Catalysts

23 pages, 13097 KB

Open AccessEditor’s ChoiceReview

Recent Advances in Acyl Suzuki Cross-Coupling

by Jonathan Buchspies and Michal Szostak

Catalysts 2019, 9(1), 53; https://doi.org/10.3390/catal9010053 - 8 Jan 2019

Cited by 161 | Viewed by 16700

Acyl Suzuki cross-coupling involves the coupling of an organoboron reagent with an acyl electrophile (acyl halide, anhydride, ester, amide). This review provides a timely overview of the very important advances that have recently taken place in the acylative Suzuki cross-coupling. Particular emphasis is [...] Read more.

Acyl Suzuki cross-coupling involves the coupling of an organoboron reagent with an acyl electrophile (acyl halide, anhydride, ester, amide). This review provides a timely overview of the very important advances that have recently taken place in the acylative Suzuki cross-coupling. Particular emphasis is directed toward the type of acyl electrophiles, catalyst systems and new cross-coupling partners. This review will be of value to synthetic chemists involved in this rapidly developing field of Suzuki cross-coupling as well as those interested in using acylative Suzuki cross-coupling for the synthesis of ketones as a catalytic alternative to stoichiometric nucleophilic additions or Friedel-Crafts reactions. Full article

(This article belongs to the Section Catalysis in Organic and Polymer Chemistry)

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14 pages, 2349 KB

Open AccessEditor’s ChoiceArticle

Efficient Heterogeneous Activation of Persulfate by Iron-Modified Biochar for Removal of Antibiotic from Aqueous Solution: A Case Study of Tetracycline Removal

by Van-Truc Nguyen, Chang-Mao Hung, Thanh-Binh Nguyen, Jih-Hsing Chang, Tsing-Hai Wang, Chung-Hsin Wu, Yi-Li Lin, Chiu-Wen Chen and Cheng-Di Dong

Catalysts 2019, 9(1), 49; https://doi.org/10.3390/catal9010049 - 7 Jan 2019

Cited by 67 | Viewed by 7587

Abstract

Waste reutilization is always highly desired in the environmental engineering and science community. In this study, Fe-SCG biochar was functionalized by modifying spent coffee grounds (SCG) with magnetite (Fe³⁺) at 700 °C and applied for the oxidative removal of tetracycline (TC) [...] Read more.

Waste reutilization is always highly desired in the environmental engineering and science community. In this study, Fe-SCG biochar was functionalized by modifying spent coffee grounds (SCG) with magnetite (Fe³⁺) at 700 °C and applied for the oxidative removal of tetracycline (TC) with the presence of persulfate (PS). The effects of pH, dosage of biochar and sodium persulfate and initial TC concentration on TC degradation were investigated in a batch system. Our results show that higher TC degradation efficiency was obtained at low pH, low initial TC concentration, and at high dosages of PS and biochar. The highest removal efficiency (96%) was achieved by Fe-SCG/PS under the conditions of pH = 2.0, [Fe-SCG] = 2.5 g/L, [PS] = 60 mM and [TC] = 1 mM. The proposed Fe-SCG catalyst could be a promising effective biochar for the remediation of other emerging organic contaminants. Full article

(This article belongs to the Special Issue Preparation of Catalysts from Renewable and Waste Materials)

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43 pages, 4827 KB

Open AccessEditor’s ChoiceReview

A Review on the Synthesis and Characterization of Metal Organic Frameworks for Photocatalytic Water Purification

by Jorge Bedia, Virginia Muelas-Ramos, Manuel Peñas-Garzón, Almudena Gómez-Avilés, Juan J. Rodríguez and Carolina Belver

Catalysts 2019, 9(1), 52; https://doi.org/10.3390/catal9010052 - 7 Jan 2019

Cited by 296 | Viewed by 25485

Abstract

This review analyzes the preparation and characterization of metal organic frameworks (MOFs) and their application as photocatalysts for water purification. The study begins by highlighting the problem of water scarcity and the different solutions for purification, including photocatalysis with semiconductors, such as MOFs. [...] Read more.

This review analyzes the preparation and characterization of metal organic frameworks (MOFs) and their application as photocatalysts for water purification. The study begins by highlighting the problem of water scarcity and the different solutions for purification, including photocatalysis with semiconductors, such as MOFs. It also describes the different methodologies that can be used for the synthesis of MOFs, paying attention to the purification and activation steps. The characterization of MOFs and the different approaches that can be followed to learn the photocatalytic processes are also detailed. Finally, the work reviews literature focused on the degradation of contaminants from water using MOF-based photocatalysts under light irradiation. Full article

(This article belongs to the Section Photocatalysis)

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31 pages, 5907 KB

Open AccessEditor’s ChoiceReview

Catalytic Transfer Hydrogenolysis Reactions for Lignin Valorization to Fuels and Chemicals

by Antigoni Margellou and Konstantinos S. Triantafyllidis

Catalysts 2019, 9(1), 43; https://doi.org/10.3390/catal9010043 - 4 Jan 2019

Cited by 66 | Viewed by 10630

Abstract

Lignocellulosic biomass is an abundant renewable source of chemicals and fuels. Lignin, one of biomass main structural components being widely available as by-product in the pulp and paper industry and in the process of second generation bioethanol, can provide phenolic and aromatic compounds [...] Read more.

Lignocellulosic biomass is an abundant renewable source of chemicals and fuels. Lignin, one of biomass main structural components being widely available as by-product in the pulp and paper industry and in the process of second generation bioethanol, can provide phenolic and aromatic compounds that can be utilized for the manufacture of a wide variety of polymers, fuels, and other high added value products. The effective depolymerisation of lignin into its primary building blocks remains a challenge with regard to conversion degree and monomers selectivity and stability. This review article focuses on the state of the art in the liquid phase reductive depolymerisation of lignin under relatively mild conditions via catalytic hydrogenolysis/hydrogenation reactions, discussing the effect of lignin type/origin, hydrogen donor solvents, and related transfer hydrogenation or reforming pathways, catalysts, and reaction conditions. Full article

(This article belongs to the Special Issue Solid Catalysts for the Upgrading of Renewable Sources)

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27 pages, 3942 KB

Open AccessEditor’s ChoiceReview

Recent Progress in Application of Molybdenum-Based Catalysts for Epoxidation of Alkenes

by Yirui Shen, Pingping Jiang, Phyu Thin Wai, Qian Gu and Weijie Zhang

Catalysts 2019, 9(1), 31; https://doi.org/10.3390/catal9010031 - 2 Jan 2019

Cited by 102 | Viewed by 10748

Abstract

Epoxides are important industrial intermediates applied in a variety of industrial processes. During the production of epoxides, catalysts have played an irreplaceable and unique role. In this review, the historic progress of molybdenum-based catalysts in alkene epoxidation are covered and an outlook on [...] Read more.

Epoxides are important industrial intermediates applied in a variety of industrial processes. During the production of epoxides, catalysts have played an irreplaceable and unique role. In this review, the historic progress of molybdenum-based catalysts in alkene epoxidation are covered and an outlook on future challenge discussed. Efficient catalysts are demonstrated including soluble molybdenum complexes, polyoxometalates catalysts, molybdenum-containing metal organic frameworks, silica supported molybdenum-based catalysts, polymer supported molybdenum-based catalysts, magnetic molybdenum-based catalysts, hierarchical molybdenum-based catalysts, graphene-based molybdenum containing catalysts, photocatalyzed epoxidation catalysts, and some other systems. The effects of different solvents and oxidants are discussed and the mechanisms of epoxidation are summarized. The challenges and perspectives to further enhance the catalytic performances in alkenes epoxidation are presented. Full article

(This article belongs to the Special Issue Epoxidation Catalysis)

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28 pages, 4991 KB

Open AccessFeature PaperEditor’s ChoiceReview

The Role of Surface Texture on the Photocatalytic H₂ Production on TiO₂

by Francesco Pellegrino, Fabrizio Sordello, Marco Minella, Claudio Minero and Valter Maurino

Catalysts 2019, 9(1), 32; https://doi.org/10.3390/catal9010032 - 2 Jan 2019

Cited by 38 | Viewed by 5874

Abstract

It has been often reported that an efficient and green photocatalytic dissociation of water under irradiated semiconductors likely represents the most important goal for modern chemistry. Despite decades of intensive work on this topic, the efficiency of the water photolytic process under irradiated [...] Read more.

It has been often reported that an efficient and green photocatalytic dissociation of water under irradiated semiconductors likely represents the most important goal for modern chemistry. Despite decades of intensive work on this topic, the efficiency of the water photolytic process under irradiated semiconductors is far from reaching significant photocatalytic efficiency. The use of a sacrificial agent as hole scavenger dramatically increases the hydrogen production rate and might represent the classic “kill two birds with one stone”: on the one hand, the production of hydrogen, then usable as energy carrier, on the other, the treatment of water for the abatement of pollutants used as sacrificial agents. Among metal oxides, TiO₂ has a central role due to its versatility and inexpensiveness that allows an extended applicability in several scientific and technological fields. In this review we focus on the hydrogen production on irradiated TiO₂ and its fundamental and environmental implications. Full article

(This article belongs to the Section Photocatalysis)

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17 pages, 2309 KB

Open AccessEditor’s ChoiceArticle

Effect of Y Modified Ceria Support in Mono and Bimetallic Pd–Au Catalysts for Complete Benzene Oxidation

by Lyuba Ilieva, Anna Maria Venezia, Petya Petrova, Giuseppe Pantaleo, Leonarda Francesca Liotta, Rodolfo Zanella, Zbigniew Kaszkur and Tatyana Tabakova

Catalysts 2018, 8(7), 283; https://doi.org/10.3390/catal8070283 - 16 Jul 2018

Cited by 28 | Viewed by 5066

Abstract

Mono metallic and bimetallic Pd (1 wt. %)–Au (3 wt. %) catalysts were prepared using two ceria supports doped with 1 wt. % Y₂O₃. Yttrium was added by impregnation or co-precipitation. The catalyst synthesis was carried out by deposition–precipitation [...] Read more.

Mono metallic and bimetallic Pd (1 wt. %)–Au (3 wt. %) catalysts were prepared using two ceria supports doped with 1 wt. % Y₂O₃. Yttrium was added by impregnation or co-precipitation. The catalyst synthesis was carried out by deposition–precipitation method, with sequential deposition–precipitation of palladium over previously loaded gold in the case of the bimetallic samples. The obtained materials, characterized by X-ray powder diffraction (XRD), High resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and temperature programmed reduction (TPR) techniques, were tested in the complete benzene oxidation (CBO). The results of the characterization analyses and the catalytic performance pointed to a close relationship between structural, redox, and catalytic properties of mono and bimetallic catalysts. Among the monometallic systems, Pd catalysts were more active as compared to the corresponding Au catalysts. The bimetallic systems exhibited the best combustion activity. In particular, over Pd–Au supported on Y-impregnated ceria, 100% of benzene conversion towards total oxidation at the temperature of 150 °C was obtained. Comparison of surface sensitive XPS results of fresh and spent catalysts ascertained the redox character of the reaction. Full article

(This article belongs to the Special Issue Structure–Activity Relationships in Catalysis)

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36 pages, 5215 KB

Open AccessFeature PaperEditor’s ChoiceReview

Ag/CeO₂ Composites for Catalytic Abatement of CO, Soot and VOCs

by M. V. Grabchenko, N. N. Mikheeva, G. V. Mamontov, M. A. Salaev, L. F. Liotta and O. V. Vodyankina

Catalysts 2018, 8(7), 285; https://doi.org/10.3390/catal8070285 - 16 Jul 2018

Cited by 88 | Viewed by 10327

Abstract

Nowadays catalytic technologies are widely used to purify indoor and outdoor air from harmful compounds. Recently, Ag–CeO₂ composites have found various applications in catalysis due to distinctive physical-chemical properties and relatively low costs as compared to those based on other noble metals. [...] Read more.

Nowadays catalytic technologies are widely used to purify indoor and outdoor air from harmful compounds. Recently, Ag–CeO₂ composites have found various applications in catalysis due to distinctive physical-chemical properties and relatively low costs as compared to those based on other noble metals. Currently, metal–support interaction is considered the key factor that determines high catalytic performance of silver–ceria composites. Despite thorough investigations, several questions remain debating. Among such issues, there are (1) morphology and size effects of both Ag and CeO₂ particles, including their defective structure, (2) chemical and charge state of silver, (3) charge transfer between silver and ceria, (4) role of oxygen vacancies, (5) reducibility of support and the catalyst on the basis thereof. In this review, we consider recent advances and trends on the role of silver–ceria interactions in catalytic performance of Ag/CeO₂ composites in low-temperature CO oxidation, soot oxidation, and volatile organic compounds (VOCs) abatement. Promising photo- and electrocatalytic applications of Ag/CeO₂ composites are also discussed. Full article

(This article belongs to the Special Issue New Concepts in Oxidation Processes)

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13 pages, 9033 KB

Open AccessEditor’s ChoiceArticle

PdO/ZnO@mSiO₂ Hybrid Nanocatalyst for Reduction of Nitroarenes

by Jinwoo Kim, Aram Kim, Nallal Muthuchamy and Kang Hyun Park

Catalysts 2018, 8(7), 280; https://doi.org/10.3390/catal8070280 - 14 Jul 2018

Cited by 61 | Viewed by 4800

Abstract

Development of a novel approach for synthesizing nanostructured catalysts and achieving further improvements in catalytic activity, effectiveness, and efficiency remains a major challenge. In this report, we describe the preparation of a nanostructured PdO/ZnO@mSiO₂ hybrid nanocatalyst featuring well-dispersed PdO nanoparticles within hollow [...] Read more.

Development of a novel approach for synthesizing nanostructured catalysts and achieving further improvements in catalytic activity, effectiveness, and efficiency remains a major challenge. In this report, we describe the preparation of a nanostructured PdO/ZnO@mSiO₂ hybrid nanocatalyst featuring well-dispersed PdO nanoparticles within hollow ZnO@mSiO₂. The as-prepared PdO/ZnO@mSiO₂ hybrid nanocatalyst exhibited good morphological features, derived from the controlled stepwise synthesis from Pd/PS@ZIF-8@mSiO₂ (PS = polystyrene). The morphology, size, oxidation state, crystallinity, and thermal stability of the prepared PdO/ZnO@mSiO₂ hybrid nanocatalyst were confirmed by a series of physicochemical techniques. The PdO/ZnO@mSiO₂ hybrid nanocatalyst showed very high catalytic efficiency in the reduction of 4-nitrophenol and various nitroarenes under eco-friendly conditions. Therefore, the PdO/ZnO@mSiO₂ hybrid nanocatalyst is a promising alternative catalyst for applications in environmental remediation. Full article

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16 pages, 982 KB

Open AccessEditor’s ChoiceReview

Magnetic Microreactors with Immobilized Enzymes—From Assemblage to Contemporary Applications

by Elena Gkantzou, Michaela Patila and Haralambos Stamatis

Catalysts 2018, 8(7), 282; https://doi.org/10.3390/catal8070282 - 14 Jul 2018

Cited by 36 | Viewed by 7166

Abstract

Microfluidics, as the technology for continuous flow processing in microscale, is being increasingly elaborated on in enzyme biotechnology and biocatalysis. Enzymatic microreactors are a precious tool for the investigation of catalytic properties and optimization of reaction parameters in a thriving and high-yielding way. [...] Read more.

Microfluidics, as the technology for continuous flow processing in microscale, is being increasingly elaborated on in enzyme biotechnology and biocatalysis. Enzymatic microreactors are a precious tool for the investigation of catalytic properties and optimization of reaction parameters in a thriving and high-yielding way. The utilization of magnetic forces in the overall microfluidic system has reinforced enzymatic processes, paving the way for novel applications in a variety of research fields. In this review, we hold a discussion on how different magnetic particles combined with the appropriate biocatalyst under the proper system configuration may constitute a powerful microsystem and provide a highly explorable scope. Full article

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20 pages, 1503 KB

Open AccessFeature PaperEditor’s ChoiceReview

A Contribution to the Experimental Microkinetic Approach of Gas/Solid Heterogeneous Catalysis: Measurement of the Individual Heats of Adsorption of Coadsorbed Species by Using the AEIR Method

by Daniel Bianchi

Catalysts 2018, 8(7), 265; https://doi.org/10.3390/catal8070265 - 29 Jun 2018

Cited by 10 | Viewed by 3899

Abstract

The two first surface elementary steps of a gas/solid catalytic reaction are the adsorption/desorption at least one of the reactants leading to its adsorption equilibrium which can be or not disturbed by the others surface elementary steps leading to the products. The variety [...] Read more.

The two first surface elementary steps of a gas/solid catalytic reaction are the adsorption/desorption at least one of the reactants leading to its adsorption equilibrium which can be or not disturbed by the others surface elementary steps leading to the products. The variety of the sites of a conventional catalyst may lead to the formation of different coadsorbed species such as linear, bridged and threefold coordinated species for the adsorption of CO on supported metal particles. The aim of the present article is to summarize works performed in the last twenty years for the development and applications of an analytical method named Adsorption Equilibrium InfraRed spectroscopy (AEIR) for the measurement of the individual heats of adsorption of coadsorbed species and for the validation of mathematical expressions for their adsorption coefficients and adsorption models. The method uses the evolution of the IR bands characteristic of each of coadsorbed species during the increase in the adsorption temperature in isobaric conditions. The presentation shows that the versatility of AEIR leads to net advantages as compared to others conventional methods particularly in the context of the microkinetic approach of catalytic reactions. Full article

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

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18 pages, 3980 KB

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 26 | Viewed by 8360

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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20 pages, 11578 KB

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 - 5 Jun 2018

Cited by 21 | Viewed by 5450

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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8 pages, 4743 KB

Open AccessEditor’s ChoiceArticle

Selective Reduction of Ketones and Aldehydes in Continuous-Flow Microreactor—Kinetic Studies

by Katarzyna Maresz, Agnieszka Ciemięga and Julita Mrowiec-Białoń

Catalysts 2018, 8(5), 221; https://doi.org/10.3390/catal8050221 - 22 May 2018

Cited by 16 | Viewed by 5937

Abstract

In this work, the kinetics of Meerwein–Ponndorf–Verley chemoselective reduction of carbonyl compounds was studied in monolithic continuous-flow microreactors. To the best of our knowledge, this is the first report on the MPV reaction kinetics performed in a flow process. The microreactors are a [...] Read more.

In this work, the kinetics of Meerwein–Ponndorf–Verley chemoselective reduction of carbonyl compounds was studied in monolithic continuous-flow microreactors. To the best of our knowledge, this is the first report on the MPV reaction kinetics performed in a flow process. The microreactors are a very attractive alternative to the batch reactors conventionally used in this process. The proposed micro-flow system for synthesis of unsaturated secondary alcohols proved to be very efficient and easily controlled. The microreactors had reactive cores made of zirconium-functionalized silica monoliths of excellent catalytic properties and flow characteristics. The catalytic experiments were carried out with the use of 2-butanol as a hydrogen donor. Herein, we present the kinetic parameters of cyclohexanone reduction in a flow reactor and data on the reaction rate for several important ketones and aldehydes. The lack of diffusion constraints in the microreactors was demonstrated. Our results were compared with those from other authors and demonstrate the great potential of microreactor applications in fine chemical and complex intermediate manufacturing. Full article

(This article belongs to the Special Issue Catalytic Methods in Flow Chemistry)

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19 pages, 9417 KB

Open AccessEditor’s ChoiceArticle

Improved CO-PROX Performance of CuO/CeO₂ Catalysts by Using Nanometric Ceria as Support

by Almerinda Di Benedetto, Gianluca Landi and Luciana Lisi

Catalysts 2018, 8(5), 209; https://doi.org/10.3390/catal8050209 - 15 May 2018

Cited by 29 | Viewed by 6509

Abstract

Despite of the huge number of papers about the catalytic preferential oxidation of CO (CO-PROX) for the purification of H₂ streams, there is still a need for more effective catalysts in order to reduce the large required catalyst volume of CO-PROX unity. [...] Read more.

Despite of the huge number of papers about the catalytic preferential oxidation of CO (CO-PROX) for the purification of H₂ streams, there is still a need for more effective catalysts in order to reduce the large required catalyst volume of CO-PROX unity. In this work, large surface area nanometric ceria was used as support for CuO/CeO₂ catalysts with CuO load up to 10 wt % easily dispersed by wet impregnation. Catalysts were characterized by ICP-MS, XRD, SEM/EDS, N₂ physisorption, H₂ temperature programmed reduction (TPR), and CO₂ temperature programmed desorption (TPD) and tested under different reaction conditions (including under feed containing inhibiting species such as CO₂ and H₂O). Catalytic tests revealed that our samples show high activity and selectivity even under stringent reaction conditions; moreover, they result among the most active catalysts when compared to those reported in the scientific literature. The high activity can be related to the enhanced amount of highly dispersed copper sites in strong interaction with ceria related to the nature of the nanometric support, as evidenced by the characterization techniques. Despite the high concentration of active copper sites, catalytic performance is limited by CO₂ desorption from ceria in the neighborhood of copper sites, which prevents a further improvement. This suggests that new catalyst formulations should also provide a lower affinity towards CO₂. Full article

(This article belongs to the Special Issue Catalysts for Hydrogen Purification for Fuel Cell Applications)

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24 pages, 12325 KB

Open AccessFeature PaperEditor’s ChoiceReview

Artificial Biocatalytic Linear Cascades to Access Hydroxy Acids, Lactones, and α- and β-Amino Acids

by Joerg H. Schrittwieser, Stefan Velikogne and Wolfgang Kroutil

Catalysts 2018, 8(5), 205; https://doi.org/10.3390/catal8050205 - 14 May 2018

Cited by 15 | Viewed by 6591

Abstract

α-, β-, and ω-Hydroxy acids, amino acids, and lactones represent common building blocks and intermediates for various target molecules. This review summarizes artificial cascades published during the last 10 years leading to these products. Renewables as well as compounds originating from fossil resources [...] Read more.

α-, β-, and ω-Hydroxy acids, amino acids, and lactones represent common building blocks and intermediates for various target molecules. This review summarizes artificial cascades published during the last 10 years leading to these products. Renewables as well as compounds originating from fossil resources have been employed as starting material. The review provides an inspiration for new cascade designs and may be the basis to design variations of these cascades starting either from alternative substrates or extending them to even more sophisticated products. Full article

(This article belongs to the Special Issue Enzymatic Cascade Reactions)

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10 pages, 2290 KB

Open AccessEditor’s ChoiceReview

Total Synthesis and Biological Evaluation of Phaeosphaerides

by Kenichi Kobayashi, Kosaku Tanaka and Hiroshi Kogen

Catalysts 2018, 8(5), 206; https://doi.org/10.3390/catal8050206 - 14 May 2018

Cited by 5 | Viewed by 4759

Abstract

This article reviews studies regarding the total synthesis of phaeosphaerides A and B, nitrogen-containing bicyclic natural products isolated from an endophytic fungus. Numerous synthetic efforts and an X-ray crystal structure analysis of phaeosphaeride A have enabled revision of its originally proposed structure. In [...] Read more.

This article reviews studies regarding the total synthesis of phaeosphaerides A and B, nitrogen-containing bicyclic natural products isolated from an endophytic fungus. Numerous synthetic efforts and an X-ray crystal structure analysis of phaeosphaeride A have enabled revision of its originally proposed structure. In addition, a successful protic acid-mediated transformation of phaeosphaeride A to phaeosphaeride B revealed the hypothetical biosynthesis of phaeosphaeride B from phaeosphaeride A. Structure–activity relationship studies of phaeosphaeride derivatives are also discussed. Full article

(This article belongs to the Special Issue Catalyzed Synthesis of Natural Products)

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18 pages, 1513 KB

Open AccessEditor’s ChoiceArticle

Optimization of Charcoal Production Process from Woody Biomass Waste: Effect of Ni-Containing Catalysts on Pyrolysis Vapors

by Jon Solar, Blanca Maria Caballero, Isabel De Marco, Alexander López-Urionabarrenechea and Naia Gastelu

Catalysts 2018, 8(5), 191; https://doi.org/10.3390/catal8050191 - 4 May 2018

Cited by 21 | Viewed by 7178

Abstract

Woody biomass waste (Pinus radiata) coming from forestry activities has been pyrolyzed with the aim of obtaining charcoal and, at the same time, a hydrogen-rich gas fraction. The pyrolysis has been carried out in a laboratory scale continuous screw reactor, where [...] Read more.

Woody biomass waste (Pinus radiata) coming from forestry activities has been pyrolyzed with the aim of obtaining charcoal and, at the same time, a hydrogen-rich gas fraction. The pyrolysis has been carried out in a laboratory scale continuous screw reactor, where carbonization takes place, connected to a vapor treatment reactor, at which the carbonization vapors are thermo-catalytically treated. Different peak temperatures have been studied in the carbonization process (500–900 °C), while the presence of different Ni-containing catalysts in the vapor treatment has been analyzed. Low temperature pyrolysis produces high liquid and solid yields, however, increasing the temperature progressively up to 900 °C drastically increases gas yield. The amount of nickel affects the vapors treatment phase, enhancing even further the production of interesting products such as hydrogen and reducing the generated liquids to very low yields. The gases obtained at very high temperatures (700–900 °C) in the presence of Ni-containing catalysts are rich in H₂ and CO, which makes them valuable for energy production, as hydrogen source, producer gas or reducing agent. Full article

(This article belongs to the Special Issue Catalytic Pyrolysis)

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38 pages, 6570 KB

Open AccessFeature PaperEditor’s ChoiceReview

Controlling Redox Enzyme Orientation at Planar Electrodes

by Vivek Pratap Hitaishi, Romain Clement, Nicolas Bourassin, Marc Baaden, Anne De Poulpiquet, Sophie Sacquin-Mora, Alexandre Ciaccafava and Elisabeth Lojou

Catalysts 2018, 8(5), 192; https://doi.org/10.3390/catal8050192 - 4 May 2018

Cited by 82 | Viewed by 11493

Abstract

Redox enzymes, which catalyze reactions involving electron transfers in living organisms, are very promising components of biotechnological devices, and can be envisioned for sensing applications as well as for energy conversion. In this context, one of the most significant challenges is to achieve [...] Read more.

Redox enzymes, which catalyze reactions involving electron transfers in living organisms, are very promising components of biotechnological devices, and can be envisioned for sensing applications as well as for energy conversion. In this context, one of the most significant challenges is to achieve efficient direct electron transfer by tunneling between enzymes and conductive surfaces. Based on various examples of bioelectrochemical studies described in the recent literature, this review discusses the issue of enzyme immobilization at planar electrode interfaces. The fundamental importance of controlling enzyme orientation, how to obtain such orientation, and how it can be verified experimentally or by modeling are the three main directions explored. Since redox enzymes are sizable proteins with anisotropic properties, achieving their functional immobilization requires a specific and controlled orientation on the electrode surface. All the factors influenced by this orientation are described, ranging from electronic conductivity to efficiency of substrate supply. The specificities of the enzymatic molecule, surface properties, and dipole moment, which in turn influence the orientation, are introduced. Various ways of ensuring functional immobilization through tuning of both the enzyme and the electrode surface are then described. Finally, the review deals with analytical techniques that have enabled characterization and quantification of successful achievement of the desired orientation. The rich contributions of electrochemistry, spectroscopy (especially infrared spectroscopy), modeling, and microscopy are featured, along with their limitations. Full article

(This article belongs to the Special Issue Immobilized Biocatalysts)

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17 pages, 2202 KB

Open AccessEditor’s ChoiceArticle

Immobilization of Planococcus sp. S5 Strain on the Loofah Sponge and Its Application in Naproxen Removal

by Anna Dzionek, Danuta Wojcieszyńska, Katarzyna Hupert-Kocurek, Małgorzata Adamczyk-Habrajska and Urszula Guzik

Catalysts 2018, 8(5), 176; https://doi.org/10.3390/catal8050176 - 26 Apr 2018

Cited by 32 | Viewed by 6369

Abstract

Planococcus sp. S5, a Gram-positive bacterium isolated from the activated sludge is known to degrade naproxen in the presence of an additional carbon source. Due to the possible toxicity of naproxen and intermediates of its degradation, the whole cells of S5 strain were [...] Read more.

Planococcus sp. S5, a Gram-positive bacterium isolated from the activated sludge is known to degrade naproxen in the presence of an additional carbon source. Due to the possible toxicity of naproxen and intermediates of its degradation, the whole cells of S5 strain were immobilized onto loofah sponge. The immobilized cells degraded 6, 9, 12 or 15 mg/L of naproxen faster than the free cells. Planococcus sp. cells immobilized onto the loofah sponge were able to degrade naproxen efficiently for 55 days without significant damage and disintegration of the carrier. Analysis of the activity of enzymes involved in naproxen degradation showed that stabilization of S5 cells in exopolysaccharide (EPS) resulted in a significant increase of their activity. Changes in the structure of biofilm formed on the loofah sponge cubes during degradation of naproxen were observed. Developed biocatalyst system showed high resistance to naproxen and its intermediates and degraded higher concentrations of the drug in comparison to the free cells. Full article

(This article belongs to the Special Issue Immobilized Biocatalysts)

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16 pages, 1252 KB

Open AccessEditor’s ChoiceReview

Techniques for Preparation of Cross-Linked Enzyme Aggregates and Their Applications in Bioconversions

by Hiroshi Yamaguchi, Yuhei Kiyota and Masaya Miyazaki

Catalysts 2018, 8(5), 174; https://doi.org/10.3390/catal8050174 - 24 Apr 2018

Cited by 87 | Viewed by 16308

Abstract

Enzymes are biocatalysts. They are useful in environmentally friendly production processes and have high potential for industrial applications. However, because of problems with operational stability, cost, and catalytic efficiency, many enzymatic processes have limited applications. The use of cross-linked enzyme aggregates (CLEAs) has [...] Read more.

Enzymes are biocatalysts. They are useful in environmentally friendly production processes and have high potential for industrial applications. However, because of problems with operational stability, cost, and catalytic efficiency, many enzymatic processes have limited applications. The use of cross-linked enzyme aggregates (CLEAs) has been introduced as an effective carrier-free immobilization method. This immobilization method is attractive because it is simple and robust, and unpurified enzymes can be used. Coimmobilization of different enzymes can be achieved. CLEAs generally show high catalytic activities, good storage and operational stabilities, and good reusability. In this review, we summarize techniques for the preparation of CLEAs for use as biocatalysts. Some important applications of these techniques in chemical synthesis and environmental applications are also included. CLEAs provide feasible and efficient techniques for improving the properties of immobilized enzymes for use in industrial applications. Full article

(This article belongs to the Special Issue Immobilized Biocatalysts)

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16 pages, 4962 KB

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 34 | Viewed by 6149

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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18 pages, 5062 KB

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 127 | Viewed by 17191

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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11 pages, 3321 KB

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 16 | Viewed by 6943

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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15 pages, 7391 KB

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 10 | Viewed by 5391

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 KB

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 27 | Viewed by 5957

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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9 pages, 1017 KB

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 - 9 Apr 2018

Cited by 48 | Viewed by 6363

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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19 pages, 9260 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Polystyrene-Supported Acyclic Diaminocarbene Palladium Complexes in Sonogashira Cross-Coupling: Stability vs. Catalytic Activity

by Vladimir N. Mikhaylov, Viktor N. Sorokoumov, Denis Martin Liakhov, Alexander G. Tskhovrebov and Irina A. Balova

Catalysts 2018, 8(4), 141; https://doi.org/10.3390/catal8040141 - 2 Apr 2018

Cited by 44 | Viewed by 7076

Abstract

Two types of immobilized on the amino-functionalized polystyrene-supported acyclic diaminocarbene palladium complexes (ADC-Pd^II) are investigated under Sonogashira cross-coupling conditions. Depending on substituents in the diaminocarbene fragment immobilized ADC-Pd^II, systems are found to have different catalytic activity and stability regarding [...] Read more.

Two types of immobilized on the amino-functionalized polystyrene-supported acyclic diaminocarbene palladium complexes (ADC-Pd^II) are investigated under Sonogashira cross-coupling conditions. Depending on substituents in the diaminocarbene fragment immobilized ADC-Pd^II, systems are found to have different catalytic activity and stability regarding Pd-leaching. Pd^II-diaminocarbenes possessing protons at both nitrogen atoms smoothly decompose into Pd⁰-containing species providing a catalytic “cocktail system” with high activity and ability to reuse within nine runs. Polymer-supported palladium (II) complex bearing NBn–C_carbene–NH-moiety exhibits greater stability while noticeably lower activity under Sonogashira cross-coupling. Four molecular ADC-Pd^II complexes are also synthesized and investigated with the aim of confirming proposed base-promoted pathway of ADC-Pd^II conversion through carbodiimide into an active Pd⁰ forms. Full article

(This article belongs to the Special Issue Solid-Supported Reagents in Palladium-Catalyzed Transformations)

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23 pages, 36332 KB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Progress in Atomic-Level Understanding of Cu/SSZ-13 Selective Catalytic Reduction Catalysts

by Feng Gao and Charles H. F. Peden

Catalysts 2018, 8(4), 140; https://doi.org/10.3390/catal8040140 - 31 Mar 2018

Cited by 117 | Viewed by 11151

Abstract

Cu/SSZ-13 Selective Catalytic Reduction (SCR) catalysts have been extensively studied for the past five-plus years. New and exciting fundamental and applied science has appeared in the literature quite frequently over this time. In this short review, a few topics specifically focused on a [...] Read more.

Cu/SSZ-13 Selective Catalytic Reduction (SCR) catalysts have been extensively studied for the past five-plus years. New and exciting fundamental and applied science has appeared in the literature quite frequently over this time. In this short review, a few topics specifically focused on a molecular-level understanding of this catalyst are summarized: (1) The nature of the active sites and, in particular, their transformations under varying reaction conditions that include dehydration, the presence of the various SCR reactants and hydrothermal aging; (2) Discussions of standard and fast SCR reaction mechanisms. Considerable progress has been made, especially in the last couple of years, on standard SCR mechanisms. In contrast, mechanisms for fast SCR are much less understood. Possible reaction paths are hypothesized for this latter case to stimulate further investigations; (3) Discussions of rational catalyst design based on new knowledge obtained regarding catalyst stability, overall catalytic performance and mechanistic catalytic chemistry. Full article

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

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11 pages, 805 KB

Open AccessFeature PaperEditor’s ChoiceReview

Strategies of Coping with Deactivation of NH₃-SCR Catalysts Due to Biomass Firing

by Leonhard Schill and Rasmus Fehrmann

Catalysts 2018, 8(4), 135; https://doi.org/10.3390/catal8040135 - 30 Mar 2018

Cited by 12 | Viewed by 5618

Abstract

Firing of biomass can lead to rapid deactivation of the vanadia-based NH₃-SCR catalyst, which reduces NO_x to harmless N₂. The deactivation is mostly due to the high potassium content in biomasses, which results in submicron aerosols containing mostly [...] Read more.

Firing of biomass can lead to rapid deactivation of the vanadia-based NH₃-SCR catalyst, which reduces NO_x to harmless N₂. The deactivation is mostly due to the high potassium content in biomasses, which results in submicron aerosols containing mostly KCl and K₂SO₄. The main mode of deactivation is neutralization of the catalyst’s acid sites. Four ways of dealing with high potassium contents were identified: (1) potassium removal by adsorption, (2) tail-end placement of the SCR unit, (3) coating SCR monoliths with a protective layer, and (4) intrinsically potassium tolerant catalysts. Addition of alumino silicates, often in the form of coal fly ash, is an industrially proven method of removing K aerosols from flue gases. Tail-end placement of the SCR unit was also reported to result in acceptable catalyst stability; however, flue-gas reheating after the flue gas desulfurization is, at present, unavoidable due to the lack of sulfur and water tolerant low temperature catalysts. Coating the shaped catalysts with thin layers of, e.g., MgO or sepiolite reduces the K uptake by hindering the diffusion of K⁺ into the catalyst pore system. Intrinsically potassium tolerant catalysts typically contain a high number of acid sites. This can be achieved by, e.g., using zeolites as support, replacing WO₃ with heteropoly acids, and by preparing highly loaded, high surface area, very active V₂O₅/TiO₂ catalyst using a special sol-gel method. Full article

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

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13 pages, 25203 KB

Open AccessEditor’s ChoiceArticle

Investigation of Iron Vanadates for Simultaneous Carbon Soot Abatement and NH₃-SCR

by Marzia Casanova, Sara Colussi and Alessandro Trovarelli

Catalysts 2018, 8(4), 130; https://doi.org/10.3390/catal8040130 - 26 Mar 2018

Cited by 9 | Viewed by 5003

Abstract

FeVO₄ and Fe_0.5Er_0.5VO₄ were prepared and loaded over standard Selective Catalytic Reduction (SCR) supports based on TiO₂-WO₃-SiO₂ (TWS) and redox active supports like CeO₂ and CeZrO₂ with the aim of [...] Read more.

FeVO₄ and Fe_0.5Er_0.5VO₄ were prepared and loaded over standard Selective Catalytic Reduction (SCR) supports based on TiO₂-WO₃-SiO₂ (TWS) and redox active supports like CeO₂ and CeZrO₂ with the aim of finding a suitable formulation for simultaneous soot abatement and NH₃-SCR and to understand the level of interaction between the two reactions. A suitable bi-functional material was identified in the composition FeVO₄/CeZrO₂ where an SCR active component is added over a redox active support, to increase carbon oxidation properties. The influence of the presence of ammonia in soot oxidation and the effect of the presence of soot on SCR reaction have been addressed. It is found that the addition of NO and NO/NH₃ mixtures decreases at different levels the oxidation temperature of carbon soot, while the presence of carbon adversely affects the NH₃-SCR reaction by increasing the oxidation of NH₃ to NO, thus lowering the NO removal efficiency. Full article

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

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14 pages, 6651 KB

Open AccessEditor’s ChoiceArticle

Liquid-Phase Hydrodeoxygenation of Guaiacol over Mo₂C Supported on Commercial CNF. Effects of Operating Conditions on Conversion and Product Selectivity

by Rui Moreira, Elba Ochoa, José Luis Pinilla, António Portugal and Isabel Suelves

Catalysts 2018, 8(4), 127; https://doi.org/10.3390/catal8040127 - 22 Mar 2018

Cited by 33 | Viewed by 5587

Abstract

In this work, a Mo₂C catalyst that was supported on commercial carbon nanofibers (CNF) was synthetized and tested in the hydrodeoxygenation (HDO) of guaiacol. The effects of operating conditions (temperature and pressure) and reaction time (2 and 4 h) on the [...] Read more.

In this work, a Mo₂C catalyst that was supported on commercial carbon nanofibers (CNF) was synthetized and tested in the hydrodeoxygenation (HDO) of guaiacol. The effects of operating conditions (temperature and pressure) and reaction time (2 and 4 h) on the conversion of guaiacol and products selectivity were studied. The major reaction products were cresol and phenol, followed by xylenols and toluene. The use of more severe operating conditions during the HDO of guaiacol caused a diversification in the reaction pathways, and consequently in the selectivity to products. The formation of phenol may have occurred by demethylation of guaiacol, followed by dehydroxylation of catechol, together with other reaction pathways, including direct guaiacol demethoxylation, and demethylation of cresols. X-ray diffraction (XRD) analysis of spent catalysts did not reveal any significant changes as compared to the fresh catalyst. Full article

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22 pages, 3749 KB

Open AccessEditor’s ChoiceReview

Platinum Group Metal Phosphides as Efficient Catalysts in Hydroprocessing and Syngas-Related Catalysis

by Luis Alvarado Rupflin, Chiara Boscagli and Stephan Andreas Schunk

Catalysts 2018, 8(3), 122; https://doi.org/10.3390/catal8030122 - 20 Mar 2018

Cited by 16 | Viewed by 7015

Abstract

Platinum group metal phosphides are reviewed as catalytic materials for hydroprocessing and syngas-related catalysis. Starting from synthetic procedures leading to highly disperse nano-particular compounds, their properties in the applications are discussed and compared with relevant benchmarks, if available. Regarding their mode of action, [...] Read more.

Platinum group metal phosphides are reviewed as catalytic materials for hydroprocessing and syngas-related catalysis. Starting from synthetic procedures leading to highly disperse nano-particular compounds, their properties in the applications are discussed and compared with relevant benchmarks, if available. Regarding their mode of action, two confronting mechanistic scenarios are presented: (i) a cooperative scenario in which catalytic sites of different functionalities are active in hydroprocessing and (ii) single site catalysis, which appears to be the relevant mode of action in syngas-related catalysis and which occurs over “frustrated” active sites. 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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14 pages, 2207 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Use of Lactobacillus rhamnosus (ATCC 53103) as Whole-Cell Biocatalyst for the Regio- and Stereoselective Hydration of Oleic, Linoleic, and Linolenic Acid

by Stefano Serra and Davide De Simeis

Catalysts 2018, 8(3), 109; https://doi.org/10.3390/catal8030109 - 9 Mar 2018

Cited by 21 | Viewed by 8851

Abstract

Natural hydroxy fatty acids are relevant starting materials for the production of a number of industrial fine chemicals, such as different high-value flavour ingredients. Only a few of the latter hydroxy acid derivatives are available on a large scale. Therefore, their preparation by [...] Read more.

Natural hydroxy fatty acids are relevant starting materials for the production of a number of industrial fine chemicals, such as different high-value flavour ingredients. Only a few of the latter hydroxy acid derivatives are available on a large scale. Therefore, their preparation by microbial hydration of unsaturated fatty acids, affordable from vegetable oils, is a new biotechnological challenge. In this study, we describe the use of the probiotic bacterium Lactobacillus rhamnosus (ATCC 53103) as whole-cell biocatalyst for the hydration of the most common unsaturated octadecanoic acids, namely oleic acid, linoleic acid, and linolenic acid. We discovered that the addition of the latter fatty acids to an anaerobic colture of the latter strain, during the early stage of its exponential growth, allows the production of the corresponding mono-hydroxy derivatives. In these experimental conditions, the hydration reaction proceeds with high regio- and stereoselectivity. Only 10-hydroxy derivatives were formed and the resulting (R)-10-hydroxystearic acid, (S)-(12Z)-10-hydroxy-octadecenoic acid, and (S)-(12Z,15Z)-10-hydroxy-octadecadienoic acid were obtained in very high enantiomeric purity (ee > 95%). Although overall conversions usually do not exceed 50% yield, our biotransformation protocol is stereoselective, scalable, and holds preparative significance. Full article

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

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36 pages, 4326 KB

Open AccessEditor’s ChoiceReview

The Role of Yeast-Surface-Display Techniques in Creating Biocatalysts for Consolidated BioProcessing

by Ian Dominic Flormata Tabañag, I-Ming Chu, Yu-Hong Wei and Shen-Long Tsai

Catalysts 2018, 8(3), 94; https://doi.org/10.3390/catal8030094 - 25 Feb 2018

Cited by 20 | Viewed by 9405

Abstract

Climate change is directly linked to the rapid depletion of our non-renewable fossil resources and has posed concerns on sustainability. Thus, imploring the need for us to shift from our fossil based economy to a sustainable bioeconomy centered on biomass utilization. The efficient [...] Read more.

Climate change is directly linked to the rapid depletion of our non-renewable fossil resources and has posed concerns on sustainability. Thus, imploring the need for us to shift from our fossil based economy to a sustainable bioeconomy centered on biomass utilization. The efficient bioconversion of lignocellulosic biomass (an ideal feedstock) to a platform chemical, such as bioethanol, can be achieved via the consolidated bioprocessing technology, termed yeast surface engineering, to produce yeasts that are capable of this feat. This approach has various strategies that involve the display of enzymes on the surface of yeast to degrade the lignocellulosic biomass, then metabolically convert the degraded sugars directly into ethanol, thus elevating the status of yeast from an immobilization material to a whole-cell biocatalyst. The performance of the engineered strains developed from these strategies are presented, visualized, and compared in this article to highlight the role of this technology in moving forward to our quest against climate change. Furthermore, the qualitative assessment synthesized in this work can serve as a reference material on addressing the areas of improvement of the field and on assessing the capability and potential of the different yeast surface display strategies on the efficient degradation, utilization, and ethanol production from lignocellulosic biomass. Full article

(This article belongs to the Special Issue Immobilized Biocatalysts)

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32 pages, 4795 KB

Open AccessEditor’s ChoiceReview

The Design of MnO_x Based Catalyst in Post-Plasma Catalysis Configuration for Toluene Abatement

by Zhiping Ye, Jean-Marc Giraudon, Nathalie De Geyter, Rino Morent and Jean-François Lamonier

Catalysts 2018, 8(2), 91; https://doi.org/10.3390/catal8020091 - 23 Feb 2018

Cited by 49 | Viewed by 11020

Abstract

This review provides an overview of our present state of knowledge using manganese oxide (MnO_x)-based catalysts for toluene abatement in PPC (Post plasma-catalysis) configuration. The context of this study is concisely sum-up. After briefly screening the main depollution methods, the principles [...] Read more.

This review provides an overview of our present state of knowledge using manganese oxide (MnO_x)-based catalysts for toluene abatement in PPC (Post plasma-catalysis) configuration. The context of this study is concisely sum-up. After briefly screening the main depollution methods, the principles of PPC are exposed based on the coupling of two mature technologies such as NTP (Non thermal plasma) and catalysis. In that respect, the presentation of the abundant manganese oxides will be firstly given. Then in a second step the main features of MnO_x allowing better performances in the reactions expected to occur in the abatement of toluene in PPC process are reviewed including ozone decomposition, toluene ozonation, CO oxidation and toluene total oxidation. Finally, in a last part the current status of the applications of PPC using MnO_x on toluene abatement are discussed. In a first step, the selected variables of the hybrid process related to the experimental conditions of toluene abatement in air are identified. The selected variables are those expected to play a role in the performances of PPC system towards toluene abatement. Then the descriptors linked to the performances of the hybrid process in terms of efficiency are given and the effects of the variables on the experimental outcomes (descriptors) are discussed. The review would serve as a reference guide for the optimization of the PPC process using MnO_x-based oxides for toluene abatement. Full article

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28 pages, 6004 KB

Open AccessFeature PaperEditor’s ChoiceReview

One-Pot Combination of Metal- and Bio-Catalysis in Water for the Synthesis of Chiral Molecules

by Nicolás Ríos-Lombardía, Joaquín García-Álvarez and Javier González-Sabín

Catalysts 2018, 8(2), 75; https://doi.org/10.3390/catal8020075 - 10 Feb 2018

Cited by 54 | Viewed by 9357

Abstract

During the last decade, the combination of different metal- and bio-catalyzed organic reactions in aqueous media has permitted the flourishing of a variety of one-pot asymmetric multi-catalytic reactions devoted to the construction of enantiopure and high added-value chemicals under mild reaction conditions (usually [...] Read more.

During the last decade, the combination of different metal- and bio-catalyzed organic reactions in aqueous media has permitted the flourishing of a variety of one-pot asymmetric multi-catalytic reactions devoted to the construction of enantiopure and high added-value chemicals under mild reaction conditions (usually room temperature) and in the presence of air. Herein, a comprehensive account of the state-of-the-art in the development of catalytic networks by combining metallic and biological catalysts in aqueous media (the natural environment of enzymes) is presented. Among others, the combination of metal-catalyzed isomerizations, cycloadditions, hydrations, olefin metathesis, oxidations, C-C cross-coupling and hydrogenation reactions, with several biocatalyzed transformations of organic groups (enzymatic reduction, epoxidation, halogenation or ester hydrolysis), are discussed. Full article

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11 pages, 1863 KB

Open AccessFeature PaperEditor’s ChoiceArticle

New Trendy Magnetic C-Scorpionate Iron Catalyst and Its Performance towards Cyclohexane Oxidation

by Ana P. C. Ribeiro, Inês A. S. Matias, Elisabete C. B. A. Alegria, Ana M. Ferraria, Ana M. Botelho do Rego, Armando J. L. Pombeiro and Luísa M. D. R. S. Martins

Catalysts 2018, 8(2), 69; https://doi.org/10.3390/catal8020069 - 8 Feb 2018

Cited by 15 | Viewed by 5446

Abstract

For the first time, a magnetic C-scorpionate catalyst was prepared from the iron(II) complex [FeCl₂{κ³-HC(pz)₃}] (pz = pyrazol-1-yl) and ferrite, using the sustainable mechanochemical synthetic procedure. Its catalytic activity for the cyclohexane oxidation with tert-butyl hydroperoxide [...] Read more.

For the first time, a magnetic C-scorpionate catalyst was prepared from the iron(II) complex [FeCl₂{κ³-HC(pz)₃}] (pz = pyrazol-1-yl) and ferrite, using the sustainable mechanochemical synthetic procedure. Its catalytic activity for the cyclohexane oxidation with tert-butyl hydroperoxide (TBHP) was evaluated in different conditions, namely under microwave irradiation and under the effect of an external magnetic field. The use of such magnetic conditions significantly shifted the catalyst alcohol/ketone selectivity, thus revealing a promising, easy new protocol for tuning selectivity in important catalytic processes. Full article

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21 pages, 4778 KB

Open AccessEditor’s ChoiceArticle

1,3-Diene Polymerization Mediated by Homoleptic Tetramethylaluminates of the Rare-Earth Metals

by Christoph O. Hollfelder, Lars N. Jende, Dominic Diether, Theresa Zelger, Rita Stauder, Cäcilia Maichle-Mössmer and Reiner Anwander

Catalysts 2018, 8(2), 61; https://doi.org/10.3390/catal8020061 - 3 Feb 2018

Cited by 26 | Viewed by 6386

Abstract

During the past two decades homoleptic tetramethylaluminates of the trivalent rare-earth metals, Ln(AlMe₄)₃, have emerged as useful components for efficient catalyst design in the field of 1,3-diene polymerization. Previous work had focused on isoprene polymerization applying Ln(AlMe₄) [...] Read more.

During the past two decades homoleptic tetramethylaluminates of the trivalent rare-earth metals, Ln(AlMe₄)₃, have emerged as useful components for efficient catalyst design in the field of 1,3-diene polymerization. Previous work had focused on isoprene polymerization applying Ln(AlMe₄)₃ precatalysts with Ln = La, Ce, Pr, Nd, Gd and Y, in the presence of Et₂AlCl as an activator. Polymerizations employing Ln(AlMe₄)₃ with Ln = La, Y and Nd along with borate/borane co-catalysts [Ph₃C][B(C₆F₅)₄], [PhNMe₂H][B(C₆F₅)₄] and [B(C₆F₅)₃] were mainly investigated for reasons of comparison with ancillary ligand-supported systems (cf. half-sandwich complexes). The present study investigates into a total of eleven rare-earth elements, namely Ln = La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Y, Er and Lu. A full overview on the polymerization behavior of Ln(AlMe₄)₃ in the presence of perfluorinated borate/borane cocatalysts and R₂AlCl-type activators (R = Me, Et) is provided, probing the monomers isoprene and 1,3-butadiene (and preliminary ethylene). Virtually complete cis-1,4-selectivities are obtained for several catalyst/cocatalyst combinations (e.g., Gd(AlMe₄)₃/Me₂AlCl, >99.9%). Insights into the ‘black box’ of active species are obtained by indirect observations via screening of pre-reaction time and cocatalyst concentration. The microstructure of the polydienes is investigated by combined ¹H/¹³C NMR and ATR-IR spectroscopies. Furthermore, the reaction of [LuMe₆(Li(thf)_x)₃] with AlMe₃ has been applied as a new strategy for the efficient synthesis of Lu(AlMe₄)₃. The solid-state structures of Gd(AlMe₄)₃ and Tb(AlMe₄)₃ are reported. Full article

(This article belongs to the Special Issue Catalysts for the Controlled Polymerization of Conjugated Dienes)

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12 pages, 2297 KB

Open AccessFeature PaperEditor’s ChoiceCommunication

Whole-Cell Biocatalyst for Chemoenzymatic Total Synthesis of Rivastigmine

by Paola Vitale, Filippo Maria Perna, Gennaro Agrimi, Isabella Pisano, Francesco Mirizzi, Roberto Vito Capobianco and Vito Capriati

Catalysts 2018, 8(2), 55; https://doi.org/10.3390/catal8020055 - 31 Jan 2018

Cited by 49 | Viewed by 7837

Abstract

Biocatalytic processes are increasingly playing a key role in the development of sustainable asymmetric syntheses, which are central to pharmaceutical companies for the production of chiral enantiopure drugs. This work describes a simple and economically viable chemoenzymatic process for the production of ( [...] Read more.

Biocatalytic processes are increasingly playing a key role in the development of sustainable asymmetric syntheses, which are central to pharmaceutical companies for the production of chiral enantiopure drugs. This work describes a simple and economically viable chemoenzymatic process for the production of (S)-rivastigmine, which is an important drug for the treatment of mild to moderate dementia of the Alzheimer’s type. The described protocol involves the R-regioselective bioreduction of an aromatic ketone by Lactobacillus reuteri DSM 20016 whole cells in phosphate buffered saline (PBS) (37 °C, 24 h) as a key step. Biocatalytic performance of baker’s yeast whole cells in water and in aqueous eutectic mixtures have been evaluated and discussed as well. The route is scalable, environmentally friendly, and the target drug is obtained via four steps in overall 78% yield and 98% ee. Full article

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10 pages, 1006 KB

Open AccessEditor’s ChoiceArticle

Genetically Fused T4L Acts as a Shield in Covalent Enzyme Immobilisation Enhancing the Rescued Activity

by Matteo Planchestainer, David Roura Padrosa, Martina Letizia Contente and Francesca Paradisi

Catalysts 2018, 8(1), 40; https://doi.org/10.3390/catal8010040 - 20 Jan 2018

Cited by 14 | Viewed by 6406

Abstract

Enzyme immobilisation is a common strategy to increase enzymes resistance and reusability in a variety of excellent ‘green’ applications. However, the interaction with the solid support often leads to diminished specific activity, especially when non-specific covalent binding to the carrier takes place which [...] Read more.

Enzyme immobilisation is a common strategy to increase enzymes resistance and reusability in a variety of excellent ‘green’ applications. However, the interaction with the solid support often leads to diminished specific activity, especially when non-specific covalent binding to the carrier takes place which affects the delicate architecture of the enzyme. Here we developed a broadly applicable strategy where the T4-lysozyme (T4L) is genetically fused at the N-terminus of different enzymes and used as inert protein spacer which directly attaches to the carrier preventing shape distortion of the catalyst. Halomonas elongata aminotransferase (HEWT), Bacillus subtilis engineered esterase (BS2m), and horse liver alcohol dehydrogenase (HLADH) were used as model enzymes to elucidate the benefits of the spacer. While HEWT and HLADH activity and expression were diminished by the fused T4L, both enzymes retained almost quantitative activity after immobilisation. In the case of BS2m, the protective effect of the T4L effectively was important and led to up to 10-fold improvement in the rescued activity. Full article

(This article belongs to the Special Issue Immobilized Biocatalysts)

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16 pages, 4240 KB

Open AccessEditor’s ChoiceArticle

“Deceived” Concentrated Immobilized Cells as Biocatalyst for Intensive Bacterial Cellulose Production from Various Sources

by Nikolay Stepanov and Elena Efremenko

Catalysts 2018, 8(1), 33; https://doi.org/10.3390/catal8010033 - 18 Jan 2018

Cited by 32 | Viewed by 7145

Abstract

A new biocatalyst in the form of Komagataeibacter xylinum B-12429 cells immobilized in poly(vinyl alcohol) cryogel for production of bacterial cellulose was demonstrated. Normally, the increased bacteria concentration causes an enlarged bacterial cellulose synthesis while cells push the polysaccharide out to pack themselves [...] Read more.

A new biocatalyst in the form of Komagataeibacter xylinum B-12429 cells immobilized in poly(vinyl alcohol) cryogel for production of bacterial cellulose was demonstrated. Normally, the increased bacteria concentration causes an enlarged bacterial cellulose synthesis while cells push the polysaccharide out to pack themselves into this polymer and go into a stasis. Immobilization of cells into the poly(vinyl alcohol) cryogel allowed “deceiving” them: bacteria producing cellulose pushed it out, which further passed through the pores of cryogel matrix and was accumulated in the medium while not covering the cells; hence, the latter were deprived of a possible transition to inactivity and worked on the synthesis of bacterial cellulose even more actively. The repeated use of immobilized cells retaining 100% of their metabolic activity for at least 10 working cycles (60 days) was performed. The immobilized cells produce bacterial cellulose with crystallinity and porosity similar to polysaccharide of free cells, but having improved stiffness and tensile strength. Various media containing sugars and glycerol, based on hydrolysates of renewable biomass sources (aspen, Jerusalem artichoke, rice straw, microalgae) were successfully applied for bacterial cellulose production by immobilized cells, and the level of polysaccharide accumulation was 1.3–1.8-times greater than suspended cells could produce. Full article

(This article belongs to the Special Issue Immobilized Biocatalysts)

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8 pages, 1882 KB

Open AccessFeature PaperEditor’s ChoiceCommunication

Relationships between Substrate Promiscuity and Chiral Selectivity of Esterases from Phylogenetically and Environmentally Diverse Microorganisms

by Cristina Coscolín, Mónica Martínez-Martínez, Jennifer Chow, Rafael Bargiela, Antonio García-Moyano, Gro E. K. Bjerga, Alexander Bollinger, Runar Stokke, Ida H. Steen, Olga V. Golyshina, Michail M. Yakimov, Karl-Erich Jaeger, Alexander F. Yakunin, Wolfgang R. Streit, Peter N. Golyshin and Manuel Ferrer

Catalysts 2018, 8(1), 10; https://doi.org/10.3390/catal8010010 - 5 Jan 2018

Cited by 11 | Viewed by 5654

Abstract

Substrate specificity and selectivity of a biocatalyst are determined by the protein sequence and structure of its active site. Finding versatile biocatalysts acting against multiple substrates while at the same time being chiral selective is of interest for the pharmaceutical and chemical industry. [...] Read more.

Substrate specificity and selectivity of a biocatalyst are determined by the protein sequence and structure of its active site. Finding versatile biocatalysts acting against multiple substrates while at the same time being chiral selective is of interest for the pharmaceutical and chemical industry. However, the relationships between these two properties in natural microbial enzymes remain underexplored. Here, we performed an experimental analysis of substrate promiscuity and chiral selectivity in a set of 145 purified esterases from phylogenetically and environmentally diverse microorganisms, which were assayed against 96 diverse esters, 20 of which were enantiomers. Our results revealed a negative correlation between substrate promiscuity and chiral selectivity in the evaluated enzymes. Esterases displaying prominent substrate promiscuity and large catalytic environments are characterized by low chiral selectivity, a feature that has limited commercial value. Although a low level of substrate promiscuity does not guarantee high chiral selectivity, the probability that esterases with smaller active sites possess chiral selectivity factors of interest for industry (>25) is significantly higher than for promiscuous enzymes. Together, the present study unambiguously demonstrates that promiscuous and selective esterases appear to be rare in nature and that substrate promiscuity can be used as an indicator of the chiral selectivity level of esterases, and vice versa. Full article

(This article belongs to the Special Issue Biocatalysis and Biotransformations)

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