradation of phenol in the aqueous phase was observed in 16% of Ti85Cu15_30V after 1 h of visible light irradiation (λ > 420 nm). Scavenger tests for phenol degradation process in presence of NT samples exposed the responsibility of superoxide radicals for degradation of organic compounds in Vis light region. Inactivation of bacteria strains Escherichia coli (E. coli), Bacillus subtilis (B. subtilis), and Clostridium sp. in presence of obtained TiO2/CuxOy NT photocatalysts, and Vis light has been studied showing a great improvement in inactivation efficiency with a response rate of 97% inactivation for E. coli and 98% for Clostridium sp. in 60 min. Evidently, TEM (transmission electron microscopy) images confirmed the bacteria cells’ damage. Full article
(This article belongs to the Special Issue Nanomaterials for Environmental Purification and Energy Conversion)
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Open AccessArticle Studied Localized Surface Plasmon Resonance Effects of Au Nanoparticles on TiO2 by FDTD Simulations
Catalysts 2018, 8(6), 236; https://doi.org/10.3390/catal8060236
Received: 7 April 2018 / Revised: 20 May 2018 / Accepted: 21 May 2018 / Published: 5 June 2018
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Abstract
Localized surface plasmon resonance (LSPR) plays a significant role in the fields of photocatalysis and solar cells. It can not only broaden the spectral response range of materials, but also improve the separation probability of photo-generated electron-hole pairs through local field enhancement or
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Localized surface plasmon resonance (LSPR) plays a significant role in the fields of photocatalysis and solar cells. It can not only broaden the spectral response range of materials, but also improve the separation probability of photo-generated electron-hole pairs through local field enhancement or hot electron injection. In this article, the LSPR effects of Au/TiO2 composite photocatalyst, with different sizes and shapes, have been simulated by the finite difference time domain (FDTD) method. The variation tendency of the resonance-absorption peaks and the intensity of enhanced local enhanced electric field were systematically compared and emphasized. When the location of Au nanosphere is gradually immersed into the TiO2 substrate, the local enhanced electric field of the boundary is gradually enhanced. When Au nanoshperes are covered by TiO2 at 100 nm depths, the local enhanced electric field intensities reach the maximum value. However, when Au nanorods are loaded on the surface of the TiO2 substrate, the intensity of the corresponding enhanced local enhanced electric field is the maximum. Au nanospheres produce two strong absorption peaks in the visible light region, which are induced by the LSPR effect and interband transitions between Au nanoparticles and the TiO2 substrate. For the LSPR resonance-absorption peaks, the corresponding position is red-shifted by about 100 nm, as the location of Au nanospheres are gradually immersed into the TiO2 substrate. On the other hand, the size change of the Au nanorods do not lead to a similar variation of the LSPR resonance-absorption peaks, except to change the length-diameter ratio. Meanwhile, the LSPR effects are obviously interfered with by the interband transitions between the Au nanorods and TiO2 substrate. At the end of this article, three photo-generated carrier separation mechanisms are proposed. Among them, the existence of direct electron transfer between Au nanoparticles and the TiO2 substrate leads to the enhanced local enhanced electric field at the boundaries, which is favorable for the improvement of photocatalytic performance of TiO2. These findings could explain the underlying mechanism of some experimental observations in published experimental works, and helpful to design highly efficient composite photocatalysts that contain noble metal co-catalyst nanoparticles. Full article
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Open AccessArticle Prickly Pear-Like Three-Dimensional Porous MoS2: Synthesis, Characterization and Advanced Hydrogen Evolution Reaction
Catalysts 2018, 8(6), 235; https://doi.org/10.3390/catal8060235
Received: 8 April 2018 / Revised: 28 May 2018 / Accepted: 29 May 2018 / Published: 4 June 2018
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Abstract
Herein, we hydrothermally synthesize a type of prickly pear-like three-dimensional (3D) porous MoS2 (ZT-MoS2), using a zinc oxide (ZnO) rod deposited on quartz glass substrates, as a template for an advanced hydrogen evolution reaction (HER) catalyst. Microscopic and spectroscopic tools
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Herein, we hydrothermally synthesize a type of prickly pear-like three-dimensional (3D) porous MoS2 (ZT-MoS2), using a zinc oxide (ZnO) rod deposited on quartz glass substrates, as a template for an advanced hydrogen evolution reaction (HER) catalyst. Microscopic and spectroscopic tools comprehensively characterize the morphology of the ZT-MoS2 nanostructure, which exhibits adequate edge active sites and defects, as well as a high component of active octahedral MoS2 (1T-MoS2). Electrochemical characterizations reveal the good HER performance of the ZT-MoS2 that presents a good overpotential of 110 mV, and a Tafel slope of 63 mV·dec−1, superior to most of the previously reported MoS2-based HER catalysts. This work contributes to the design and fabrication of 3D MoS2 with enhanced HER performance, which holds great promise for fuel cells and energy conversion. Full article
(This article belongs to the Special Issue Active Sites in Catalytic Reaction)
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Open AccessArticle Immobilization of an Antarctic Pseudomonas AMS8 Lipase for Low Temperature Ethyl Hexanoate Synthesis
Catalysts 2018, 8(6), 234; https://doi.org/10.3390/catal8060234
Received: 31 March 2018 / Revised: 28 April 2018 / Accepted: 2 May 2018 / Published: 4 June 2018
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Abstract
The demand for synthetic flavor ester is high, especially in the food, beverage, and cosmetic and pharmaceutical industries. It is derived from the reaction between a short-chain fatty acid and alcohol. Lipases from Antarctic bacteria have gained huge interest in the industry due
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The demand for synthetic flavor ester is high, especially in the food, beverage, and cosmetic and pharmaceutical industries. It is derived from the reaction between a short-chain fatty acid and alcohol. Lipases from Antarctic bacteria have gained huge interest in the industry due to its ability react at low temperatures. The use of immobilization enzymes is one of the methods that can improve the stability of the enzyme. The current work encompasses the low temperature enzymatic synthesis of ethyl hexanoate by direct esterification of ethanol with hexanoic acid in a toluene and solvent-free system. The effects of various reaction parameters such as the organic solvent, temperature, time, substrate, substrate ratio and concentration, enzyme concentration on ethyl hexanoate synthesis were tested. Several matrices were used for immobilization and comparisons of the efficiency of immobilized enzyme with free enzyme in the synthesis of flavor ester were conducted. Ester production was optimally synthesized at 20 °C in both systems— immobilized and free enzyme. A 69% ester conversion rate was achieved after a two-hour incubation in toluene, compared to 47% in a solvent-free system for free enzyme. Immobilized AMS8 lipase showed a higher conversion of ester in toluene with respect to free-solvents, from 80% to 59%, respectively. Immobilized enzymes showed enhancement to the stability of the enzyme in the presence of the organic solvent. The development of AMS8 lipase as an immobilized biocatalyst demonstrates great potential as a cost-effective enzyme for biocatalysis and biotransformation in the food industry. Full article
(This article belongs to the Special Issue Immobilized Biocatalysts) Printed Edition available
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Open AccessArticle Electrochemical Biosensor for the Determination of Amlodipine Besylate Based on Gelatin–Polyaniline Iron Oxide Biocomposite Film
Catalysts 2018, 8(6), 233; https://doi.org/10.3390/catal8060233
Received: 19 April 2018 / Revised: 10 May 2018 / Accepted: 18 May 2018 / Published: 4 June 2018
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Abstract
In the present study, a new biosensor based on lipase from Candida rugosa (CRL) was developed for amlodipine besylate drug (AMD) with biodegradable material using a mixture of polyaniline iron oxide and gelatin. Polyaniline/Fe2O3 (PANI@Fe2O3) was
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In the present study, a new biosensor based on lipase from Candida rugosa (CRL) was developed for amlodipine besylate drug (AMD) with biodegradable material using a mixture of polyaniline iron oxide and gelatin. Polyaniline/Fe2O3 (PANI@Fe2O3) was prepared by a chemical polymerization method in a medium of ammonium persulfate as an oxidant and characterized by employing Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FTIR), and Ultra-violet (UV) spectroscopy. The purified enzyme was entrapped in the biocomposite matrix film with the aid of a glutaraldehyde cross-linking reagent to establish the immobilization of the lipase. The principle of the biosensor is based on the electrochemical properties of amlodipine besylate (AMD), which were studied for the first time using the cyclic voltammetric method. The cathodic behavior of AMD was measured on the irreversible reduction signal at −0.185 V versus Ag/AgCl at pH 7.4 and 30 °C in a phosphate alkaline buffer. Full article
(This article belongs to the Special Issue Biocatalysts: Design and Application)
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Open AccessArticle Nitrogen-Doped Porous Carbon Derived from Bamboo Shoot as Solid Base Catalyst for Knoevenagel Condensation and Transesterification Reactions
Catalysts 2018, 8(6), 232; https://doi.org/10.3390/catal8060232
Received: 30 April 2018 / Revised: 27 May 2018 / Accepted: 29 May 2018 / Published: 4 June 2018
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Abstract
Highly porous nitrogen-doped carbons derived from bamboo shoots (BSNCs) were prepared through an in-situ synthesis method. The results showed that BSNCs had a large specific surface area, a relatively high nitrogen content and hierarchically porous structures. The catalytic properties of BSNCs were evaluated
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Highly porous nitrogen-doped carbons derived from bamboo shoots (BSNCs) were prepared through an in-situ synthesis method. The results showed that BSNCs had a large specific surface area, a relatively high nitrogen content and hierarchically porous structures. The catalytic properties of BSNCs were evaluated based on Knoevenagel condensation and transesterification reactions. Deprotonated BSNC-700 exhibited high efficiency for the model reactions as a solid base catalyst, and the superior sample deprotonated in tBuOK solution with a concentration of 0.1 increased the conversion rate from 16.1% to 76.0% for Knoevenagel condensation. The two reactions proceeded smoothly in the presence of deprotonated BSNC-700. The results also showed that the catalyst could be recycled for several times for Knoevenagel condensation. The results from this research will provide a guideline to develop bamboo shoot as a precursor to fabricate a superb solid base catalyst. Full article
(This article belongs to the Special Issue Active Sites in Catalytic Reaction)
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Open AccessArticle Ammonia Concentration Distribution Measurements on Selective Catalytic Reduction Catalysts
Catalysts 2018, 8(6), 231; https://doi.org/10.3390/catal8060231
Received: 18 April 2018 / Revised: 16 May 2018 / Accepted: 22 May 2018 / Published: 1 June 2018
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Abstract
This work presents the methodology and accurate evaluation of ammonia concentration distribution measurements at the selective catalytic reduction (SCR) catalyst outlet cross-section. The uniformity of ammonia concentration is a crucial factor influencing overall SCR effectiveness, and it contributes to the necessity of employing
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This work presents the methodology and accurate evaluation of ammonia concentration distribution measurements at the selective catalytic reduction (SCR) catalyst outlet cross-section. The uniformity of ammonia concentration is a crucial factor influencing overall SCR effectiveness, and it contributes to the necessity of employing a reliable test method. The aftertreatment system design (mainly its geometrical features) can be evaluated in detail. The ammonia concentration is measured at the SCR catalyst outlet at grid points covering from the center to the outer edges of the catalyst. Its execution requires the introduction of a probe hovering over the back face of the SCR. To obtain the expected accuracy, it is necessary to measure a sufficient number of points in a reasonable timeframe. In order to achieve that, a fully automatic sampling device was developed. Sample results are presented showing the capabilities of the created test stand and its importance for the design development and validation stages of SCR-based engine aftertreatment. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction of NOx)
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Open AccessArticle MgO-Templated Mesoporous Carbon as a Catalyst Support for Polymer Electrolyte Fuel Cells
Catalysts 2018, 8(6), 230; https://doi.org/10.3390/catal8060230
Received: 5 April 2018 / Revised: 28 May 2018 / Accepted: 29 May 2018 / Published: 1 June 2018
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Abstract
An MgO-templated mesoporous carbon, CNovel®, was employed as a catalyst support for the cathode of polymer electrolyte fuel cells (PEFCs) after modifying its dimensional, crystalline, surface and porous structures and the electrochemical oxygen reduction reaction (ORR) activities were examined by the
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An MgO-templated mesoporous carbon, CNovel®, was employed as a catalyst support for the cathode of polymer electrolyte fuel cells (PEFCs) after modifying its dimensional, crystalline, surface and porous structures and the electrochemical oxygen reduction reaction (ORR) activities were examined by the thin-film rotating disk electrode (RDE) method and as well as the membrane electrode assembly (MEA) method. Although the catalytic activity of Pt on CNovel® was comparable with that on a non-porous carbon, Vulcan®, in the RDE configuration without Nafion®, Pt/CNovel showed a considerably higher activity than Pt/Vulcan in the MEA condition with Nafion®. The mechanism inducing this difference was discussed from the results of electrochemical surface area and sulfonic coverage measurements which suggested that Pt particles on inside pores of CNovel® are not covered with Nafion® ionomer while protons can still reach those Pt particles through water network. The MEA performance in the middle and high current-density regions was drastically improved by heat-treatment in air, which modified the pore structure to through-pored ones. Full article
(This article belongs to the Special Issue Catalysts for Polymer Membrane Fuel Cells)
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Open AccessArticle Gallium-Promoted Ni Catalyst Supported on MCM-41 for Dry Reforming of Methane
Catalysts 2018, 8(6), 229; https://doi.org/10.3390/catal8060229
Received: 4 April 2018 / Revised: 12 May 2018 / Accepted: 23 May 2018 / Published: 1 June 2018
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Abstract
The stability and catalytic activity of mesoporous Ni/MCM-41 promoted with a Ga loading of (0.0, 1.0, 1.5, 2.0, 2.5, and 3.0 wt %) as an innovative catalyst was examined for syngas production via CO2 reforming of CH4. The objective of
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The stability and catalytic activity of mesoporous Ni/MCM-41 promoted with a Ga loading of (0.0, 1.0, 1.5, 2.0, 2.5, and 3.0 wt %) as an innovative catalyst was examined for syngas production via CO2 reforming of CH4. The objective of present work was to develop a potential catalyst for CO2 reforming of methane. For this purpose different loadings of gallium were used to promote 5% nickel catalyst supported on MCM-41. An incipient wetness impregnation method was used for preparing the catalysts and investigated at 800 °C. Physicochemical characterization techniques—including BET, XRD, TPD, TPR, TEM, and TGA—were used to characterize the catalysts. The addition of small amounts of Ga resulted in higher surface areas with a maximum surface area of 1036 m2/g for 2.5% Ga. The incorporation of Ga to the catalyst decreased the medium and strong basic sites and reduced the amount of carbon deposited. There was no weight loss for 3%Ga+5%Ni/MCM-41. The 2% Ga loading showed the highest CH4 conversion of 88.2% and optimum stability, with an activity loss of only 1.58%. The Ga promoter raised the H2/CO ratio from 0.9 to unity. Full article
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Open AccessArticle On the Impact of the Preparation Method on the Surface Basicity of Mg–Zr Mixed Oxide Catalysts for Tributyrin Transesterification
Catalysts 2018, 8(6), 228; https://doi.org/10.3390/catal8060228
Received: 9 May 2018 / Revised: 24 May 2018 / Accepted: 25 May 2018 / Published: 28 May 2018
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Abstract
Mixed metal oxides are promising heterogeneous catalysts for biofuel production from lipids via alcoholysis, however, the impact of solid acidity and/or basicity on reactivity is comparatively poorly understood. Two systematically related families of MgO–ZrO2 mixed oxide catalysts were therefore prepared by different
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Mixed metal oxides are promising heterogeneous catalysts for biofuel production from lipids via alcoholysis, however, the impact of solid acidity and/or basicity on reactivity is comparatively poorly understood. Two systematically related families of MgO–ZrO2 mixed oxide catalysts were therefore prepared by different synthetic routes to elucidate the impact of surface acid-base properties on catalytic performance in the transesterification of tributyrin with methanol. The resulting materials were characterized by TGA-MS, ICP-OES, N2 porosimetry, XRD, TEM, XPS, DRIFTS, and CO2-temperature-programmed desorption (TPD). MgO–ZrO2 catalysts prepared by both non-aqueous impregnation and citric acid-mediated sol–gel routes exhibit excellent activity and stability. The citrate routes favor highly dispersed MgO and concomitant Lewis acid-base pair formation at the interface with zirconia. However, for both the citrate and impregnation routes, tributyrin transesterification occurs over a common, strongly basic MgO active site. Full article
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Open AccessArticle Photocatalytic Behavior of Strontium Aluminates Co-Doped with Europium and Dysprosium Synthesized by Hydrothermal Reaction in Degradation of Methylene Blue
Catalysts 2018, 8(6), 227; https://doi.org/10.3390/catal8060227
Received: 4 April 2018 / Revised: 22 May 2018 / Accepted: 22 May 2018 / Published: 28 May 2018
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Abstract
Strontium aluminates co-doped with europium and dysprosium were prepared by a hydrothermal reaction through a sintering process at lower temperatures. The physicochemical properties of the strontium aluminates co-doped with europium and dysprosium were characterized and compared with those of strontium aluminates prepared by
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Strontium aluminates co-doped with europium and dysprosium were prepared by a hydrothermal reaction through a sintering process at lower temperatures. The physicochemical properties of the strontium aluminates co-doped with europium and dysprosium were characterized and compared with those of strontium aluminates prepared by a sol–gel method. The photocatalytic properties of the strontium aluminates co-doped with europium and dysprosium were evaluated through the photocatalytic decomposition of methylene blue dye. The strontium aluminates co-doped with europium and dysprosium prepared by the hydrothermal reaction exhibited good phosphorescence and photocatalytic activities that were similar to those prepared by the sol–gel method. The photocatalytic activity of these catalysts for methylene blue degradation was higher than that of the titanium dioxide (TiO2) photocatalyst. Full article
(This article belongs to the Special Issue Photocatalysts for Organics Degradation)
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Open AccessReview Molecular Orientations Change Reaction Kinetics and Mechanism: A Review on Catalytic Alcohol Oxidation in Gas Phase and Liquid Phase on Size-Controlled Pt Nanoparticles
Catalysts 2018, 8(6), 226; https://doi.org/10.3390/catal8060226
Received: 30 April 2018 / Revised: 25 May 2018 / Accepted: 26 May 2018 / Published: 27 May 2018
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Abstract
Catalytic oxidation of alcohols is an essential process for energy conversion, production of fine chemicals and pharmaceutical intermediates. Although it has been broadly utilized in industry, the basic understanding for catalytic alcohol oxidations at a molecular level, especially under both gas and liquid
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Catalytic oxidation of alcohols is an essential process for energy conversion, production of fine chemicals and pharmaceutical intermediates. Although it has been broadly utilized in industry, the basic understanding for catalytic alcohol oxidations at a molecular level, especially under both gas and liquid phases, is still lacking. In this paper, we systematically summarized our work on catalytic alcohol oxidation over size-controlled Pt nanoparticles. The studied alcohols included methanol, ethanol, 1-propanol, 2-propanol, and 2-butanol. The turnover rates of different alcohols on Pt nanoparticles and also the apparent activation energy in gas and liquid phase reactions were compared. The Pt nanoparticle size dependence of reaction rates and product selectivity was also carefully examined. Water showed very distinct effects for gas and liquid phase alcohol oxidations, either as an inhibitor or as a promoter depending on alcohol type and reaction phase. A deep understanding of different alcohol molecular orientations on Pt surface in gas and liquid phase reactions was established using sum-frequency generation spectroscopy analysis for in situ alcohol oxidations, as well as density functional theory calculation. This approach can not only explain the entirely different behaviors of alcohol oxidations in gas and liquid phases, but can also provide guidance for future catalyst/process design. Full article
(This article belongs to the Special Issue New Concepts in Oxidation Processes)
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Open AccessArticle Electrocatalytic Performance of Carbon Supported WO3-Containing Pd–W Nanoalloys for Oxygen Reduction Reaction in Alkaline Media
Catalysts 2018, 8(6), 225; https://doi.org/10.3390/catal8060225
Received: 7 April 2018 / Revised: 16 May 2018 / Accepted: 21 May 2018 / Published: 24 May 2018
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Abstract
In this paper, we report that WOx containing nanoalloys exhibit stable electrocatalytic performance in alkaline media, though bulk WO3 is easy to dissolve in NaOH solution. Carbon supported oxide-rich Pd–W alloy nanoparticles (PdW/C) with different Pd:W atom ratios were prepared by
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In this paper, we report that WOx containing nanoalloys exhibit stable electrocatalytic performance in alkaline media, though bulk WO3 is easy to dissolve in NaOH solution. Carbon supported oxide-rich Pd–W alloy nanoparticles (PdW/C) with different Pd:W atom ratios were prepared by the reduction–oxidation method. Among the catalysts, the oxide-rich Pd0.8W0.2/C (Pd/W = 8:2, atom ratio) exhibits the highest catalytic activity for the oxygen reduction reaction. The X-ray photoelectron spectroscopy data shows that ~40% of Pd atoms and ~60% of the W atoms are in their oxide form. The Pd 3d5/2 binding energy of the oxide-rich Pd–W nanoalloys is higher than that of Pd/C, indicating the electronic structure of Pd is affected by the strong interaction between Pd and W/WO3. Compare to Pd/C, the onset potential of the oxygen reduction reaction at the oxide-rich Pd0.8W0.2/C shifts to a higher potential. The current density (mA·mg Pd−1) at the oxide-rich Pd0.8W0.2/C is ~1.6 times of that at Pd/C. The oxide-rich Pd0.8W0.2/C also exhibits higher catalytic stability than Pd/C, which demonstrates that it is a prospective candidate for the cathode of fuel cells operating with alkaline electrolyte. Full article
(This article belongs to the Special Issue Catalysts for Oxygen Reduction Reaction)
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Open AccessArticle Exploring Basic Components Effect on the Catalytic Efficiency of Chevron-Phillips Catalyst in Ethylene Trimerization
Catalysts 2018, 8(6), 224; https://doi.org/10.3390/catal8060224
Received: 26 April 2018 / Revised: 17 May 2018 / Accepted: 18 May 2018 / Published: 24 May 2018
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Abstract
In the present work, the effect of basic components on the energy pathway of ethylene oligomerization using the landmark Chevron-Phillips catalyst has been explored in detail, using density functional theory (DFT). Studied factors were chosen considering the main components of the Chevron-Phillips catalyst,
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In the present work, the effect of basic components on the energy pathway of ethylene oligomerization using the landmark Chevron-Phillips catalyst has been explored in detail, using density functional theory (DFT). Studied factors were chosen considering the main components of the Chevron-Phillips catalyst, i.e., ligand, cocatalyst, and halocarbon compounds, comprising (i) the type of alkyl substituents in pyrrole ligand, i.e., methyl, iso-propyl, tert-butyl, and phenyl, as well as the simple hydrogen and the electron withdrawing fluoro and trifluoromethyl; (ii) the number of Cl atoms in Al compounds (as AlMe2Cl, AlMeCl2 and AlCl3), which indicate the halocarbon level, and (iii) cocatalyst type, i.e., alkylboron, alkylaluminium, or alkylgallium. Besides the main ingredients, the solvent effect (using toluene or methylcyclohexane) on the oligomerization pathway was also explored. In this regard, the full catalytic cycles for the main product (1-hexene) formation, as well as side reactions, i.e., 1-butene release and chromacyclononane formation, were calculated on the basis of the metallacycle-based mechanism. According to the obtained results, a modification on the Chevron-Phillips catalyst system, which demonstrates higher 1-hexene selectivity and activity, is suggested. Full article
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