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Open AccessEditor’s ChoiceArticle
NaBH4-Reduction Induced Evolution of Bi Nanoparticles from BiOCl Nanoplates and Construction of Promising [email protected] Hybrid Photocatalysts
Catalysts 2019, 9(10), 795; https://doi.org/10.3390/catal9100795 - 24 Sep 2019
Cited by 52
Abstract
In this work, we have synthesized BiOCl nanoplates (diameter 140–220 nm, thickness 60–70 nm) via a co-precipitation method, and then created Bi nanoparticles (diameter 35–50 nm) on the surface of BiOCl nanoplates via a NaBH4 reduction method. By varying the NaBH4 [...] Read more.
In this work, we have synthesized BiOCl nanoplates (diameter 140–220 nm, thickness 60–70 nm) via a co-precipitation method, and then created Bi nanoparticles (diameter 35–50 nm) on the surface of BiOCl nanoplates via a NaBH4 reduction method. By varying the NaBH4 concentration and reaction time, the evolution of Bi nanoparticles was systematically investigated. It is demonstrated that with increasing the NaBH4 concentration (at a fixing reaction time of 30 min), BiOCl crystals are gradually reduced into Bi nanoparticles, and pure Bi nanoparticles are formed at 120 mM NaBH4 solution treatment. At low-concentration NaBH4 solutions (e.g., 10 and 30 mM), with increasing the reaction time, BiOCl crystals are partially reduced into Bi nanoparticles, and then the Bi nanoparticles return to form BiOCl crystals. At high-concentration NaBH4 solutions (e.g., 120 mM), BiOCl crystals are reduced to Bi nanoparticles completely with a short reaction time, and further prolong the treatment time leads to the transformation of the Bi nanoparticles into a two-phase mixture of BiOCl and Bi2O3 nanowires. The photodegradation performances of the samples were investigated by choosing rhodamine B (RhB) as the model pollutant and using simulated sunlight as the light source. It is demonstrated that an enhanced photodegradation performance can be achieved for the created [email protected] hybrid composites with appropriate NaBH4 treatment. The underlying photocatalytic mechanism was systematically investigated and discussed. Full article
(This article belongs to the Special Issue Photocatalysis and Environment)
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Open AccessFeature PaperEditor’s ChoiceArticle
The Relationship between Reaction Temperature and Carbon Deposition on Nickel Catalysts Based on Al2O3, ZrO2 or SiO2 Supports during the Biogas Dry Reforming Reaction
Catalysts 2019, 9(8), 676; https://doi.org/10.3390/catal9080676 - 09 Aug 2019
Cited by 25
Abstract
The tackling of carbon deposition during the dry reforming of biogas (BDR) necessitates research of the surface of spent catalysts in an effort to obtain a better understanding of the effect that different carbon allotropes have on the deactivation mechanism and correlation of [...] Read more.
The tackling of carbon deposition during the dry reforming of biogas (BDR) necessitates research of the surface of spent catalysts in an effort to obtain a better understanding of the effect that different carbon allotropes have on the deactivation mechanism and correlation of their formation with catalytic properties. The work presented herein provides a comparative assessment of catalytic stability in relation to carbon deposition and metal particle sintering on un-promoted Ni/Al2O3, Ni/ZrO2 and Ni/SiO2 catalysts for different reaction temperatures. The spent catalysts were examined using thermogravimetric analysis (TGA), Raman spectroscopy, high angle annular dark field scanning transmission electron microscopy (STEM-HAADF) and X-ray photoelectron spectroscopy (XPS). The results show that the formation and nature of carbonaceous deposits on catalytic surfaces (and thus catalytic stability) depend on the interplay of a number of crucial parameters such as metal support interaction, acidity/basicity characteristics, O2– lability and active phase particle size. When a catalytic system possesses only some of these beneficial characteristics, then competition with adverse effects may overshadow any potential benefits. Full article
(This article belongs to the Special Issue Catalyst Deactivation in Hydrocarbon Processing)
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Open AccessEditor’s ChoiceArticle
Combi-CLEAs of Glucose Oxidase and Catalase for Conversion of Glucose to Gluconic Acid Eliminating the Hydrogen Peroxide to Maintain Enzyme Activity in a Bubble Column Reactor
Catalysts 2019, 9(8), 657; https://doi.org/10.3390/catal9080657 - 31 Jul 2019
Cited by 15
Abstract
In this study combined cross-linked aggregates of catalase from bovine liver and glucose-oxidase from Aspergillus niger were prepared, and the effects of the precipitant and crosslinking agents, as well as the use of bovine serum albumin (BSA) as a feeder protein, on enzyme [...] Read more.
In this study combined cross-linked aggregates of catalase from bovine liver and glucose-oxidase from Aspergillus niger were prepared, and the effects of the precipitant and crosslinking agents, as well as the use of bovine serum albumin (BSA) as a feeder protein, on enzyme immobilization yield and thermal stability of both enzymes, were evaluated. Combi- crosslinking of enzyme aggregates (CLEAs) prepared using dimethoxyethane as precipitant, 25 mM glutaraldehyde and BSA/enzymes mass ratio of 5.45 (w/w), exhibited the highest enzyme activities and stabilities at 40 °C, pH 6.0, and 250 rpm for 5 h. The stability of both immobilized enzymes was fairly similar, eliminating one of the problems of enzyme coimmobilization. Combi-CLEAs were used in gluconic acid (GA) production in a bubble column reactor operated at 40 °C, pH 6.0 and 10 vvm of aeration, using 26 g L−1 glucose as the substrate. Results showed conversion of around 96% and a reaction course very similar to the same process using free enzymes. The operational half-life was 34 h, determined from kinetic profiles and the first order inactivation model. Combi-CLEAs of glucose-oxidase and catalase were shown to be a robust biocatalyst for applications in the production of gluconic acid from glucose. Full article
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Open AccessEditor’s ChoiceArticle
Reuse of Lipase from Pseudomonas fluorescens via Its Step-by-Step Coimmobilization on Glyoxyl-Octyl Agarose Beads with Least Stable Lipases
Catalysts 2019, 9(5), 487; https://doi.org/10.3390/catal9050487 - 27 May 2019
Cited by 19
Abstract
Coimmobilization of lipases may be interesting in many uses, but this means that the stability of the least stable enzyme determines the stability of the full combilipase. Here, we propose a strategy that permits the reuse the most stable enzyme. Lecitase Ultra (LU) [...] Read more.
Coimmobilization of lipases may be interesting in many uses, but this means that the stability of the least stable enzyme determines the stability of the full combilipase. Here, we propose a strategy that permits the reuse the most stable enzyme. Lecitase Ultra (LU) (a phospholipase) and the lipases from Rhizomucor miehei (RML) and from Pseudomonas fluorescens (PFL) were immobilized on octyl agarose, and their stabilities were studied under a broad range of conditions. Immobilized PFL was found to be the most stable enzyme under all condition ranges studied. Furthermore, in many cases it maintained full activity, while the other enzymes lost more than 50% of their initial activity. To coimmobilize these enzymes without discarding fully active PFL when LU or RML had been inactivated, PFL was covalently immobilized on glyoxyl-agarose beads. After biocatalysts reduction, the other enzyme was coimmobilized just by interfacial activation. After checking that glyoxyl-octyl-PFL was stable in 4% Triton X-100, the biocatalysts of PFL coimmobilized with LU or RML were submitted to inactivation under different conditions. Then, the inactivated least stable coimmobilized enzyme was desorbed (using 4% detergent) and a new enzyme reloading (using in some instances RML and in some others employing LU) was performed. The initial activity of immobilized PFL was maintained intact for several of these cycles. This shows the great potential of this lipase coimmobilization strategy. Full article
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Open AccessEditor’s ChoiceArticle
Activation of Persulfate by Biochars from Valorized Olive Stones for the Degradation of Sulfamethoxazole
Catalysts 2019, 9(5), 419; https://doi.org/10.3390/catal9050419 - 03 May 2019
Cited by 20
Abstract
Biochars from spent olive stones were tested for the degradation of sulfamethoxazole (SMX) in water matrices. Batch degradation experiments were performed using sodium persulfate (SPS) as the source of radicals in the range 250–1500 mg/L, with biochar as the SPS activator in the [...] Read more.
Biochars from spent olive stones were tested for the degradation of sulfamethoxazole (SMX) in water matrices. Batch degradation experiments were performed using sodium persulfate (SPS) as the source of radicals in the range 250–1500 mg/L, with biochar as the SPS activator in the range 100–300 mg/L and SMX as the model micro-pollutant in the range 250–2000 μg/L. Ultrapure water (UPW), bottled water (BW), and secondary treated wastewater (WW) were employed as the water matrix. Removal of SMX by adsorption only was moderate and favored at acidic conditions, while SPS alone did not practically oxidize SMX. At these conditions, biochar was capable of activating SPS and, consequently, of degrading SMX, with the pseudo-first order rate increasing with increasing biochar and oxidant concentration and decreasing SMX concentration. Experiments in BW or UPW spiked with various anions showed little or no effect on degradation. Similar experiments in WW resulted in a rate reduction of about 30%, and this was attributed to the competitive consumption of reactive radicals by non-target water constituents. Experiments with methanol and t-butanol at excessive concentrations resulted in partial but generally not complete inhibition of degradation; this indicates that, besides the liquid bulk, reactions may also occur close to or on the biochar surface. Full article
(This article belongs to the Special Issue Trends in Catalytic Wet Peroxide Oxidation Processes)
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Open AccessEditor’s ChoiceArticle
Facet-Dependent Reactivity of Fe2O3/CeO2 Nanocomposites: Effect of Ceria Morphology on CO Oxidation
Catalysts 2019, 9(4), 371; https://doi.org/10.3390/catal9040371 - 19 Apr 2019
Cited by 23
Abstract
Ceria has been widely studied either as catalyst itself or support of various active phases in many catalytic reactions, due to its unique redox and surface properties in conjunction to its lower cost, compared to noble metal-based catalytic systems. The rational design of [...] Read more.
Ceria has been widely studied either as catalyst itself or support of various active phases in many catalytic reactions, due to its unique redox and surface properties in conjunction to its lower cost, compared to noble metal-based catalytic systems. The rational design of catalytic materials, through appropriate tailoring of the particles’ shape and size, in order to acquire highly efficient nanocatalysts, is of major significance. Iron is considered to be one of the cheapest transition metals while its interaction with ceria support and their shape-dependent catalytic activity has not been fully investigated. In this work, we report on ceria nanostructures morphological effects (cubes, polyhedra, rods) on the textural, structural, surface, redox properties and, consequently, on the CO oxidation performance of the iron-ceria mixed oxides (Fe2O3/CeO2). A full characterization study involving N2 adsorption at –196 °C, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), temperature programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS) was performed. The results clearly revealed the key role of support morphology on the physicochemical properties and the catalytic behavior of the iron-ceria binary system, with the rod-shaped sample exhibiting the highest catalytic performance, both in terms of conversion and specific activity, due to its improved reducibility and oxygen mobility, along with its abundance in Fe2+ species. Full article
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Open AccessEditor’s ChoiceArticle
Photocatalytic Hydrogen Production: Role of Sacrificial Reagents on the Activity of Oxide, Carbon, and Sulfide Catalysts
Catalysts 2019, 9(3), 276; https://doi.org/10.3390/catal9030276 - 18 Mar 2019
Cited by 53
Abstract
Photocatalytic water splitting is a sustainable technology for the production of clean fuel in terms of hydrogen (H2). In the present study, hydrogen (H2) production efficiency of three promising photocatalysts (titania (TiO2-P25), graphitic carbon nitride (g [...] Read more.
Photocatalytic water splitting is a sustainable technology for the production of clean fuel in terms of hydrogen (H2). In the present study, hydrogen (H2) production efficiency of three promising photocatalysts (titania (TiO2-P25), graphitic carbon nitride (g-C3N4), and cadmium sulfide (CdS)) was evaluated in detail using various sacrificial agents. The effect of most commonly used sacrificial agents in the recent years, such as methanol, ethanol, isopropanol, ethylene glycol, glycerol, lactic acid, glucose, sodium sulfide, sodium sulfite, sodium sulfide/sodium sulfite mixture, and triethanolamine, were evaluated on TiO2-P25, g-C3N4, and CdS. H2 production experiments were carried out under simulated solar light irradiation in an immersion type photo-reactor. All the experiments were performed without any noble metal co-catalyst. Moreover, photolysis experiments were executed to study the H2 generation in the absence of a catalyst. The results were discussed specifically in terms of chemical reactions, pH of the reaction medium, hydroxyl groups, alpha hydrogen, and carbon chain length of sacrificial agents. The results revealed that glucose and glycerol are the most suitable sacrificial agents for an oxide photocatalyst. Triethanolamine is the ideal sacrificial agent for carbon and sulfide photocatalyst. A remarkable amount of H2 was produced from the photolysis of sodium sulfide and sodium sulfide/sodium sulfite mixture without any photocatalyst. The findings of this study would be highly beneficial for the selection of sacrificial agents for a particular photocatalyst. Full article
(This article belongs to the Special Issue Photocatalytic Hydrogen Evolution)
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Open AccessEditor’s ChoiceArticle
Fischer–Tropsch: Product Selectivity–The Fingerprint of Synthetic Fuels
Catalysts 2019, 9(3), 259; https://doi.org/10.3390/catal9030259 - 14 Mar 2019
Cited by 29
Abstract
The bulk of the products that were synthesized from Fischer–Tropsch synthesis (FTS) is a wide range (C1–C70+) of hydrocarbons, primarily straight-chained paraffins. Additional hydrocarbon products, which can also be a majority, are linear olefins, specifically: 1-olefin, trans-2-olefin, and [...] Read more.
The bulk of the products that were synthesized from Fischer–Tropsch synthesis (FTS) is a wide range (C1–C70+) of hydrocarbons, primarily straight-chained paraffins. Additional hydrocarbon products, which can also be a majority, are linear olefins, specifically: 1-olefin, trans-2-olefin, and cis-2-olefin. Minor hydrocarbon products can include isomerized hydrocarbons, predominantly methyl-branched paraffin, cyclic hydrocarbons mainly derived from high-temperature FTS and internal olefins. Combined, these products provide 80–95% of the total products (excluding CO2) generated from syngas. A vast number of different oxygenated species, such as aldehydes, ketones, acids, and alcohols, are also embedded in this product range. These materials can be used to probe the FTS mechanism or to produce alternative chemicals. The purpose of this article is to compare the product selectivity over several FTS catalysts. Discussions center on typical product selectivity of commonly used catalysts, as well as some uncommon formulations that display selectivity anomalies. Reaction tests were conducted while using an isothermal continuously stirred tank reactor. Carbon mole percentages of CO that are converted to specific materials for Co, Fe, and Ru catalysts vary, but they depend on support type (especially with cobalt and ruthenium) and promoters (especially with iron). All three active metals produced linear alcohols as the major oxygenated product. In addition, only iron produced significant selectivities to acids, aldehydes, and ketones. Iron catalysts consistently produced the most isomerized products of the catalysts that were tested. Not only does product selectivity provide a fingerprint of the catalyst formulation, but it also points to a viable proposed mechanistic route. Full article
(This article belongs to the Special Issue Iron and Cobalt Catalysts)
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Open AccessEditor’s ChoiceArticle
In-Situ Synthesis of Nb2O5/g-C3N4 Heterostructures as Highly Efficient Photocatalysts for Molecular H2 Evolution under Solar Illumination
Catalysts 2019, 9(2), 169; https://doi.org/10.3390/catal9020169 - 11 Feb 2019
Cited by 16
Abstract
This work focuses on the synthesis of heterostructures with compatible band positions and a favourable surface area for the efficient photocatalytic production of molecular hydrogen (H2). In particular, 3-dimensional Nb2O5/g-C3N4 heterostructures with suitable band [...] Read more.
This work focuses on the synthesis of heterostructures with compatible band positions and a favourable surface area for the efficient photocatalytic production of molecular hydrogen (H2). In particular, 3-dimensional Nb2O5/g-C3N4 heterostructures with suitable band positions and high surface area have been synthesized employing a hydrothermal method. The combination of a Nb2O5 with a low charge carrier recombination rate and a g-C3N4 exhibiting high visible light absorption resulted in remarkable photocatalytic activity under simulated solar irradiation in the presence of various hole scavengers (triethanolamine (TEOA) and methanol). The following aspects of the novel material have been studied systematically: the influence of different molar ratios of Nb2O5 to g-C3N4 on the heterostructure properties, the role of the employed hole scavengers, and the impact of the co-catalyst and the charge carrier densities affecting the band alignment. The separation/transfer efficiency of the photogenerated electron-hole pairs is found to increase significantly as compared to that of pure Nb2O5 and g-C3N4, respectively, with the highest molecular H2 production of 110 mmol/g·h being obtained for 10 wt % of g-C3N4 over Nb2O5 as compared with that of g-C3N4 (33.46 mmol/g·h) and Nb2O5 (41.20 mmol/g·h). This enhanced photocatalytic activity is attributed to a sufficient interfacial interaction thus favouring the fast photogeneration of electron-hole pairs at the Nb2O5/g-C3N4 interface through a direct Z-scheme. Full article
(This article belongs to the Special Issue Photocatalytic Hydrogen Evolution)
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Open AccessFeature PaperEditor’s ChoiceArticle
Preparation of Visible Light Photocatalytic Graphene Embedded Rutile Titanium(IV) Oxide Composite Nanowires and Enhanced NOx Removal
Catalysts 2019, 9(2), 170; https://doi.org/10.3390/catal9020170 - 11 Feb 2019
Cited by 21
Abstract
The quest for developing highly efficient TiO2-based photocatalysts is continuing and, in particular, evolving a new strategy is an important aspect in this regard. In general, much effort has been devoted to the anatase TiO2 modifications, despite there being only [...] Read more.
The quest for developing highly efficient TiO2-based photocatalysts is continuing and, in particular, evolving a new strategy is an important aspect in this regard. In general, much effort has been devoted to the anatase TiO2 modifications, despite there being only a few recent studies on rutile TiO2 (rTiO2). To the best of our knowledge, studies on the preparation and characterization of the photocatalysts based on the intentional inclusion of graphene (G) into rTiO2 nanostructures have not been reported yet. Herein, we develop a new type of TiO2-based photocatalyst comprising of G included pure rTiO2 nanowire (abbreviated as rTiO2(G) NW) with enhanced visible light absorption capability. To prepare rTiO2(G) NW, the G incorporated titanate electrospun fibers were obtained by electrospinning and subsequently heat treated at various temperatures (500 to 800 °C). Electrospinning conditions were optimized for producing good quality rTiO2(G) NW. The rTiO2(G) NW and their corresponding samples were characterized by appropriate techniques such as X-ray diffraction (XRD), scanning electron microscopy, high-resolution transmission electron microscopy and UV-vis diffuse reflectance spectroscopy to ascertain their material characteristics. XRD results show that the lattice strain occurs upon inclusion of G. We present here the first observation of an apparent bandgap lowering because of the G inclusion into TiO2 NW. While anatase TiO2 NW exhibited poor visible light photocatalysis towards NOx removal, the rTiO2(G) NW photocatalyst witnessed a significantly enhanced (~67%) photocatalytic performance as compared to anatase TiO2(G) NW. We concluded that the inclusion of G into rTiO2 nanostructures enhances the visible light photoactivity. A plausible mechanism for photocatalysis is suggested. Full article
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Open AccessEditor’s ChoiceArticle
Efficient Heterogeneous Activation of Persulfate by Iron-Modified Biochar for Removal of Antibiotic from Aqueous Solution: A Case Study of Tetracycline Removal
Catalysts 2019, 9(1), 49; https://doi.org/10.3390/catal9010049 - 07 Jan 2019
Cited by 19
Abstract
Waste reutilization is always highly desired in the environmental engineering and science community. In this study, Fe-SCG biochar was functionalized by modifying spent coffee grounds (SCG) with magnetite (Fe3+) at 700 °C and applied for the oxidative removal of tetracycline (TC) [...] Read more.
Waste reutilization is always highly desired in the environmental engineering and science community. In this study, Fe-SCG biochar was functionalized by modifying spent coffee grounds (SCG) with magnetite (Fe3+) at 700 °C and applied for the oxidative removal of tetracycline (TC) with the presence of persulfate (PS). The effects of pH, dosage of biochar and sodium persulfate and initial TC concentration on TC degradation were investigated in a batch system. Our results show that higher TC degradation efficiency was obtained at low pH, low initial TC concentration, and at high dosages of PS and biochar. The highest removal efficiency (96%) was achieved by Fe-SCG/PS under the conditions of pH = 2.0, [Fe-SCG] = 2.5 g/L, [PS] = 60 mM and [TC] = 1 mM. The proposed Fe-SCG catalyst could be a promising effective biochar for the remediation of other emerging organic contaminants. Full article
(This article belongs to the Special Issue Preparation of Catalysts from Renewable and Waste Materials)
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Open AccessEditor’s ChoiceArticle
Effect of Y Modified Ceria Support in Mono and Bimetallic Pd–Au Catalysts for Complete Benzene Oxidation
Catalysts 2018, 8(7), 283; https://doi.org/10.3390/catal8070283 - 16 Jul 2018
Cited by 9
Abstract
Mono metallic and bimetallic Pd (1 wt. %)–Au (3 wt. %) catalysts were prepared using two ceria supports doped with 1 wt. % Y2O3. Yttrium was added by impregnation or co-precipitation. The catalyst synthesis was carried out by deposition–precipitation [...] Read more.
Mono metallic and bimetallic Pd (1 wt. %)–Au (3 wt. %) catalysts were prepared using two ceria supports doped with 1 wt. % Y2O3. Yttrium was added by impregnation or co-precipitation. The catalyst synthesis was carried out by deposition–precipitation method, with sequential deposition–precipitation of palladium over previously loaded gold in the case of the bimetallic samples. The obtained materials, characterized by X-ray powder diffraction (XRD), High resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and temperature programmed reduction (TPR) techniques, were tested in the complete benzene oxidation (CBO). The results of the characterization analyses and the catalytic performance pointed to a close relationship between structural, redox, and catalytic properties of mono and bimetallic catalysts. Among the monometallic systems, Pd catalysts were more active as compared to the corresponding Au catalysts. The bimetallic systems exhibited the best combustion activity. In particular, over Pd–Au supported on Y-impregnated ceria, 100% of benzene conversion towards total oxidation at the temperature of 150 °C was obtained. Comparison of surface sensitive XPS results of fresh and spent catalysts ascertained the redox character of the reaction. Full article
(This article belongs to the Special Issue Structure–Activity Relationships in Catalysis)
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Open AccessEditor’s ChoiceArticle
PdO/[email protected]2 Hybrid Nanocatalyst for Reduction of Nitroarenes
Catalysts 2018, 8(7), 280; https://doi.org/10.3390/catal8070280 - 14 Jul 2018
Cited by 14
Abstract
Development of a novel approach for synthesizing nanostructured catalysts and achieving further improvements in catalytic activity, effectiveness, and efficiency remains a major challenge. In this report, we describe the preparation of a nanostructured PdO/[email protected]2 hybrid nanocatalyst featuring well-dispersed PdO nanoparticles within hollow [...] Read more.
Development of a novel approach for synthesizing nanostructured catalysts and achieving further improvements in catalytic activity, effectiveness, and efficiency remains a major challenge. In this report, we describe the preparation of a nanostructured PdO/[email protected]2 hybrid nanocatalyst featuring well-dispersed PdO nanoparticles within hollow [email protected]2. The as-prepared PdO/[email protected]2 hybrid nanocatalyst exhibited good morphological features, derived from the controlled stepwise synthesis from Pd/[email protected]@mSiO2 (PS = polystyrene). The morphology, size, oxidation state, crystallinity, and thermal stability of the prepared PdO/[email protected]2 hybrid nanocatalyst were confirmed by a series of physicochemical techniques. The PdO/[email protected]2 hybrid nanocatalyst showed very high catalytic efficiency in the reduction of 4-nitrophenol and various nitroarenes under eco-friendly conditions. Therefore, the PdO/[email protected]2 hybrid nanocatalyst is a promising alternative catalyst for applications in environmental remediation. Full article
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Open AccessFeature PaperEditor’s ChoiceArticle
Simulating Real World Soot-Catalyst Contact Conditions for Lab-Scale Catalytic Soot Oxidation Studies
Catalysts 2018, 8(6), 247; https://doi.org/10.3390/catal8060247 - 14 Jun 2018
Cited by 12
Abstract
In diesel soot oxidation studies, both well-defined model soot and a reliable means to simulate realistic contact conditions with catalysts are crucial. This study is the first attempt in the field to establish a lab-scale continuous flame soot deposition method in simulating the [...] Read more.
In diesel soot oxidation studies, both well-defined model soot and a reliable means to simulate realistic contact conditions with catalysts are crucial. This study is the first attempt in the field to establish a lab-scale continuous flame soot deposition method in simulating the “contact condition” of soot and a structured diesel particulate filter (DPF) catalyst. The properties of this flame soot were examined by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM) for structure analysis, Brunauer-Emmett-Teller (BET) for surface area analysis, and thermogravimetric analysis (TGA) for reactivity and kinetics analysis. For validation purposes, catalytic oxidation of Tiki® soot using the simulated contact condition was conducted to compare with the diesel particulates collected from a real diesel engine exhaust system. It was found that the flame soot is more uniform and controllable than similar samples of collected diesel particulates. The change in T50 due to the presence of the catalyst is very similar in both cases, implying that the flame deposit method is able to produce comparably realistic contact conditions to that resulting from the real exhaust system. Comparing against the expensive engine testing, this novel method allows researchers to quickly set up a procedure in the laboratory scale to reveal the catalytic soot oxidation properties in a comparable loose contact condition. Full article
(This article belongs to the Special Issue Catalytic Oxidation in Environmental Protection)
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Open AccessEditor’s ChoiceArticle
Electrochemically Obtained TiO2/CuxOy Nanotube Arrays Presenting a Photocatalytic Response in Processes of Pollutants Degradation and Bacteria Inactivation in Aqueous Phase
Catalysts 2018, 8(6), 237; https://doi.org/10.3390/catal8060237 - 05 Jun 2018
Cited by 10
Abstract
TiO2/CuxOy nanotube (NT) arrays were synthesized using the anodization method in the presence of ethylene glycol and different parameters applied. The presence, morphology, and chemical character of the obtained structures was characterized using a variety of methods—SEM (scanning [...] Read more.
TiO2/CuxOy nanotube (NT) arrays were synthesized using the anodization method in the presence of ethylene glycol and different parameters applied. The presence, morphology, and chemical character of the obtained structures was characterized using a variety of methods—SEM (scanning electron microscopy), XPS (X-ray photoelectron spectroscopy), XRD (X-ray crystallography), PL (photoluminescence), and EDX (energy-dispersive X-ray spectroscopy). A p-n mixed oxide heterojunction of Ti-Cu was created with a proved response to the visible light range and the stable form that were in contact with Ti. TiO2/CuxOy NTs presented the appearance of both Cu2O (mainly) and CuO components influencing the dimensions of the NTs (1.1–1.3 µm). Additionally, changes in voltage have been proven to affect the NTs’ length, which reached a value of 3.5 µm for Ti90Cu10_50V. Degradation of phenol in the aqueous phase was observed in 16% of Ti85Cu15_30V after 1 h of visible light irradiation (λ > 420 nm). Scavenger tests for phenol degradation process in presence of NT samples exposed the responsibility of superoxide radicals for degradation of organic compounds in Vis light region. Inactivation of bacteria strains Escherichia coli (E. coli), Bacillus subtilis (B. subtilis), and Clostridium sp. in presence of obtained TiO2/CuxOy NT photocatalysts, and Vis light has been studied showing a great improvement in inactivation efficiency with a response rate of 97% inactivation for E. coli and 98% for Clostridium sp. in 60 min. Evidently, TEM (transmission electron microscopy) images confirmed the bacteria cells’ damage. Full article
(This article belongs to the Special Issue Nanomaterials for Environmental Purification and Energy Conversion)
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Open AccessEditor’s ChoiceArticle
Selective Reduction of Ketones and Aldehydes in Continuous-Flow Microreactor—Kinetic Studies
Catalysts 2018, 8(5), 221; https://doi.org/10.3390/catal8050221 - 22 May 2018
Cited by 9
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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Open AccessEditor’s ChoiceArticle
Improved CO-PROX Performance of CuO/CeO2 Catalysts by Using Nanometric Ceria as Support
Catalysts 2018, 8(5), 209; https://doi.org/10.3390/catal8050209 - 15 May 2018
Cited by 15
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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Open AccessEditor’s ChoiceArticle
Optimization of Charcoal Production Process from Woody Biomass Waste: Effect of Ni-Containing Catalysts on Pyrolysis Vapors
Catalysts 2018, 8(5), 191; https://doi.org/10.3390/catal8050191 - 04 May 2018
Cited by 9
Abstract
Woody biomass waste (Pinus radiata) coming from forestry activities has been pyrolyzed with the aim of obtaining charcoal and, at the same time, a hydrogen-rich gas fraction. The pyrolysis has been carried out in a laboratory scale continuous screw reactor, where [...] Read more.
Woody biomass waste (Pinus radiata) coming from forestry activities has been pyrolyzed with the aim of obtaining charcoal and, at the same time, a hydrogen-rich gas fraction. The pyrolysis has been carried out in a laboratory scale continuous screw reactor, where carbonization takes place, connected to a vapor treatment reactor, at which the carbonization vapors are thermo-catalytically treated. Different peak temperatures have been studied in the carbonization process (500–900 °C), while the presence of different Ni-containing catalysts in the vapor treatment has been analyzed. Low temperature pyrolysis produces high liquid and solid yields, however, increasing the temperature progressively up to 900 °C drastically increases gas yield. The amount of nickel affects the vapors treatment phase, enhancing even further the production of interesting products such as hydrogen and reducing the generated liquids to very low yields. The gases obtained at very high temperatures (700–900 °C) in the presence of Ni-containing catalysts are rich in H2 and CO, which makes them valuable for energy production, as hydrogen source, producer gas or reducing agent. Full article
(This article belongs to the Special Issue Catalytic Pyrolysis)
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Open AccessEditor’s ChoiceArticle
Immobilization of Planococcus sp. S5 Strain on the Loofah Sponge and Its Application in Naproxen Removal
Catalysts 2018, 8(5), 176; https://doi.org/10.3390/catal8050176 - 26 Apr 2018
Cited by 12
Abstract
Planococcus sp. S5, a Gram-positive bacterium isolated from the activated sludge is known to degrade naproxen in the presence of an additional carbon source. Due to the possible toxicity of naproxen and intermediates of its degradation, the whole cells of S5 strain were [...] Read more.
Planococcus sp. S5, a Gram-positive bacterium isolated from the activated sludge is known to degrade naproxen in the presence of an additional carbon source. Due to the possible toxicity of naproxen and intermediates of its degradation, the whole cells of S5 strain were immobilized onto loofah sponge. The immobilized cells degraded 6, 9, 12 or 15 mg/L of naproxen faster than the free cells. Planococcus sp. cells immobilized onto the loofah sponge were able to degrade naproxen efficiently for 55 days without significant damage and disintegration of the carrier. Analysis of the activity of enzymes involved in naproxen degradation showed that stabilization of S5 cells in exopolysaccharide (EPS) resulted in a significant increase of their activity. Changes in the structure of biofilm formed on the loofah sponge cubes during degradation of naproxen were observed. Developed biocatalyst system showed high resistance to naproxen and its intermediates and degraded higher concentrations of the drug in comparison to the free cells. Full article
(This article belongs to the Special Issue Immobilized Biocatalysts)
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Open AccessFeature PaperEditor’s ChoiceArticle
A Biorefinery Cascade Conversion of Hemicellulose-Free Eucalyptus Globulus Wood: Production of Concentrated Levulinic Acid Solutions for γ-Valerolactone Sustainable Preparation
Catalysts 2018, 8(4), 169; https://doi.org/10.3390/catal8040169 - 21 Apr 2018
Cited by 18
Abstract
Eucalyptus globulus wood samples were subjected to preliminary aqueous processing to remove water-soluble extractives and hemicelluloses, and the resulting solid (mainly made up of cellulose and lignin) was employed as a substrate for converting the cellulosic fraction into mixtures of levulinic and formic [...] Read more.
Eucalyptus globulus wood samples were subjected to preliminary aqueous processing to remove water-soluble extractives and hemicelluloses, and the resulting solid (mainly made up of cellulose and lignin) was employed as a substrate for converting the cellulosic fraction into mixtures of levulinic and formic acid through a sulfuric acid-catalyzed reaction. These runs were carried out in a microwave-heated reactor at different temperatures and reaction times, operating in single-batch or cross-flow modes, in order to identify the most favorable operational conditions. Selected liquid phases deriving from these experiments, which resulted in concentrated levulinic acid up to 408 mmol/L, were then employed for γ-valerolactone production by levulinc acid hydrogenation in the presence of the commercial 5% Ru/C catalyst. In order to assess the effects of the main reaction parameters, hydrogenation experiments were performed at different temperatures, reaction times, amounts of ruthenium catalyst and hydrogen pressure. Yields of γ-valerolactone in the range of 85–90 mol % were obtained from the hydrogenation of the wood-derived solutions containing levulinic acid, obtained by single-batch operation or by the cross-flow process. The negative effect of co-produced formic acid present in crude levulinic acid solutions was evidenced and counteracted efficiently by allowing the preliminary thermal decomposition of formic acid itself. Full article
(This article belongs to the Special Issue Catalytic Transformation of Lignocellulosic Platform Chemicals)
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Open AccessFeature PaperEditor’s ChoiceArticle
Immobilization of Enterobacter aerogenes by a Trimeric Autotransporter Adhesin, AtaA, and Its Application to Biohydrogen Production
Catalysts 2018, 8(4), 159; https://doi.org/10.3390/catal8040159 - 16 Apr 2018
Cited by 8
Abstract
Biological hydrogen production by microbial cells has been extensively researched as an energy-efficient and environmentally-friendly process. In this study, we propose a fast, easy method for immobilizing Enterobacter aerogenes by expressing ataA, which encodes the adhesive protein of Acinetobacter sp. Tol 5. [...] Read more.
Biological hydrogen production by microbial cells has been extensively researched as an energy-efficient and environmentally-friendly process. In this study, we propose a fast, easy method for immobilizing Enterobacter aerogenes by expressing ataA, which encodes the adhesive protein of Acinetobacter sp. Tol 5. AtaA protein on the E. aerogenes cells carrying the ataA gene was demonstrated by immunoblotting and flow cytometry. The AtaA-producing cells exhibited stronger adherence and auto-agglutination characteristics than wild-type cells, and were successfully immobilized (at approximately 2.5 mg/cm3) on polyurethane foam. Hydrogen production from the cell-immobilized polyurethane foams was monitored in repetitive batch reactions and flow reactor studies. The total hydrogen production in triple-repetitive batch reactions reached 0.6 mol/mol glucose, and the hydrogen production rate in the flow reactor was 42 mL·h−1·L−1. The AtaA production achieved simple and immediate immobilization of E. aerogenes on the foam, enabling repetitive and continuous hydrogen production. This report newly demonstrates the production of AtaA on the cell surfaces of bacterial genera other than Acinetobacter, and can simplify and accelerate the immobilization of whole-cell catalysts. Full article
(This article belongs to the Special Issue Immobilized Biocatalysts)
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Open AccessFeature PaperEditor’s ChoiceArticle
Gas-Phase Phosphorous Poisoning of a Pt/Ba/Al2O3 NOx Storage Catalyst
Catalysts 2018, 8(4), 155; https://doi.org/10.3390/catal8040155 - 11 Apr 2018
Cited by 6
Abstract
The effect of phosphorous exposure on the NOx storage capacity of a Pt/Ba/Al2O3 catalyst coated on a ceramic monolith substrate has been studied. The catalyst was exposed to phosphorous by evaporating phosphoric acid in presence of H2O [...] Read more.
The effect of phosphorous exposure on the NOx storage capacity of a Pt/Ba/Al2O3 catalyst coated on a ceramic monolith substrate has been studied. The catalyst was exposed to phosphorous by evaporating phosphoric acid in presence of H2O and O2. The NOx storage capacity was measured before and after the phosphorus exposure and a significant loss of the NOx storage capacity was detected after phosphorous exposure. The phosphorous poisoned samples were characterized by X-ray photoelectron spectroscopy (XPS), environmental scanning electron microscopy (ESEM), N2-physisorption and inductive coupled plasma atomic emission spectroscopy (ICP-AES). All characterization methods showed an axial distribution of phosphorous ranging from the inlet to the outlet of the coated monolith samples with a higher concentration at the inlet of the samples. Elemental analysis, using ICP-AES, confirmed this distribution of phosphorous on the catalyst surface. The specific surface area and pore volume were significantly lower at the inlet section of the monolith where the phosphorous concentration was higher, and higher at the outlet where the phosphorous concentration was lower. The results from the XPS and scanning electron microscopy (SEM)-energy dispersive X-ray (EDX) analyses showed higher accumulation of phosphorus towards the surface of the catalyst at the inlet of the monolith and the phosphorus was to a large extent present in the form of P4O10. However, in the middle section of the monolith, the XPS analysis revealed the presence of more metaphosphate (PO3). Moreover, the SEM-EDX analysis showed that the phosphorous to higher extent had diffused into the washcoat and was less accumulated at the surface close to the outlet of the sample. Full article
(This article belongs to the Special Issue Emissions Control Catalysis)
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Open AccessEditor’s ChoiceArticle
Preparation of Stable Cross-Linked Enzyme Aggregates (CLEAs) of a Ureibacillus thermosphaericus Esterase for Application in Malathion Removal from Wastewater
Catalysts 2018, 8(4), 154; https://doi.org/10.3390/catal8040154 - 11 Apr 2018
Cited by 17
Abstract
In this study, the active and stable cross-linked enzyme aggregates (CLEAs) of the thermostable esterase estUT1 of the bacterium Ureibacillus thermosphaericus were prepared for application in malathion removal from municipal wastewater. Co-expression of esterase with an E. coli chaperone team (KJE, ClpB, and [...] Read more.
In this study, the active and stable cross-linked enzyme aggregates (CLEAs) of the thermostable esterase estUT1 of the bacterium Ureibacillus thermosphaericus were prepared for application in malathion removal from municipal wastewater. Co-expression of esterase with an E. coli chaperone team (KJE, ClpB, and ELS) increased the activity of the soluble enzyme fraction up to 200.7 ± 15.5 U mg−1. Response surface methodology (RSM) was used to optimize the preparation of the CLEA-estUT1 biocatalyst to maximize its activity and minimize enzyme loss. CLEA-estUT1 with the highest activity of 29.4 ± 0.5 U mg−1 (90.6 ± 2.7% of the recovered activity) was prepared with 65.1% (w/v) ammonium sulfate, 120.6 mM glutaraldehyde, and 0.2 mM bovine serum albumin at 5.1 h of cross-linking. The biocatalyst has maximal activity at 80 °С and pH 8.0. Analysis of the properties of CLEA-estUT1 and free enzyme at 50–80 °C and pH 5.0–10.0 showed higher stability of the biocatalyst. CLEA-estUT1 showed marked tolerance against a number of chemicals and high operational stability and activity in the reaction of malathion hydrolysis in wastewater (up to 99.5 ± 1.4%). After 25 cycles of malathion hydrolysis at 37 °С, it retained 55.2 ± 1.1% of the initial activity. The high stability and reusability of CLEA-estUT1 make it applicable for the degradation of insecticides. Full article
(This article belongs to the Special Issue Immobilized Biocatalysts)
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Open AccessEditor’s ChoiceCommunication
Catalytic Efficiency of Basidiomycete Laccases: Redox Potential versus Substrate-Binding Pocket Structure
Catalysts 2018, 8(4), 152; https://doi.org/10.3390/catal8040152 - 09 Apr 2018
Cited by 19
Abstract
Laccases are copper-containing oxidases that catalyze a one-electron abstraction from various phenolic and non-phenolic compounds with concomitant reduction of molecular oxygen to water. It is well-known that laccases from various sources have different substrate specificities, but it is not completely clear what exactly [...] Read more.
Laccases are copper-containing oxidases that catalyze a one-electron abstraction from various phenolic and non-phenolic compounds with concomitant reduction of molecular oxygen to water. It is well-known that laccases from various sources have different substrate specificities, but it is not completely clear what exactly provides these differences. The purpose of this work was to study the features of the substrate specificity of four laccases from basidiomycete fungi Trametes hirsuta, Coriolopsis caperata, Antrodiella faginea, and Steccherinum murashkinskyi, which have different redox potentials of the T1 copper center and a different structure of substrate-binding pockets. Enzyme activity toward 20 monophenolic substances and 4 phenolic dyes was measured spectrophotometrically. The kinetic parameters of oxidation of four lignans and lignan-like substrates were determined by monitoring of the oxygen consumption. For the oxidation of the high redox potential (>700 mV) monophenolic substrates and almost all large substrates, such as phenolic dyes and lignans, the redox potential difference between the enzyme and the substrate (ΔE) played the defining role. For the low redox potential monophenolic substrates, ΔE did not directly influence the laccase activity. Also, in the special cases, the structure of the large substrates, such as dyes and lignans, as well as some structural features of the laccases (flexibility of the substrate-binding pocket loops and some amino acid residues in the key positions) affected the resulting catalytic efficiency. Full article
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Open AccessFeature PaperEditor’s ChoiceArticle
Polystyrene-Supported Acyclic Diaminocarbene Palladium Complexes in Sonogashira Cross-Coupling: Stability vs. Catalytic Activity
Catalysts 2018, 8(4), 141; https://doi.org/10.3390/catal8040141 - 02 Apr 2018
Cited by 19
Abstract
Two types of immobilized on the amino-functionalized polystyrene-supported acyclic diaminocarbene palladium complexes (ADC-PdII) are investigated under Sonogashira cross-coupling conditions. Depending on substituents in the diaminocarbene fragment immobilized ADC-PdII, systems are found to have different catalytic activity and stability regarding [...] Read more.
Two types of immobilized on the amino-functionalized polystyrene-supported acyclic diaminocarbene palladium complexes (ADC-PdII) are investigated under Sonogashira cross-coupling conditions. Depending on substituents in the diaminocarbene fragment immobilized ADC-PdII, systems are found to have different catalytic activity and stability regarding Pd-leaching. PdII-diaminocarbenes possessing protons at both nitrogen atoms smoothly decompose into Pd0-containing species providing a catalytic “cocktail system” with high activity and ability to reuse within nine runs. Polymer-supported palladium (II) complex bearing NBn–Ccarbene–NH-moiety exhibits greater stability while noticeably lower activity under Sonogashira cross-coupling. Four molecular ADC-PdII complexes are also synthesized and investigated with the aim of confirming proposed base-promoted pathway of ADC-PdII conversion through carbodiimide into an active Pd0 forms. Full article
(This article belongs to the Special Issue Solid-Supported Reagents in Palladium-Catalyzed Transformations)
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Open AccessEditor’s ChoiceArticle
Investigation of Iron Vanadates for Simultaneous Carbon Soot Abatement and NH3-SCR
Catalysts 2018, 8(4), 130; https://doi.org/10.3390/catal8040130 - 26 Mar 2018
Cited by 5
Abstract
FeVO4 and Fe0.5Er0.5VO4 were prepared and loaded over standard Selective Catalytic Reduction (SCR) supports based on TiO2-WO3-SiO2 (TWS) and redox active supports like CeO2 and CeZrO2 with the aim of [...] Read more.
FeVO4 and Fe0.5Er0.5VO4 were prepared and loaded over standard Selective Catalytic Reduction (SCR) supports based on TiO2-WO3-SiO2 (TWS) and redox active supports like CeO2 and CeZrO2 with the aim of finding a suitable formulation for simultaneous soot abatement and NH3-SCR and to understand the level of interaction between the two reactions. A suitable bi-functional material was identified in the composition FeVO4/CeZrO2 where an SCR active component is added over a redox active support, to increase carbon oxidation properties. The influence of the presence of ammonia in soot oxidation and the effect of the presence of soot on SCR reaction have been addressed. It is found that the addition of NO and NO/NH3 mixtures decreases at different levels the oxidation temperature of carbon soot, while the presence of carbon adversely affects the NH3-SCR reaction by increasing the oxidation of NH3 to NO, thus lowering the NO removal efficiency. Full article
(This article belongs to the Special Issue Selective Catalytic Reduction of NOx)
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Open AccessEditor’s ChoiceArticle
Liquid-Phase Hydrodeoxygenation of Guaiacol over Mo2C Supported on Commercial CNF. Effects of Operating Conditions on Conversion and Product Selectivity
Catalysts 2018, 8(4), 127; https://doi.org/10.3390/catal8040127 - 22 Mar 2018
Cited by 20
Abstract
In this work, a Mo2C catalyst that was supported on commercial carbon nanofibers (CNF) was synthetized and tested in the hydrodeoxygenation (HDO) of guaiacol. The effects of operating conditions (temperature and pressure) and reaction time (2 and 4 h) on the [...] Read more.
In this work, a Mo2C catalyst that was supported on commercial carbon nanofibers (CNF) was synthetized and tested in the hydrodeoxygenation (HDO) of guaiacol. The effects of operating conditions (temperature and pressure) and reaction time (2 and 4 h) on the conversion of guaiacol and products selectivity were studied. The major reaction products were cresol and phenol, followed by xylenols and toluene. The use of more severe operating conditions during the HDO of guaiacol caused a diversification in the reaction pathways, and consequently in the selectivity to products. The formation of phenol may have occurred by demethylation of guaiacol, followed by dehydroxylation of catechol, together with other reaction pathways, including direct guaiacol demethoxylation, and demethylation of cresols. X-ray diffraction (XRD) analysis of spent catalysts did not reveal any significant changes as compared to the fresh catalyst. Full article
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Open AccessFeature PaperEditor’s ChoiceArticle
Use of Lactobacillus rhamnosus (ATCC 53103) as Whole-Cell Biocatalyst for the Regio- and Stereoselective Hydration of Oleic, Linoleic, and Linolenic Acid
Catalysts 2018, 8(3), 109; https://doi.org/10.3390/catal8030109 - 09 Mar 2018
Cited by 10
Abstract
Natural hydroxy fatty acids are relevant starting materials for the production of a number of industrial fine chemicals, such as different high-value flavour ingredients. Only a few of the latter hydroxy acid derivatives are available on a large scale. Therefore, their preparation by [...] Read more.
Natural hydroxy fatty acids are relevant starting materials for the production of a number of industrial fine chemicals, such as different high-value flavour ingredients. Only a few of the latter hydroxy acid derivatives are available on a large scale. Therefore, their preparation by microbial hydration of unsaturated fatty acids, affordable from vegetable oils, is a new biotechnological challenge. In this study, we describe the use of the probiotic bacterium Lactobacillus rhamnosus (ATCC 53103) as whole-cell biocatalyst for the hydration of the most common unsaturated octadecanoic acids, namely oleic acid, linoleic acid, and linolenic acid. We discovered that the addition of the latter fatty acids to an anaerobic colture of the latter strain, during the early stage of its exponential growth, allows the production of the corresponding mono-hydroxy derivatives. In these experimental conditions, the hydration reaction proceeds with high regio- and stereoselectivity. Only 10-hydroxy derivatives were formed and the resulting (R)-10-hydroxystearic acid, (S)-(12Z)-10-hydroxy-octadecenoic acid, and (S)-(12Z,15Z)-10-hydroxy-octadecadienoic acid were obtained in very high enantiomeric purity (ee > 95%). Although overall conversions usually do not exceed 50% yield, our biotransformation protocol is stereoselective, scalable, and holds preparative significance. Full article
(This article belongs to the Special Issue Enzyme-Mediated Stereoselective Synthesis)
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Open AccessFeature PaperEditor’s ChoiceArticle
New Trendy Magnetic C-Scorpionate Iron Catalyst and Its Performance towards Cyclohexane Oxidation
Catalysts 2018, 8(2), 69; https://doi.org/10.3390/catal8020069 - 08 Feb 2018
Cited by 11
Abstract
For the first time, a magnetic C-scorpionate catalyst was prepared from the iron(II) complex [FeCl23-HC(pz)3}] (pz = pyrazol-1-yl) and ferrite, using the sustainable mechanochemical synthetic procedure. Its catalytic activity for the cyclohexane oxidation with tert-butyl hydroperoxide [...] Read more.
For the first time, a magnetic C-scorpionate catalyst was prepared from the iron(II) complex [FeCl23-HC(pz)3}] (pz = pyrazol-1-yl) and ferrite, using the sustainable mechanochemical synthetic procedure. Its catalytic activity for the cyclohexane oxidation with tert-butyl hydroperoxide (TBHP) was evaluated in different conditions, namely under microwave irradiation and under the effect of an external magnetic field. The use of such magnetic conditions significantly shifted the catalyst alcohol/ketone selectivity, thus revealing a promising, easy new protocol for tuning selectivity in important catalytic processes. Full article
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Open AccessEditor’s ChoiceArticle
1,3-Diene Polymerization Mediated by Homoleptic Tetramethylaluminates of the Rare-Earth Metals
Catalysts 2018, 8(2), 61; https://doi.org/10.3390/catal8020061 - 03 Feb 2018
Cited by 10
Abstract
During the past two decades homoleptic tetramethylaluminates of the trivalent rare-earth metals, Ln(AlMe4)3, have emerged as useful components for efficient catalyst design in the field of 1,3-diene polymerization. Previous work had focused on isoprene polymerization applying Ln(AlMe4) [...] Read more.
During the past two decades homoleptic tetramethylaluminates of the trivalent rare-earth metals, Ln(AlMe4)3, have emerged as useful components for efficient catalyst design in the field of 1,3-diene polymerization. Previous work had focused on isoprene polymerization applying Ln(AlMe4)3 precatalysts with Ln = La, Ce, Pr, Nd, Gd and Y, in the presence of Et2AlCl as an activator. Polymerizations employing Ln(AlMe4)3 with Ln = La, Y and Nd along with borate/borane co-catalysts [Ph3C][B(C6F5)4], [PhNMe2H][B(C6F5)4] and [B(C6F5)3] were mainly investigated for reasons of comparison with ancillary ligand-supported systems (cf. half-sandwich complexes). The present study investigates into a total of eleven rare-earth elements, namely Ln = La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Y, Er and Lu. A full overview on the polymerization behavior of Ln(AlMe4)3 in the presence of perfluorinated borate/borane cocatalysts and R2AlCl-type activators (R = Me, Et) is provided, probing the monomers isoprene and 1,3-butadiene (and preliminary ethylene). Virtually complete cis-1,4-selectivities are obtained for several catalyst/cocatalyst combinations (e.g., Gd(AlMe4)3/Me2AlCl, >99.9%). Insights into the ‘black box’ of active species are obtained by indirect observations via screening of pre-reaction time and cocatalyst concentration. The microstructure of the polydienes is investigated by combined 1H/13C NMR and ATR-IR spectroscopies. Furthermore, the reaction of [LuMe6(Li(thf)x)3] with AlMe3 has been applied as a new strategy for the efficient synthesis of Lu(AlMe4)3. The solid-state structures of Gd(AlMe4)3 and Tb(AlMe4)3 are reported. Full article
(This article belongs to the Special Issue Catalysts for the Controlled Polymerization of Conjugated Dienes)
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Open AccessFeature PaperEditor’s ChoiceCommunication
Whole-Cell Biocatalyst for Chemoenzymatic Total Synthesis of Rivastigmine
Catalysts 2018, 8(2), 55; https://doi.org/10.3390/catal8020055 - 31 Jan 2018
Cited by 28
Abstract
Biocatalytic processes are increasingly playing a key role in the development of sustainable asymmetric syntheses, which are central to pharmaceutical companies for the production of chiral enantiopure drugs. This work describes a simple and economically viable chemoenzymatic process for the production of ( [...] Read more.
Biocatalytic processes are increasingly playing a key role in the development of sustainable asymmetric syntheses, which are central to pharmaceutical companies for the production of chiral enantiopure drugs. This work describes a simple and economically viable chemoenzymatic process for the production of (S)-rivastigmine, which is an important drug for the treatment of mild to moderate dementia of the Alzheimer’s type. The described protocol involves the R-regioselective bioreduction of an aromatic ketone by Lactobacillus reuteri DSM 20016 whole cells in phosphate buffered saline (PBS) (37 °C, 24 h) as a key step. Biocatalytic performance of baker’s yeast whole cells in water and in aqueous eutectic mixtures have been evaluated and discussed as well. The route is scalable, environmentally friendly, and the target drug is obtained via four steps in overall 78% yield and 98% ee. Full article
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Open AccessEditor’s ChoiceArticle
Genetically Fused T4L Acts as a Shield in Covalent Enzyme Immobilisation Enhancing the Rescued Activity
Catalysts 2018, 8(1), 40; https://doi.org/10.3390/catal8010040 - 20 Jan 2018
Cited by 7
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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Open AccessEditor’s ChoiceArticle
“Deceived” Concentrated Immobilized Cells as Biocatalyst for Intensive Bacterial Cellulose Production from Various Sources
Catalysts 2018, 8(1), 33; https://doi.org/10.3390/catal8010033 - 18 Jan 2018
Cited by 15
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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Open AccessFeature PaperEditor’s ChoiceCommunication
Relationships between Substrate Promiscuity and Chiral Selectivity of Esterases from Phylogenetically and Environmentally Diverse Microorganisms
Catalysts 2018, 8(1), 10; https://doi.org/10.3390/catal8010010 - 05 Jan 2018
Cited by 5
Abstract
Substrate specificity and selectivity of a biocatalyst are determined by the protein sequence and structure of its active site. Finding versatile biocatalysts acting against multiple substrates while at the same time being chiral selective is of interest for the pharmaceutical and chemical industry. [...] Read more.
Substrate specificity and selectivity of a biocatalyst are determined by the protein sequence and structure of its active site. Finding versatile biocatalysts acting against multiple substrates while at the same time being chiral selective is of interest for the pharmaceutical and chemical industry. However, the relationships between these two properties in natural microbial enzymes remain underexplored. Here, we performed an experimental analysis of substrate promiscuity and chiral selectivity in a set of 145 purified esterases from phylogenetically and environmentally diverse microorganisms, which were assayed against 96 diverse esters, 20 of which were enantiomers. Our results revealed a negative correlation between substrate promiscuity and chiral selectivity in the evaluated enzymes. Esterases displaying prominent substrate promiscuity and large catalytic environments are characterized by low chiral selectivity, a feature that has limited commercial value. Although a low level of substrate promiscuity does not guarantee high chiral selectivity, the probability that esterases with smaller active sites possess chiral selectivity factors of interest for industry (>25) is significantly higher than for promiscuous enzymes. Together, the present study unambiguously demonstrates that promiscuous and selective esterases appear to be rare in nature and that substrate promiscuity can be used as an indicator of the chiral selectivity level of esterases, and vice versa. Full article
(This article belongs to the Special Issue Biocatalysis and Biotransformations)
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Review

Jump to: Research

Open AccessEditor’s ChoiceReview
Biocatalysis as Useful Tool in Asymmetric Synthesis: An Assessment of Recently Granted Patents (2014–2019)
Catalysts 2019, 9(10), 802; https://doi.org/10.3390/catal9100802 - 25 Sep 2019
Cited by 25
Abstract
The broad interdisciplinary nature of biocatalysis fosters innovation, as different technical fields are interconnected and synergized. A way to depict that innovation is by conducting a survey on patent activities. This paper analyses the intellectual property activities of the last five years (2014–2019) [...] Read more.
The broad interdisciplinary nature of biocatalysis fosters innovation, as different technical fields are interconnected and synergized. A way to depict that innovation is by conducting a survey on patent activities. This paper analyses the intellectual property activities of the last five years (2014–2019) with a specific focus on biocatalysis applied to asymmetric synthesis. Furthermore, to reflect the inventive and innovative steps, only patents that were granted during that period are considered. Patent searches using several keywords (e.g., enzyme names) have been conducted by using several patent engine servers (e.g., Espacenet, SciFinder, Google Patents), with focus on granted patents during the period 2014–2019. Around 200 granted patents have been identified, covering all enzyme types. The inventive pattern focuses on the protection of novel protein sequences, as well as on new substrates. In some other cases, combined processes, multi-step enzymatic reactions, as well as process conditions are the innovative basis. Both industries and academic groups are active in patenting. As a conclusion of this survey, we can assert that biocatalysis is increasingly recognized as a useful tool for asymmetric synthesis and being considered as an innovative option to build IP and protect synthetic routes. Full article
(This article belongs to the Special Issue Biocatalysis: Chemical Biosynthesis)
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Open AccessFeature PaperEditor’s ChoiceReview
Recent Advances in Catalytic Hydrogenation of Furfural
Catalysts 2019, 9(10), 796; https://doi.org/10.3390/catal9100796 - 24 Sep 2019
Cited by 38
Abstract
Furfural has been considered as one of the most promising platform molecules directly derived from biomass. The hydrogenation of furfural is one of the most versatile reactions to upgrade furanic components to biofuels. For instance, it can lead to plenty of downstream products, [...] Read more.
Furfural has been considered as one of the most promising platform molecules directly derived from biomass. The hydrogenation of furfural is one of the most versatile reactions to upgrade furanic components to biofuels. For instance, it can lead to plenty of downstream products, such as (tetrahydro)furfuryl alcohol, 2-methyl(tetrahydro)furan, lactones, levulinates, cyclopentanone(l), or diols, etc. The aim of this review is to discuss recent advances in the catalytic hydrogenation of furfural towards (tetrahydro)furfuryl alcohol and 2-methyl(tetrahydro)furan in terms of different non-noble metal and noble metal catalytic systems. Reaction mechanisms that are related to the different catalytic materials and reaction conditions are properly discussed. Selective hydrogenation of furfural could be modified not only by varying the types of catalyst (nature of metal, support, and preparation method) and reaction conditions, but also by altering the reaction regime, namely from batch to continuous flow. In any case, furfural catalytic hydrogenation is an open research line, which represents an attractive option for biomass valorization towards valuable chemicals and fuels. Full article
(This article belongs to the Section Biomass Catalysis)
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Open AccessFeature PaperEditor’s ChoiceReview
PdI2-Based Catalysis for Carbonylation Reactions: A Personal Account
Catalysts 2019, 9(7), 610; https://doi.org/10.3390/catal9070610 - 18 Jul 2019
Cited by 23
Abstract
In this account, we review our efforts in the field of carbonylation reactions promoted by palladium iodide-based catalysts, which have proven to be particularly efficient in diverse kinds of carbonylation processes (oxidative carbonylations as well as additive and substitutive carbonylations). Particularly in the [...] Read more.
In this account, we review our efforts in the field of carbonylation reactions promoted by palladium iodide-based catalysts, which have proven to be particularly efficient in diverse kinds of carbonylation processes (oxidative carbonylations as well as additive and substitutive carbonylations). Particularly in the case of oxidative carbonylations, more emphasis has been given to the most recent results and applications. Full article
(This article belongs to the Special Issue Catalytic Carbonylation Reactions)
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European Regulatory Framework and Particulate Matter Emissions of Gasoline Light-Duty Vehicles: A Review
Catalysts 2019, 9(7), 586; https://doi.org/10.3390/catal9070586 - 04 Jul 2019
Cited by 30
Abstract
The particulate matter (PM) emissions of gasoline vehicles were much lower than those of diesel vehicles until the introduction of diesel particulate filters (DPFs) in the early 2000s. At the same time, gasoline direct injection (GDI) engines started to become popular in the [...] Read more.
The particulate matter (PM) emissions of gasoline vehicles were much lower than those of diesel vehicles until the introduction of diesel particulate filters (DPFs) in the early 2000s. At the same time, gasoline direct injection (GDI) engines started to become popular in the market due to their improved efficiency over port fuel injection (PFI) ones. However, the PM mass and number emissions of GDI vehicles were higher than their PFI counterparts and diesel ones equipped with DPFs. Stringent PM mass levels and the introduction of particle number limits for GDI vehicles in the European Union (EU) resulted in significant PM reductions. The EU requirement to fulfill the proposed limits on the road resulted to the introduction of gasoline particulate filters (GPFs) in EU GDI models. This review summarizes the evolution of PM mass emissions from gasoline vehicles placed in the market from early 1990s until 2019 in different parts of the world. The analysis then extends to total and nonvolatile particle number emissions. Care is given to reveal the impact of ambient temperature on emission levels. The discussion tries to provide scientific input to the following policy-relevant questions. Whether particle number limits should be extended to gasoline PFI vehicles, whether the lower limit of 23 nm for particle number measurements should be decreased to 10 nm, and whether low ambient temperature tests for PM should be included. Full article
(This article belongs to the Special Issue Catalytic Diesel and Gasoline Particulate Filters)
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Open AccessEditor’s ChoiceReview
Base Metal Catalysts for Deoxygenative Reduction of Amides to Amines
Catalysts 2019, 9(6), 490; https://doi.org/10.3390/catal9060490 - 28 May 2019
Cited by 14
Abstract
The development of efficient methodologies for production of amines attracts significant attention from synthetic chemists, because amines serve as essential building blocks in the synthesis of many pharmaceuticals, natural products, and agrochemicals. In this regard, deoxygenative reduction of amides to amines by means [...] Read more.
The development of efficient methodologies for production of amines attracts significant attention from synthetic chemists, because amines serve as essential building blocks in the synthesis of many pharmaceuticals, natural products, and agrochemicals. In this regard, deoxygenative reduction of amides to amines by means of transition-metal-catalyzed hydrogenation, hydrosilylation, and hydroboration reactions represents an attractive alternative to conventional wasteful techniques based on stoichiometric reductions of the corresponding amides and imines, and reductive amination of aldehydes with metal hydride reagents. The relatively low electrophilicity of the amide carbonyl group makes this transformation more challenging compared to reduction of other carbonyl compounds, and the majority of the reported catalytic systems employ precious metals such as platinum, rhodium, iridium, and ruthenium. Despite the application of more abundant and environmentally benign base metal (Mn, Fe, Co, and Ni) complexes for deoxygenative reduction of amides have been developed to a lesser extent, such catalytic systems are of great importance. This review is focused on the current achievements in the base-metal-catalyzed deoxygenative hydrogenation, hydrosilylation, and hydroboration of amides to amines. Special attention is paid to the design of base metal catalysts and the mechanisms of such catalytic transformations. Full article
(This article belongs to the Special Issue Coordination Chemistry and Catalysis)
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Mechanistic Insights into Photodegradation of Organic Dyes Using Heterostructure Photocatalysts
Catalysts 2019, 9(5), 430; https://doi.org/10.3390/catal9050430 - 09 May 2019
Cited by 144
Abstract
Due to its low cost, environmentally friendly process, and lack of secondary contamination, the photodegradation of dyes is regarded as a promising technology for industrial wastewater treatment. This technology demonstrates the light-enhanced generation of charge carriers and reactive radicals that non-selectively degrade various [...] Read more.
Due to its low cost, environmentally friendly process, and lack of secondary contamination, the photodegradation of dyes is regarded as a promising technology for industrial wastewater treatment. This technology demonstrates the light-enhanced generation of charge carriers and reactive radicals that non-selectively degrade various organic dyes into water, CO2, and other organic compounds via direct photodegradation or a sensitization-mediated degradation process. The overall efficiency of the photocatalysis system is closely dependent upon operational parameters that govern the adsorption and photodegradation of dye molecules, including the initial dye concentration, pH of the solution, temperature of the reaction medium, and light intensity. Additionally, the charge-carrier properties of the photocatalyst strongly affect the generation of reactive species in the heterogeneous photodegradation and thereby dictate the photodegradation efficiency. Herein, this comprehensive review discusses the pseudo kinetics and mechanisms of the photodegradation reactions. The operational factors affecting the photodegradation of either cationic or anionic dye molecules, as well as the charge-carrier properties of the photocatalyst, are also fully explored. By further analyzing past works to clarify key active species for photodegradation reactions and optimal conditions, this review provides helpful guidelines that can be applied to foster the development of efficient photodegradation systems. Full article
(This article belongs to the Special Issue Sustainable Applications in Surface Chemistry and Catalysis)
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Open AccessEditor’s ChoiceReview
A Review of the Enhancement of Bio-Hydrogen Generation by Chemicals Addition
Catalysts 2019, 9(4), 353; https://doi.org/10.3390/catal9040353 - 11 Apr 2019
Cited by 18
Abstract
Bio-hydrogen production (BHP) produced from renewable bio-resources is an attractive route for green energy production, due to its compelling advantages of relative high efficiency, cost-effectiveness, and lower ecological impact. This study reviewed different BHP pathways, and the most important enzymes involved in these [...] Read more.
Bio-hydrogen production (BHP) produced from renewable bio-resources is an attractive route for green energy production, due to its compelling advantages of relative high efficiency, cost-effectiveness, and lower ecological impact. This study reviewed different BHP pathways, and the most important enzymes involved in these pathways, to identify technological gaps and effective approaches for process intensification in industrial applications. Among the various approaches reviewed in this study, a particular focus was set on the latest methods of chemicals/metal addition for improving hydrogen generation during dark fermentation (DF) processes; the up-to-date findings of different chemicals/metal addition methods have been quantitatively evaluated and thoroughly compared in this paper. A new efficiency evaluation criterion is also proposed, allowing different BHP processes to be compared with greater simplicity and validity. Full article
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Open AccessFeature PaperEditor’s ChoiceReview
A Review of Low Temperature NH3-SCR for Removal of NOx
Catalysts 2019, 9(4), 349; https://doi.org/10.3390/catal9040349 - 10 Apr 2019
Cited by 68
Abstract
The importance of the low-temperature selective catalytic reduction (LT-SCR) of NOx by NH3 is increasing due to the recent severe pollution regulations being imposed around the world. Supported and mixed transition metal oxides have been widely investigated for LT-SCR technology. However, [...] Read more.
The importance of the low-temperature selective catalytic reduction (LT-SCR) of NOx by NH3 is increasing due to the recent severe pollution regulations being imposed around the world. Supported and mixed transition metal oxides have been widely investigated for LT-SCR technology. However, these catalytic materials have some drawbacks, especially in terms of catalyst poisoning by H2O or/and SO2. Hence, the development of catalysts for the LT-SCR process is still under active investigation throughout seeking better performance. Extensive research efforts have been made to develop new advanced materials for this technology. This article critically reviews the recent research progress on supported transition and mixed transition metal oxide catalysts for the LT-SCR reaction. The review covered the description of the influence of operating conditions and promoters on the LT-SCR performance. The reaction mechanism, reaction intermediates, and active sites are also discussed in detail using isotopic labelling and in situ FT-IR studies. Full article
(This article belongs to the Special Issue Emissions Control Catalysis)
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Open AccessEditor’s ChoiceReview
Hybrid Catalysts for CO2 Conversion into Cyclic Carbonates
Catalysts 2019, 9(4), 325; https://doi.org/10.3390/catal9040325 - 02 Apr 2019
Cited by 23
Abstract
The conversion of carbon dioxide into valuable chemicals such as cyclic carbonates is an appealing topic for the scientific community due to the possibility of valorizing waste into an inexpensive, available, nontoxic, and renewable carbon feedstock. In this regard, last-generation heterogeneous catalysts are [...] Read more.
The conversion of carbon dioxide into valuable chemicals such as cyclic carbonates is an appealing topic for the scientific community due to the possibility of valorizing waste into an inexpensive, available, nontoxic, and renewable carbon feedstock. In this regard, last-generation heterogeneous catalysts are of great interest owing to their high catalytic activity, robustness, and easy recovery and recycling. In the present review, recent advances on CO2 cycloaddition to epoxide mediated by hybrid catalysts through organometallic or organo-catalytic species supported onto silica-, nanocarbon-, and metal–organic framework (MOF)-based heterogeneous materials, are highlighted and discussed. Full article
(This article belongs to the Special Issue Sustainable Applications in Surface Chemistry and Catalysis)
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Transition Metal Phosphides for the Catalytic Hydrodeoxygenation of Waste Oils into Green Diesel
Catalysts 2019, 9(3), 293; https://doi.org/10.3390/catal9030293 - 22 Mar 2019
Cited by 23
Abstract
Recently, catalysts based on transition metal phosphides (TMPs) have attracted increasing interest for their use in hydrodeoxygenation (HDO) processes destined to synthesize biofuels (green or renewable diesel) from waste vegetable oils and fats (known as hydrotreated vegetable oils (HVO)), or from bio-oils. This [...] Read more.
Recently, catalysts based on transition metal phosphides (TMPs) have attracted increasing interest for their use in hydrodeoxygenation (HDO) processes destined to synthesize biofuels (green or renewable diesel) from waste vegetable oils and fats (known as hydrotreated vegetable oils (HVO)), or from bio-oils. This fossil-free diesel product is produced completely from renewable raw materials with exceptional quality. These efficient HDO catalysts present electronic properties similar to noble metals, are cost-efficient, and are more stable and resistant to the presence of water than other classical catalytic formulations used for hydrotreatment reactions based on transition metal sulfides, but they do not require the continuous supply of a sulfide source. TMPs develop a bifunctional character (metallic and acidic) and present tunable catalytic properties related to the metal type, phosphorous-metal ratio, support nature, texture properties, and so on. Here, the recent progress in TMP-based catalysts for HDO of waste oils is reviewed. First, the use of TMPs in catalysis is addressed; then, the general aspects of green diesel (from bio-oils or from waste vegetable oils and fats) production by HDO of nonedible oil compounds are presented; and, finally, we attempt to describe the main advances in the development of catalysts based on TMPs for HDO, with an emphasis on the influence of the nature of active phases and effects of phosphorous, promoters, and preparation methods on reactivity. Full article
(This article belongs to the Special Issue Development of Catalysts for Green Diesel Production)
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Reactor Selection for Effective Continuous Biocatalytic Production of Pharmaceuticals
Catalysts 2019, 9(3), 262; https://doi.org/10.3390/catal9030262 - 14 Mar 2019
Cited by 22
Abstract
Enzyme catalyzed reactions are rapidly becoming an invaluable tool for the synthesis of many active pharmaceutical ingredients. These reactions are commonly performed in batch, but continuous biocatalysis is gaining interest in industry because it would allow seamless integration of chemical and enzymatic reaction [...] Read more.
Enzyme catalyzed reactions are rapidly becoming an invaluable tool for the synthesis of many active pharmaceutical ingredients. These reactions are commonly performed in batch, but continuous biocatalysis is gaining interest in industry because it would allow seamless integration of chemical and enzymatic reaction steps. However, because this is an emerging field, little attention has been paid towards the suitability of different reactor types for continuous biocatalytic reactions. Two types of continuous flow reactor are possible: continuous stirred tank and continuous plug-flow. These reactor types differ in a number of ways, but in this contribution, we focus on residence time distribution and how enzyme kinetics are affected by the unique mass balance of each reactor. For the first time, we present a tool to facilitate reactor selection for continuous biocatalytic production of pharmaceuticals. From this analysis, it was found that plug-flow reactors should generally be the system of choice. However, there are particular cases where they may need to be coupled with a continuous stirred tank reactor or replaced entirely by a series of continuous stirred tank reactors, which can approximate plug-flow behavior. This systematic approach should accelerate the implementation of biocatalysis for continuous pharmaceutical production. Full article
(This article belongs to the Special Issue Flow Biocatalysis)
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