Catalysts

11 pages, 5756 KiB

Open AccessArticle

CuO Nanoparticles Supported on TiO₂ with High Efficiency for CO₂ Electrochemical Reduction to Ethanol

by Jing Yuan, Jing-Jie Zhang, Man-Ping Yang, Wang-Jun Meng, Huan Wang and Jia-Xing Lu

Catalysts 2018, 8(4), 171; https://doi.org/10.3390/catal8040171 - 21 Apr 2018

Cited by 105 | Viewed by 9368

Non-noble metal oxides consisting of CuO and TiO₂ (CuO/TiO₂ catalyst) for CO₂ reduction were fabricated using a simple hydrothermal method. The designed catalysts of CuO could be in situ reduced to a metallic Cu-forming Cu/TiO₂ catalyst, which could efficiently [...] Read more.

Non-noble metal oxides consisting of CuO and TiO₂ (CuO/TiO₂ catalyst) for CO₂ reduction were fabricated using a simple hydrothermal method. The designed catalysts of CuO could be in situ reduced to a metallic Cu-forming Cu/TiO₂ catalyst, which could efficiently catalyze CO₂ reduction to multi-carbon oxygenates (ethanol, acetone, and n-propanol) with a maximum overall faradaic efficiency of 47.4% at a potential of −0.85 V vs. reversible hydrogen electrode (RHE) in 0.5 M KHCO₃ solution. The catalytic activity for CO₂ electroreduction strongly depends on the CuO contents of the catalysts as-prepared, resulting in different electrochemistry surface areas. The significantly improved CO₂ catalytic activity of CuO/TiO₂ might be due to the strong CO₂ adsorption ability. Full article

(This article belongs to the Special Issue Emissions Control Catalysis)

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19 pages, 2524 KiB

Open AccessArticle

Maltose Production Using Starch from Cassava Bagasse Catalyzed by Cross-Linked β-Amylase Aggregates

by Rafael Araujo-Silva, Agnes Cristina Oliveira Mafra, Mayerlenis Jimenez Rojas, Willian Kopp, Roberto De Campos Giordano, Roberto Fernandez-Lafuente and Paulo Waldir Tardioli

Catalysts 2018, 8(4), 170; https://doi.org/10.3390/catal8040170 - 21 Apr 2018

Cited by 28 | Viewed by 6936

Abstract

Barley β-amylase was immobilized using different techniques. The highest global yield was obtained using the cross-linked enzyme aggregates (CLEA) technique, employing bovine serum albumin (BSA) or soy protein isolate (SPI) as feeder proteins to reduce diffusion problems. The CLEAs produced using BSA or [...] Read more.

Barley β-amylase was immobilized using different techniques. The highest global yield was obtained using the cross-linked enzyme aggregates (CLEA) technique, employing bovine serum albumin (BSA) or soy protein isolate (SPI) as feeder proteins to reduce diffusion problems. The CLEAs produced using BSA or SPI showed 82.7 ± 5.8 and 53.3 ± 2.4% global yield, respectively, and a stabilization effect was observed upon immobilization at neutral pH value, e.g., after 12 h at 55 °C, the free β-amylase is fully inactivated, while CLEAs retained 25 and 15% of activity (using BSA and SPI, respectively). CLEA using SPI was selected because of its easier recovery, being chosen to convert the residual starch contained in cassava bagasse into maltose. This biocatalyst permitted to reach almost 70% of maltose conversion in 4 h using 30.0 g/L bagasse starch solution (Dextrose Equivalent of 15.88) and 1.2 U of biocatalyst per gram of starch at pH 7.0 and 40 °C. After 4 reuses (batches of 12 h) the CLEA using SPI maintained 25.50 ± 0.01% of conversion due to the difficulty of recovering. Full article

(This article belongs to the Special Issue Immobilized Biocatalysts)

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16 pages, 4962 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Biorefinery Cascade Conversion of Hemicellulose-Free Eucalyptus Globulus Wood: Production of Concentrated Levulinic Acid Solutions for γ-Valerolactone Sustainable Preparation

by Sandra Rivas, Anna Maria Raspolli Galletti, Claudia Antonetti, Domenico Licursi, Valentín Santos and Juan Carlos Parajó

Catalysts 2018, 8(4), 169; https://doi.org/10.3390/catal8040169 - 21 Apr 2018

Cited by 29 | Viewed by 5169

Abstract

Eucalyptus globulus wood samples were subjected to preliminary aqueous processing to remove water-soluble extractives and hemicelluloses, and the resulting solid (mainly made up of cellulose and lignin) was employed as a substrate for converting the cellulosic fraction into mixtures of levulinic and formic [...] Read more.

Eucalyptus globulus wood samples were subjected to preliminary aqueous processing to remove water-soluble extractives and hemicelluloses, and the resulting solid (mainly made up of cellulose and lignin) was employed as a substrate for converting the cellulosic fraction into mixtures of levulinic and formic acid through a sulfuric acid-catalyzed reaction. These runs were carried out in a microwave-heated reactor at different temperatures and reaction times, operating in single-batch or cross-flow modes, in order to identify the most favorable operational conditions. Selected liquid phases deriving from these experiments, which resulted in concentrated levulinic acid up to 408 mmol/L, were then employed for γ-valerolactone production by levulinc acid hydrogenation in the presence of the commercial 5% Ru/C catalyst. In order to assess the effects of the main reaction parameters, hydrogenation experiments were performed at different temperatures, reaction times, amounts of ruthenium catalyst and hydrogen pressure. Yields of γ-valerolactone in the range of 85–90 mol % were obtained from the hydrogenation of the wood-derived solutions containing levulinic acid, obtained by single-batch operation or by the cross-flow process. The negative effect of co-produced formic acid present in crude levulinic acid solutions was evidenced and counteracted efficiently by allowing the preliminary thermal decomposition of formic acid itself. Full article

(This article belongs to the Special Issue Catalytic Transformation of Lignocellulosic Platform Chemicals)

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9 pages, 2750 KiB

Open AccessArticle

Co-Immobilization of Ketoreductase and Glucose Dehydrogenase

by Tatiana Petrovičová, Kristína Markošová, Zuzana Hegyi, Ioulia Smonou, Michal Rosenberg and Martin Rebroš

Catalysts 2018, 8(4), 168; https://doi.org/10.3390/catal8040168 - 20 Apr 2018

Cited by 20 | Viewed by 5674

Abstract

A two-enzyme system composed of immobilized ketoreductase (Hansenula polymorpha) and glucose dehydrogenase (Bacillus megaterium) was developed for the asymmetric reduction of keto esters to optically active hydroxy esters via immobilization in polyvinyl alcohol (PVA) gel particles. The concentration of [...] Read more.

A two-enzyme system composed of immobilized ketoreductase (Hansenula polymorpha) and glucose dehydrogenase (Bacillus megaterium) was developed for the asymmetric reduction of keto esters to optically active hydroxy esters via immobilization in polyvinyl alcohol (PVA) gel particles. The concentration of enzymes was optimized, and the final particles were used 18 times in a row in a batch mode to achieve minimal loss of activity and complete conversion of the model substrate, β-ketoester ethyl-2-methylacetoacetate. Excellent stability was also achieved using new storage conditions of PVA particles, with 80% of activity being retained after almost 10 months. Full article

(This article belongs to the Special Issue Immobilized Biocatalysts)

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11 pages, 2977 KiB

Open AccessArticle

Unprecedented Proline-Based Heterogeneous Organocatalyst for Selective Production of Vanillin

by Farveh Saberi, Daily Rodriguez-Padrón, Araceli Garcia, Hamid Reza Shaterian and Rafael Luque

Catalysts 2018, 8(4), 167; https://doi.org/10.3390/catal8040167 - 20 Apr 2018

Cited by 11 | Viewed by 4767

Abstract

An organocatalytic system based on an unprecedented proline analogue and iron oxide magnetic nanoparticles (Prn/Fe₂O₃@SiO₂) was designed and employed in vanillin production from isoeugenol and vanillyl alcohol. Full characterization of the obtained catalyst revealed the successful functionalization [...] Read more.

An organocatalytic system based on an unprecedented proline analogue and iron oxide magnetic nanoparticles (Prn/Fe₂O₃@SiO₂) was designed and employed in vanillin production from isoeugenol and vanillyl alcohol. Full characterization of the obtained catalyst revealed the successful functionalization of the nanoparticle surface with the organic moieties. The activity of the magnetic bifunctional material was compared with its proton-unexchanged counterpart. Interestingly, the oxidation of isoeugenol resulted in being highly dependent on the acidic functionalities of the organocatalyst. Nonetheless, the catalytic performance of the proton-unexchanged catalyst suggested that the acidic and basic sites of the Prn/Fe₂O₃@SiO₂ exhibited a synergic effect, giving rise to higher conversion and selectivity. The presence of bifunctional groups in the proline analogue, together with the magnetic properties of the iron oxide nanoparticles, could lead to high efficiency, versatility, recoverability, and reusability. Full article

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10 pages, 1767 KiB

Open AccessReview

Applications of Immobilized Bio-Catalyst in Metal-Organic Frameworks

by Qi Wang, Xizhen Lian, Yu Fang and Hong-Cai Zhou

Catalysts 2018, 8(4), 166; https://doi.org/10.3390/catal8040166 - 20 Apr 2018

Cited by 27 | Viewed by 7601

Abstract

Immobilization of bio-catalysts in solid porous materials has attracted much attention in the last few decades due to its vast application potential in ex vivo catalysis. Despite the high efficiency and selectivity of enzymatic catalytic processes, enzymes may suffer from denaturation under industrial [...] Read more.

Immobilization of bio-catalysts in solid porous materials has attracted much attention in the last few decades due to its vast application potential in ex vivo catalysis. Despite the high efficiency and selectivity of enzymatic catalytic processes, enzymes may suffer from denaturation under industrial production conditions, which, in turn, diminish their catalytic performances and long-term recyclability. Metal-organic frameworks (MOFs), as a growing type of hybrid materials, have been identified as promising platforms for enzyme immobilization owing to their enormous structural and functional tunability, and extraordinary porosity. This review mainly focuses on the applications of enzyme@MOFs hybrid materials in catalysis, sensing, and detection. The improvements of catalytic activity and robustness of encapsulated enzymes over the free counterpart are discussed in detail. Full article

(This article belongs to the Special Issue Immobilized Biocatalysts)

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16 pages, 1968 KiB

Open AccessArticle

Asymmetric Ketone Reduction by Immobilized Rhodotorula mucilaginosa

by Hui Liu, Wen-Di Duan, Fayene Zeferino Ribeiro De Souza, Lan Liu and Bi-Shuang Chen

Catalysts 2018, 8(4), 165; https://doi.org/10.3390/catal8040165 - 19 Apr 2018

Cited by 12 | Viewed by 3413

Abstract

In our previous study, Rhodotorula mucilaginosa (R. mucilaginosa) was selected via high throughput screening as a very active and selective whole-cell biocatalyst for the asymmetric reduction of ketones. In this study, the reduction of ketones to the desired chiral alcohols by [...] Read more.

In our previous study, Rhodotorula mucilaginosa (R. mucilaginosa) was selected via high throughput screening as a very active and selective whole-cell biocatalyst for the asymmetric reduction of ketones. In this study, the reduction of ketones to the desired chiral alcohols by immobilized cells of this strain was investigated. Characterization with Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) showed that whole R. mucilaginosa cells were successfully immobilized on support matrices composed of agar, calcium alginate, PVA-alginate and chitosan. The immobilized cells were applied to the enantioselective reduction of fourteen different aromatic ketones. Good to excellent results were achieved with R. mucilaginosa cells immobilized on agar and calcium alginate. The immobilized cells on the selected support matrix composed of agar exhibited a significant increase in pH tolerance at pH 3.5–9 and demonstrated highly improved thermal stability compared to free cells. The cells immobilized on agar retained 90% activity after 60 days storage at 4 °C and retained almost 100% activity after 6 reuse cycles. In addition, the immobilization procedures are very simple and cause minimal pollution. These results suggest that the application of immobilized R. mucilaginosa can be practical on an industrial scale to produce chiral alcohols. Full article

(This article belongs to the Special Issue Immobilized Biocatalysts)

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11 pages, 5008 KiB

Open AccessArticle

Surface Reduced CeO₂ Nanowires for Direct Conversion of CO₂ and Methanol to Dimethyl Carbonate: Catalytic Performance and Role of Oxygen Vacancy

by Zhongwei Fu, Yuehong Yu, Zhen Li, Dongmei Han, Shuanjin Wang, Min Xiao and Yuezhong Meng

Catalysts 2018, 8(4), 164; https://doi.org/10.3390/catal8040164 - 19 Apr 2018

Cited by 27 | Viewed by 5690

Abstract

Ultralong 1D CeO₂ nanowires were synthesized via an advanced solvothermal method, surface reduced under H₂ atmosphere, and first applied in direct synthesis of dimethyl carbonate (DMC) from CO₂ and CH₃OH. The micro morphologies, physical parameters of nanowires were [...] Read more.

Ultralong 1D CeO₂ nanowires were synthesized via an advanced solvothermal method, surface reduced under H₂ atmosphere, and first applied in direct synthesis of dimethyl carbonate (DMC) from CO₂ and CH₃OH. The micro morphologies, physical parameters of nanowires were fully investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), N₂ adsorption, X-ray photoelectron spectrum (XPS), and temperature-programmed desorption of ammonia/carbon dioxide (NH₃-TPD/CO₂-TPD). The effects of surface oxygen vacancy and acidic/alkaline sites on the catalytic activity was explored. After reduction, the acidic/alkaline sites of CeO₂ nanowires can be dramatically improved and evidently raised the catalytic performance. CeO₂ nanowires reduced at 500 °C (CeO₂_NW_500) exhibited notably superior activity with DMC yield of 16.85 mmol gcat⁻¹. Furthermore, kinetic insights of initial rate were carried out and the apparent activation energy barrier of CeO₂_NW_500 catalyst was found to be 41.9 kJ/mol, much tiny than that of CeO₂_NW catalyst (74.7 KJ/mol). Full article

(This article belongs to the Special Issue Nanomaterials for Environmental Purification and Energy Conversion)

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18 pages, 5062 KiB

Open AccessEditor’s ChoiceReview

An Overview on Zeolite Shaping Technology and Solutions to Overcome Diffusion Limitations

by Rogéria Bingre, Benoît Louis and Patrick Nguyen

Catalysts 2018, 8(4), 163; https://doi.org/10.3390/catal8040163 - 18 Apr 2018

Cited by 81 | Viewed by 13039

Abstract

Synthetic zeolites are widely used as catalysts/carriers for many petrochemical reactions and in refining processes. These materials are usually synthesized in a powder form and must be shaped prior to use in industrial reactors. This review presents the state-of-the-art of the zeolite shaping [...] Read more.

Synthetic zeolites are widely used as catalysts/carriers for many petrochemical reactions and in refining processes. These materials are usually synthesized in a powder form and must be shaped prior to use in industrial reactors. This review presents the state-of-the-art of the zeolite shaping technology describing the main modifications induced by the interactions between the zeolite and the binder. Additionally, a strategy is presented to overcome the diffusion limitations associated to the microporous structure of zeolites, consisting in the introduction of hierarchical porosity in the binder. Several developments in the field of hierarchical aluminas are summarized in this article, highlighting the possibility to design different ordered/disordered mesoporous and macroporous structures. Full article

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13 pages, 5206 KiB

Open AccessArticle

Mobility of NH₃-Solvated Cu^II Ions in Cu-SSZ-13 and Cu-ZSM-5 NH₃-SCR Catalysts: A Comparative Impedance Spectroscopy Study

by Valentina Rizzotto, Peirong Chen and Ulrich Simon

Catalysts 2018, 8(4), 162; https://doi.org/10.3390/catal8040162 - 18 Apr 2018

Cited by 23 | Viewed by 5227

Abstract

The mobility of NH₃-solvated Cu ions within the zeolite framework has been recently identified as a key factor for the kinetics of the selective catalytic reduction of NO_x with NH₃ (NH₃-SCR) over Cu-zeolite catalysts at low temperatures. [...] Read more.

The mobility of NH₃-solvated Cu ions within the zeolite framework has been recently identified as a key factor for the kinetics of the selective catalytic reduction of NO_x with NH₃ (NH₃-SCR) over Cu-zeolite catalysts at low temperatures. Here, we utilize in situ impedance spectroscopy to explore the mobility of NH₃-solvated Cu^II ions, i.e., Cu^II(NH₃)_n, in Cu-SSZ-13 and Cu-ZSM-5 zeolites with varied Cu ion exchange levels, and observed that both the zeolite framework (CHA or MFI) and the Cu exchange level influence the high-frequency dielectric relaxation processes that are associated with the short-range (local) motion of Cu^II(NH₃)_n. Our results suggest that the local motion of Cu^II(NH₃)_n species is favored within the CHA framework due to the unique cage structure, and thereby contribute to the overall ion conductivity at high frequencies, which, on the contrary, is not observed for ZSM-5, where NH₃-solvated Cu²⁺ ions do not experience a comparable constrained space for local motion. This study sheds new light on the mobility of Cu active sites under NH₃-SCR related reaction conditions and may contribute to an advanced understanding of the underlying mechanism. Full article

(This article belongs to the Special Issue Selective Catalytic Reduction of NO_x)

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14 pages, 2661 KiB

Open AccessArticle

A Comparative Study of Gold Impregnation Methods for Obtaining Metal/Semiconductor Nanophotocatalysts: Direct Turkevich, Inverse Turkevich, and Progressive Heating Methods

by Mayra Matamoros-Ambrocio, María De Lourdes Ruiz-Peralta, Ernesto Chigo-Anota, Jesús García-Serrano, Armando Pérez-Centeno, Manuel Sánchez-Cantú, Efraín Rubio-Rosas and Alejandro Escobedo-Morales

Catalysts 2018, 8(4), 161; https://doi.org/10.3390/catal8040161 - 18 Apr 2018

Cited by 4 | Viewed by 4715

Abstract

ZnO nanostructures decorated with gold nanoparticles (Au-NPs) were synthesized by thermal decomposition of ZnO₂ powders and their subsequent impregnation of metal nanoparticles using either the Direct Turkevich Method, the Inverse Turkevich Method, or the Progressive Heating Method. It was found that the [...] Read more.

ZnO nanostructures decorated with gold nanoparticles (Au-NPs) were synthesized by thermal decomposition of ZnO₂ powders and their subsequent impregnation of metal nanoparticles using either the Direct Turkevich Method, the Inverse Turkevich Method, or the Progressive Heating Method. It was found that the impregnation approach influences the resulting microstructure and photocatalytic activity of the obtained materials. While the Direct Turkevich approach gave the highest yield of metal loading, the smallest Au-NPs were obtained by Inverse Turkevich and the Progressive Heating Method. The photocatalytic activity of the pristine support and gold-loaded samples was studied in the decolorization of Rhodamine B solutions using UV- and pure visible-light illumination. All Au-NPs/ZnO samples showed higher photocatalytic activity than the bare support when UV-light was used. This effect is attributed to a charge carrier separation due to electron transfer from ZnO to the metal nanoparticles and the built-in electric field at the interfaces. Contrarily to most reports, visible-light sensitization using plasmonic nanoparticles was not observed. The experimental evidence points against hot-electron injection from Au-NPs to the semiconductor component. This behavior is associated with the height of the Schottky barrier at the metal-semiconductor junctions. The differences in the photocatalytic performance among the samples under UV- and visible-light are explained in terms of the characteristics of the Au-NPs driven by the growth mechanism involved in each impregnation method and the physicochemical properties of the generated interfaces. Full article

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12 pages, 2256 KiB

Open AccessArticle

Catalytic Activities of Noble Metal Phosphides for Hydrogenation and Hydrodesulfurization Reactions

by Yasuharu Kanda, Kota Kawanishi, Taiki Tsujino, Ahmad MFM Al-otaibi and Yoshio Uemichi

Catalysts 2018, 8(4), 160; https://doi.org/10.3390/catal8040160 - 17 Apr 2018

Cited by 22 | Viewed by 5475

Abstract

In this work, the development of a highly active noble metal phosphide (NM_XP_Y)-based hydrodesulfurization (HDS) catalyst with a high hydrogenating ability for heavy oils was studied. NM_XP_Y catalysts were obtained by reduction of P-added noble metals [...] Read more.

In this work, the development of a highly active noble metal phosphide (NM_XP_Y)-based hydrodesulfurization (HDS) catalyst with a high hydrogenating ability for heavy oils was studied. NM_XP_Y catalysts were obtained by reduction of P-added noble metals (NM-P, NM: Rh, Pd, Ru) supported on SiO₂. The order of activities for the hydrogenation of biphenyl was Rh-P > NiMoS > Pd-P > Ru-P. This order was almost the same as that of the catalytic activities for the HDS of dibenzothiophene. In the HDS of 4,6-dimethyldibenzothiophene (4,6-DMDBT), the HDS activity of the Rh-P catalyst increased with increasing reaction temperature, but the maximum HDS activity for the NiMoS catalyst was observed at 270 °C. The Rh-P catalyst yielded fully hydrogenated products with high selectivity compared with the NiMoS catalyst. Furthermore, XRD analysis of the spent Rh-P catalysts revealed that the Rh₂P phase possessed high sulfur tolerance and resistance to sintering. Full article

(This article belongs to the Special Issue Recent Progress in Transition Metal Phosphide Catalysts for the Hydroprocessing of Petroleum or Biomass Feedstocks)

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11 pages, 3321 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Immobilization of Enterobacter aerogenes by a Trimeric Autotransporter Adhesin, AtaA, and Its Application to Biohydrogen Production

by Hajime Nakatani, Nan Ding, Yuki Ohara and Katsutoshi Hori

Catalysts 2018, 8(4), 159; https://doi.org/10.3390/catal8040159 - 16 Apr 2018

Cited by 12 | Viewed by 5296

Abstract

Biological hydrogen production by microbial cells has been extensively researched as an energy-efficient and environmentally-friendly process. In this study, we propose a fast, easy method for immobilizing Enterobacter aerogenes by expressing ataA, which encodes the adhesive protein of Acinetobacter sp. Tol 5. [...] Read more.

Biological hydrogen production by microbial cells has been extensively researched as an energy-efficient and environmentally-friendly process. In this study, we propose a fast, easy method for immobilizing Enterobacter aerogenes by expressing ataA, which encodes the adhesive protein of Acinetobacter sp. Tol 5. AtaA protein on the E. aerogenes cells carrying the ataA gene was demonstrated by immunoblotting and flow cytometry. The AtaA-producing cells exhibited stronger adherence and auto-agglutination characteristics than wild-type cells, and were successfully immobilized (at approximately 2.5 mg/cm³) on polyurethane foam. Hydrogen production from the cell-immobilized polyurethane foams was monitored in repetitive batch reactions and flow reactor studies. The total hydrogen production in triple-repetitive batch reactions reached 0.6 mol/mol glucose, and the hydrogen production rate in the flow reactor was 42 mL·h⁻¹·L⁻¹. The AtaA production achieved simple and immediate immobilization of E. aerogenes on the foam, enabling repetitive and continuous hydrogen production. This report newly demonstrates the production of AtaA on the cell surfaces of bacterial genera other than Acinetobacter, and can simplify and accelerate the immobilization of whole-cell catalysts. Full article

(This article belongs to the Special Issue Immobilized Biocatalysts)

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13 pages, 5353 KiB

Open AccessFeature PaperArticle

Binary Nitrogen Precursor-Derived Porous Fe-N-S/C Catalyst for Efficient Oxygen Reduction Reaction in a Zn-Air Battery

by Xiao Liu, Chi Chen, Qingqing Cheng, Liangliang Zou, Zhiqing Zou and Hui Yang

Catalysts 2018, 8(4), 158; https://doi.org/10.3390/catal8040158 - 13 Apr 2018

Cited by 9 | Viewed by 4853

Abstract

It is still a challenge to synthesize non-precious-metal catalysts with high activity and stability for the oxygen reduction reaction (ORR) to replace the state-of-the art Pt/C catalyst. Herein, a Fe, N, S co-doped porous carbon (Fe-NS/PC) is developed by using g-C₃N [...] Read more.

It is still a challenge to synthesize non-precious-metal catalysts with high activity and stability for the oxygen reduction reaction (ORR) to replace the state-of-the art Pt/C catalyst. Herein, a Fe, N, S co-doped porous carbon (Fe-NS/PC) is developed by using g-C₃N₄ and 2,4,6-tri(2-pyridyl)-1,3,5-triazine (TPTZ) as binary nitrogen precursors. The interaction of binary nitrogen precursors not only leads to the formation of more micropores, but also increases the doping amount of both iron and nitrogen dispersed in the carbon matrix. After a second heat-treatment, the best Fe/NS/C-g-C₃N₄/TPTZ-1000 catalyst exhibits excellent ORR performance with an onset potential of 1.0 V vs. reversible hydrogen electrode (RHE) and a half-wave potential of 0.868 V (RHE) in alkaline medium. The long-term durability is even superior to the commercial Pt/C catalyst. In the meantime, an assembled Zn-air battery with Fe/NS/C-g-C₃N₄/TPTZ-1000 as the cathode shows a maximal power density of 225 mW·cm⁻² and excellent durability, demonstrating the great potential of practical applications in energy conversion devices. Full article

(This article belongs to the Special Issue Novel Non-Precious Metal Electrocatalysts for Oxygen Electrode Reactions)

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14 pages, 963 KiB

Open AccessArticle

Catalytic Role of H₂O Molecules in Oxidation of CH₃OH in Water

by Satoshi Inaba

Catalysts 2018, 8(4), 157; https://doi.org/10.3390/catal8040157 - 12 Apr 2018

Cited by 9 | Viewed by 7344

Abstract

We have examined the catalytic role of H₂O molecules in the oxidation of CH₃OH in water by quantum chemical simulations. A CH₃OH is decomposed into molecules, a formaldehyde and an H₂, in water, while it [...] Read more.

We have examined the catalytic role of H₂O molecules in the oxidation of CH₃OH in water by quantum chemical simulations. A CH₃OH is decomposed into molecules, a formaldehyde and an H₂, in water, while it is converted into radicals in a gas phase reaction at a high temperature. H₂O molecules located near a CH₃OH form a first hydration shell and act as catalyst for the oxidation of CH₃OH in water. The oxidation process of a CH₃OH in water begins when a proton is delivered to a neighbor H₂O molecule from a hydroxyl of a CH₃OH. The H₂O molecule transfers an extra proton to a second H₂O molecule, a proton of which is combined with a proton detached from the methyl of the CH₃OH, forming an H₂. The energy barrier to decompose a CH₃OH is significantly reduced by the catalyst of H₂O molecules in water. A cluster of H₂O molecules arise in water as an enclosed chain of hydrogen bonds between H₂O molecules. A proton is transferred with less energy between H₂O molecules within a cluster of H₂O molecules. A cluster of five H₂O molecules further reduces the energy barrier. The calculated oxidation rate of CH₃OH with the transition state theory agrees well with that determined by experiments. Full article

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16 pages, 20743 KiB

Open AccessArticle

The Effects of Coordinated Molecules of Two Gly-Schiff Base Copper Complexes on Their Oxygen Reduction Reaction Performance

by Zhe Ma, Ya Chu, Chonggang Fu, Hongmei Du, Xianqiang Huang and Jinsheng Zhao

Catalysts 2018, 8(4), 156; https://doi.org/10.3390/catal8040156 - 12 Apr 2018

Cited by 8 | Viewed by 4358

Abstract

In this study, two simple Schiff base copper complexes [Cu(H₂O)₂(HL)]·2H₂O (Complex 1) (H₃L = 2-OH-4-(OH)-C₆H₂CH=NCH₂CO₂H) and [Cu(py)₂(HL)] (Complex 2) (Py = pyridine) were [...] Read more.

In this study, two simple Schiff base copper complexes [Cu(H₂O)₂(HL)]·2H₂O (Complex 1) (H₃L = 2-OH-4-(OH)-C₆H₂CH=NCH₂CO₂H) and [Cu(py)₂(HL)] (Complex 2) (Py = pyridine) were initially achieved and authenticated by single-crystal X-ray structure analyses (SXRD), powder X-ray diffraction analyses (PXRD), FT-IR spectroscopy, and elemental analyses. The SXRD reveals that the Cu²⁺ center in Complex 1 exhibited a distorted square pyramidal geometry, which is constructed based on phenolate oxygen, water molecules, carboxylate oxygen, and imine nitrogen from a deprotonated H₃L ligand in an NO₄ fashion. The Cu²⁺ atom in Complex 2 had distorted square pyramidal geometry, and was coordinated with two pyridine molecules and one Gly-Schiff base ligand, exhibiting an N₃O₂ binding set. Additionally, the free water molecules in Complex 1 linked independent copper complexes by intermolecular hydrogen bond to form a 2D framework. However, the one-dimensional chain supramolecular structure of Complex 2 was formed by the intermolecular O–H…O hydrogen bonds. The oxygen reduction performance of the two complexes was analyzed by cyclic voltammetry (CV) and the rotating disk electrode (RDE) method. Both complexes could catalyze the conversion of oxygen to water through a predominant four-electron pathway, and the Cu–N_xO_y moieties might be the functional moieties for the catalytic activity. The catalytic pathways and underlying mechanisms are also discussed in detail, from which the structure–activity relationship of the complexes was obtained. Full article

(This article belongs to the Special Issue Platinum-Free Electrocatalysts)

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15 pages, 7391 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Gas-Phase Phosphorous Poisoning of a Pt/Ba/Al₂O₃ NO_x Storage Catalyst

by Rasmus Jonsson, Oana Mihai, Jungwon Woo, Magnus Skoglundh, Eva Olsson, Malin Berggrund and Louise Olsson

Catalysts 2018, 8(4), 155; https://doi.org/10.3390/catal8040155 - 11 Apr 2018

Cited by 6 | Viewed by 4276

Abstract

The effect of phosphorous exposure on the NO_x storage capacity of a Pt/Ba/Al₂O₃ catalyst coated on a ceramic monolith substrate has been studied. The catalyst was exposed to phosphorous by evaporating phosphoric acid in presence of H₂O [...] Read more.

The effect of phosphorous exposure on the NO_x storage capacity of a Pt/Ba/Al₂O₃ catalyst coated on a ceramic monolith substrate has been studied. The catalyst was exposed to phosphorous by evaporating phosphoric acid in presence of H₂O and O₂. The NO_x storage capacity was measured before and after the phosphorus exposure and a significant loss of the NO_x storage capacity was detected after phosphorous exposure. The phosphorous poisoned samples were characterized by X-ray photoelectron spectroscopy (XPS), environmental scanning electron microscopy (ESEM), N₂-physisorption and inductive coupled plasma atomic emission spectroscopy (ICP-AES). All characterization methods showed an axial distribution of phosphorous ranging from the inlet to the outlet of the coated monolith samples with a higher concentration at the inlet of the samples. Elemental analysis, using ICP-AES, confirmed this distribution of phosphorous on the catalyst surface. The specific surface area and pore volume were significantly lower at the inlet section of the monolith where the phosphorous concentration was higher, and higher at the outlet where the phosphorous concentration was lower. The results from the XPS and scanning electron microscopy (SEM)-energy dispersive X-ray (EDX) analyses showed higher accumulation of phosphorus towards the surface of the catalyst at the inlet of the monolith and the phosphorus was to a large extent present in the form of P₄O₁₀. However, in the middle section of the monolith, the XPS analysis revealed the presence of more metaphosphate (PO₃⁻). Moreover, the SEM-EDX analysis showed that the phosphorous to higher extent had diffused into the washcoat and was less accumulated at the surface close to the outlet of the sample. Full article

(This article belongs to the Special Issue Emissions Control Catalysis)

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19 pages, 16248 KiB

Open AccessEditor’s ChoiceArticle

Preparation of Stable Cross-Linked Enzyme Aggregates (CLEAs) of a Ureibacillus thermosphaericus Esterase for Application in Malathion Removal from Wastewater

by Yuliya V. Samoylova, Ksenia N. Sorokina, Alexander V. Piligaev and Valentin N. Parmon

Catalysts 2018, 8(4), 154; https://doi.org/10.3390/catal8040154 - 11 Apr 2018

Cited by 26 | Viewed by 5070

Abstract

In this study, the active and stable cross-linked enzyme aggregates (CLEAs) of the thermostable esterase estUT1 of the bacterium Ureibacillus thermosphaericus were prepared for application in malathion removal from municipal wastewater. Co-expression of esterase with an E. coli chaperone team (KJE, ClpB, and [...] Read more.

In this study, the active and stable cross-linked enzyme aggregates (CLEAs) of the thermostable esterase estUT1 of the bacterium Ureibacillus thermosphaericus were prepared for application in malathion removal from municipal wastewater. Co-expression of esterase with an E. coli chaperone team (KJE, ClpB, and ELS) increased the activity of the soluble enzyme fraction up to 200.7 ± 15.5 U mg⁻¹. Response surface methodology (RSM) was used to optimize the preparation of the CLEA-estUT1 biocatalyst to maximize its activity and minimize enzyme loss. CLEA-estUT1 with the highest activity of 29.4 ± 0.5 U mg⁻¹ (90.6 ± 2.7% of the recovered activity) was prepared with 65.1% (w/v) ammonium sulfate, 120.6 mM glutaraldehyde, and 0.2 mM bovine serum albumin at 5.1 h of cross-linking. The biocatalyst has maximal activity at 80 °С and pH 8.0. Analysis of the properties of CLEA-estUT1 and free enzyme at 50–80 °C and pH 5.0–10.0 showed higher stability of the biocatalyst. CLEA-estUT1 showed marked tolerance against a number of chemicals and high operational stability and activity in the reaction of malathion hydrolysis in wastewater (up to 99.5 ± 1.4%). After 25 cycles of malathion hydrolysis at 37 °С, it retained 55.2 ± 1.1% of the initial activity. The high stability and reusability of CLEA-estUT1 make it applicable for the degradation of insecticides. Full article

(This article belongs to the Special Issue Immobilized Biocatalysts)

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20 pages, 22551 KiB

Open AccessArticle

The Deoxygenation Pathways of Palmitic Acid into Hydrocarbons on Silica-Supported Ni₁₂P₅ and Ni₂P Catalysts

by Wenjun Zhou, Hui Xin, Huiru Yang, Xiangze Du, Rui Yang, Dan Li and Changwei Hu

Catalysts 2018, 8(4), 153; https://doi.org/10.3390/catal8040153 - 11 Apr 2018

Cited by 31 | Viewed by 5761

Abstract

Pure Ni₁₂P₅/SiO₂ and pure Ni₂P/SiO₂ catalysts were obtained by adjusting the Ni and P molar ratios, while Ni/SiO₂ catalyst was prepared as a reference against which the deoxygenation pathways of palmitic acid were investigated. [...] Read more.

Pure Ni₁₂P₅/SiO₂ and pure Ni₂P/SiO₂ catalysts were obtained by adjusting the Ni and P molar ratios, while Ni/SiO₂ catalyst was prepared as a reference against which the deoxygenation pathways of palmitic acid were investigated. The catalysts were characterized by N₂ adsorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission election microscopy (TEM), infrared spectroscopy of pyridine adsorption (Py-IR), H₂-adsorption and temperature-programmed desorption of hydrogen (H₂-TPD). The crystallographic planes of Ni(111), Ni₁₂P₅(400), Ni₂P(111) were found mainly exposed on the above three catalysts, respectively. It was found that the deoxygenation pathway of palmitic acid mainly proceeded via direct decarboxylation (DCO₂) to form C15 on Ni/SiO₂. In contrast, on the Ni₁₂P₅/SiO₂ catalyst, there were two main competitive pathways producing C15 and C16, one of which mainly proceeded via the decarbonylation (DCO) to form C15 accompanying water formation, and the other pathway produced C16 via the dehydration of hexadecanol intermediate, and the yield of C15 was approximately twofold that of C16. Over the Ni₂P/SiO₂ catalyst, two main deoxygenation pathways formed C15, one of which was mainly the DCO pathway and the other was dehydration accompanying the hexadecanal intermediate and then direct decarbonylation without water formation. The turn over frequency (TOF) followed the order: Ni₁₂P₅/SiO₂ > Ni/SiO₂ > Ni₂P/SiO₂. Full article

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9 pages, 1017 KiB

Open AccessEditor’s ChoiceCommunication

Catalytic Efficiency of Basidiomycete Laccases: Redox Potential versus Substrate-Binding Pocket Structure

by Olga A. Glazunova, Nikita A. Trushkin, Konstantin V. Moiseenko, Ivan S. Filimonov and Tatyana V. Fedorova

Catalysts 2018, 8(4), 152; https://doi.org/10.3390/catal8040152 - 09 Apr 2018

Cited by 36 | Viewed by 5013

Abstract

Laccases are copper-containing oxidases that catalyze a one-electron abstraction from various phenolic and non-phenolic compounds with concomitant reduction of molecular oxygen to water. It is well-known that laccases from various sources have different substrate specificities, but it is not completely clear what exactly [...] Read more.

Laccases are copper-containing oxidases that catalyze a one-electron abstraction from various phenolic and non-phenolic compounds with concomitant reduction of molecular oxygen to water. It is well-known that laccases from various sources have different substrate specificities, but it is not completely clear what exactly provides these differences. The purpose of this work was to study the features of the substrate specificity of four laccases from basidiomycete fungi Trametes hirsuta, Coriolopsis caperata, Antrodiella faginea, and Steccherinum murashkinskyi, which have different redox potentials of the T1 copper center and a different structure of substrate-binding pockets. Enzyme activity toward 20 monophenolic substances and 4 phenolic dyes was measured spectrophotometrically. The kinetic parameters of oxidation of four lignans and lignan-like substrates were determined by monitoring of the oxygen consumption. For the oxidation of the high redox potential (>700 mV) monophenolic substrates and almost all large substrates, such as phenolic dyes and lignans, the redox potential difference between the enzyme and the substrate (ΔE) played the defining role. For the low redox potential monophenolic substrates, ΔE did not directly influence the laccase activity. Also, in the special cases, the structure of the large substrates, such as dyes and lignans, as well as some structural features of the laccases (flexibility of the substrate-binding pocket loops and some amino acid residues in the key positions) affected the resulting catalytic efficiency. Full article

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6 pages, 1358 KiB

Open AccessArticle

Synthesis and Characterization of CNT/TiO₂/ZnO Composites with High Photocatalytic Performance

by Yanzhen Huang, Rongkai Li, Dongping Chen, Xinling Hu, Pengxin Chen, Zhibin Chen and Dongxu Li

Catalysts 2018, 8(4), 151; https://doi.org/10.3390/catal8040151 - 09 Apr 2018

Cited by 29 | Viewed by 9602

Abstract

Novel carbon nanotubes (CNTs)/titanium dioxide (TiO₂)/zinc oxide (ZnO) composites have been successfully synthesized via a two-step solution method using titanyl sulfate as the titanium precursor. Its structural performances were researched by various characterization methods, such as X-ray powder diffraction (XRD), scanning [...] Read more.

Novel carbon nanotubes (CNTs)/titanium dioxide (TiO₂)/zinc oxide (ZnO) composites have been successfully synthesized via a two-step solution method using titanyl sulfate as the titanium precursor. Its structural performances were researched by various characterization methods, such as X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-vis diffuse reflectance spectroscopy (UV-vis DRS). The performance of the composites was tested by degrading rhodamine B (RhB) under UV-vis illumination and found to strongly rely on the content of ZnO. The experimental results showed that the CNT/TiO₂/ZnO-90 wt % expressed more outstanding photocatalytic performance compared to the corresponding binary composites and the CNT/TiO₂/ZnO-85 wt %, CNT/TiO₂/ZnO-95 wt % materials. The improved photocatalytic activity was attributed to synergistic effect of CNT, TiO₂ and ZnO, in which ZnO can absorb photons to produce electrons and holes, whereas TiO₂ and CNT can reduce the electron-hole recombination. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis for Energy Conversion)

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11 pages, 1224 KiB

Open AccessArticle

Stereoselective Enzymatic Reduction of 1,4-Diaryl-1,4-Diones to the Corresponding Diols Employing Alcohol Dehydrogenases

by Ángela Mourelle-Insua, Gonzalo De Gonzalo, Iván Lavandera and Vicente Gotor-Fernández

Catalysts 2018, 8(4), 150; https://doi.org/10.3390/catal8040150 - 06 Apr 2018

Cited by 8 | Viewed by 4396

Abstract

Due to the steric hindrance of the starting prochiral ketones, the preparation of chiral 1,4-diaryl-1,4-diols through the asymmetric hydrogen transfer reaction has been mainly restricted to the use of metal-based catalysts, oxazaborolidines, or organocatalysts. Herein, we demonstrated the versatility of oxidoreductases, finding overexpressed [...] Read more.

Due to the steric hindrance of the starting prochiral ketones, the preparation of chiral 1,4-diaryl-1,4-diols through the asymmetric hydrogen transfer reaction has been mainly restricted to the use of metal-based catalysts, oxazaborolidines, or organocatalysts. Herein, we demonstrated the versatility of oxidoreductases, finding overexpressed alcohol dehydrogenase from Ralstonia sp. (E. coli/RasADH) as the most active and stereoselective biocatalyst. Thus, the preparation of a set of 1,4-diaryl-1,4-diols bearing different pattern substitutions in the aromatic ring was achieved with complete diastereo- and enantioselectivity under mild reaction conditions. Full article

(This article belongs to the Special Issue Enzyme-Mediated Stereoselective Synthesis)

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14 pages, 17097 KiB

Open AccessArticle

Immobilization/Stabilization of Ficin Extract on Glutaraldehyde-Activated Agarose Beads. Variables That Control the Final Stability and Activity in Protein Hydrolyses

by El-Hocine Siar, Sara Arana-Peña, Oveimar Barbosa, Mohammed Nasreddine Zidoune and Roberto Fernandez-Lafuente

Catalysts 2018, 8(4), 149; https://doi.org/10.3390/catal8040149 - 06 Apr 2018

Cited by 70 | Viewed by 5589

Abstract

Ficin extract has been immobilized on different 4% aminated-agarose beads. Using just ion exchange, immobilization yield was poor and expressed activity did not surpass 10% of the offered enzyme, with no significant effects on enzyme stability. The treatment with glutaraldehyde of this ionically [...] Read more.

Ficin extract has been immobilized on different 4% aminated-agarose beads. Using just ion exchange, immobilization yield was poor and expressed activity did not surpass 10% of the offered enzyme, with no significant effects on enzyme stability. The treatment with glutaraldehyde of this ionically exchanged enzyme produced an almost full enzyme inactivation. Using aminated supports activated with glutaraldehyde, immobilization was optimal at pH 7 (at pH 5 immobilization yield was 80%, while at pH 9, the immobilized enzyme became inactivated). At pH 7, full immobilization was accomplished maintaining 40% activity versus a small synthetic substrate and 30% versus casein. Ficin stabilization upon immobilization could be observed but it depended on the inactivation pH and the substrate employed, suggesting the complexity of the mechanism of inactivation of the immobilized enzyme. The maximum enzyme loading on the support was determined to be around 70 mg/g. The loading has no significant effect on the enzyme stability or enzyme activity using the synthetic substrate but it had a significant effect on the activity using casein; the biocatalysts activity greatly decreased using more than 30 mg/g, suggesting that the near presence of other immobilized enzyme molecules may generate some steric hindrances for the casein hydrolysis. Full article

(This article belongs to the Special Issue Immobilized Biocatalysts)

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22 pages, 32410 KiB

Open AccessArticle

Insights in the Rhodium-Catalyzed Tandem Isomerization-Hydroformylation of 10-Undecenitrile: Evidence for a Fast Isomerization Regime

by Lucas Le Goanvic, Jean-Luc Couturier, Jean-Luc Dubois and Jean-François Carpentier

Catalysts 2018, 8(4), 148; https://doi.org/10.3390/catal8040148 - 05 Apr 2018

Cited by 3 | Viewed by 3245

Abstract

The tandem isomerization-hydroformylation of 10-undecenitrile (1) into the corresponding linear aldehyde (2) with a Rh-biphephos system was studied and the formation of internal olefin isomers (1-int-x) was monitored over time. The existence of an “isomerization [...] Read more.

The tandem isomerization-hydroformylation of 10-undecenitrile (1) into the corresponding linear aldehyde (2) with a Rh-biphephos system was studied and the formation of internal olefin isomers (1-int-x) was monitored over time. The existence of an “isomerization phenomenon” was evidenced, where fast isomerization of 1 into up to 70% of 1-int-x followed by fast back-isomerization of 1-int-x into 1 and, in turn, into 2 occurs. This fast dynamic isomerization regime is favored at high syngas pressure (40 bar) and low biphephos-to-Rh ratio (5–10), and it is best observed at relatively high catalyst loadings ([1]₀/[Rh] ≤ 3000). The latter regime is indeed evanescent, and gives place to a second stage in which isomerization of internal olefins (and eventual conversion into 2) proceeds much more slowly. The results are tentatively rationalized by the formation of an unstable species that promotes dynamic isomerization and which slowly vanishes or collapses into a Rh-biphephos species which is the one responsible for hydroformylation. Full article

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13 pages, 8224 KiB

Open AccessArticle

Enhancing Light-Driven Production of Hydrogen Peroxide by Anchoring Au onto C₃N₄ Catalysts

by Xiaoyu Chang, Junjiao Yang, Dandan Han, Bing Zhang, Xu Xiang and Jing He

Catalysts 2018, 8(4), 147; https://doi.org/10.3390/catal8040147 - 04 Apr 2018

Cited by 33 | Viewed by 5146

Abstract

Light-driven production of hydrogen peroxide (H₂O₂) is a green and sustainable way to achieve solar-to-chemical energy conversion. During such a conversion, both the high activity and the stability of catalysts were critical. We prepared an Au-supported C₃N [...] Read more.

Light-driven production of hydrogen peroxide (H₂O₂) is a green and sustainable way to achieve solar-to-chemical energy conversion. During such a conversion, both the high activity and the stability of catalysts were critical. We prepared an Au-supported C₃N₄ catalyst—i.e., Au/C₃N₄-500(N₂)—by strongly anchoring Au nanoparticles (~5 nm) onto a C₃N₄ matrix—which simultaneously enhanced the activity towards the photosynthesis of H₂O₂ and the stability when it was reused. The yield of H₂O₂ reached 1320 μmol L⁻¹ on Au/C₃N₄-500(N₂) after 4 h of light irradiation in an acidic solution (pH 3), which was higher than that (1067 μmol L⁻¹) of the control sample Au/C₃N₄-500(Air) and 2.3 times higher than that of the pristine C₃N₄. Particularly, the catalyst Au/C₃N₄-500(N₂) retained a much higher stability. The yield of H₂O₂ had a marginal decrease on the spent catalyst—i.e., 98% yield was kept. In comparison, only 70% yield was obtained from the spent control catalyst. The robust anchoring of Au onto C₃N₄ improved their interaction, which remarkably decreased the Au leaching when it was used and avoided the aggregation and aging of Au particles. Minimal Au leaching was detected on the spent catalyst. The kinetic analyses indicated that the highest formation rate of H₂O₂ was achieved on the Au/C₃N₄-500(N₂) catalyst. The decomposition tests and kinetic behaviors of H₂O₂ were also carried out. These findings suggested that the formation rate of H₂O₂ could be a determining factor for efficient production of H₂O₂. Full article

(This article belongs to the Special Issue Development of Photocatalytic Processes for Air Pollution Remediation and Fuels Production)

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17 pages, 17993 KiB

Open AccessArticle

Porous Organic Polymers-Supported Metallocene Catalysts for Ethylene/1-Hexene Copolymerization

by Xiong Wang, Xiaoyu Han, Feng Ren, Renwei Xu and Yongxiao Bai

Catalysts 2018, 8(4), 146; https://doi.org/10.3390/catal8040146 - 04 Apr 2018

Cited by 22 | Viewed by 4812

Abstract

Porous organic polymers (POPs) have received much attention in adsorption, separation, and catalysis. In this paper, porous organic polymers with different pore structure were used as metallocene catalyst supports, and ethylene/1-hexene copolymerizations were conducted using the POPs-supported metallocene catalyst. The pore structure of [...] Read more.

Porous organic polymers (POPs) have received much attention in adsorption, separation, and catalysis. In this paper, porous organic polymers with different pore structure were used as metallocene catalyst supports, and ethylene/1-hexene copolymerizations were conducted using the POPs-supported metallocene catalyst. The pore structure of the prepared POPs and the supported metallocene catalyst were characterized by nitrogen sorption porosimetry and non-local density functional theory simulation, and the molecular chain structure of the produced ethylene/1-hexene copolymers were investigated through gel permeation chromatography (GPC), IR analysis, differential scanning calorimetry (DSC), and temperature rising elution fractionation (TREF). The results show that the loading amount of active sites varied with different pore structures of the POP supports, and the active species scattered in different pore sizes had a moderate impact on the molecular chain growth and the molecular weight distribution. The IR, DSC, and TREF analysis revealedthat different branching degree, double bond content, and chemical composition distributions were detected from the molecular chain structure of the ethylene/α-olefin copolymers from different POPs and silica-supported metallocene catalysts, despite their similar IR, DSC, and TREF curves due to the same active species. Scanning electron microscopy (SEM) showed that porous ethylene/α-olefin copolymers with varied surface morphology were obtained from the POPs-supported metallocene catalysts with different pore structure. Full article

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18 pages, 52855 KiB

Open AccessFeature PaperArticle

Gaseous Nitric Acid Activated Graphite Felts as Hierarchical Metal-Free Catalyst for Selective Oxidation of H₂S

by Zhenxin Xu, Cuong Duong-Viet, Housseinou Ba, Bing Li, Tri Truong-Huu, Lam Nguyen-Dinh and Cuong Pham-Huu

Catalysts 2018, 8(4), 145; https://doi.org/10.3390/catal8040145 - 04 Apr 2018

Cited by 16 | Viewed by 6259

Abstract

In this study, we reported on the influence of gaseous HNO₃ treatment on the formation of defects decorated with oxygenated functional groups on commercial graphite felts (GFs). The gaseous acid treatment also leads to a remarkable increase of the specific as well [...] Read more.

In this study, we reported on the influence of gaseous HNO₃ treatment on the formation of defects decorated with oxygenated functional groups on commercial graphite felts (GFs). The gaseous acid treatment also leads to a remarkable increase of the specific as well as effective surface area through the formation of a highly porous graphite structure from dense graphite filamentous. The as-synthesized catalyst was further used as a metal-free catalyst in the selective oxidation of H₂S in industrial waste effluents. According to the results, the defects decorated with oxygenated groups were highly active for performing selective oxidation of H₂S into elemental sulfur. The desulfurization activity was relatively high and extremely stable as a function of time on stream which indicated the high efficiency of these oxidized un-doped GFs as metal-free catalysts for the selective oxidation process. The high catalytic performance was attributed to both the presence of structural defects on the filamentous carbon wall, which acting as a dissociative adsorption center for the oxygen, and the oxygenated functional groups, which could play the role of active sites for the selective oxidation process. Full article

(This article belongs to the Special Issue Multiscale and Innovative Kinetic Approaches in Heterogeneous Catalysis)

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12 pages, 19799 KiB

Open AccessArticle

Controlled Synthesis of Heterostructured SnO₂-CuO Composite Hollow Microspheres as Efficient Cu-Based Catalysts for the Rochow Reaction

by Hezhi Liu, Yongjun Ji, Xiujing Zou, Jing Li, Yu Zhang, Xueguang Wang, Ziyi Zhong and Fabing Su

Catalysts 2018, 8(4), 144; https://doi.org/10.3390/catal8040144 - 03 Apr 2018

Cited by 6 | Viewed by 3621

Abstract

In this work, we report the design and synthesis of a series of heterostructured SnO₂-CuO hollow microspherical catalysts (H-SnO₂(x)-CuO, x is the weight ratio of Sn/Cu) for the Rochow reaction. The microspherical catalysts with nanosheets and nanoparticles [...] Read more.

In this work, we report the design and synthesis of a series of heterostructured SnO₂-CuO hollow microspherical catalysts (H-SnO₂(x)-CuO, x is the weight ratio of Sn/Cu) for the Rochow reaction. The microspherical catalysts with nanosheets and nanoparticles as building blocks were prepared by a facile one-pot hydrothermal method coupled with calcination. When tested for the Rochow reaction, the prepared H-SnO₂(0.2)-CuO composite exhibited higher dimethyldichlorosilane selectivity (88.2%) and Si conversion (36.7%) than the solid CuO, hollow CuO and other H-SnO₂(x)-CuO microspherical samples, because in the former there is a stronger synergistic interaction between CuO and SnO₂. Full article

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10 pages, 23788 KiB

Open AccessArticle

DRIFT Study on Promotion Effect of the Keggin Structure over V₂O₅-MoO₃/TiO₂ Catalysts for Low Temperature NH₃-SCR Reaction

by Rui Wu, Ningqiang Zhang, Lingcong Li, Hong He, Liyun Song and Wenge Qiu

Catalysts 2018, 8(4), 143; https://doi.org/10.3390/catal8040143 - 03 Apr 2018

Cited by 25 | Viewed by 5412

Abstract

Heteropoly acids (HPAs) with the Keggin structure have been widely used in NO_x removal. Two kinds of catalysts (those with and without the Keggin structure) are prepared for studying the effect of the Keggin structure on the NH₃-SCR reaction. A [...] Read more.

Heteropoly acids (HPAs) with the Keggin structure have been widely used in NO_x removal. Two kinds of catalysts (those with and without the Keggin structure) are prepared for studying the effect of the Keggin structure on the NH₃-SCR reaction. A series of in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) analyses are conducted to investigate the surface-adsorbed species on the catalysts during the SCR reaction. The mechanism for enhancing low-temperature activity of the catalysts is proposed. Furthermore, the effect of NH₄⁺ in the Keggin structure is also investigated. Results indicate that both the Langmuir–Hinshelwood (L-H) and Eley–Rideal (E-R) mechanisms occurred in the NH₃-SCR reaction over the catalyst with the Keggin structure (Cat-A); in addition, when more acid sites are provided, NO_x species activity is improved and more NH₄⁺ ions participate in reaction over Cat-A, thus promoting SCR activity. Full article

(This article belongs to the Special Issue Selective Catalytic Reduction of NO_x)

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14 pages, 6938 KiB

Open AccessArticle

Continuous Dimethyl Carbonate Synthesis from CO₂ and Methanol Using Cu-Ni@VSiO as Catalyst Synthesized by a Novel Sulfuration Method

by Meng Zhang, Kirill A. Alferov, Min Xiao, Dongmei Han, Shuanjin Wang and Yuezhong Meng

Catalysts 2018, 8(4), 142; https://doi.org/10.3390/catal8040142 - 03 Apr 2018

Cited by 15 | Viewed by 5370

Abstract

Conversion of carbon dioxide into useful chemicals is a valuable task. One way to perform it is to transform CO₂ into dimethyl carbonate (DMC) by a reaction with methanol. Catalyst exerts significant impact on this process. During this work, Cu-Ni@VSiO bimetallic catalysts [...] Read more.

Conversion of carbon dioxide into useful chemicals is a valuable task. One way to perform it is to transform CO₂ into dimethyl carbonate (DMC) by a reaction with methanol. Catalyst exerts significant impact on this process. During this work, Cu-Ni@VSiO bimetallic catalysts were successfully synthesized by traditional solution and novel sulfuration methods. The catalytic materials were characterized by several analytical techniques and were tested in a continuous fixed-bed reactor under different reaction conditions to promote DMC synthesis from CO₂ and methanol in the absence of dehydrating agents. The effects of reaction temperature, pressure, space velocity, metal loading, and bulk density on the catalytic performance were investigated in detail. It was found that the activity of Cu-Ni@VSiO catalyst with the support obtained by the novel sulfuration method is about three times higher when compared to that of the catalyst with the support that is synthesized by the traditional solution method. This result may stem from the difference in microstructure of the studied catalytic materials. Full article

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