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Volume 8
Issue 5
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Catalysts, Volume 8, Issue 5 (May 2018) – 50 articles

Cover Story (view full-size image): The cover design represents the core idea of our research, which is the exploitation of woody biomass waste to produce bioproducts (mainly charcoal) that could replace fossil fuel utilization in metallurgical industries, helping them reduce their massive CO2 emissions. For this purpose pyrolysis has been proven as a suitable technology, however, in order to make process profitable and sustainable a proper catalytic optimization of the vapors composition is mandatory. The picture shows the characteristic closed carbon loop associated to biomass, the wastes produced from forest activities are pyrolysed and the vapors thermal-catalytically treated. The charcoal and pyro gas are then used by the metallurgical industry and finally the CO2 is fixed again by the growing plant species. View this paper.
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8 pages, 4743 KiB  
Article
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 15 | Viewed by 5077
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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13 pages, 3932 KiB  
Article
Effects of Synthesis on the Structural Properties and Methane Partial Oxidation Activity of Ni/CeO2 Catalyst
by Valeria La Parola, Giuseppe Pantaleo and Anna Maria Venezia
Catalysts 2018, 8(5), 220; https://doi.org/10.3390/catal8050220 - 21 May 2018
Cited by 17 | Viewed by 4326
Abstract
Nickel catalysts supported on homemade CeO2 oxide were prepared by two procedures intending to achieve different degree of metal-support interaction. One method consisted of a co-precipitation that was assisted by microwave; the other method was based on a modified wetness impregnation in [...] Read more.
Nickel catalysts supported on homemade CeO2 oxide were prepared by two procedures intending to achieve different degree of metal-support interaction. One method consisted of a co-precipitation that was assisted by microwave; the other method was based on a modified wetness impregnation in the presence of the organic complexing ligand, nitrilotriacetic acid (NTA). The support and catalysts were characterized by temperature programmed reduction (TPR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) techniques. Significant differences in the structure, in redox properties and in the elemental surface composition emerged. The catalytic behavior in the partial oxidation of methane was tested at atmospheric pressure, in a range of temperature between 400–800 °C, using diluted feed gas mixture with CH4/O2 = 2 and GHSV= 60,000 mL g−1 h−1. Moreover, the effect of the catalyst reduction pretreatment was investigated. The better catalytic performance of the microwave-assisted sample as compared to the NTA prepared sample was attributed to the stronger interaction of nickel with CeO2. Indeed, according to the structural and reducibility results, an adequate electronic contact between the metal and the support favors the formation of oxygen vacancies of ceria and inhibits the sintering of the catalyst active species, with an improvement of the catalytic performance. Full article
(This article belongs to the Special Issue Structure–Activity Relationships in Catalysis)
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20 pages, 4267 KiB  
Article
Catalytic Ozonation by Iron Coated Pumice for the Degradation of Natural Organic Matters
by Alper Alver and Ahmet Kılıç
Catalysts 2018, 8(5), 219; https://doi.org/10.3390/catal8050219 - 21 May 2018
Cited by 29 | Viewed by 5034
Abstract
The use of iron-coated pumice (ICP) in heterogeneous catalytic ozonation significantly enhanced the removal efficiency of natural organic matters (NOMs) in water, due to the synergistic effect of hybrid processes when compared to sole ozonation and adsorption. Multiple characterization analyses (BET, TEM, XRD, [...] Read more.
The use of iron-coated pumice (ICP) in heterogeneous catalytic ozonation significantly enhanced the removal efficiency of natural organic matters (NOMs) in water, due to the synergistic effect of hybrid processes when compared to sole ozonation and adsorption. Multiple characterization analyses (BET, TEM, XRD, DLS, FT-IR, and pHPZC) were employed for a systematic investigation of the catalyst surface properties. This analysis indicated that the ICP crystal structure was α-FeOOH, the surface hydroxyl group of ICP was significantly increased after coating, the particle size of ICP was about 200–250 nm, the BET surface area of ICP was about 10.56 m2 g−1, the pHPZC value of ICP was about 7.13, and that enhancement by iron loading was observed in the FT-IR spectra. The contribution of surface adsorption, hydroxyl radicals, and sole ozonation to catalytic ozonation was determined as 21.29%, 66.22%, and 12.49%, respectively. The reaction kinetic analysis with tert-Butyl alcohol (TBA) was used as a radical scavenger, confirming that surface ferrous iron loading promoted the role of the hydroxyl radicals. The phosphate was used as an inorganic probe, and significantly inhibited the removal efficiency of catalytic NOM ozonation. This is an indication that the reactions which occur are more dominant in the solution phase. Full article
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16 pages, 3478 KiB  
Article
Activation of Persulfate Using an Industrial Iron-Rich Sludge as an Efficient Nanocatalyst for Landfill Leachate Treatment
by Alaa Mohamad Soubh, Majid Baghdadi, Mohammad Ali Abdoli and Behnoush Aminzadeh
Catalysts 2018, 8(5), 218; https://doi.org/10.3390/catal8050218 - 20 May 2018
Cited by 19 | Viewed by 4309
Abstract
In this research, the performance of nanomaterials obtained from the converter sludge (CS) of Esfahan Steel Company, Iran was investigated for the activation of persulfate (PS). The experiments were conducted on real and synthetic leachates. CS showed high catalytic activity for removal of [...] Read more.
In this research, the performance of nanomaterials obtained from the converter sludge (CS) of Esfahan Steel Company, Iran was investigated for the activation of persulfate (PS). The experiments were conducted on real and synthetic leachates. CS showed high catalytic activity for removal of chemical oxygen demand COD and NH3 because of its high iron oxide content. The effects of pH, CS dosage, and PS/COD ratio, temperature, and reaction time on the removal of COD and NH3 were evaluated to optimize operational conditions (pH 2, CS dosage: 1.2 g L−1, PS/COD: 4, and reaction time: 60 min). Maximum COD and NH3 removal efficiencies were 73.56 and 63.87%, respectively. Finally, the optimized process was applied for treatment of a real leachate sample. Although the treated leachate was not suitable to discharge into the environment, an increase in the 5-day biochemical oxygen demand (BOD5) and biodegradability (BOD5/COD) of leachate after treatment indicated that the effluent can be biologically treated. As a consequence, it can be combined with sewage or can be returned to the landfill. Full article
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11 pages, 5188 KiB  
Article
Deep Eutectic Mixtures as Reaction Media for the Enantioselective Organocatalyzed α-Amination of 1,3-Dicarbonyl Compounds
by Diego Ros Ñíguez, Pegah Khazaeli, Diego A. Alonso and Gabriela Guillena
Catalysts 2018, 8(5), 217; https://doi.org/10.3390/catal8050217 - 18 May 2018
Cited by 19 | Viewed by 5955
Abstract
The enantioselective α-amination of 1,3-dicarbonyl compounds has been performed using deep eutectic solvents (DES) as a reaction media and chiral 2-amino benzimidazole-derived compounds as a catalytic system. With this procedure, the use of toxic volatile organic compounds (VOCs) as reaction media is avoided. [...] Read more.
The enantioselective α-amination of 1,3-dicarbonyl compounds has been performed using deep eutectic solvents (DES) as a reaction media and chiral 2-amino benzimidazole-derived compounds as a catalytic system. With this procedure, the use of toxic volatile organic compounds (VOCs) as reaction media is avoided. Furthermore, highly functionalized chiral molecules, which are important intermediates for the natural product synthesis, are synthetized by an efficient and stereoselective protocol. Moreover, the reaction can be done on a preparative scale, with the recycling of the catalytic system being possible for at least five consecutive reaction runs. This procedure represents a cheap, simple, clean, and scalable method that meets most of the principles to be considered a green and sustainable process. Full article
(This article belongs to the Special Issue Catalyzed Synthesis of Natural Products)
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6 pages, 199 KiB  
Editorial
Biocatalysis and Biotransformations
by Manuel Ferrer
Catalysts 2018, 8(5), 216; https://doi.org/10.3390/catal8050216 - 17 May 2018
Cited by 3 | Viewed by 3516
Abstract
n/a Full article
(This article belongs to the Special Issue Biocatalysis and Biotransformations)
10 pages, 2892 KiB  
Article
The Pros and Cons of Polydopamine-Sensitized Titanium Oxide for the Photoreduction of CO2
by Tongyao Wang, Ming Xia and Xueqian Kong
Catalysts 2018, 8(5), 215; https://doi.org/10.3390/catal8050215 - 17 May 2018
Cited by 18 | Viewed by 5661
Abstract
Photocatalytic reduction of CO2 into fuels is a promising route to reduce greenhouse gas emission, and it demands high-performance photocatalysts that can use visible light in the solar spectrum. Due to its broadband light adsorption, polydopamine (PDA) is considered as a promising [...] Read more.
Photocatalytic reduction of CO2 into fuels is a promising route to reduce greenhouse gas emission, and it demands high-performance photocatalysts that can use visible light in the solar spectrum. Due to its broadband light adsorption, polydopamine (PDA) is considered as a promising photo-sensitization material for semiconductor photocatalysts. In this work, titanium oxides have been coated with PDA through an in-situ oxidation polymerization method to pursue CO2 reduction under visible light. We have shown that the surface coated PDA with a thickness of around 1 nm can enhance the photocatalytic performance of anatase under visible light to reduce CO2 into CO. Assisted with additional UV-vis adsorption and photoluminescence characterizations, we confirmed the sensitization effect of PDA on anatase. Furthermore, our study shows that thicker PDA coating might not be favorable, as PDA could decompose under both visible and UV-vis light irradiations. 13C solid-state nuclear magnetic resonance showed structural differences between thin and thick PDA coatings and revealed compositional changes of PDA after light irradiation. Full article
(This article belongs to the Special Issue Nanomaterials for Environmental Purification and Energy Conversion)
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19 pages, 3576 KiB  
Review
Host-Guest Engineering of Layered Double Hydroxides towards Efficient Oxygen Evolution Reaction: Recent Advances and Perspectives
by Jianming Li, Shan Jiang, Mingfei Shao and Min Wei
Catalysts 2018, 8(5), 214; https://doi.org/10.3390/catal8050214 - 17 May 2018
Cited by 26 | Viewed by 9274
Abstract
Electrochemical water splitting has great potential in the storage of intermittent energy from the sun, wind, or other renewable sources for sustainable clean energy applications. However, the anodic oxygen evolution reaction (OER) usually determines the efficiency of practical water electrolysis due to its [...] Read more.
Electrochemical water splitting has great potential in the storage of intermittent energy from the sun, wind, or other renewable sources for sustainable clean energy applications. However, the anodic oxygen evolution reaction (OER) usually determines the efficiency of practical water electrolysis due to its sluggish four-electron process. Layered double hydroxides (LDHs) have attracted increasing attention as one of the ideal and promising electrocatalysts for water oxidation due to their excellent activity, high stability in basic conditions, as well as their earth-abundant compositions. In this review, we discuss the recent progress on LDH-based OER electrocatalysts in terms of active sites, host-guest engineering, and catalytic performances. Moreover, further developments and challenges in developing promising electrocatalysts based on LDHs are discussed from the viewpoint of molecular design and engineering. Full article
(This article belongs to the Special Issue Novel Non-Precious Metal Electrocatalysts for Oxygen Electrode Reactions)
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12 pages, 6692 KiB  
Article
The Role of Pulse Voltage Amplitude on Chemical Processes Induced by Streamer Discharge at Water Surface
by Ruma, Hamid Hosano, Takashi Sakugawa and Hidenori Akiyama
Catalysts 2018, 8(5), 213; https://doi.org/10.3390/catal8050213 - 17 May 2018
Cited by 21 | Viewed by 4799
Abstract
The paper reports the effects of pulse voltage amplitude on streamer discharge propagation at water surface. The subsequent chemical processes in a reactor following the surface discharges with different voltages are presented. A pulsed power modulator (PPM) system equipped with a control unit [...] Read more.
The paper reports the effects of pulse voltage amplitude on streamer discharge propagation at water surface. The subsequent chemical processes in a reactor following the surface discharges with different voltages are presented. A pulsed power modulator (PPM) system equipped with a control unit was employed to generate 0–25 kV pulses at 500 Hz. A point-plane electrode configuration was used for experiments, with the point electrode placed with 1 mm gap from the water surface in atmospheric air, and plane ground submerged with 30 mm gap in water. The streamer length at water surface was significantly influenced by the pulse voltage amplitude. Colorimetric measurement of hydrogen peroxide (H2O2) and treatment of indigo carmine organic dye solution were carried out to elucidate the chemical processes produced at various pulse voltages. The experimental results reveal that the applied voltage is a factor that greatly affects water surface discharges and their chemical processes. Full article
(This article belongs to the Special Issue Catalytic Wet-Air Oxidation Processes)
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28 pages, 4631 KiB  
Review
Nanostructured Oxides Synthesised via scCO2-Assisted Sol-Gel Methods and Their Application in Catalysis
by Yehan Tao and Paolo P. Pescarmona
Catalysts 2018, 8(5), 212; https://doi.org/10.3390/catal8050212 - 17 May 2018
Cited by 19 | Viewed by 10514
Abstract
Nanostructured metal oxides and silicates are increasingly applied in catalysis, either as supports or as active species in heterogeneous catalysts, owing to the physicochemical properties that typically distinguish them from bulk oxides, such as higher surface area and a larger fraction of coordinatively [...] Read more.
Nanostructured metal oxides and silicates are increasingly applied in catalysis, either as supports or as active species in heterogeneous catalysts, owing to the physicochemical properties that typically distinguish them from bulk oxides, such as higher surface area and a larger fraction of coordinatively unsaturated sites at their surface. Among the different synthetic routes for preparing these oxides, sol-gel is a relatively facile and efficient method. The use of supercritical CO2 (scCO2) in the sol-gel process can be functional to the formation of nanostructured materials. The physical properties of the scCO2 medium can be controlled by adjusting the processing temperature and the pressure of CO2, thus enabling the synthesis conditions to be tuned. This paper provides a review of the studies on the synthesis of oxide nanomaterials via scCO2-assisted sol-gel methods and their catalytic applications. The advantages brought about by scCO2 in the synthesis of oxides are described, and the performance of oxide-based catalysts prepared by scCO2 routes is compared to their counterparts prepared via non-scCO2-assisted methods. Full article
(This article belongs to the Special Issue Sol–Gel Chemistry: A Toolbox for Catalyst Preparation)
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12 pages, 4686 KiB  
Article
Catalytic Ozonation of Toluene Using Chilean Natural Zeolite: The Key Role of Brønsted and Lewis Acid Sites
by Serguei Alejandro-Martín, Héctor Valdés, Marie-Hélène Manero and Claudio A. Zaror
Catalysts 2018, 8(5), 211; https://doi.org/10.3390/catal8050211 - 17 May 2018
Cited by 15 | Viewed by 4496
Abstract
The influence of surface physical-chemical characteristics of Chilean natural zeolite on the catalytic ozonation of toluene is presented in this article. Surface characteristics of natural zeolite were modified by acid treatment with hydrochloric acid and ion-exchange with ammonium sulphate. Prior to catalytic ozonation [...] Read more.
The influence of surface physical-chemical characteristics of Chilean natural zeolite on the catalytic ozonation of toluene is presented in this article. Surface characteristics of natural zeolite were modified by acid treatment with hydrochloric acid and ion-exchange with ammonium sulphate. Prior to catalytic ozonation assays, natural and chemically modified zeolite samples were thermally treated at 623 and 823 K in order to enhance Brønsted and Lewis acid sites formation, respectively. Natural and modified zeolite samples were characterised by N2 adsorption at 77 K, elemental analysis, X-ray fluorescence, and Fourier transform infrared (FTIR) spectroscopy, using pyridine as a probe molecule. The highest values of the reaction rate of toluene oxidation were observed when NH4Z1 and 2NH4Z1 zeolite samples were used. Those samples registered the highest density values of Lewis acid sites compared to other samples used here. Results indicate that the presence of strong Lewis acid sites at the 2NH4Z1 zeolite surface causes an increase in the reaction rate of toluene oxidation, confirming the role of Lewis acid sites during the catalytic ozonation of toluene at room temperature. Lewis acid sites decompose gaseous ozone into atomic oxygen, which reacts with the adsorbed toluene at Brønsted acid sites. On the other hand, no significant contribution of Brønsted acid sites on the reaction rate was registered when NH4Z1 and 2NH4Z1 zeolite samples were used. Full article
(This article belongs to the Special Issue Catalytic Oxidation in Environmental Protection)
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15 pages, 27615 KiB  
Article
Synthesis, Characterization of Nanosized ZnCr2O4 and Its Photocatalytic Performance in the Degradation of Humic Acid from Drinking Water
by Raluca Dumitru, Florica Manea, Cornelia Păcurariu, Lavinia Lupa, Aniela Pop, Adrian Cioablă, Adrian Surdu and Adelina Ianculescu
Catalysts 2018, 8(5), 210; https://doi.org/10.3390/catal8050210 - 15 May 2018
Cited by 23 | Viewed by 5799
Abstract
Zinc chromite (ZnCr2O4) has been synthesized by the thermolysis of a new Zn(II)-Cr(III) oxalate coordination compound, namely [Cr2Zn(C2O4)4(OH2)6]·4H2O. The coordination compound has been characterized by [...] Read more.
Zinc chromite (ZnCr2O4) has been synthesized by the thermolysis of a new Zn(II)-Cr(III) oxalate coordination compound, namely [Cr2Zn(C2O4)4(OH2)6]·4H2O. The coordination compound has been characterized by chemical analysis, infrared spectroscopy (IR), and thermal analysis. The zinc chromite obtained after a heating treatment of the coordination compound at 450 °C for 1 h has been investigated by XRD, FE-SEM, TEM/HR-TEM coupled with selected area electron diffraction (SAED) measurements. The photocatalytic performance of nanosized zinc chromite was assessed for the degradation and mineralization of humic acid (HA) from a drinking water source, envisaging the development of the advanced oxidation process for drinking water treatment technology. A mineralization efficiency of 60% was achieved after 180 min of 50 mg L−1 HA photocatalysis using zinc chromite under UV irradiation, in comparison with 7% efficiency reached by photolysis. Full article
(This article belongs to the Special Issue Nanomaterials for Environmental Purification and Energy Conversion)
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19 pages, 9417 KiB  
Article
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 26 | Viewed by 5706
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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15 pages, 4679 KiB  
Article
Cross-Linked Enzyme Aggregates of Feruloyl Esterase Preparations from Thermothelomyces thermophila and Talaromyces wortmannii
by Anastasia Zerva, Io Antonopoulou, Josefine Enman, Laura Iancu, Ulrika Rova and Paul Christakopoulos
Catalysts 2018, 8(5), 208; https://doi.org/10.3390/catal8050208 - 15 May 2018
Cited by 16 | Viewed by 4101
Abstract
Cross-linked enzyme aggregates (CLEA®) technology is a well-established method in the current literature for the low-cost and effective immobilization of several enzymes. The main advantage of this particular method is the simplicity of the process, since it consists of only two [...] Read more.
Cross-linked enzyme aggregates (CLEA®) technology is a well-established method in the current literature for the low-cost and effective immobilization of several enzymes. The main advantage of this particular method is the simplicity of the process, since it consists of only two steps. However, CLEA immobilization must be carefully designed for each desired enzyme, since the optimum conditions for enzymes can vary significantly, according to their physicochemical properties. In the present study, an investigation of the optimum CLEA immobilization conditions was carried out for eight feruloyl esterase preparations. Feruloyl esterases are a very important enzyme group in the valorization of lignocellulosic biomass, since they act in a synergistic way with other enzymes for the breakdown of plant biomass. Specifically, we investigated the type and concentration of precipitant and the crosslinker concentration, for retaining optimal activity. FAE68 was found to be the most promising enzyme for CLEA immobilization, since in this case, the maximum retained activity, over 98%, was observed. Subsequently, we examined the operational stability and the stability in organic solvents for the obtained CLEA preparations, as well as their structure. Overall, our results support that the maximum activity retaining and the stability properties of the final CLEAs can vary greatly in different FAE preparations. Nevertheless, some of the examined FAEs show a significant potential for further applications in harsh industrial conditions. Full article
(This article belongs to the Special Issue Novel Enzyme and Whole-Cell Biocatalysis)
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14 pages, 2663 KiB  
Article
Fe Oxides Loaded on Carbon Cloth by Hydrothermal Process as an Effective and Reusable Heterogenous Fenton Catalyst
by Honghui Yang, Bofang Shi and Silan Wang
Catalysts 2018, 8(5), 207; https://doi.org/10.3390/catal8050207 - 15 May 2018
Cited by 24 | Viewed by 5741
Abstract
Iron based heterogeneous Fenton catalysts are attracting much attention for its economic and environmental friendly characteristics. In this study, iron oxides loaded carbon cloth (assigned as Fe@CC) was prepared using hydrothermal hydrolysis of Fe(NO3)3. The specific surface area of [...] Read more.
Iron based heterogeneous Fenton catalysts are attracting much attention for its economic and environmental friendly characteristics. In this study, iron oxides loaded carbon cloth (assigned as Fe@CC) was prepared using hydrothermal hydrolysis of Fe(NO3)3. The specific surface area of Fe@CC determined by N2 adsorption–desorption Brunauer–Emmett–Teller method was up to 1325.5 m2/g, which increased by 81.8% compared with that of native carbon cloth mainly due to the loading of iron oxide. XPS (X-ray photoelectron spectroscopy) spectra confirmed that the iron oxide on the carbon surface included mainly FeOOH. Its heterogeneous Fenton-like activity was determined using Acid Red G as a model substrate for degradation. Fe@CC maintained high and relatively stable activity during 11 tests, and it showed high COD (Chemical Oxygen Demand) removal efficiency and high apparent H2O2 utilization efficiency. The homogeneous Fenton reaction using the amount of leached Fe(III) suggested that the surficial reaction on Fe@CC was dominant. The stability and the mechanism for gradual decrease of activity during the first 4 tests were also discussed. Full article
(This article belongs to the Special Issue Catalytic Oxidation in Environmental Protection)
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10 pages, 2290 KiB  
Review
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 4 | Viewed by 4278
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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24 pages, 12325 KiB  
Review
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 13 | Viewed by 5690
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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6 pages, 1233 KiB  
Article
A Demonstration of Pt L3-Edge EXAFS Free from Au L3-Edge Using Log–Spiral Bent Crystal Laue Analyzers
by Yuki Wakisaka, Daiki Kido, Hiromitsu Uehara, Qiuyi Yuan, Satoru Takakusagi, Yohei Uemura, Toshihiko Yokoyama, Takahiro Wada, Motohiro Uo, Tomohiro Sakata, Oki Sekizawa, Tomoya Uruga, Yasuhiro Iwasawa and Kiyotaka Asakura
Catalysts 2018, 8(5), 204; https://doi.org/10.3390/catal8050204 - 13 May 2018
Cited by 2 | Viewed by 5378
Abstract
Pt-Au nanostructures are important and well-studied fuel cell catalysts for their promising catalytic performance. However, a detailed quantitative local structure analysis, using extended X-ray absorption fine structure (EXAFS) spectroscopy, have been inhibited by interference between Pt and Au L3-edges. In this [...] Read more.
Pt-Au nanostructures are important and well-studied fuel cell catalysts for their promising catalytic performance. However, a detailed quantitative local structure analysis, using extended X-ray absorption fine structure (EXAFS) spectroscopy, have been inhibited by interference between Pt and Au L3-edges. In this paper, Pt L3-edge XAFS analysis, free of Au L3 edge, is demonstrated for a Pt-Au reference sample using a low-cost log–spiral bent crystal Laue analyzer (BCLA). This method facilitates the EXAFS structural analysis of Pt-Au catalysts, which are important to improve fuel cell catalysts. Full article
(This article belongs to the Special Issue Nanomaterials for Environmental Purification and Energy Conversion)
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18 pages, 7144 KiB  
Article
Ru–Pd Bimetallic Catalysts Supported on CeO2-MnOX Oxides as Efficient Systems for H2 Purification through CO Preferential Oxidation
by Roberto Fiorenza, Luca Spitaleri, Antonino Gulino and Salvatore Scirè
Catalysts 2018, 8(5), 203; https://doi.org/10.3390/catal8050203 - 12 May 2018
Cited by 35 | Viewed by 5739
Abstract
The catalytic performances of Ru/ceria-based catalysts in the CO preferential oxidation (CO-PROX) reaction are discussed here. Specifically, the effect of the addition of different oxides to Ru/CeO2 has been assessed. The Ru/CeO2-MnOx system showed the best performance in the [...] Read more.
The catalytic performances of Ru/ceria-based catalysts in the CO preferential oxidation (CO-PROX) reaction are discussed here. Specifically, the effect of the addition of different oxides to Ru/CeO2 has been assessed. The Ru/CeO2-MnOx system showed the best performance in the 80–120 °C temperature range, advantageous for polymer-electrolyte membrane fuel cell (PEMFC) applications. Furthermore, the influence of the addition of different metals to this mixed oxide system has been evaluated. The bimetallic Ru–Pd/CeO2-MnOx catalyst exhibited the highest yield to CO2 (75%) at 120 °C whereas the monometallic Ru/CeO2-MnOx sample was that one with the highest CO2 yield (60%) at 100 °C. The characterization data (H2-temperature programmed reduction (H2-TPR), X-ray diffraction (XRD), N2 adsorption-desorption, diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), X-ray photoelectron spectroscopy (XPS)) pointed out that the co-presence of manganese oxide and ruthenium enhances the mobility/reactivity of surface ceria oxygens accounting for the good CO-PROX performance of this system. Reducible oxides as CeO2 and MnOx, in fact, play two important functions, namely weakening the CO adsorption on the metal active sites and providing additional sites for adsorption/activation of O2, thus changing the mechanism from competitive Langmuir–Hinshelwood into non-competitive one-step dual site Langmuir–Hinshelwood/Mars–van Krevelen. As confirmed by H2-TPR and XPS measurements, these features are boosted by the simultaneous presence of ruthenium and palladium. The strong reciprocal interaction of these metals between them and with the CeO2-MnOx support was assumed to be responsible of the promoted reducibility/reactivity of CeO2 oxygens, thus resulting in the best CO-PROX efficiency at low temperature of the Ru-Pd/CeO2-MnOx catalyst. The higher selectivity to CO2 found on the Ru–Pd system, which reduces the undesired H2 consumption, represents a promising result of this research, being one of the key aims of the design of CO-PROX catalysts. Full article
(This article belongs to the Special Issue Catalysts for Hydrogen Purification for Fuel Cell Applications)
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39 pages, 13950 KiB  
Review
Solid-Supported Palladium Catalysts in Sonogashira Reactions: Recent Developments
by Diego A. Alonso, Alejandro Baeza, Rafael Chinchilla, Cecilia Gómez, Gabriela Guillena, Isidro M. Pastor and Diego J. Ramón
Catalysts 2018, 8(5), 202; https://doi.org/10.3390/catal8050202 - 11 May 2018
Cited by 56 | Viewed by 8372
Abstract
The Sonogashira cross-coupling reaction is the most frequently employed synthetic procedure for the preparation of arylated alkynes, which are important conjugated compounds with multiple applications. Despite of their rather high price, this reaction is usually catalyzed by palladium species, making the recovery and [...] Read more.
The Sonogashira cross-coupling reaction is the most frequently employed synthetic procedure for the preparation of arylated alkynes, which are important conjugated compounds with multiple applications. Despite of their rather high price, this reaction is usually catalyzed by palladium species, making the recovery and reuse of the catalyst an interesting topic, mainly for industrial purposes. Easy recycle can be achieved anchoring the palladium catalyst to a separable support. This review shows recent developments in the use of palladium species anchored to different solid supports as recoverable catalysts for Sonogashira cross-coupling reactions. Full article
(This article belongs to the Special Issue Solid-Supported Reagents in Palladium-Catalyzed Transformations)
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12 pages, 1963 KiB  
Article
Immobilization of the β-fructofuranosidase from Xanthophyllomyces dendrorhous by Entrapment in Polyvinyl Alcohol and Its Application to Neo-Fructooligosaccharides Production
by Noa Míguez, María Gimeno-Pérez, David Fernández-Polo, Fadia V. Cervantes, Antonio O. Ballesteros, María Fernández-Lobato, María H. Ribeiro and Francisco J. Plou
Catalysts 2018, 8(5), 201; https://doi.org/10.3390/catal8050201 - 11 May 2018
Cited by 18 | Viewed by 4802
Abstract
The β-fructofuranosidase (Xd-INV) from the basidiomycota yeast Xanthophyllomyces dendrorhous (formerly Phaffia rhodozyma) is unique in its ability to synthesize neo- fructooligosaccharides (neo-FOS). In order to facilitate its industrial application, the recombinant enzyme expressed in Pichia pastoris (pXd-INV) was immobilized by entrapment in [...] Read more.
The β-fructofuranosidase (Xd-INV) from the basidiomycota yeast Xanthophyllomyces dendrorhous (formerly Phaffia rhodozyma) is unique in its ability to synthesize neo- fructooligosaccharides (neo-FOS). In order to facilitate its industrial application, the recombinant enzyme expressed in Pichia pastoris (pXd-INV) was immobilized by entrapment in polyvinyl alcohol (PVA) hydrogels. The encapsulation efficiency exceeded 80%. The PVA lenticular particles of immobilized pXd-INV were stable up to approximately 40 °C. Using 600 g/L sucrose, the immobilized biocatalyst synthesized 18.9% (w/w) FOS (59.1 g/L of neokestose, 30.2 g/L of 1-kestose, 11.6 g/L of neonystose and 12.6 g/L of blastose). The operational stability of PVA-immobilized biocatalyst was assayed in a batch reactor at 30 °C. The enzyme preserved its initial activity during at least 7 cycles of 26 h. Full article
(This article belongs to the Special Issue Immobilized Biocatalysts)
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16 pages, 3232 KiB  
Article
Improvement Effect of Ni to Pd-Ni/SBA-15 Catalyst for Selective Hydrogenation of Cinnamaldehyde to Hydrocinnamaldehyde
by Shiying Han, Yunfei Liu, Jiang Li, Rui Li, Fulong Yuan and Yujun Zhu
Catalysts 2018, 8(5), 200; https://doi.org/10.3390/catal8050200 - 11 May 2018
Cited by 29 | Viewed by 5063
Abstract
A series of Pd-Ni bimetallic catalysts supported on SBA-15 (0.2%Pd-x%Ni/SBA-15, x = 0.4, 0.7, and 1.2) were prepared through the impregnation method combined with the NaBH4 reduction method. X-ray diffraction (XRD), N2 adsorption-desorption, X-ray photoemission spectroscopy (XPS) and transmission electron microscope [...] Read more.
A series of Pd-Ni bimetallic catalysts supported on SBA-15 (0.2%Pd-x%Ni/SBA-15, x = 0.4, 0.7, and 1.2) were prepared through the impregnation method combined with the NaBH4 reduction method. X-ray diffraction (XRD), N2 adsorption-desorption, X-ray photoemission spectroscopy (XPS) and transmission electron microscope (TEM) were used to characterize the prepared catalysts. All the synthesized catalysts were evaluated for the liquid-phase hydrogenation of cinnamaldehyde (CAL). The addition of Ni obviously enhanced the CAL conversion and selectivity of C=C hydrogenation to hydrocinnamaldehyde (HALD) over the 0.2%Pd-x%Ni/SBA-15 catalysts. Meanwhile, 0.2%Pd-1.2%Ni/SBA-15 showed the best performance with 96.3% conversion and 87.8% selectivity toward HALD. This improvement was attributed to the synergistic effect between the Pd and Ni nanoparticles, enhancing the dispersion of Pd metal particles and increasing the content of surface Pd0 species. In addition, the influences of a few reaction factors including H2 pressure, reaction temperature, and reaction time were studied over 0.2%Pd-1.2%Ni/SBA-15. Full article
(This article belongs to the Special Issue Solid-Supported Reagents in Palladium-Catalyzed Transformations)
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16 pages, 2263 KiB  
Article
Effect of Mesoporous Chitosan Action and Coordination on the Catalytic Activity of Mesoporous Chitosan-Grafted Cobalt Tetrakis(p-Sulfophenyl)Porphyrin for Ethylbenzene Oxidation
by Guan Huang, Lin Qiang Mo, Yan Xun Wei, Hong Zhou, Yong An Guo and Su Juan Wei
Catalysts 2018, 8(5), 199; https://doi.org/10.3390/catal8050199 - 10 May 2018
Cited by 19 | Viewed by 4432
Abstract
To simulate the active site cavity structure function and axial coordination of cytochrome P-450 enzymes, mesoporous chitosan(mesp-CTS) was used as a scaffold for a meso-sized cavity to immobilize cobalt tetrakis(p-sulphophenyl)porphyrin chloride(Co TPPS). Immobilization was achieved via an acid–base reaction and axial coordination of [...] Read more.
To simulate the active site cavity structure function and axial coordination of cytochrome P-450 enzymes, mesoporous chitosan(mesp-CTS) was used as a scaffold for a meso-sized cavity to immobilize cobalt tetrakis(p-sulphophenyl)porphyrin chloride(Co TPPS). Immobilization was achieved via an acid–base reaction and axial coordination of the H2N-C group to the Co ion in Co TPPS, thus forming the biomimetic catalyst Co TPPS/mesp-CTS. Several approaches, including scanning electron microscopy (SEM), the Brunauer–Emmett–Teller (BET)technique, Fourier transform infrared (FT-IR) spectroscopy, ultraviolet-visible (UV-vis) spectroscopy, thermogravimetric and differential scanning calorimetry (TG-DSC), and X-ray photoelectron spectroscopy (XPS), were used to characterize the grafted catalyst. The catalytic performance of Co TPPS/mesp-CTS in ethylbenzene oxidation without any solvents and additives was investigated. The results showed that only 0.96 × 10 mol of Co TPPS grafted onto mesp-CTS could be recycled three times for 200 mL of ethylbenzene oxidation, with an average yield of 44.6% and selectivity of 68.8%. The highly efficient catalysis can be attributed to promotion by mesp-CTS, including the effect of the mesoporous structure and the axial coordination to the Co ion in Co TPPS. This biomimetic methodology provides a method for clean production of acetophenone via ethylbenzene oxidation. Full article
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11 pages, 10463 KiB  
Article
Metal-Carbon-CNF Composites Obtained by Catalytic Pyrolysis of Urban Plastic Residues as Electro-Catalysts for the Reduction of CO2
by Jesica Castelo-Quibén, Abdelhakim Elmouwahidi, Francisco J. Maldonado-Hódar, Francisco Carrasco-Marín and Agustín F. Pérez-Cadenas
Catalysts 2018, 8(5), 198; https://doi.org/10.3390/catal8050198 - 9 May 2018
Cited by 7 | Viewed by 4993
Abstract
Metal–carbon–carbon nanofibers composites obtained by catalytic pyrolysis of urban plastic residues have been prepared using Fe, Co or Ni as pyrolitic catalysts. The composite materials have been fully characterized from a textural and chemical point of view. The proportion of carbon nanofibers and [...] Read more.
Metal–carbon–carbon nanofibers composites obtained by catalytic pyrolysis of urban plastic residues have been prepared using Fe, Co or Ni as pyrolitic catalysts. The composite materials have been fully characterized from a textural and chemical point of view. The proportion of carbon nanofibers and the final content of carbon phases depend on the used pyrolitic metal with Ni being the most active pyrolitic catalysts. The composites show the electro-catalyst activity in the CO2 reduction to hydrocarbons, favoring all the formation of C1 to C4 hydrocarbons. The tendency of this activity is in accordance with the apparent faradaic efficiencies and the linear sweep voltammetries. The cobalt-based composite shows high selectivity to C3 hydrocarbons within this group of compounds. Full article
(This article belongs to the Special Issue Catalytic, Photocatalytic and Electrocatalytic Processes for the Valorisation of CO2)
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12 pages, 1656 KiB  
Article
Isolation, Characterization, and Environmental Application of Bio-Based Materials as Auxiliaries in Photocatalytic Processes
by Davide Palma, Alessandra Bianco Prevot, Luisella Celi, Maria Martin, Debora Fabbri, Giuliana Magnacca, Michele R. Chierotti and Roberto Nisticò
Catalysts 2018, 8(5), 197; https://doi.org/10.3390/catal8050197 - 8 May 2018
Cited by 18 | Viewed by 4327
Abstract
Sustainable alternative substrates for advanced applications represent an increasing field of research that attracts the attention of worldwide experts (in accordance with green chemistry principles). In this context, bio-based substances (BBS) isolated from urban composted biowaste were purified and characterized. Additionally, these materials [...] Read more.
Sustainable alternative substrates for advanced applications represent an increasing field of research that attracts the attention of worldwide experts (in accordance with green chemistry principles). In this context, bio-based substances (BBS) isolated from urban composted biowaste were purified and characterized. Additionally, these materials were tested as auxiliaries in advanced oxidizing photocatalytic processes for the abatement of organic contaminants in aqueous medium. Results highlighted the capability of these substances to enhance efficiency in water remediation treatments under mild conditions, favoring the entire light-driven photocatalytic process. Full article
(This article belongs to the Special Issue Reactions in Water and in Micelles)
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17 pages, 2035 KiB  
Review
Recent Progress in Nitrogen-Doped Metal-Free Electrocatalysts for Oxygen Reduction Reaction
by Zexing Wu, Min Song, Jie Wang and Xien Liu
Catalysts 2018, 8(5), 196; https://doi.org/10.3390/catal8050196 - 7 May 2018
Cited by 67 | Viewed by 7595
Abstract
Electrocatalysis for the oxygen reduction reaction (ORR) at the cathode plays a critical role in fuel cells and metal-air batteries. However, the high-cost and sluggish kinetics of the catalytic reaction have hindered its development. Therefore, developing efficient catalysts to address these issues is [...] Read more.
Electrocatalysis for the oxygen reduction reaction (ORR) at the cathode plays a critical role in fuel cells and metal-air batteries. However, the high-cost and sluggish kinetics of the catalytic reaction have hindered its development. Therefore, developing efficient catalysts to address these issues is of vital significance. In this work, we summarized the recent progress of nitrogen (N)-doped metal-free catalysts for the ORR, owing to their high catalytic activity (comparable to Pt/C) and cost-effectiveness. The synthetic strategy and the morphology structure to catalytic performance are mainly discussed. Furthermore, the design of N-doped nanomaterials with other heteroatoms in aiming to further enhance the ORR performance is also reviewed. At the end of the review, we provide a brief summary of the N-doped carbon-based catalysts in enhancing the ORR performance and give future perspectives for their further development. Full article
(This article belongs to the Special Issue Catalysts for Oxygen Reduction Reaction)
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2 pages, 144 KiB  
Editorial
Metal-Free Organocatalysis
by Aurelio G. Csákÿ
Catalysts 2018, 8(5), 195; https://doi.org/10.3390/catal8050195 - 6 May 2018
Cited by 2 | Viewed by 2856
Abstract
Fostering research in fundamental organic transformations is of utmost importance for the development of science.[...] Full article
(This article belongs to the Special Issue Metal-free Organocatalysis)
23 pages, 7282 KiB  
Article
Palladium-Catalyzed Isomerization-Coupling Reactions of Allyl Chloride with Amines to Generate Functionalized Phosphorus Derivatives
by Jing-Hong Wen, Qiang Li, Shao-Zhen Nie, Jing-Jing Ye, Qing Xu and Chang-Qiu Zhao
Catalysts 2018, 8(5), 194; https://doi.org/10.3390/catal8050194 - 5 May 2018
Cited by 1 | Viewed by 4368
Abstract
A Pd-catalyzed isomerization-coupling reaction of P-containing allyl chloride with amine afforded imine or enamine that was converted to various functionalized phosphorus derivatives via hydrolysis, reduction, or Stork reactions. The reaction was confirmed to proceed via an isomerization of a starting material and [...] Read more.
A Pd-catalyzed isomerization-coupling reaction of P-containing allyl chloride with amine afforded imine or enamine that was converted to various functionalized phosphorus derivatives via hydrolysis, reduction, or Stork reactions. The reaction was confirmed to proceed via an isomerization of a starting material and a coupling of the resulting vinyl chloride with amine. Full article
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10 pages, 2702 KiB  
Article
Selective Conversion of Furfural to Cyclopentanone or Cyclopentanol Using Co-Ni Catalyst in Water
by Yaru Li, Xingcui Guo, Daosheng Liu, Xindong Mu, Xiufang Chen and Yan Shi
Catalysts 2018, 8(5), 193; https://doi.org/10.3390/catal8050193 - 4 May 2018
Cited by 30 | Viewed by 5075
Abstract
Co-Ni catalysts, prepared by a typical wetness impregnation method, can selectively convert furfural (FFA) to cyclopentanone (CPO) or cyclopentanol (CPL) in water, respectively. The catalytic performance depends strongly on the support. It is also strongly influenced by the Co-Ni loadings of the catalyst. [...] Read more.
Co-Ni catalysts, prepared by a typical wetness impregnation method, can selectively convert furfural (FFA) to cyclopentanone (CPO) or cyclopentanol (CPL) in water, respectively. The catalytic performance depends strongly on the support. It is also strongly influenced by the Co-Ni loadings of the catalyst. The 10%Co-10%Ni/TiO2 catalyst showed the highest selectivity toward CPO (53.3%) with almost complete FFA conversion, and the main product was CPL (45.4%) over 20%Co/TiO2 at the optimized conditions (150 °C, 4 MPa H2, 4 h). The surface morphology, surface area, composition and reducibility properties of these catalysts were fully characterized by XRD, H2-TPR, ICP-AES and SEM. The factors that influenced the activity of catalysts were also investigated in detail. Additionally, the stability of catalyst for the hydrogenative rearrangement of FFA was studied. Full article
(This article belongs to the Special Issue Catalytic Conversion of Biomass-Derived Molecules to Chemicals and Fuels)
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38 pages, 6570 KiB  
Review
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 77 | Viewed by 9966
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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