Catalysts

22 pages, 2755 KiB

Open AccessFeature PaperArticle

Sustainable Carbon Dioxide Photoreduction by a Cooperative Effect of Reactor Design and Titania Metal Promotion

by Alberto Olivo, Elena Ghedini, Paolina Pascalicchio, Maela Manzoli, Giuseppe Cruciani and Michela Signoretto

Catalysts 2018, 8(1), 41; https://doi.org/10.3390/catal8010041 - 22 Jan 2018

Cited by 16 | Viewed by 7902

Abstract

An effective process based on the photocatalytic reduction of CO₂ to face on the one hand, the crucial problem of environmental pollution, and, on the other hand, to propose an efficient way to product clean and sustainable energy sources has been developed [...] Read more.

An effective process based on the photocatalytic reduction of CO₂ to face on the one hand, the crucial problem of environmental pollution, and, on the other hand, to propose an efficient way to product clean and sustainable energy sources has been developed in this work. Particular attention has been paid to the sustainability of the process by using a green reductant (water) and TiO₂ as a photocatalyst under very mild operative conditions (room temperature and atmospheric pressure). It was shown that the efficiency in carbon dioxide photoreduction is strictly related to the process parameters and to the catalyst features. In order to formulate a versatile and high performing catalyst, TiO₂ was modified by oxide or metal species. Copper (in the oxide CuO form) or gold (as nanoparticles) were employed as promoting metal. Both photocatalytic activity and selectivity displayed by CuO-TiO₂ and Au-TiO₂ were compared, and it was found that the nature of the promoter (either Au or CuO) shifts the selectivity of the process towards two strategic products: CH₄ or H₂. The catalytic results were discussed in depth and correlated with the physicochemical features of the photocatalysts. Full article

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

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10 pages, 1006 KiB

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 13 | Viewed by 5730

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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18 pages, 2015 KiB

Open AccessArticle

Kinetic Modelling and Experimental Studies for the Effects of Fe²⁺ Ions on Xylan Hydrolysis with Dilute-Acid Pretreatment and Subsequent Enzymatic Hydrolysis

by Hui Wei, Xiaowen Chen, Joseph Shekiro, Erik Kuhn, Wei Wang, Yun Ji, Evguenii Kozliak, Michael E. Himmel and Melvin P. Tucker

Catalysts 2018, 8(1), 39; https://doi.org/10.3390/catal8010039 - 20 Jan 2018

Cited by 18 | Viewed by 6425

Abstract

High-temperature (150–170 °C) pretreatment of lignocellulosic biomass with mineral acids is well established for xylan breakdown. Fe²⁺ is known to be a cocatalyst of this process although kinetics of its action remains unknown. The present work addresses the effect of ferrous ion [...] Read more.

High-temperature (150–170 °C) pretreatment of lignocellulosic biomass with mineral acids is well established for xylan breakdown. Fe²⁺ is known to be a cocatalyst of this process although kinetics of its action remains unknown. The present work addresses the effect of ferrous ion concentration on sugar yield and degradation product formation from corn stover for the entire two-step treatment, including the subsequent enzymatic cellulose hydrolysis. The feedstock was impregnated with 0.5% acid and 0.75 mM iron cocatalyst, which was found to be optimal in preliminary experiments. The detailed kinetic data of acid pretreatment, with and without iron, was satisfactorily modelled with a four-step linear sequence of first-order irreversible reactions accounting for the formation of xylooligomers, xylose and furfural as intermediates to provide the values of Arrhenius activation energy. Based on this kinetic modelling, Fe²⁺ turned out to accelerate all four reactions, with a significant alteration of the last two steps, that is, xylose degradation. Consistent with this model, the greatest xylan conversion occurred at the highest severity tested under 170 °C/30 min with 0.75 mM Fe²⁺, with a total of 8% xylan remaining in the pretreated solids, whereas the operational conditions leading to the highest xylose monomer yield, 63%, were milder, 150 °C with 0.75 mM Fe²⁺ for 20 min. Furthermore, the subsequent enzymatic hydrolysis with the prior addition of 0.75 mM of iron(II) increased the glucose production to 56.3% from 46.3% in the control (iron-free acid). The detailed analysis indicated that conducting the process at lower temperatures yet long residence times benefits the yield of sugars. The above kinetic modelling results of Fe²⁺ accelerating all four reactions are in line with our previous mechanistic research showing that the pretreatment likely targets multiple chemistries in plant cell wall polymer networks, including those represented by the C–O–C and C–H bonds in cellulose, resulting in enhanced sugar solubilization and digestibility. Full article

(This article belongs to the Special Issue Catalytic Sustainable Processes in Biorefineries)

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14 pages, 2283 KiB

Open AccessArticle

Surface Species and Metal Oxidation State during H₂-Assisted NH₃-SCR of NO_x over Alumina-Supported Silver and Indium

by Linda Ström, Per-Anders Carlsson, Magnus Skoglundh and Hanna Härelind

Catalysts 2018, 8(1), 38; https://doi.org/10.3390/catal8010038 - 19 Jan 2018

Cited by 19 | Viewed by 5306

Abstract

Alumina-supported silver and indium catalysts are investigated for the hydrogen-assisted selective catalytic reduction (SCR) of NO_x with ammonia. Particularly, we focus on the active phase of the catalyst and the formation of surface species, as a function of the gas environment. Diffuse [...] Read more.

Alumina-supported silver and indium catalysts are investigated for the hydrogen-assisted selective catalytic reduction (SCR) of NO_x with ammonia. Particularly, we focus on the active phase of the catalyst and the formation of surface species, as a function of the gas environment. Diffuse reflectance ultraviolet-visible (UV-vis) spectroscopy was used to follow the oxidation state of the silver and indium phases, and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to elucidate the formation of surface species during SCR conditions. In addition, the NO_x reduction efficiency of the materials was evaluated using H₂-assisted NH₃-SCR. The DRIFTS results show that the Ag/Al₂O₃ sample forms NO-containing surface species during SCR conditions to a higher extent compared to the In/Al₂O₃ sample. The silver sample also appears to be more reduced by H₂ than the indium sample, as revealed by UV-vis spectroscopic experiments. Addition of H₂, however, may promote the formation of highly dispersed In₂O₃ clusters, which previously have been suggested to be important for the SCR reaction. The affinity to adsorb NH₃ is confirmed by both temperature programmed desorption (NH₃-TPD) and in situ DRIFTS to be higher for the In/Al₂O₃ sample compared to Ag/Al₂O₃. The strong adsorption of NH₃ may inhibit (self-poison) the NH₃ activation, thereby hindering further reaction over this catalyst, which is also shown by the lower SCR activity compared to Ag/Al₂O₃. Full article

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

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14 pages, 3949 KiB

Open AccessArticle

Catalytic Degradation of Ortho-Chlorophenol Using Activated Carbon Modified by Different Methods

by Yang Zheng, Yangyang Guo, Lei Luo and Tingyu Zhu

Catalysts 2018, 8(1), 37; https://doi.org/10.3390/catal8010037 - 19 Jan 2018

Cited by 8 | Viewed by 4711

Abstract

The performance of activated carbon (AC) modified by different methods was compared for its catalytic degradation of ortho-chlorophenol (o-CP). For the chemically treated AC, the catalytic effect of AC–NH₃·H₂O was superior to the other catalysts examined, having [...] Read more.

The performance of activated carbon (AC) modified by different methods was compared for its catalytic degradation of ortho-chlorophenol (o-CP). For the chemically treated AC, the catalytic effect of AC–NH₃·H₂O was superior to the other catalysts examined, having an o-CP removal efficiency of 82.2% at 330 °C. For the metal-modified catalysts, AC–V and AC–Co showed similar removal performances of 93.2% at 330 °C. N₂ adsorption-desorption isotherms, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and gas chromatography—mass spectrometry (GC-MS) analyses were used to characterize the reaction products, and different reaction mechanisms were proposed for both AC–NH₃·H₂O and AC–V according to the results. Complete oxidative degradation of o-CP was achieved by AC–V, with AC–NH₃·H₂O leading to the formation of additional dioxins. It can be deduced that a risk of dioxin synthesis and escape during the regeneration process is possible when nitrogen-modified carbon is used in selective catalytic reduction (SCR) denitrification reactions, especially in the presence of chlorine atoms, benzene rings, and oxygen. Full article

(This article belongs to the Special Issue Catalysts for Oxidative Destruction of Volatile Organic Compounds)

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18 pages, 8450 KiB

Open AccessArticle

Catalytic Activity of Sulfated and Phosphated Catalysts towards the Synthesis of Substituted Coumarin

by Nagi R. E. Radwan, Mohamed Hagar, Tarek H. Afifi, Fahd Al-wadaani and Rawda M. Okasha

Catalysts 2018, 8(1), 36; https://doi.org/10.3390/catal8010036 - 19 Jan 2018

Cited by 17 | Viewed by 4747

Abstract

New modified acidic catalysts were prepared from the treatment of silica, titania and silica prepared from hydrolyzed tetraethyl orthosilicate (TEOS) with sulfuric and phosphoric acid. The sulfated and phosphated silica synthesized from TEOS were calcined at 450 and 650 °C. These catalysts were [...] Read more.

New modified acidic catalysts were prepared from the treatment of silica, titania and silica prepared from hydrolyzed tetraethyl orthosilicate (TEOS) with sulfuric and phosphoric acid. The sulfated and phosphated silica synthesized from TEOS were calcined at 450 and 650 °C. These catalysts were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), and scanning electron microscope (SEM). The surface areas, total pore volume, and mean pore radius of the acidic catalysts were investigated, while the pore size distribution was determined by the Barrett, Joyner and Halenda (BJH) method. The catalytic activity of the sulfated and phosphated silica and/or titania were examined with the Pechmann condensation reaction, in which different phenols reacted with ethyl acetoacetate as a neat reaction to obtain the corresponding coumarin derivatives. The results indicated that the treatment of the catalysts with sulfuric or phosphoric acid led to a decrease in the phases’ crystallinity to a certain degree. The morphology and the structure of the acidified catalysts were examined and their particle size was calculated. Furthermore, the amount of the used catalysts played a vital role in controlling the formation of the products as well as their performance was manipulated by the number and nature of the active acidic sites on their surfaces. The obtained results suggested that the highest catalytic conversion of the reaction was attained at 20 wt % of the catalyst and no further increase in the product yield was detected when the amount of catalyst exceeded this value. Meanwhile the phenol molecules were a key feature in obtaining the final product. Full article

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16 pages, 2756 KiB

Open AccessArticle

Preparation and Performance of Modified Red Mud-Based Catalysts for Selective Catalytic Reduction of NO_x with NH₃

by Jingkun Wu, Zhiqiang Gong, Chunmei Lu, Shengli Niu, Kai Ding, Liting Xu and Kang Zhang

Catalysts 2018, 8(1), 35; https://doi.org/10.3390/catal8010035 - 19 Jan 2018

Cited by 42 | Viewed by 5905

Abstract

Bayer red mud was selected, and the NH₃-SCR activity was tested in a fixed bed in which the typical flue gas atmosphere was simulated. Combined with XRF, XRD, BET, SEM, TG and NH₃-Temperature Programmed Desorption (TPD) characterization, the denitration [...] Read more.

Bayer red mud was selected, and the NH₃-SCR activity was tested in a fixed bed in which the typical flue gas atmosphere was simulated. Combined with XRF, XRD, BET, SEM, TG and NH₃-Temperature Programmed Desorption (TPD) characterization, the denitration characteristics of Ce-doped red mud catalysts were studied on the basis of alkali-removed red mud. The results showed that typical red mud was a feasible material for denitration catalyst. Acid washing and calcining comprised the best treatment process for raw red mud, which reduced the content of alkaline substances, cleared the catalyst pore and optimized the particle morphology with dispersion. In the temperature range of 300–400 °C, the denitrification efficiency of calcined acid washing of red mud catalyst (ARM) was more than 70%. The doping of Ce significantly enhanced NH₃ adsorption from weak, medium and strong acid sites, reduced the crystallinity of α-Fe₂O₃ in ARM, optimized the specific surface area and broadened the active temperature window, which increased the NO_x conversion rate by an average of nearly 20% points from 250–350 °C. The denitration efficiency of Ce_0.3/ARM at 300 °C was as high as 88%. The optimum conditions for the denitration reaction of the Ce_0.3/ARM catalyst were controlled as follows: Gas Hourly Space Velocity (GHSV) of 30,000 h⁻¹, O₂ volume fraction of 3.5–4% and the NH₃/NO molar ratio ([NH₃/NO]) of 1.0. The presence of SO₂ in the feed had an irreversible negative effect on the activity of the Ce_0.3/ARM catalyst. Full article

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

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10 pages, 1804 KiB

Open AccessCommunication

Co-Detection of Dopamine and Glucose with High Temporal Resolution

by Jenny Bergman, Lisa Mellander, Yuanmo Wang and Ann-Sofie Cans

Catalysts 2018, 8(1), 34; https://doi.org/10.3390/catal8010034 - 19 Jan 2018

Cited by 13 | Viewed by 5549

Abstract

Neuronal activity and brain glucose metabolism are tightly coupled, where triggered neurotransmission leads to a higher demand for glucose. To better understand the regulation of neuronal activity and its relation to high-speed metabolism, development of analytical tools that can temporally resolve the transients [...] Read more.

Neuronal activity and brain glucose metabolism are tightly coupled, where triggered neurotransmission leads to a higher demand for glucose. To better understand the regulation of neuronal activity and its relation to high-speed metabolism, development of analytical tools that can temporally resolve the transients of vesicular neurotransmitter release and fluctuations of metabolites such as glucose in the local vicinity of the activated neurons is needed. Here we present an amperometric biosensor design for rapid co-detection of glucose and the neurotransmitter dopamine. The sensor is based on the immobilization of an ultra-thin layer of glucose oxidase on to a gold-nanoparticle-covered carbon fiber microelectrode. Our electrode, by altering the potential applied at the sensor surface, allows for the high-speed recording of both glucose and dopamine. We demonstrate that, even though glucose is electrochemically detected indirectly through the enzymatic product and the electroactive dopamine is sensed directly, when exposing the sensor surface to a mixture of the two analytes, fluctuations in glucose and dopamine concentrations can be visualized with similar speed and at a millisecond time scale. Hence, by minimizing the enzyme coating thickness at the sensor surface, dual detection of glucose and dopamine can be realized at the same sensor surface and at time scales necessary for monitoring fast metabolic alterations during neurotransmission. Full article

(This article belongs to the Special Issue Immobilized Biocatalysts)

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16 pages, 4240 KiB

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 26 | Viewed by 6246

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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16 pages, 2092 KiB

Open AccessArticle

Chloroperoxidase-Mediated Halogenation of Selected Pharmaceutical Micropollutants

by José Luis García-Zamora, Karina León-Aguirre, René Quiroz-Morales, Roberto Parra-Saldívar, Mayra Beatriz Gómez-Patiño, Daniel Arrieta-Baez, Georgette Rebollar-Pérez and Eduardo Torres

Catalysts 2018, 8(1), 32; https://doi.org/10.3390/catal8010032 - 18 Jan 2018

Cited by 20 | Viewed by 6091

Abstract

The oxidation of eight pharmaceutical micropollutants by chloroperoxidase derived from Caldaromyces fumago using hydrogen peroxide as an electron acceptor is reported. All the tested compounds, namely trazadone, sulfamethoxazole, naproxen, tetracycline, estradiol, ketoconazole, ketorolac, and diclofenac, were found to be substrates for oxidation by [...] Read more.

The oxidation of eight pharmaceutical micropollutants by chloroperoxidase derived from Caldaromyces fumago using hydrogen peroxide as an electron acceptor is reported. All the tested compounds, namely trazadone, sulfamethoxazole, naproxen, tetracycline, estradiol, ketoconazole, ketorolac, and diclofenac, were found to be substrates for oxidation by chloroperoxidase. The respective oxidation products were identified by electrospray ionization–mass spectrometry. All the products contain at least one chloride atom in their structure after the enzymatic oxidation. Degradability experiments indicated that most of the reaction products are more biodegradable than the corresponding unmodified compounds. The enzyme was found to be catalytically active in effluent from a water treatment facility, transforming the micropollutants with high reaction rates and conversions. The enzyme was immobilized in chitosan macrospheres, which allowed the catalyst to be recycled for up to three treatment cycles in simulated samples of treated residual water. The conversion was high in the first two cycles; however, in the third, a 50% reduction in the capacity of the enzyme to oxidize ketorolac was observed. Additionally, immobilization improved the performance of the enzyme over a wider pH range, achieving the conversion of ketorolac at pH 5, while the free enzyme was not active at this pH. Overall, the results of this study suggest that chloroperoxidase represents a powerful potential catalyst in terms of its catalytic activity for the transformation of pharmaceutical micropollutants. Full article

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13 pages, 4013 KiB

Open AccessArticle

Highly Efficient and Visible Light Responsive Heterojunction Composites as Dual Photoelectrodes for Photocatalytic Fuel Cell

by Honghui Pan, Wenjuan Liao, Na Sun, Muthu Murugananthan and Yanrong Zhang

Catalysts 2018, 8(1), 30; https://doi.org/10.3390/catal8010030 - 18 Jan 2018

Cited by 23 | Viewed by 5094

Abstract

In the present work, a novel photocatalytic fuel cell (PFC) system involving a dual heterojunction photoelectrodes, viz. polyaniline/TiO₂ nanotubes (PANI/TiO₂ NTs) photoanode and CuO/Co₃O₄ nanorods (CuO/Co₃O₄ NRs) photocathode, has been designed. Compared to TiO₂ [...] Read more.

In the present work, a novel photocatalytic fuel cell (PFC) system involving a dual heterojunction photoelectrodes, viz. polyaniline/TiO₂ nanotubes (PANI/TiO₂ NTs) photoanode and CuO/Co₃O₄ nanorods (CuO/Co₃O₄ NRs) photocathode, has been designed. Compared to TiO₂ NTs electrode of PFC, the present heterojunction design not only enhances the visible light absorption but also offers the higher efficiency in degrading Rhodamine B–a model organic pollutant. The study includes an evaluation of the dual performance of the photoelectrodes as well. Under visible-light irradiation of 3 mW cm⁻², the cell composed of the photoanode PANI/TiO₂ NTs and CuO/Co₃O₄ NRs photocathode forms an interior bias of +0.24 V within the PFC system. This interior bias facilitated the transfer of electrons from the photoanode to photocathode across the external circuit and combined with the holes generated therein along with a simultaneous power production. In this manner, the separation of electron/hole pair was achieved in the photoelectrodes by releasing the holes and electrons of PANI/TiO₂ NTs photoanode and CuO/Co₃O₄ NRs photocathode, respectively. Using this PFC system, the degradation of Rhodamine B in aqueous media was achieved to an extent of 68.5% within a reaction duration of a four-hour period besides a simultaneous power generation of 85 μA cm⁻². Full article

(This article belongs to the Special Issue Photocatalysts for Organics Degradation)

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12 pages, 3775 KiB

Open AccessCommunication

Catalytic Isomerization of Dihydroxyacetone to Lactic Acid and Alkyl Lactates over Hierarchical Zeolites Containing Tin

by Agnieszka Feliczak-Guzik, Myroslav Sprynskyy, Izabela Nowak and Bogusław Buszewski

Catalysts 2018, 8(1), 31; https://doi.org/10.3390/catal8010031 - 17 Jan 2018

Cited by 23 | Viewed by 4623

Abstract

Hierarchical zeolites containing tin were obtained, characterized and used in a reaction of catalytic isomerization of dihydroxyacetone (DHA) to lactic acid and alkyl lactates. These catalysts are characterized by preserved crystallinity and primary microporosity with the simultaneous existence of secondary porosity regarding mesopores, [...] Read more.

Hierarchical zeolites containing tin were obtained, characterized and used in a reaction of catalytic isomerization of dihydroxyacetone (DHA) to lactic acid and alkyl lactates. These catalysts are characterized by preserved crystallinity and primary microporosity with the simultaneous existence of secondary porosity regarding mesopores, which facilitates access of large molecules of reagents to active centers. Creation of additional porosity was confirmed by X-ray diffraction and low-temperature nitrogen adsorption/desorption studies. The reaction of dihydroxyacetone isomerization was conducted in different reaction media such as methanol, ethanol or water with the use of two heating methods: microwave radiation and conventional heating. The application of microwave radiation enabled to reduce the reaction time to 1 h and achieve dihydroxyacetone conversion of >90% and high yields of the desired reaction products. Full article

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10 pages, 3092 KiB

Open AccessArticle

Construction of an Ultrasensitive and Highly Selective Nitrite Sensor Using Piroxicam-Derived Copper Oxide Nanostructures

by Ali Alsalme, Munazza Arain, Ayman Nafady and Sirajuddin

Catalysts 2018, 8(1), 29; https://doi.org/10.3390/catal8010029 - 17 Jan 2018

Cited by 11 | Viewed by 4101

Abstract

In this work, piroxicam-based copper oxide nanostructures (Px-CuO NSs) were synthesized via hydrothermal precipitation in the presence of ammonia. The prepared Px-CuO NSs were subjected to scanning electron microscopy (SEM) and X-ray diffraction (XRD) to obtain morphology and crystallinity, respectively. The SEM study [...] Read more.

In this work, piroxicam-based copper oxide nanostructures (Px-CuO NSs) were synthesized via hydrothermal precipitation in the presence of ammonia. The prepared Px-CuO NSs were subjected to scanning electron microscopy (SEM) and X-ray diffraction (XRD) to obtain morphology and crystallinity, respectively. The SEM study reveals that these Px-CuO NSs are in the form of porous rose-like nanopetals with dotted particles on their surface, while the XRD study confirms their crystalline nature. The Px-CuO NS-based sensors were fabricated by drop-casting them onto the surface of a glassy carbon electrode (GCE) and they were tested for nitrite detection using voltammetry and amperometry. The results show these Px-CuO NSs to be highly stable on the GCE surface with linear amperometric (current vs. time) responses to wide range of nitrite concentrations from 100 to 1800 nM, with limits of detection (LOD) and quantification (LOQ) being 12 nM and 40 nM, respectively. Importantly, the fabricated sensor showed negligible effects for a 10-fold higher concentration of common interfering agents and exhibited excellent selectivity. It was applied successfully for nitrite detection in water samples such as river water, mineral water, and tap water. Full article

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12 pages, 1405 KiB

Open AccessArticle

Microbial Kinetic Resolution of Aroma Compounds Using Solid-State Fermentation

by Filip Boratyński, Ewa Szczepańska, Aleksandra Grudniewska and Teresa Olejniczak

Catalysts 2018, 8(1), 28; https://doi.org/10.3390/catal8010028 - 16 Jan 2018

Cited by 21 | Viewed by 5793

Abstract

A novel microbial approach to the production of enantiomerically enriched and pure aroma compounds based on kinetic resolution via solid-state fermentation is proposed. Twenty-five filamentous fungi were screened for lipase activity and enantioselective hydrolysis of a volatile racemic ester (1-phenylethyl acetate (1 [...] Read more.

A novel microbial approach to the production of enantiomerically enriched and pure aroma compounds based on kinetic resolution via solid-state fermentation is proposed. Twenty-five filamentous fungi were screened for lipase activity and enantioselective hydrolysis of a volatile racemic ester (1-phenylethyl acetate (1)) and several racemic lactones (trans and cis whisky lactones (4, 5), γ-decalactone (7), δ-decalactone (8), (cis-3a,4,7,7a-tetrahydro-1(3H)-isobenzofuranone) (9)). Solid-state fermentation was conducted with linseed and rapeseed cakes. Kinetic resolution afforded enantiomerically enriched products with high enantiomeric excesses (ee = 82–99%). The results highlight the potential economic value of solid-state fermentation using agroindustrial side-stream feedstocks as an alternative to more expensive processes conducted in submerged fermentation. Full article

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

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15 pages, 5356 KiB

Open AccessArticle

Inhibiting Fe–Al Spinel Formation on a Narrowed Mesopore-Sized MgAl₂O₄ Support as a Novel Catalyst for H₂ Production in Chemical Looping Technology

by Ali Hafizi and Mohammad Reza Rahimpour

Catalysts 2018, 8(1), 27; https://doi.org/10.3390/catal8010027 - 15 Jan 2018

Cited by 19 | Viewed by 4959

Abstract

In this paper, the structure of Al₂O₃ is modified with magnesium to synthesize MgAl₂O₄ as an oxygen carrier (OC) support. The surface properties and structural stability of the modified support are improved by the incorporation of magnesium [...] Read more.

In this paper, the structure of Al₂O₃ is modified with magnesium to synthesize MgAl₂O₄ as an oxygen carrier (OC) support. The surface properties and structural stability of the modified support are improved by the incorporation of magnesium in the structure of the support and additionally by narrowing the pore size distribution (about 2.3 nm). Then, iron oxide is impregnated on both an Al₂O₃ support and a MgAl₂O₄ support as the oxygen transfer active site. The XRD results showed the formation of solely Fe₂O₃ on the MgAl₂O₄ support, while both Fe₂O₃ and Fe₃O₄ are detected in the synthesized Fe₂O₃-Al₂O₃ structure. The synthesized samples are investigated in chemical looping cycles, including CO reduction (as one of the most important side reactions of chemical looping reforming), at different temperatures (300–500 °C) and oxidation with steam at 700 °C for hydrogen production. The obtained results showed the inhibition of Fe–Al spinel formation in the structure of the Fe₂O₃-MgAl₂O₄ OC. In addition, H₂ with a purity higher than 98% is achievable in oxidation of the OC with steam. In addition, the activity and crystalline change of the Fe₂O₃-MgAl₂O₄ OC is investigated after 20 reduction-oxidation cycles. Full article

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

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18 pages, 11584 KiB

Open AccessArticle

Hydrogen-Etched TiO_2−x as Efficient Support of Gold Catalysts for Water–Gas Shift Reaction

by Li Song, Zhufeng Lu, Yuting Zhang, Qi Su and Lei Li

Catalysts 2018, 8(1), 26; https://doi.org/10.3390/catal8010026 - 15 Jan 2018

Cited by 21 | Viewed by 6841

Abstract

Hydrogen-etching technology was used to prepare TiO_2−x nanoribbons with abundant stable surface oxygen vacancies. Compared with traditional Au-TiO₂, gold supported on hydrogen-etched TiO_2−x nanoribbons had been proven to be efficient and stable water–gas shift (WGS) catalysts. The [...] Read more.

Hydrogen-etching technology was used to prepare TiO_2−x nanoribbons with abundant stable surface oxygen vacancies. Compared with traditional Au-TiO₂, gold supported on hydrogen-etched TiO_2−x nanoribbons had been proven to be efficient and stable water–gas shift (WGS) catalysts. The disorder layer and abundant stable surface oxygen vacancies of hydrogen-etched TiO_2−x nanoribbons lead to higher microstrain and more metallic Au⁰ species, respectively, which all facilitate the improvement of WGS catalytic activities. Furthermore, we successfully correlated the WGS thermocatalytic activities with their optoelectronic properties, and then tried to understand WGS pathways from the view of electron flow process. Hereinto, the narrowed forbidden band gap leads to the decreased Ohmic barrier, which enhances the transmission efficiency of “hot-electron flow”. Meanwhile, the abundant surface oxygen vacancies are considered as electron traps, thus promoting the flow of “hot-electron” and reduction reaction of H₂O. As a result, the WGS catalytic activity was enhanced. The concept involved hydrogen-etching technology leading to abundant surface oxygen vacancies can be attempted on other supported catalysts for WGS reaction or other thermocatalytic reactions. Full article

(This article belongs to the Special Issue Catalysis in Steam Reforming)

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14 pages, 5829 KiB

Open AccessArticle

TiO₂ Nanotubes on Transparent Substrates: Control of Film Microstructure and Photoelectrochemical Water Splitting Performance

by Matus Zelny, Stepan Kment, Radim Ctvrtlik, Sarka Pausova, Hana Kmentova, Jan Tomastik, Zdenek Hubicka, Yalavarthi Rambabu, Josef Krysa, Alberto Naldoni, Patrik Schmuki and Radek Zboril

Catalysts 2018, 8(1), 25; https://doi.org/10.3390/catal8010025 - 15 Jan 2018

Cited by 18 | Viewed by 6037

Abstract

Transfer of semiconductor thin films on transparent and or flexible substrates is a highly desirable process to enable photonic, catalytic, and sensing technologies. A promising approach to fabricate nanostructured TiO₂ films on transparent substrates is self-ordering by anodizing of thin metal films [...] Read more.

Transfer of semiconductor thin films on transparent and or flexible substrates is a highly desirable process to enable photonic, catalytic, and sensing technologies. A promising approach to fabricate nanostructured TiO₂ films on transparent substrates is self-ordering by anodizing of thin metal films on fluorine-doped tin oxide (FTO). Here, we report pulsed direct current (DC) magnetron sputtering for the deposition of titanium thin films on conductive glass substrates at temperatures ranging from room temperature to 450 °C. We describe in detail the influence that deposition temperature has on mechanical, adhesion and microstructural properties of titanium film, as well as on the corresponding TiO₂ nanotube array obtained after anodization and annealing. Finally, we measure the photoelectrochemical water splitting activity of different TiO₂ nanotube samples showing that the film deposited at 150 °C has much higher activity correlating well with the lower crystallite size and the higher degree of self-organization observed in comparison with the nanotubes obtained at different temperatures. Importantly, the film showing higher water splitting activity does not have the best adhesion on glass substrate, highlighting an important trade-off for future optimization. Full article

(This article belongs to the Special Issue Titanium Dioxide Photocatalysis)

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10 pages, 1679 KiB

Open AccessArticle

Over-Expression of the Thermobifida fusca β-Glucosidase in a Yarrowia lipolytica Transformant to Degrade Soybean Isoflavones

by Wei-Lin Chen, Yo-Ming Yang, Gui-Wen Guo, Cheng-Yu Chen, Yu-Chun Huang, Wen-Hsiung Liu, Keh-Feng Huang and Chao-Hsun Yang

Catalysts 2018, 8(1), 24; https://doi.org/10.3390/catal8010024 - 14 Jan 2018

Cited by 3 | Viewed by 5100

Abstract

A gene (bgl) encoding a β-glucosidase in thermophilic actinomycete Thermobifida fusca NTU 22 was cloned into a Yarrowia lipolytica expression system. Heterologous expression resulted in extracellular β-glucosidase production with activity as high as 630 U/mL in a Hinton flask culture filtrate. [...] Read more.

A gene (bgl) encoding a β-glucosidase in thermophilic actinomycete Thermobifida fusca NTU 22 was cloned into a Yarrowia lipolytica expression system. Heterologous expression resulted in extracellular β-glucosidase production with activity as high as 630 U/mL in a Hinton flask culture filtrate. This recombinant β-glucosidase was purified 9.2-fold from crude culture filtrate by DEAE-Sepharose FF column chromatography as measured by its increase in specific activity. The overall yield of the purified enzyme was 47.5%. The molecular weight of the purified β-glucosidase estimated by SDS-PAGE was 45 kDa, which agreed with the predicted molecular weight based on the nucleotide sequence. About 15% enzyme activity loss was observed after the enzyme was heat-treated at 50 °C for 180 min. It was also found that the activity of the enzyme was inhibited by Hg²⁺, Cu²⁺, Ba²⁺, Ag⁺, p-chloromercuribenzene, and iodoacetate. The β-glucosidase from T. fusca had the most activity for daidzein-7-glucoside and genistein-7-glucoside among the tested flavonoid glycosides, but there was moderate or little activity for luteolin-7-glucoside, cyanidine-3-glucoside, and quercetin-3-glucoside. These properties are important for the soybean isoflavone applications of this β-glucosidase. Full article

(This article belongs to the Special Issue Novel Enzyme and Whole-Cell Biocatalysis)

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35 pages, 8289 KiB

Open AccessReview

Pd-Catalyzed Mizoroki-Heck Reactions Using Fluorine-Containing Agents as the Cross-Coupling Partners

by Jing Yang, Hua-Wen Zhao, Jian He and Cheng-Pan Zhang

Catalysts 2018, 8(1), 23; https://doi.org/10.3390/catal8010023 - 14 Jan 2018

Cited by 27 | Viewed by 11774

Abstract

The Mizoroki-Heck reaction represents one of the most convenient methods for carbon-carbon double bond formation in the synthesis of small organic molecules, natural products, pharmaceuticals, agrochemicals, and functional materials. Fluorine-containing organic compounds have found wide applications in the research areas of materials and [...] Read more.

The Mizoroki-Heck reaction represents one of the most convenient methods for carbon-carbon double bond formation in the synthesis of small organic molecules, natural products, pharmaceuticals, agrochemicals, and functional materials. Fluorine-containing organic compounds have found wide applications in the research areas of materials and life sciences over the past several decades. The incorporation of fluorine-containing segments into the target molecules by the Mizoroki-Heck reactions is highly attractive, as these reactions efficiently construct carbon-carbon double bonds bearing fluorinated functional groups by simple procedures. This review summarizes the palladium-catalyzed Mizoroki-Heck reactions using various fluorine-containing reagents as the cross-coupling partners. The first part of the review describes the Pd-catalyzed Mizoroki-Heck reactions of aryl halides or pseudo-halides with the fluorinated alkenes, and the second part discusses the Pd-catalyzed Mizoroki-Heck reactions of the fluorinated halides or pseudo-halides with alkenes. Variants of the Pd-catalyzed Mizoroki-Heck reactions with fluorine-containing reagents are also briefly depicted. This work supplies an overview, as well as a guide, to both younger and more established researchers in order to attract more attention and contributions in the realm of Mizoroki-Heck reactions with fluorine-containing participants. Full article

(This article belongs to the Special Issue Catalyzed Mizoroki–Heck Reaction or C–H activation)

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9 pages, 7209 KiB

Open AccessArticle

Tuning the Activity and Selectivity of Phenylacetylene Hydrosilylation with Triethylsilane in the Liquid Phase over Size Controlled Pt Nanoparticles

by Dorina G. Dobó, Dániel Sipos, András Sápi, Gábor London, Koppány L. Juhász, Ákos Kukovecz and Zoltán Kónya

Catalysts 2018, 8(1), 22; https://doi.org/10.3390/catal8010022 - 13 Jan 2018

Cited by 6 | Viewed by 4900

Abstract

Pt nanoparticles with controlled sizes between 1.6–7.0 nm were anchored onto the surface and pores of SBA-15 silica support. The catalysts were characterized by TEM-ED, BET, XRD, and ICP-MS techniques and were tested in liquid phase hydrosilylation of phenylacetylene with triethylsilane. The activity [...] Read more.

Pt nanoparticles with controlled sizes between 1.6–7.0 nm were anchored onto the surface and pores of SBA-15 silica support. The catalysts were characterized by TEM-ED, BET, XRD, and ICP-MS techniques and were tested in liquid phase hydrosilylation of phenylacetylene with triethylsilane. The activity of the 7.0 nm Pt nanoparticles anchored onto the surface of SBA-15 in hydrosilylation (TOF = 0.107 molecules·site⁻¹·s⁻¹) was ~2 times higher compared to the 5.0 nm Pt/SBA-15 (TOF = 0.049 molecules·site⁻¹·s⁻¹) catalyst and ~10 times higher compared to the 1.6 nm Pt/SBA-15 (TOF = 0.017 molecules·site⁻¹·s⁻¹) catalyst. Regarding the selectivity, bigger nanoparticles produced more vinylsilane-type products (α- and β-(E)-products) and less side products (mainly ditriethylsilane, triethyl(1-phenylethyl)silane and triethyl(phenethyl)silane derived likely from the reduction of the vinylsilane products). However, the selectivity towards the β-(E)-triethyl(styryl)silane was higher in the case of 1.6 nm Pt/SBA-15 catalyst compared to 5.0 nm Pt/SBA-15 and 7.0 nm Pt/SBA-15, respectively, which can be attributed to the beneficial effect of the size differences of the Pt nanoparticles as well as the differences of the quality and quantity of Pt/SiO₂ interfaces. Full article

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9 pages, 1625 KiB

Open AccessArticle

Rhodium-Biphephos-Catalyzed Tandem Isomerization–Hydroformylation of Oleonitrile

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

Catalysts 2018, 8(1), 21; https://doi.org/10.3390/catal8010021 - 12 Jan 2018

Cited by 6 | Viewed by 5949

Abstract

Tandem isomerization–hydroformylation of oleonitrile (an 18-carbon nitrile with a remote internal (9-)C=C bond) has been studied using Rh-bisphosphite catalyst systems, targeting formation of the linear aldehyde. The best compromise between regioselectivity (l/b = 58:42) and chemoselectivity (60%) was obtained at 120 °C [...] Read more.

Tandem isomerization–hydroformylation of oleonitrile (an 18-carbon nitrile with a remote internal (9-)C=C bond) has been studied using Rh-bisphosphite catalyst systems, targeting formation of the linear aldehyde. The best compromise between regioselectivity (l/b = 58:42) and chemoselectivity (60%) was obtained at 120 °C and 10 bar CO/H₂ (1:1) with a catalyst based on Biphephos at a 0.5 mol % catalyst load and a low ligand excess (2 equiv. versus Rh). These values stand among the better reported ones for the tandem isomerization–hydroformylation of long chain olefins with a single-component catalyst system. Full article

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12 pages, 2600 KiB

Open AccessArticle

Promoting Role of Bismuth on Hydrotalcite-Supported Platinum Catalysts in Aqueous Phase Oxidation of Glycerol to Dihydroxyacetone

by Wenjie Xue, Zenglong Wang, Yu Liang, Hong Xu, Lei Liu and Jinxiang Dong

Catalysts 2018, 8(1), 20; https://doi.org/10.3390/catal8010020 - 11 Jan 2018

Cited by 25 | Viewed by 6719

Abstract

Bismuth plays important roles in promoting the oxidation of alcohols towards high-value-added chemicals over a noble metal loading catalyst. Herein, Mg–Al hydrotalcite-supported platinum–bismuth nanoparticles (Pt–Bi/HT) were prepared by the co-impregnation method and used in the selective oxidation of glycerol towards dihydroxyacetone (DHA). The [...] Read more.

Bismuth plays important roles in promoting the oxidation of alcohols towards high-value-added chemicals over a noble metal loading catalyst. Herein, Mg–Al hydrotalcite-supported platinum–bismuth nanoparticles (Pt–Bi/HT) were prepared by the co-impregnation method and used in the selective oxidation of glycerol towards dihydroxyacetone (DHA). The incorporation of Bi species into Pt/HT significantly enhances the conversion of glycerol and the selectivity of DHA. The high selectivity of DHA with 80.6% could be achieved at 25.1% conversion of glycerol. The Bi species of the Pt–Bi/HT catalyst mainly exist in the form of BiOCl and Bi metal, which is different from the previous Pt–Bi based catalyst, confirmed by a combination of powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HR-TEM). A plausible mechanism is proposed to elucidate the promoting role of Bi species on the Pt/HT catalyst in the selective oxidation of glycerol towards DHA. Full article

(This article belongs to the Special Issue Glycerol Conversion by Heterogeneous Catalysis)

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8 pages, 248 KiB

Open AccessEditorial

Acknowledgement to Reviewers of Catalysts in 2017

by Catalysts Editorial Office

Catalysts 2018, 8(1), 15; https://doi.org/10.3390/catal8010015 - 11 Jan 2018

Viewed by 3173

Abstract

Peer review is an essential part in the publication process, ensuring that Catalysts maintains high quality standards for its published papers[...] Full article

12 pages, 5639 KiB

Open AccessArticle

Synthesis of Three-Dimensionally Ordered Macroporous NiCe Catalysts for Oxidative Dehydrogenation of Propane to Propene

by Kegong Fang, Lulu Liu, Mingwei Zhang, Lu Zhao, Juan Zhou, Wenbin Li, Xiaoliang Mu and Cheng Yang

Catalysts 2018, 8(1), 19; https://doi.org/10.3390/catal8010019 - 10 Jan 2018

Cited by 15 | Viewed by 5149

Abstract

Three-dimensionally ordered macroporous (3DOM) NiCe catalysts with different Ni/Ce molar ratio were fabricated using the colloidal crystal templating method. The physic-chemical properties of the samples were characterized by various techniques, including N₂ adsorption–desorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman, and [...] Read more.

Three-dimensionally ordered macroporous (3DOM) NiCe catalysts with different Ni/Ce molar ratio were fabricated using the colloidal crystal templating method. The physic-chemical properties of the samples were characterized by various techniques, including N₂ adsorption–desorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman, and H₂-temperature-programmed reduction (TPR) characterizations. The results revealed that the 3DOM NiCe samples preserved the three-dimensionally ordered macroporous channels with interlinked micro- or mesoporous structure and highly dispersed nickel oxide species in the framework upon different amount of nickel incorporation. In the evaluation of the oxidative dehydrogenation (ODH) of propane, the 3DOM NiCe catalysts exhibited higher selectivity and yield to propene than the amorphous NiCe catalyst. An optimum yield of propene of 11.9% with the 30.3% propane conversion at 375 °C was obtained over the 3DOM 2NiCe catalyst. Combining XRD, TPR, and Raman analysis, it could be found that the nickel incorporation in CeO₂ lattice produced a high concentration of oxygen vacancies that were the active sites for the oxidative dehydrogenation of propane. Besides this, the 3DOM structure promoted the rapid diffusion of the reactants and products—favorable for the generation of propene in the ODH of propane. Full article

(This article belongs to the Special Issue Catalysts for Oxygen Reduction Reaction)

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17 pages, 6611 KiB

Open AccessArticle

Synthesis and Application of Cerium-Incorporated SBA-16 Supported Ni-Based Oxygen Carrier in Cyclic Chemical Looping Steam Methane Reforming

by Maryam Meshksar, Mohammad Reza Rahimpour, Sanaz Daneshmand-Jahromi and Ali Hafizi

Catalysts 2018, 8(1), 18; https://doi.org/10.3390/catal8010018 - 10 Jan 2018

Cited by 29 | Viewed by 4944

Abstract

Hydrogen, as a clean energy carrier, could be produced aided by cyclic oxidation-reduction of oxygen carriers (OCs) in contact with carbonaceous fuel in chemical looping steam methane reforming (CL-SMR) process. In this study, the cerium was incorporated into the SBA-16 support structure to [...] Read more.

Hydrogen, as a clean energy carrier, could be produced aided by cyclic oxidation-reduction of oxygen carriers (OCs) in contact with carbonaceous fuel in chemical looping steam methane reforming (CL-SMR) process. In this study, the cerium was incorporated into the SBA-16 support structure to synthesize the Ni/Ce-SBA-16 OC. The supports were synthesized using hydrothermal method followed by impregnation of Ni and characterized via low and wide angle X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), coupled with energy dispersive X-ray (EDX) spectroscopy, and transmission electron micrograph (TEM) techniques. In addition, the effect of various Si/Ce molar ratios (20–60) in the support structure, Ni loading (10–30 wt %), reaction temperature (500–750 °C), and life time of optimal oxygen carrier over 16 cycles were investigated. The results of wide angle XRD and SEM revealed that the incorporation of CeO₂ in the channels of SBA-16 caused the formation of nickel metallic particles with smaller size and prevents the coke formation. The results showed that OC with 15 wt % Ni and Si/Ce molar ratio of 40 (15Ni/Ce-SBA-16(40)) has the best performance when compared with other OCs in terms of catalytic activity and structural properties. The methane conversion of about 99.7% was achieved at 700 °C using 15Ni/Ce-SBA-16(40) OC. We anticipate that the strategy can be extended to investigate a variety of novel modified mesoporous silica as the supporting material for the Ni based OCs. Full article

(This article belongs to the Special Issue Porous Materials in Catalysis)

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8 pages, 2193 KiB

Open AccessFeature PaperArticle

Solid Acid Catalyst Based on Single-Layer α-Zirconium Phosphate Nanosheets for Biodiesel Production via Esterification

by Yingjie Zhou, Iman Noshadi, Hao Ding, Jingjing Liu, Richard S. Parnas, Abraham Clearfield, Min Xiao, Yuezhong Meng and Luyi Sun

Catalysts 2018, 8(1), 17; https://doi.org/10.3390/catal8010017 - 10 Jan 2018

Cited by 50 | Viewed by 6629

Abstract

In this study, a solid acid was prepared by the sulfonation of surface modified α-zirconium phosphate (ZrP) single-layer nanosheets (SO₃H@ZrP), and the prepared solid acid was investigated for the esterification of oleic acid with methanol to produce biodiesel. For comparison, liquid [...] Read more.

In this study, a solid acid was prepared by the sulfonation of surface modified α-zirconium phosphate (ZrP) single-layer nanosheets (SO₃H@ZrP), and the prepared solid acid was investigated for the esterification of oleic acid with methanol to produce biodiesel. For comparison, liquid H₂SO₄ and commercial Amberlyst^® 15 catalyst were also evaluated for the same reaction under the same conditions. The experimental results showed that the SO₃H@ZrP solid acid catalyst has a superior catalytic efficiency for the esterification reaction, as well as excellent recyclability. The SO₃H@ZrP single-layer solid acid catalyst can be uniformly dispersed in the reaction media, but remains heterogeneous and thus can be easily separated and recycled. Full article

(This article belongs to the Special Issue Zirconium Phosphate Catalysts)

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16 pages, 16440 KiB

Open AccessArticle

Stacked Wire Mesh Monoliths for the Simultaneous Abatement of VOCs and Diesel Soot

by María Laura Godoy, Ezequiel David Banús, Oihane Sanz, Mario Montes, Eduardo Miró and Viviana Guadalupe Milt

Catalysts 2018, 8(1), 16; https://doi.org/10.3390/catal8010016 - 10 Jan 2018

Cited by 24 | Viewed by 7828

Abstract

Structured catalysts based on Pt,CeO₂ deposited on stainless steel wire meshes were developed to build catalytic cartridges for the treatment of diesel exhaust gases. The cartridges were tested for the simultaneous combustion of volatile organic compounds (VOCs) and soot. To this end, [...] Read more.

Structured catalysts based on Pt,CeO₂ deposited on stainless steel wire meshes were developed to build catalytic cartridges for the treatment of diesel exhaust gases. The cartridges were tested for the simultaneous combustion of volatile organic compounds (VOCs) and soot. To this end, n-hexane, acetyl acetate, and toluene were selected as probe molecules. Each of them were loaded together with real soot into the cartridges showing that while VOCs abatement takes place between 200 °C and 350 °C, soot combustion occurs in the 300–500 °C temperature range with an average maximum combustion rate at 420 °C. The catalytic cartridges were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and Brunauer-Emmett-Teller (BET) techniques. The mechanical stability of the coatings was confirmed by the ultrasound method. Air permeability of the cartridges prepared with different mesh sizes was also measured and the results were correlated using the Payri equation. Full article

(This article belongs to the Special Issue Structured and Micro-Structured Catalysts and Reactors)

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12 pages, 1452 KiB

Open AccessArticle

Efficient Production of N-Butyl Levulinate Fuel Additive from Levulinic Acid Using Amorphous Carbon Enriched with Oxygenated Groups

by Jinfan Yang, Guangyi Li, Lulu Zhang and Sufeng Zhang

Catalysts 2018, 8(1), 14; https://doi.org/10.3390/catal8010014 - 9 Jan 2018

Cited by 44 | Viewed by 6052

Abstract

The aim of this study was to develop an effective carbonaceous solid acid for synthesizing green fuel additive through esterification of lignocellulose-derived levulinic acid (LA) and n-butanol. Two different sulfonated carbons were prepared from glucose-derived amorphous carbon (GC400) and commercial active carbon (AC400). [...] Read more.

The aim of this study was to develop an effective carbonaceous solid acid for synthesizing green fuel additive through esterification of lignocellulose-derived levulinic acid (LA) and n-butanol. Two different sulfonated carbons were prepared from glucose-derived amorphous carbon (GC400) and commercial active carbon (AC400). They were contrastively studied by a series of characterizations (N₂ adsorption, X-ray diffraction, elemental analysis, transmission electron microscopy, Fourier transform infrared spectroscopy and NH₃ temperature programmed desorption). The results indicated that GC400 possessed stronger acidity and higher –SO₃H density than AC400, and the amorphous structure qualified GC400 for good swelling capacity in the reaction solution. Assessment experiments showed that GC400 displayed remarkably higher catalytic efficiency than AC400 and other typical solid acids (HZSM-5, Hβ, Amberlyst-15 and Nafion-212 resin). Up to 90.5% conversion of LA and 100% selectivity of n-butyl levulinate could be obtained on GC400 under the optimal reaction conditions. The sulfonated carbon retained 92% of its original catalytic activity even after five cycles. Full article

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

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12 pages, 2895 KiB

Open AccessArticle

Immobilized Burkholderia cepacia Lipase on pH-Responsive Pullulan Derivatives with Improved Enantioselectivity in Chiral Resolution

by Li Xu, Guli Cui, Caixia Ke, Yanli Fan and Yunjun Yan

Catalysts 2018, 8(1), 13; https://doi.org/10.3390/catal8010013 - 9 Jan 2018

Cited by 16 | Viewed by 4803

Abstract

A kind of pH-responsive particle was synthesized using modified pullulan polysaccharide. The synthesized particle possessed a series of merits, such as good dispersity, chemical stability and variability of particle size, making it a suitable carrier for enzyme immobilization. Then, Burkholderia cepacia lipase (BCL), [...] Read more.

A kind of pH-responsive particle was synthesized using modified pullulan polysaccharide. The synthesized particle possessed a series of merits, such as good dispersity, chemical stability and variability of particle size, making it a suitable carrier for enzyme immobilization. Then, Burkholderia cepacia lipase (BCL), a promising biocatalyst in transesterification reaction, was immobilized on the synthesized particle. The highest catalytic activity and immobilization efficiency were achieved at pH 6.5 because the particle size was obviously enlarged and correspondingly the adsorption surface for BCL was significantly increased. The immobilization enzyme loading was further optimized, and the derivative lipase was applied in chiral resolution. Under the optimal reaction conditions, the immobilized BCL showed a very good performance and significantly shortened the reaction equilibrium time from 30 h of the free lipase to 2 h with a conversion rate of 50.0% and ee_s at 99.2%. The immobilized lipase also exhibited good operational stability; after being used for 10 cycles, it still retained over 80% of its original activity. Moreover, it could keep more than 80% activity after storage for 20 days at room temperature in a dry environment. In addition, to learn the potential mechanism, the morphology of the particles and the immobilized lipase were both characterized with a scanning electron microscope and confocal laser scanning microscopy. It was found that the enlarged spherical surface of the particle in low pH values probably led to high immobilized efficiency, resulting in the improvement of enantioselectivity activity in chiral resolution. Full article

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

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19 pages, 4152 KiB

Open AccessArticle

Catalyst Deactivation and Regeneration Processes in Biogas Tri-Reforming Process. The Effect of Hydrogen Sulfide Addition

by Urko Izquierdo, Iker García-García, Ángel María Gutierrez, Juan Ramón Arraibi, Victoria Laura Barrio, José Francisco Cambra and Pedro Luis Arias

Catalysts 2018, 8(1), 12; https://doi.org/10.3390/catal8010012 - 9 Jan 2018

Cited by 35 | Viewed by 6818

Abstract

This work studies Ni-based catalyst deactivation and regeneration processes in the presence of H₂S under a biogas tri-reforming process for hydrogen production, which is an energy vector of great interest. 25 ppm of hydrogen sulfide were continuously added to the system [...] Read more.

This work studies Ni-based catalyst deactivation and regeneration processes in the presence of H₂S under a biogas tri-reforming process for hydrogen production, which is an energy vector of great interest. 25 ppm of hydrogen sulfide were continuously added to the system in order to provoke an observable catalyst deactivation, and once fully deactivated two different regeneration processes were studied: a self-regeneration and a regeneration by low temperature oxidation. For that purpose, several Ni-based catalysts and a bimetallic Rh-Ni catalyst supported on alumina modified with CeO₂ and ZrO₂ were used as well as a commercial Katalco 57-5 for comparison purposes. Ni/Ce-Al₂O₃ and Ni/Ce-Zr-Al₂O₃ catalysts almost recovered their initial activity. For these catalysts, after the regeneration under oxidative conditions at low temperature, the CO₂ conversions achieved—79.5% and 86.9%, respectively—were significantly higher than the ones obtained before sulfur poisoning—66.7% and 45.2%, respectively. This effect could be attributed to the support modification with CeO₂ and the higher selectivity achieved for the Reverse Water-Gas-Shift (rWGS) reaction after catalysts deactivation. As expected, the bimetallic Rh-Ni/Ce-Al₂O₃ catalyst showed higher resistance to deactivation and its sulfur poisoning seems to be reversible. In the case of the commercial and Ni/Zr-Al₂O₃ catalysts, they did not recover their activity. Full article

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