Catalysts

18 pages, 5594 KiB

Open AccessArticle

Desilicated ZSM-5 Zeolites for the Production of Renewable p-Xylene via Diels–Alder Cycloaddition of Dimethylfuran and Ethylene

by Joel McGlone, Peter Priecel, Luigi Da Vià, Liqaa Majdal and Jose A. Lopez-Sanchez

Catalysts 2018, 8(6), 253; https://doi.org/10.3390/catal8060253 - 20 Jun 2018

Cited by 28 | Viewed by 5696

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 [...] Read more.

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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17 pages, 5367 KiB

Open AccessArticle

Ti-Doped Pd-Au Catalysts for One-Pot Hydrogenation and Ring Opening of Furfural

by Nandan Shreehari Date, Valeria La Parola, Chandrashekhar Vasant Rode and Maria Luisa Testa

Catalysts 2018, 8(6), 252; https://doi.org/10.3390/catal8060252 - 20 Jun 2018

Cited by 19 | Viewed by 4034

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 [...] Read more.

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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17 pages, 4038 KiB

Open AccessArticle

An Efficient Photocatalyst for Fast Reduction of Cr(VI) by Ultra-Trace Silver Enhanced Titania in Aqueous Solution

by Shengyan Pu, Yaqi Hou, Hongyu Chen, Daili Deng, Zeng Yang, Shengyang Xue, Rongxin Zhu, Zenghui Diao and Wei Chu

Catalysts 2018, 8(6), 251; https://doi.org/10.3390/catal8060251 - 19 Jun 2018

Cited by 35 | Viewed by 4185

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 [...] Read more.

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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12 pages, 1731 KiB

Open AccessArticle

Diastereoselective Synthesis of 7,8-Carvone Epoxides

by Sofia Pombal, Ignacio E. Tobal, Alejandro M. Roncero, Jesus M. Rodilla, Narciso M. Garrido, Francisca Sanz, Alberto Esteban, Jaime Tostado, Rosalina F. Moro, Maria Jose Sexmero, Pablo G. Jambrina and David Diez

Catalysts 2018, 8(6), 250; https://doi.org/10.3390/catal8060250 - 19 Jun 2018

Cited by 4 | Viewed by 5623

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, [...] Read more.

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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12 pages, 8154 KiB

Open AccessCommunication

Enzymatic Synthesis of Thioesters from Thiols and Vinyl Esters in a Continuous-Flow Microreactor

by Nani Zhou, Le Shen, Zhen Dong, Jiahong Shen, Lihua Du and Xiping Luo

Catalysts 2018, 8(6), 249; https://doi.org/10.3390/catal8060249 - 16 Jun 2018

Cited by 7 | Viewed by 3846

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 [...] Read more.

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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18 pages, 5364 KiB

Open AccessArticle

Mode Transition of Filaments in Packed-Bed Dielectric Barrier Discharges

by Mingxiang Gao, Ya Zhang, Hongyu Wang, Bin Guo, Quanzhi Zhang and Annemie Bogaerts

Catalysts 2018, 8(6), 248; https://doi.org/10.3390/catal8060248 - 15 Jun 2018

Cited by 23 | Viewed by 4480

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 [...] Read more.

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

_{2}

and O

_{2}

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 N

_{2}

content in the gas mixture, and slower with increasing O

_{2}

content, due to the loss of electrons by attachment to O

_{2}

molecules. Indeed, the negative O

_{2}^{-}

ion density produced by electron impact attachment is much higher than the electron and positive O

_{2}^{+}

ion density. The different ionization rates between N

_{2}

and O

_{2}

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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18 pages, 3980 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Simulating Real World Soot-Catalyst Contact Conditions for Lab-Scale Catalytic Soot Oxidation Studies

by Changsheng Su, Yujun Wang, Ashok Kumar and Paul J. McGinn

Catalysts 2018, 8(6), 247; https://doi.org/10.3390/catal8060247 - 14 Jun 2018

Cited by 20 | Viewed by 6900

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 [...] Read more.

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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13 pages, 1825 KiB

Open AccessArticle

Synthesis of Sulfur-Resistant TiO₂-CeO₂ Composite and Its Catalytic Performance in the Oxidation of a Soluble Organic Fraction from Diesel Exhaust

by Na Zhang, Zhengzheng Yang, Zhi Chen, Yunxiang Li, Yunwen Liao, Youping Li, Maochu Gong and Yaoqiang Chen

Catalysts 2018, 8(6), 246; https://doi.org/10.3390/catal8060246 - 14 Jun 2018

Cited by 20 | Viewed by 3871

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 [...] Read more.

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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21 pages, 3453 KiB

Open AccessArticle

Carbon Supported Multi-Branch Nitrogen-Containing Polymers as Oxygen Reduction Catalysts

by Ya Chu, Lin Gu, Xiuping Ju, Hongmei Du, Jinsheng Zhao and Konggang Qu

Catalysts 2018, 8(6), 245; https://doi.org/10.3390/catal8060245 - 12 Jun 2018

Cited by 14 | Viewed by 3757

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 [...] Read more.

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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10 pages, 3343 KiB

Open AccessArticle

Theoretical Study of the Mechanism for CO₂ Hydrogenation to Methanol Catalyzed by trans-RuH₂(CO)(dpa)

by Jinxia Zhou, Liangliang Huang, Wei Yan, Jun Li, Chang Liu and Xiaohua Lu

Catalysts 2018, 8(6), 244; https://doi.org/10.3390/catal8060244 - 11 Jun 2018

Cited by 8 | Viewed by 4136

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 [...] Read more.

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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13 pages, 5185 KiB

Open AccessArticle

An Iron-Based Catalyst with Multiple Active Components Synergetically Improved Electrochemical Performance for Oxygen Reduction Reaction

by Jian Zhang, Xiaoming Song, Ping Li, Shuai Wang, Zexing Wu and Xien Liu

Catalysts 2018, 8(6), 243; https://doi.org/10.3390/catal8060243 - 07 Jun 2018

Cited by 5 | Viewed by 4184

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 [...] Read more.

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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22 pages, 3589 KiB

Open AccessArticle

The Synthetic Potential of Fungal Feruloyl Esterases: A Correlation with Current Classification Systems and Predicted Structural Properties

by Io Antonopoulou, Adiphol Dilokpimol, Laura Iancu, Miia R. Mäkelä, Simona Varriale, Gabriella Cerullo, Silvia Hüttner, Stefan Uthoff, Peter Jütten, Alexander Piechot, Alexander Steinbüchel, Lisbeth Olsson, Vincenza Faraco, Kristiina S. Hildén, Ronald P. De Vries, Ulrika Rova and Paul Christakopoulos

Catalysts 2018, 8(6), 242; https://doi.org/10.3390/catal8060242 - 07 Jun 2018

Cited by 14 | Viewed by 5398

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 [...] Read more.

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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15 pages, 3541 KiB

Open AccessArticle

The Promoting Effect of Ce on the Performance of Au/Ce_xZr_1−xO₂ for γ-Valerolactone Production from Biomass-Based Levulinic Acid and Formic Acid

by Xiaoling Li, Jianmei Li, Xudong Liu, Qi Tian and Changwei Hu

Catalysts 2018, 8(6), 241; https://doi.org/10.3390/catal8060241 - 07 Jun 2018

Cited by 11 | Viewed by 3371

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/Ce_xZr_1−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/Ce_xZr_1−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/Ce_xZr_1−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/Ce_0.4Zr_0.6O₂ 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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12 pages, 2111 KiB

Open AccessFeature PaperArticle

Synergistic Effect of Cu₂O and Urea as Modifiers of TiO₂ for Enhanced Visible Light Activity

by Marcin Janczarek, Kunlei Wang and Ewa Kowalska

Catalysts 2018, 8(6), 240; https://doi.org/10.3390/catal8060240 - 06 Jun 2018

Cited by 7 | Viewed by 4986

Abstract

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 [...] Read more.

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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10 pages, 2305 KiB

Open AccessArticle

A Novel High-Activity Zn-Co Catalyst for Acetylene Acetoxylation

by Peijie He, Liuhua Huang, Xueyi Wu, Zhuang Xu, Mingyuan Zhu, Xugen Wang and Bin Dai

Catalysts 2018, 8(6), 239; https://doi.org/10.3390/catal8060239 - 06 Jun 2018

Cited by 13 | Viewed by 3944

Abstract

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 [...] Read more.

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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26 pages, 2705 KiB

Open AccessReview

Industrial Applications of Enzymes: Recent Advances, Techniques, and Outlooks

by Jordan Chapman, Ahmed E. Ismail and Cerasela Zoica Dinu

Catalysts 2018, 8(6), 238; https://doi.org/10.3390/catal8060238 - 05 Jun 2018

Cited by 504 | Viewed by 41682

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 [...] Read more.

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)

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20 pages, 11578 KiB

Open AccessEditor’s ChoiceArticle

Electrochemically Obtained TiO₂/Cu_xO_y Nanotube Arrays Presenting a Photocatalytic Response in Processes of Pollutants Degradation and Bacteria Inactivation in Aqueous Phase

by Magda Kozak, Paweł Mazierski, Joanna Żebrowska, Marek Kobylański, Tomasz Klimczuk, Wojciech Lisowski, Grzegorz Trykowski, Grzegorz Nowaczyk and Adriana Zaleska-Medynska

Catalysts 2018, 8(6), 237; https://doi.org/10.3390/catal8060237 - 05 Jun 2018

Cited by 19 | Viewed by 4462

Abstract

TiO₂/Cu_xO_y 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 [...] Read more.

TiO₂/Cu_xO_y 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/Cu_xO_y 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/Cu_xO_y 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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15 pages, 4792 KiB

Open AccessArticle

Studied Localized Surface Plasmon Resonance Effects of Au Nanoparticles on TiO₂ by FDTD Simulations

by Guo-Ying Yao, Qing-Lu Liu and Zong-Yan Zhao

Catalysts 2018, 8(6), 236; https://doi.org/10.3390/catal8060236 - 05 Jun 2018

Cited by 55 | Viewed by 7368

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 [...] Read more.

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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10 pages, 1911 KiB

Open AccessArticle

Prickly Pear-Like Three-Dimensional Porous MoS₂: Synthesis, Characterization and Advanced Hydrogen Evolution Reaction

by Huiting Lu, Xin Chen, Wenhao Dai, Kai Zhang, Conghui Liu and Haifeng Dong

Catalysts 2018, 8(6), 235; https://doi.org/10.3390/catal8060235 - 04 Jun 2018

Cited by 3 | Viewed by 4380

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 [...] Read more.

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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18 pages, 3887 KiB

Open AccessArticle

Immobilization of an Antarctic Pseudomonas AMS8 Lipase for Low Temperature Ethyl Hexanoate Synthesis

by Nurshakila Musa, Wahhida Latip, Raja Noor Zaliha Abd Rahman, Abu Bakar Salleh and Mohd Shukuri Mohamad Ali

Catalysts 2018, 8(6), 234; https://doi.org/10.3390/catal8060234 - 04 Jun 2018

Cited by 27 | Viewed by 4927

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 [...] Read more.

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)

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13 pages, 5960 KiB

Open AccessArticle

Electrochemical Biosensor for the Determination of Amlodipine Besylate Based on Gelatin–Polyaniline Iron Oxide Biocomposite Film

by Elbahi Djaalab, Mohamed El Hadi Samar, Saida Zougar and Rochdi Kherrat

Catalysts 2018, 8(6), 233; https://doi.org/10.3390/catal8060233 - 04 Jun 2018

Cited by 18 | Viewed by 5783

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 [...] Read more.

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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10 pages, 4361 KiB

Open AccessArticle

Nitrogen-Doped Porous Carbon Derived from Bamboo Shoot as Solid Base Catalyst for Knoevenagel Condensation and Transesterification Reactions

by Bingbing Mi, Xiufang Chen, Changle Jiang, Jingxin Wang, Xiujuan Chen, Bo Zhang, Xianmiao Liu, Zhijia Liu and Benhua Fei

Catalysts 2018, 8(6), 232; https://doi.org/10.3390/catal8060232 - 04 Jun 2018

Cited by 9 | Viewed by 3548

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 [...] Read more.

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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9 pages, 2141 KiB

Open AccessArticle

Ammonia Concentration Distribution Measurements on Selective Catalytic Reduction Catalysts

by Rafal Sala, Jakub Dzida and Jaroslaw Krasowski

Catalysts 2018, 8(6), 231; https://doi.org/10.3390/catal8060231 - 01 Jun 2018

Cited by 10 | Viewed by 3837

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 [...] Read more.

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 NO_x)

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15 pages, 5807 KiB

Open AccessArticle

MgO-Templated Mesoporous Carbon as a Catalyst Support for Polymer Electrolyte Fuel Cells

by Yuji Kamitaka, Tomohiro Takeshita and Yu Morimoto

Catalysts 2018, 8(6), 230; https://doi.org/10.3390/catal8060230 - 01 Jun 2018

Cited by 34 | Viewed by 6011

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 [...] Read more.

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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14 pages, 3187 KiB

Open AccessArticle

Gallium-Promoted Ni Catalyst Supported on MCM-41 for Dry Reforming of Methane

by Ahmed S. Al-Fatesh, Ahmed A. Ibrahim, Jehad K. Abu-Dahrieh, Abdulrahman S. Al-Awadi, Ahmed Mohamed El-Toni, Anis H. Fakeeha and Ahmed E. Abasaeed

Catalysts 2018, 8(6), 229; https://doi.org/10.3390/catal8060229 - 01 Jun 2018

Cited by 22 | Viewed by 4282

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 [...] Read more.

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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14 pages, 4935 KiB

Open AccessArticle

On the Impact of the Preparation Method on the Surface Basicity of Mg–Zr Mixed Oxide Catalysts for Tributyrin Transesterification

by Abdallah I. M. Rabee, Jinesh C. Manayil, Mark A. Isaacs, Christopher M. A. Parlett, Lee J. Durndell, Mohamed I. Zaki, Adam F. Lee and Karen Wilson

Catalysts 2018, 8(6), 228; https://doi.org/10.3390/catal8060228 - 28 May 2018

Cited by 12 | Viewed by 4935

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 [...] Read more.

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

(This article belongs to the Special Issue Catalytic Conversion of Biomass-Derived Molecules to Chemicals and Fuels)

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10 pages, 5750 KiB

Open AccessArticle

Photocatalytic Behavior of Strontium Aluminates Co-Doped with Europium and Dysprosium Synthesized by Hydrothermal Reaction in Degradation of Methylene Blue

by Byung-Geon Park

Catalysts 2018, 8(6), 227; https://doi.org/10.3390/catal8060227 - 28 May 2018

Cited by 11 | Viewed by 3572

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 [...] Read more.

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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16 pages, 4229 KiB

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

by Fudong Liu, Hailiang Wang, Andras Sapi, Hironori Tatsumi, Danylo Zherebetskyy, Hui-Ling Han, Lindsay M. Carl and Gabor A. Somorjai

Catalysts 2018, 8(6), 226; https://doi.org/10.3390/catal8060226 - 27 May 2018

Cited by 19 | Viewed by 6559

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 [...] Read more.

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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14 pages, 7139 KiB

Open AccessArticle

Electrocatalytic Performance of Carbon Supported WO₃-Containing Pd–W Nanoalloys for Oxygen Reduction Reaction in Alkaline Media

by Nan Cui, Wenpeng Li, Zengfeng Guo, Xun Xu and Hongxia Zhao

Catalysts 2018, 8(6), 225; https://doi.org/10.3390/catal8060225 - 24 May 2018

Cited by 10 | Viewed by 4326

Abstract

In this paper, we report that WO_x 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 [...] Read more.

In this paper, we report that WO_x 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 Pd_0.8W_0.2/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 3d_5/2 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 Pd_0.8W_0.2/C shifts to a higher potential. The current density (mA·mg Pd⁻¹) at the oxide-rich Pd_0.8W_0.2/C is ~1.6 times of that at Pd/C. The oxide-rich Pd_0.8W_0.2/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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11 pages, 1562 KiB

Open AccessArticle

Exploring Basic Components Effect on the Catalytic Efficiency of Chevron-Phillips Catalyst in Ethylene Trimerization

by Ebtehal Naji-Rad, Martí Gimferrer, Naeimeh Bahri-Laleh, Mehdi Nekoomanesh-Haghighi, Roghieh Jamjah and Albert Poater

Catalysts 2018, 8(6), 224; https://doi.org/10.3390/catal8060224 - 24 May 2018

Cited by 14 | Viewed by 4826

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, [...] Read more.

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

(This article belongs to the Special Issue Catalysis Assisted by Calculations: From Organic and Metal Catalysts to Enzymes)

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Catalysts, Volume 8, Issue 6 (June 2018) – 32 articles

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