Catalysts

14 pages, 2454 KiB

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

by Nathalia S. Rios, Sara Arana-Peña, Carmen Mendez-Sanchez, Claudia Ortiz, Luciana R. B. Gonçalves and Roberto Fernandez-Lafuente

Catalysts 2019, 9(5), 487; https://doi.org/10.3390/catal9050487 - 27 May 2019

Cited by 37 | Viewed by 4835

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

(This article belongs to the Special Issue Advances in the Design and Characterization of Heterogeneous Biocatalysts)

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19 pages, 7850 KiB

Open AccessArticle

Facile Mechanochemical Synthesis of Nickel/Graphene Oxide Nanocomposites with Unique and Tunable Morphology: Applications in Heterogeneous Catalysis and Supercapacitors

by Mayakrishnan Gopiraman, Somasundaram Saravanamoorthy, Dian Deng, Andivelu Ilangovan, Ick Soo Kim and Ill Min Chung

Catalysts 2019, 9(5), 486; https://doi.org/10.3390/catal9050486 - 27 May 2019

Cited by 27 | Viewed by 5036

Abstract

In this study, a very simple and highly effective mechanochemical preparation method was developed for the preparation of Ni nanoparticles supported graphene oxide (GO) nanocomposites (Ni/GO, where Ni is a composition of Ni(OH)₂, NiOOH, NiO, Ni₂O₃ and NiO [...] Read more.

In this study, a very simple and highly effective mechanochemical preparation method was developed for the preparation of Ni nanoparticles supported graphene oxide (GO) nanocomposites (Ni/GO, where Ni is a composition of Ni(OH)₂, NiOOH, NiO, Ni₂O₃ and NiO₂), 3 wt% NiO/GO (Ni/GO-1) and 8 wt% NiO/GO(Ni/GO-2). The developed method is not only very simple and efficient, but also, the morphology of Ni/GO nanocomposites can be tuned by simply varying the metal loading. Morphology and specific surface area of the resultant Ni/GO nanocomposites were investigated by mean of AFM, HR-TEM and BET. Chemical sate and factual content of Ni in Ni/GO-1 and Ni/GO-2, and the presence of defective sites in Ni-nanocomposites were investigated in detail. To our delight, the prepared Ni/GO-2 demonstrated superior catalytic activity toward the reduction of 2- and 4-nitrophenol in water with high rate constant (kapp) of 35.4 × 10⁻³ s⁻¹. To the best of our knowledge, this is the best efficient Ni-based graphene nanocomposites for the reduction of 2- and 4-NP reported to date. The Ni/GO-1 and Ni/GO-2 demonstrated an excellent reusability; no loss in its catalytic activity was noticed, even after 10th cycle. Surprisingly the Ni/GO-2 as electrode material exhibited an excellent specific capacitance of 461 F/g in 6 M KOH at a scan rate of 5 mV. Moreover, the Ni/GO nanocomposites were found to possess poor electrical resistance and high stability (no significant change in the specific capacitance even after 1000 cycles). Full article

(This article belongs to the Special Issue Multifunctional Heterogeneous Catalysis)

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19 pages, 2663 KiB

Open AccessArticle

Dimethyl Ether to Olefins over Modified ZSM-5 Based Catalysts Stabilized by Hydrothermal Treatment

by Maria Magomedova, Ekaterina Galanova, Ilya Davidov, Mikhail Afokin and Anton Maximov

Catalysts 2019, 9(5), 485; https://doi.org/10.3390/catal9050485 - 27 May 2019

Cited by 17 | Viewed by 6036

Abstract

The reaction of dimethyl ether to olefin over HZSM-5/Al₂O₃ catalysts modified by Zr and Mg and stabilized by hydrothermal treatment has been studied. Regardless of the introduction method and the nature of the metal, the dependence of the key products [...] Read more.

The reaction of dimethyl ether to olefin over HZSM-5/Al₂O₃ catalysts modified by Zr and Mg and stabilized by hydrothermal treatment has been studied. Regardless of the introduction method and the nature of the metal, the dependence of the key products selectivity on X(DME) over hydrothermally treated steady-state catalysts does not change, and the experimental points are described by the same curves. Metal introduction and the corresponding changes in the acid sites distribution do not change the ratio of main reaction rates, only the absolute values of the formation rate of the products are changed. Zr doping leads to the greatest activity in the DME conversion due to an equable decrease in the total acidity of the sample. On the other hand, the Mg-modified sample has a higher amount of weak acid sites, which reduces activity. At low DME conversion, methanol is one of the primary reaction products which formed from DME simultaneously with propylene in alkene cycle. At high DME conversion, the methanol acts as a main reagent which leads to ethylene formation in the arene cycle. Based on the results, the role of the metal in the reaction chemistry is considered and the mechanism of product formation from DME over steady-state catalyst is proposed, which describes both the participation of DME and the methanol produced. Full article

(This article belongs to the Section Catalytic Materials)

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11 pages, 1368 KiB

Open AccessArticle

Combining Planar Laser-Induced Fluorescence with Stagnation Point Flows for Small Single-Crystal Model Catalysts: CO Oxidation on a Pd(100)

by Jianfeng Zhou, Sebastian Matera, Sebastian Pfaff, Sara Blomberg, Edvin Lundgren and Johan Zetterberg

Catalysts 2019, 9(5), 484; https://doi.org/10.3390/catal9050484 - 25 May 2019

Cited by 5 | Viewed by 3281

Abstract

A stagnation flow reactor has been designed and characterized for both experimental and modeling studies of single-crystal model catalysts in heterogeneous catalysis. Using CO oxidation over a Pd(100) single crystal as a showcase, we have employed planar laser-induced fluorescence (PLIF) to visualize the [...] Read more.

A stagnation flow reactor has been designed and characterized for both experimental and modeling studies of single-crystal model catalysts in heterogeneous catalysis. Using CO oxidation over a Pd(100) single crystal as a showcase, we have employed planar laser-induced fluorescence (PLIF) to visualize the CO₂ distribution over the catalyst under reaction conditions and subsequently used the 2D spatially resolved gas phase data to characterize the stagnation flow reactor. From a comparison of the experimental data and the stagnation flow model, it was found that characteristic stagnation flow can be achieved with the reactor. Furthermore, the combined stagnation flow/PLIF/modeling approach makes it possible to estimate the turnover frequency (TOF) of the catalytic surface from the measured CO₂ concentration profiles above the surface and to predict the CO₂, CO and O₂ concentrations at the surface under reaction conditions. Full article

(This article belongs to the Special Issue Reactors and Models in Catalysis)

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17 pages, 5520 KiB

Open AccessArticle

Effect of Small Molecular Organic Acids on the Structure and Catalytic Performance of Sol–Gel Prepared Cobalt Cerium Oxides towards Toluene Combustion

by Jianmeng Chen, Junhong Lin, Jinghuan Chen and Jiade Wang

Catalysts 2019, 9(5), 483; https://doi.org/10.3390/catal9050483 - 24 May 2019

Cited by 7 | Viewed by 3584

Abstract

Cobalt cerium oxide catalysts with small molecular organic acids (SOAs) as chelating agents were prepared via the sol–gel method and investigated for the complete oxidation of toluene. Four kinds of natural SOAs, i.e. malic acid (MA), citric acid (CA), glycolic acid (GA), and [...] Read more.

Cobalt cerium oxide catalysts with small molecular organic acids (SOAs) as chelating agents were prepared via the sol–gel method and investigated for the complete oxidation of toluene. Four kinds of natural SOAs, i.e. malic acid (MA), citric acid (CA), glycolic acid (GA), and tartaric acid (TA), were selected. The effect of organic acids on the composition, structure, morphology and catalytic performance of metal oxides is discussed in details. The cobalt cerium oxides catalysts were characterized by various techniques, including TG–DSC, XRD, SEM–EDS, N₂–adsorption and desorption, XPS, and H₂–TPR analyses. The results show that the nature of organic acids influenced the hydrolysis, condensation and calcination processes, as well as strongly affected the textural and physicochemical properties of the metal oxides synthesized. The best catalytic activity was obtained with the CoCe–MA catalyst, and the toluene conversion reached 90% at 242 °C. This outstanding catalytic activity could be related to its textural, redox properties and unique surface compositions and oxidation states. In addition, the CoCe–MA catalyst also showed excellent stability in long–time activity test. Full article

(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)

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16 pages, 2855 KiB

Open AccessArticle

Esterification of Palm Fatty Acid Distillate for Biodiesel Production Catalyzed by Synthesized Kenaf Seed Cake-Based Sulfonated Catalyst

by Shehu-Ibrahim Akinfalabi, Umer Rashid, Thomas Yaw Choong Shean, Imededdine Arbi Nehdi, Hassen Mohamed Sbihi and Mohamed Mossad Gewik

Catalysts 2019, 9(5), 482; https://doi.org/10.3390/catal9050482 - 24 May 2019

Cited by 33 | Viewed by 4269

Abstract

Sulfonated kenaf seed cake (SO₃H-KSC) catalyst, was synthesized to aid biodiesel production from palm fatty acid distillate (PFAD). It was chemically activated with phosphoric acid for an impregnation period of 24 h in order to enhance the porosity and the specific [...] Read more.

Sulfonated kenaf seed cake (SO₃H-KSC) catalyst, was synthesized to aid biodiesel production from palm fatty acid distillate (PFAD). It was chemically activated with phosphoric acid for an impregnation period of 24 h in order to enhance the porosity and the specific surface area of kenaf seed cake (KSC). After the carbonization and sulfonation, the resultant catalyst was characterized with powder X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscope (FESEM), NH₃-temperature programmed desorption (NH₃-TPD) and thermogravimetric analysis (TGA). The SO₃H-KSC catalyst was amorphous in nature and had an acid density of 14.32 mmol/g, specific surface area of 365.63 m²/g, pore volume of 0.31 cm³/g and pore diameter of 2.89 nm. At optimum esterification conditions--reaction time 90 mins, temperature of 338 K, methanol:PFAD molar ratio of 10:1 and catalyst concentration of 2 wt.%—a free fatty acid (FFA) conversion of 98.7% and fatty acid methyl esters (FAME) yield of 97.9% was achieved. The synthesized SO₃H-KSC catalyst underwent five reaction cycles while maintaining a fatty acid methyl esters (FAME) yield and free fatty acid (FFA) conversion of >90%. Thus, the SO₃H-KSC catalyst was shown to be an excellent application of bio-based material as a precursor for catalyst synthesis for esterification of PFAD. Full article

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

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11 pages, 21942 KiB

Open AccessArticle

Fabrication of Hollow Silica Nanospheres with Ultra-High Acid Density for Efficient Heterogeneous Catalysis

by Xiaoli Zhang, Juan Wei and Xiaoming Zhang

Catalysts 2019, 9(5), 481; https://doi.org/10.3390/catal9050481 - 24 May 2019

Cited by 4 | Viewed by 3045

Abstract

Hollow silica nanospheres with ultra-high acid density were fabricated successfully via sulfonation of phenyl-functionalized hollow silica nanospheres, which were synthesized through a single micelle (F127 (EO₁₀₆PO₇₀EO₁₀₆))-templated method, with phenyltrimethoxysilane and tetramethoxysilane (TMOS) as silane precursors under neutral [...] Read more.

Hollow silica nanospheres with ultra-high acid density were fabricated successfully via sulfonation of phenyl-functionalized hollow silica nanospheres, which were synthesized through a single micelle (F127 (EO₁₀₆PO₇₀EO₁₀₆))-templated method, with phenyltrimethoxysilane and tetramethoxysilane (TMOS) as silane precursors under neutral conditions. The density of sulfonic acid reached as high as 1.97 mmol/g. The characterization results of ³¹P-NMR using triethylphosphine oxide as a probe molecule suggested that the acid strength of hybrid solid acids could be systematically tuned by tuning the content of sulfonic acid and higher acid density results in stronger acid strength. Attributed to the unique hollow structure and high-acid density, the sulfonic acid-functionalized hollow silica nanospheres exhibited good catalytic performance in the condensation reaction of benzaldehyde with ethylene glycol. Notably, this study found that the catalytic activity was significantly influenced by the acid density and the ultra-high acid loading was beneficial for the activity due to the enhanced acid strength. This novel solid-acid catalyst also showed good recyclability and could be reused for at least 11 runs. Full article

(This article belongs to the Section Catalytic Materials)

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12 pages, 4543 KiB

Open AccessCommunication

Mild Ammonia Synthesis over Ba-Promoted Ru/MPC Catalysts: Effects of the Ba/Ru Ratio and the Mesoporous Structure

by Masayasu Nishi, Shih-Yuan Chen and Hideyuki Takagi

Catalysts 2019, 9(5), 480; https://doi.org/10.3390/catal9050480 - 23 May 2019

Cited by 19 | Viewed by 4936

Abstract

A series of novel mesoporous carbon-supported, Ba-promoted, Ru catalysts with Ba/Ru ratios of 0.1–1.6 and a Ru loading of 10 wt% (denoted as 0.1–1.6Ba-10Ru/MPC) were prepared via stepwise impregnation of Ru and Ba precursors on the mesoporous carbon materials. The catalysts were applied [...] Read more.

A series of novel mesoporous carbon-supported, Ba-promoted, Ru catalysts with Ba/Ru ratios of 0.1–1.6 and a Ru loading of 10 wt% (denoted as 0.1–1.6Ba-10Ru/MPC) were prepared via stepwise impregnation of Ru and Ba precursors on the mesoporous carbon materials. The catalysts were applied to mild ammonia synthesis and compared to reference materials, including an analog of the prepared catalyst with a Ba/Ru ratio of 1.6 and a Ru loading of 10 wt% (denoted as 1.6Ba-10Ru/AC). Characterization by X-ray diffraction (XRD), nitrogen physisorption, and electronic microscopy revealed that the 0.1–1.6Ba-10Ru/MPC catalysts contained Ru particles (approximately 2 nm) that were well-dispersed on the mesoporous structure and nanostructured Ba(NO₃)₂ species. These species decomposed into amorphous BaO_x species, acting as a promoter on the metallic Ru particles forming catalytically active sites for ammonia synthesis. All the 0.1–1.6Ba-10Ru/MPC catalysts showed a synergistic effect of the active Ba and Ru species, which were stabilized in the mesoporous carbon framework with fast molecular diffusion and could effectively catalyze mild ammonia synthesis (280–450 °C and 0.99 MPa) even under intermittently variable conditions, particularly for those with Ba/Ru ratios of >0.5. In contrast, the 1.6Ba-10Ru/AC analog showed poor activity and stability for ammonia synthesis due to the sintering of Ba and Ru particles on the outer surface of the microporous carbon framework, resulting in low molecular diffusion and weak synergistic effect of the catalytically active sites. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate “Environmental Catalysis”—Trends & Outlook)

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13 pages, 6305 KiB

Open AccessArticle

Study on Nanofibrous Catalysts Prepared by Electrospinning for Methane Partial Oxidation

by Yuyao Ma, Yuxia Ma, Min Liu, Yang Chen, Xun Hu, Zhengmao Ye and Dehua Dong

Catalysts 2019, 9(5), 479; https://doi.org/10.3390/catal9050479 - 23 May 2019

Cited by 10 | Viewed by 3319

Abstract

Electrospinning is a simple and efficient technique for fabricating fibrous catalysts. The effects of preparation parameters on catalyst performance were investigated on fibrous Ni/Al₂O₃ catalysts. The catalyst prepared with H₂O/C₂H₅OH solvent showed higher catalytic [...] Read more.

Electrospinning is a simple and efficient technique for fabricating fibrous catalysts. The effects of preparation parameters on catalyst performance were investigated on fibrous Ni/Al₂O₃ catalysts. The catalyst prepared with H₂O/C₂H₅OH solvent showed higher catalytic activity than that with DMF/C₂H₅OH solvent because of the presence of NiO in the catalyst prepared with DMF/C₂H₅OH solvent. The metal ion content of the precursor also influences catalyst properties. In this work, the Ni/Al₂O₃ catalyst prepared with a solution containing the metal ion content of 30 wt % demonstrated the highest Ni dispersion and therefore the highest catalytic performance. Additionally, the Ni dispersion decreased as calcination temperature was enhanced from 700 to 900 °C due to the increased Ni particle sizes, which also caused a high reduction temperature and low catalytic activity in methane partial oxidation. Finally, the fibrous Ni/Al₂O₃ catalysts can achieve high syngas yields at high reaction temperatures and high gas flow rates. Full article

(This article belongs to the Special Issue Rational Design of Non-precious Metal Oxide Catalysts by Means of Advanced Synthetic and Promotional Routes)

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33 pages, 5611 KiB

Open AccessReview

Wastewater Treatment by Catalytic Wet Peroxidation Using Nano Gold-Based Catalysts: A Review

by Carmen S.D. Rodrigues, Ricardo M. Silva, Sónia A.C. Carabineiro, F.J. Maldonado-Hódar and Luís M. Madeira

Catalysts 2019, 9(5), 478; https://doi.org/10.3390/catal9050478 - 23 May 2019

Cited by 17 | Viewed by 5201

Abstract

Nowadays, there is an increasing interest in the development of promising, efficient, and environmentally friendly wastewater treatment technologies. Among them are the advanced oxidation processes (AOPs), in particular, catalytic wet peroxidation (CWPO), assisted or not by radiation. One of the challenges for the [...] Read more.

Nowadays, there is an increasing interest in the development of promising, efficient, and environmentally friendly wastewater treatment technologies. Among them are the advanced oxidation processes (AOPs), in particular, catalytic wet peroxidation (CWPO), assisted or not by radiation. One of the challenges for the industrial application of this process is the development of stable and efficient catalysts, without leaching of the metal to the aqueous phase during the treatment. Gold catalysts, in particular, have attracted much attention from researchers because they show these characteristics. Recently, numerous studies have been reported in the literature regarding the preparation of gold catalysts supported on various supports and testing their catalytic performance in the treatment of real wastewaters or model pollutants by CWPO. This review summarizes this research; the properties of such catalysts and their expected effects on the overall efficiency of the CWPO process, together with a description of the effect of operational variables (such as pH, temperature, oxidant concentration, catalyst, and gold content). In addition, an overview is given of the main technical issues of this process aiming at its industrial application, namely the possibility of using the catalyst in continuous flow reactors. Such considerations will provide useful information for a faster and more effective analysis and optimization of the CWPO process. Full article

(This article belongs to the Special Issue Trends in Catalytic Wet Peroxide Oxidation Processes)

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16 pages, 4148 KiB

Open AccessReview

Recent In Situ/Operando Spectroscopy Studies of Heterogeneous Catalysis with Reducible Metal Oxides as Supports

by Fei Wang, Jianzhun Jiang and Bin Wang

Catalysts 2019, 9(5), 477; https://doi.org/10.3390/catal9050477 - 23 May 2019

Cited by 12 | Viewed by 5166

Abstract

For heterogeneous catalysis, the metal catalysts supported on reducible metal oxides, especially CeO₂ and TiO₂, have long been a research focus because of their excellent catalytic performance in a variety of catalytic reactions. Detailed understanding of the promotion effect of [...] Read more.

For heterogeneous catalysis, the metal catalysts supported on reducible metal oxides, especially CeO₂ and TiO₂, have long been a research focus because of their excellent catalytic performance in a variety of catalytic reactions. Detailed understanding of the promotion effect of reducible metal oxides on catalytic reactions is beneficial to the rational design of new catalysts. The important catalytic roles of reducible metal oxides are attributed to their intimate interactions with the supported metals (e.g., strong metal-support interaction, electronic metal-support interaction) and unique support structures (e.g., oxygen vacancy, reversible valence change, surface hydroxyl). However, the structures of the catalysts and reaction mechanisms are strongly affected by environmental conditions. For this reason, in situ/operando spectroscopy studies under working conditions are necessary to obtain accurate information about the structure-activity relationship. In this review, the recent applications of the in situ/operando spectroscopy methodology on metal catalysts with reducible metal oxides as supports are summarized. Full article

(This article belongs to the Special Issue Spectroscopy in Catalysis)

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13 pages, 2879 KiB

Open AccessArticle

Tuning Sn-Cu Catalysis for Electrochemical Reduction of CO₂ on Partially Reduced Oxides SnOx-CuOx-Modified Cu Electrodes

by Qianwen Li, Mei Li, Shengbo Zhang, Xiao Liu, Xinli Zhu, Qingfeng Ge and Hua Wang

Catalysts 2019, 9(5), 476; https://doi.org/10.3390/catal9050476 - 22 May 2019

Cited by 31 | Viewed by 4993

Abstract

Copper-based bimetallic catalysts have been recently showing promising performance for the selective electrochemical reduction of CO₂. In this work, we successfully fabricated the partially reduced oxides SnOx, CuOx modified Cu foam electrode (A-Cu/SnO₂) through an electrodeposition-annealing-electroreduction approach. Notably, in [...] Read more.

Copper-based bimetallic catalysts have been recently showing promising performance for the selective electrochemical reduction of CO₂. In this work, we successfully fabricated the partially reduced oxides SnOx, CuOx modified Cu foam electrode (A-Cu/SnO₂) through an electrodeposition-annealing-electroreduction approach. Notably, in comparison with the control electrode (Cu/SnO₂) without undergoing annealing step, A-Cu/SnO₂ exhibits a significant enhancement in terms of CO₂ reduction activity and CO selectivity. By investigating the effect of the amount of the electrodeposited SnO₂, it is found that A-Cu/SnO₂ electrodes present the characteristic Sn-Cu synergistic catalysis with a feature of dominant CO formation (CO faradaic efficiency, 70~75%), the least HCOOH formation (HCOOH faradaic efficiency, <5%) and the remarkable inhibition of hydrogen evolution reaction. In contrast, Cu/SnO₂ electrodes exhibit a SnO₂ coverage-dependent catalysis—a shift from CO selectivity to HCOOH selectivity with the increasing deposited SnO₂ on Cu foam. The different catalytic performance between Cu/SnO₂ and A-Cu/SnO₂ might be attributed to the different content of Cu atoms in SnO₂ layer, which may affect the density of Cu-Sn interface on the surface. Our work provides a facile annealing-electroreduction strategy to modify the surface composition for understanding the metal effect towards CO₂ reduction activity and selectivity for bimetallic Cu-based electrocatalysts. Full article

(This article belongs to the Special Issue Catalytic Properties of Nanostructured Electrodic Materials)

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15 pages, 2967 KiB

Open AccessFeature PaperArticle

Ceria–Zirconia Mixed Metal Oxides Prepared via Mechanochemical Grinding of Carbonates for the Total Oxidation of Propane and Naphthalene

by Parag M. Shah, Joseph W. H. Burnett, David J. Morgan, Thomas E. Davies and Stuart H. Taylor

Catalysts 2019, 9(5), 475; https://doi.org/10.3390/catal9050475 - 22 May 2019

Cited by 52 | Viewed by 5932

Abstract

A series of ceria–zirconia mixed metal oxides with varying metal ratios were prepared by the calcination of precursors synthesized by mechanochemical grinding of the metal carbonates, and tested for catalytic naphthalene and propane total combustion. The mechanically-mixed metal oxides were more active for [...] Read more.

A series of ceria–zirconia mixed metal oxides with varying metal ratios were prepared by the calcination of precursors synthesized by mechanochemical grinding of the metal carbonates, and tested for catalytic naphthalene and propane total combustion. The mechanically-mixed metal oxides were more active for both propane and naphthalene total oxidation compared to the parent metal oxides. Ce_0.95Zr_0.05O_x was the most active catalyst for the total combustion of propane and naphthalene. Catalysts were characterized by x-ray diffraction, BET surface area, laser Raman spectroscopy, temperature programmed reduction, scanning electron microscopy with energy dispersive x-ray analysis and x-ray photoelectron spectroscopy techniques. Formation of ceria–zirconia solid solutions was observed for catalysts with a zirconia content of 10% or lower, whereas ceria and zirconia phase separation was observed when zirconia content was above 25%. Surface area increased when ceria and zirconia were mixed, and the reduction temperature of the bulk shifted to lower temperatures upon increasing zirconia content. Incorporation of zirconia was found to increase the relative concentration of surface oxygen defects compared to pure ceria, with low amounts of zirconia showing the greatest increase. The concentration of oxygen defects correlates with propane and naphthalene total oxidation activity. The enhanced total oxidation activity occurs as a result of the increased number of oxygen defects and the higher surface area. The results demonstrate that mechanochemical preparation from carbonate precursors was an effective route to make active catalysts. Full article

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

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14 pages, 1851 KiB

Open AccessArticle

Enhanced Degradation of Phenol by a Fenton-Like System (Fe/EDTA/H₂O₂) at Circumneutral pH

by Selamawit Ashagre Messele, Christophe Bengoa, Frank Erich Stüber, Jaume Giralt, Agustí Fortuny, Azael Fabregat and Josep Font

Catalysts 2019, 9(5), 474; https://doi.org/10.3390/catal9050474 - 22 May 2019

Cited by 36 | Viewed by 7858

Abstract

This work deals with the degradation of phenol based on the classical Fenton process, which is enhanced by the presence of chelating agents. Several iron-chelating agents such as ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), diethylenetriamine pentaacetic acid (DTPA), and ethylenediamine-N,N’-diacetic acid (EDDA) were [...] Read more.

This work deals with the degradation of phenol based on the classical Fenton process, which is enhanced by the presence of chelating agents. Several iron-chelating agents such as ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), diethylenetriamine pentaacetic acid (DTPA), and ethylenediamine-N,N’-diacetic acid (EDDA) were explored, although particular attention was given to EDTA. The effect of the molar ligand to iron ratio, EDTA:Fe, initial pH, and temperature on the oxidation process was studied. The results demonstrate that the proposed alternative approach allows the capacity for degrading phenol to be extended from the usual acidic pH (around 3.0) to circumneutral pH range (6.5–7.5). The overall feasibility of the process depends on the concentration of the chelating agent and the initial pH of the solution. The maximum phenol conversion, over 95%, is achieved using a 0.3 to 1 molar ratio of EDTA:Fe, stoichiometric ratio of H₂O₂ at an initial pH of 7.0, and a temperature of 30 °C after 2 hours of reaction, whereas only 10% of phenol conversion is obtained without EDTA. However, in excess of ligand (EDTA:Fe > 1), the generation of radicals seems to be strongly suppressed. Improvement of the phenol removal efficiency at neutral pH also occurs for the other chelating agents tested. Full article

(This article belongs to the Special Issue Trends in Catalytic Wet Peroxide Oxidation Processes)

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17 pages, 7279 KiB

Open AccessArticle

Catalytic Behaviour of Ce-Doped Ni Systems Supported on Stabilized Zirconia under Dry Reforming Conditions

by Ahmed Sadeq Al-Fatesh, Yasir Arafat, Ahmed Aidid Ibrahim, Samsudeen Olajide Kasim, Abdulrahman Alharthi, Anis Hamza Fakeeha, Ahmed Elhag Abasaeed, Giuseppe Bonura and Francesco Frusteri

Catalysts 2019, 9(5), 473; https://doi.org/10.3390/catal9050473 - 22 May 2019

Cited by 28 | Viewed by 4494

Abstract

Ni supported on bare and modified ZrO₂ samples were synthesized using the incipient wet impregnation method. The t-ZrO₂ phase was stabilized by incorporation of La₂O₃ into ZrO₂. Moreover, the influence of CeO₂-doping on [...] Read more.

Ni supported on bare and modified ZrO₂ samples were synthesized using the incipient wet impregnation method. The t-ZrO₂ phase was stabilized by incorporation of La₂O₃ into ZrO₂. Moreover, the influence of CeO₂-doping on the physico-chemical and catalytic properties under CO₂ reforming conditions was probed. The characterization data of the investigated catalysts were obtained by using XRD, CO₂/H₂-TPD, BET, TPR, TPO, TGA, XPS and TEM characterization techniques. In the pristine Ni/Zr catalyst, the t-ZrO₂ phase transformed into the monoclinic phase. However, upon support modification by La₂O₃, significant effects on the physicochemical properties were observed due to the monoclinic-to-tetragonal ZrO₂ phase transformation also affecting the catalytic activity. As a result, superior activity on the La₂O₃ modified Ni/Zr catalyst was achieved, while no relevant change in the surface properties and activity of the catalysts was detected after doping by CeO₂. The peculiar behavior of the Ni/La-ZrO₂ sample was related to higher dispersion of the active phase, with a more pronounced stabilization of the t-ZrO₂ phase. Full article

(This article belongs to the Special Issue Catalysts Deactivation, Poisoning and Regeneration)

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16 pages, 3244 KiB

Open AccessFeature PaperArticle

Removal of Organic Micropollutants from a Municipal Wastewater Secondary Effluent by UVA-LED Photocatalytic Ozonation

by Ana M. Chávez, Ana R. Ribeiro, Nuno F. F. Moreira, Adrián M. T. Silva, Ana Rey, Pedro M. Álvarez and Fernando J. Beltrán

Catalysts 2019, 9(5), 472; https://doi.org/10.3390/catal9050472 - 22 May 2019

Cited by 26 | Viewed by 4456

Abstract

Numerous contaminants of emerging concern (CECs) have been found in different water bodies. Directive 2013/39/EU and Decision 2018/840/EU are consequently being implemented in the field of water policies. Twelve CECs (e.g., isoproturon, ciprofloxacin, and clarithromycin are among those listed) were detected in a [...] Read more.

Numerous contaminants of emerging concern (CECs) have been found in different water bodies. Directive 2013/39/EU and Decision 2018/840/EU are consequently being implemented in the field of water policies. Twelve CECs (e.g., isoproturon, ciprofloxacin, and clarithromycin are among those listed) were detected in a municipal wastewater secondary effluent by means of solid phase extraction and ultra-high-performance liquid chromatography with tandem mass spectrometry (SPE-UHPLC-MS/MS). Different advanced oxidation processes (AOPs), based on the combination of ozone, UVA-LED and powdered TiO₂, were investigated for their removal in a semi-batch operation. In addition, TiO₂-coated glass rings (P25R) were characterized with different techniques (SEM, WDXRF) and used for continuous mode operation in a packed bed reactor (PBR). Among the AOPs studied, ozone-based processes were found to be more efficient than heterogeneous photocatalysis. A kinetic study was performed showing that direct ozonation is the main oxidation pathway for CEC removal. Ozone was successfully decomposed in combination with UVA-LED and P25R, resulting in an apparent rate constant of 3.2 × 10⁻² s⁻¹ higher than in the O₃/LED system (1.0 × 10⁻³ s⁻¹) or with ozone alone (8.6 × 10⁻⁵ s⁻¹). Hydroxyl radical reaction could prevail over direct ozone reaction for the most refractory compounds (e.g., isoproturon). Full article

(This article belongs to the Special Issue Photocatalysis Science and Engineering in Europe)

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10 pages, 2636 KiB

Open AccessArticle

Ni-Based Composites from Chitosan Biopolymer a One-Step Synthesis for Oxygen Evolution Reaction

by Behzad Aghabarari, José Manuel Luque-Centeno, Maricarmen Capel-Sánchez, Maria Jesús Lázaro Elorri and Maria Victoria Martínez-Huerta

Catalysts 2019, 9(5), 471; https://doi.org/10.3390/catal9050471 - 21 May 2019

Cited by 12 | Viewed by 4073

Abstract

Cost-efficient and sustainable electrocatalysts for oxygen evolution reaction (OER) is highly desired in the search for clean and renewable energy sources. In this study, we develop a new one-step synthesis strategy of novel composites based on Ni and molybdenum carbide embedded in N- [...] Read more.

Cost-efficient and sustainable electrocatalysts for oxygen evolution reaction (OER) is highly desired in the search for clean and renewable energy sources. In this study, we develop a new one-step synthesis strategy of novel composites based on Ni and molybdenum carbide embedded in N- and P-dual doped carbon matrices using mainly chitosan biopolymer as the carbon and nitrogen source, and molybdophosphoric acid (HMoP) as the P and Mo precursor. Two composites have been investigated through annealing a mixture of Ni/chitosan and HMoP with two unlike carbon matrices, melamine and graphene oxide, at a high temperature. Both composites exhibit similar multi-active sites with high electrocatalytic activity for OER in an alkaline medium, which is comparable to the IrO₂ catalyst. For this study, an accurate measurement of the onset potential for O₂ evolution has been used by means of a rotating ring-disk electrode (RRDE). The use of this method allows confirming a better stability in the chitosan/graphene composite. This work serves as a promising approach for the conversion of feedstock and renewable chitosan into desired OER catalysts. Full article

(This article belongs to the Special Issue Waste Derived Materials for Electrocatalytic Applications)

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15 pages, 15341 KiB

Open AccessArticle

Controllable Acid/Base Propriety of Sulfate Modified Mixed Metal Oxide Derived from Hydrotalcite for Synthesis of Propylene Carbonate

by Zhongxie Ding, Wenlong Xu, Xingguang Zhang, Zhen Liu, Jiecan Shen, Jinhua Liang, Min Jiang and Xiaoqian Ren

Catalysts 2019, 9(5), 470; https://doi.org/10.3390/catal9050470 - 21 May 2019

Cited by 10 | Viewed by 3937

Abstract

Ammonium persulfate modified mixed metal oxide derived from hydrotalcite with tunable acid/base properties can be prepared via thermal decomposition of Mg-Al hydrotalcite-type precursors and ammonium persulfate. By controlling the ammonium persulfate content, these sulphur mutated samples, denoted as SMgAlO-y (y = 1; 3; [...] Read more.

Ammonium persulfate modified mixed metal oxide derived from hydrotalcite with tunable acid/base properties can be prepared via thermal decomposition of Mg-Al hydrotalcite-type precursors and ammonium persulfate. By controlling the ammonium persulfate content, these sulphur mutated samples, denoted as SMgAlO-y (y = 1; 3; 5; 7), were investigated in this research. The resulted materials were characterized by XRD, SEM, FT-IR spectra, Py-IR spectra, XPS, Hammett indicator, CO₂-TPD, as well as NH₃-TPD. Furthermore, the acid-base property of the sample surface was determined by inverse gas chromatography measurements (IGC). Among all the obtained outcomes, the target SMgAlO-5 demonstrated the maximal K_a/K_b value, and it presented the highest activity as a catalyst in the synthesis of propylene carbonate (PC) through 1,2-propylene glycol and urea, giving the yield of 97.2% at the optimized reaction condition, which indicated that the PC yield counted on the synergic effect of the acidity and basicity on catalysts. Full article

(This article belongs to the Special Issue Supported Metal Catalysts and Their Applications in Fine Chemicals)

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14 pages, 4980 KiB

Open AccessArticle

One-Pot Synthesized Pd@N-Doped Graphene: An Efficient Catalyst for Suzuki–Miyaura Couplings

by Mufsir Kuniyil, J. V. Shanmukha Kumar, Syed Farooq Adil, Mohammed Rafi Shaik, Mujeeb Khan, Mohamed E. Assal, Mohammed Rafiq H. Siddiqui and Abdulrahman Al-Warthan

Catalysts 2019, 9(5), 469; https://doi.org/10.3390/catal9050469 - 21 May 2019

Cited by 26 | Viewed by 4394

Abstract

Nitrogen-doped graphene (NDG)-palladium (Pd)-based nanocatalysts (NDG@Pd) can be potentially applied as an efficient catalyst for the preparation of biaryls in a Suzuki–Miyaura coupling reaction. Herein, we report the one-pot facile synthesis of an NDG@Pd nanocatalyst, wherein the nanocatalyst was prepared by the simultaneous [...] Read more.

Nitrogen-doped graphene (NDG)-palladium (Pd)-based nanocatalysts (NDG@Pd) can be potentially applied as an efficient catalyst for the preparation of biaryls in a Suzuki–Miyaura coupling reaction. Herein, we report the one-pot facile synthesis of an NDG@Pd nanocatalyst, wherein the nanocatalyst was prepared by the simultaneous reduction of graphene oxide (GRO) and PdCl₂ in the presence of hydrazine hydrate as a reducing agent, while ammonium hydroxide was used as a source of “N’’ on the surface of graphene. The as-synthesized NDG@Pd nanocatalyst, consisting of smaller-sized, spherical-shaped palladium nanoparticles (Pd-NPs) on the surface of NDG, was characterized by several spectroscopic and microscopic techniques, including high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), ultraviolet–visible spectroscopy (UV-Vis), Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET). The nanocatalyst displayed outstanding catalytic activity in the Suzuki–Miyaura cross-coupling reactions of phenyl halides with phenyl boronic acids under facile conditions in water. The catalytic activity of NDG@Pd was found to be a more efficient catalyst when compared to pristine highly reduced graphene oxide (HRG) based Pd nanocatalyst (HRG@Pd). Furthermore, the reusability of the catalyst was also tested by repeatedly performing the same reaction using the recovered catalyst. The N-doped catalyst displayed excellent reusability even after several reactions. Full article

(This article belongs to the Special Issue Catalysts for Suzuki–Miyaura Coupling Reaction)

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14 pages, 1540 KiB

Open AccessArticle

High Cell Density Conversion of Hydrolysed Waste Cooking Oil Fatty Acids Into Medium Chain Length Polyhydroxyalkanoate Using Pseudomonas putida KT2440

by Carolina Ruiz, Shane T. Kenny, Ramesh Babu P, Meg Walsh, Tanja Narancic and Kevin E. O’Connor

Catalysts 2019, 9(5), 468; https://doi.org/10.3390/catal9050468 - 21 May 2019

Cited by 31 | Viewed by 5427

Abstract

Waste cooking oil (WCO) is a major pollutant, primarily managed through incineration. The high cell density bioprocess developed here allows for better use of this valuable resource since it allows the conversion of WCO into biodegradable polymer polyhydroxyalkanoate (PHA). WCO was chemically hydrolysed [...] Read more.

Waste cooking oil (WCO) is a major pollutant, primarily managed through incineration. The high cell density bioprocess developed here allows for better use of this valuable resource since it allows the conversion of WCO into biodegradable polymer polyhydroxyalkanoate (PHA). WCO was chemically hydrolysed to give rise to a mixture of fatty acids identical to the fatty acid composition of waste cooking oil. A feed strategy was developed to delay the stationary phase, and therefore achieve higher final biomass and biopolymer (PHA) productivity. In fed batch (pulse feeding) experiments Pseudomonas putida KT2440 achieved a PHA titre of 58 g/l (36.4% of CDW as PHA), a PHA volumetric productivity of 1.93 g/l/h, a cell density of 159.4 g/l, and a biomass yield of 0.76 g/g with hydrolysed waste cooking oil fatty acids (HWCOFA) as the sole substrate. This is up to 33-fold higher PHA productivity compared to previous reports using saponified palm oil. The polymer (PHA) was sticky and amorphous, most likely due to the long chain monomers acting as internal plasticisers. High cell density cultivation is essential for the majority of industrial processes, and this bioprocess represents an excellent basis for the industrial conversion of WCO into PHA. Full article

(This article belongs to the Special Issue Environmental Biocatalysis: From Remediation to Waste Valorization)

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13 pages, 6422 KiB

Open AccessArticle

Catalytic Activity of Ni_1-xLi_2xWO₄ Particles for Carbon Dioxide Photoreduction

by Jongmin Shin, Jeong Yeon Do, Raeyeong Kim, Namgyu Son, No-Kuk Park, Ho-Jung Ryu, Myung Won Seo, Junhwa Chi, Young-Sang Youn and Misook Kang

Catalysts 2019, 9(5), 467; https://doi.org/10.3390/catal9050467 - 21 May 2019

Cited by 7 | Viewed by 3234

Abstract

This study introduces NiWO₄ as a main photocatalyst, where the Ni component promotes methanation to generate a WO₃-based catalyst, as a new type of catalyst that promotes the photoreduction of carbon dioxide by slowing the recombination of electrons and holes. [...] Read more.

This study introduces NiWO₄ as a main photocatalyst, where the Ni component promotes methanation to generate a WO₃-based catalyst, as a new type of catalyst that promotes the photoreduction of carbon dioxide by slowing the recombination of electrons and holes. The bandgap of NiWO₄ is 2.74 eV, which was expected to improve the initial activity for the photoreduction of carbon dioxide. However, fast recombination between the holes and electrons was also expected. To overcome this problem, attempts were made to induce structural defects by partially replacing the Ni²⁺ ions in NiWO₄ with Li⁺. The resulting CO₂ conversion reaction was greatly enhanced with the Ni_1-xLi_2xWO₄ catalysts containing Li⁺, compared to that of the pure NiWO₄ catalysts. Notably, the total amount of CO and CH₄ produced with the Ni_0.8Li_0.4WO₄ catalyst was 411.6 nmol g⁻¹. It is believed that the insertion of Li⁺ ions into the NiWO₄ skeleton results in lattice defects due to charge and structural imbalance, which play a role in the capture of CO₂ gas or excited electrons, thereby inhibiting recombination between the electrons and holes in the Ni_1-xLi_2xWO₄ particles. Full article

(This article belongs to the Special Issue Catalysis and Catalytic Processes for CO₂ Conversion)

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13 pages, 2074 KiB

Open AccessArticle

Hydroconversion of Waste Cooking Oil into Bio-Jet Fuel over NiMo/SBUY-MCM-41

by Zongwei Zhang, Qingfa Wang and Xiangwen Zhang

Catalysts 2019, 9(5), 466; https://doi.org/10.3390/catal9050466 - 21 May 2019

Cited by 26 | Viewed by 4481

Abstract

A hierarchical SBUY-MCM-41 catalyst was prepared by sacrificing USY (a microporous molecular sieve) to synthesize the MCM-41 zeolite via a hydrothermal method. The hydroconversion of waste cooking oil into hydrocarbon fuel over a NiMo/SBUY-MCM-41 catalyst was investigated. The micropores of the Y building [...] Read more.

A hierarchical SBUY-MCM-41 catalyst was prepared by sacrificing USY (a microporous molecular sieve) to synthesize the MCM-41 zeolite via a hydrothermal method. The hydroconversion of waste cooking oil into hydrocarbon fuel over a NiMo/SBUY-MCM-41 catalyst was investigated. The micropores of the Y building units were inherited by the SBUY-MCM-41 zeolite, in which a special hierarchical structure was formed and the accessibility of reactants to the micropore active sites was improved. The hierarchical SBUY-MCM-41 showed high acidity and hydrothermal stability. Compared with mesoporous Al-MCM-41 and microporous USY zeolites, the SBUY-MCM-41-supported NiMo catalyst significantly enhanced the selective cracking of waste cooking oil for the production of jet-fuel-range hydrocarbons (37.3%), with the highest selectivity for the formation of C₁₀–C₁₄ hydrocarbons and a satisfactory selectivity for the formation of jet-fuel-range aromatics (7.6%), as well as a few cyclic compounds. The improved selectivity is the result of the special hierarchical structure and acid distribution of SBUY-MCM-41. This work provides a new strategy to synthesize a hierarchical catalyst for producing alternative jet fuel from waste cooking oil and vegetable oils. Full article

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13 pages, 1640 KiB

Open AccessArticle

Influence of Chemical Surface Characteristics of Ammonium-Modified Chilean Zeolite on Oak Catalytic Pyrolysis

by Serguei Alejandro-Martín, Adán Montecinos Acaricia, Cristian Cerda-Barrera and Hatier Díaz Pérez

Catalysts 2019, 9(5), 465; https://doi.org/10.3390/catal9050465 - 21 May 2019

Cited by 5 | Viewed by 3535

Abstract

The influence of chemical surface characteristics of Chilean natural and modified zeolites on Chilean Oak catalytic pyrolysis was investigated in this study. Chilean zeolite samples were characterised by nitrogen absorption at 77 K, X-ray powder diffraction (XRD), and X-ray fluorescence (XRF). The nature [...] Read more.

The influence of chemical surface characteristics of Chilean natural and modified zeolites on Chilean Oak catalytic pyrolysis was investigated in this study. Chilean zeolite samples were characterised by nitrogen absorption at 77 K, X-ray powder diffraction (XRD), and X-ray fluorescence (XRF). The nature and strength of zeolite acid sites were studied by diffuse reflectance infrared Fourier transform (DRIFT), using pyridine as a probe molecule. Experimental pyrolysis was conducted in a quartz cylindrical reactor and bio-oils were obtained by condensation of vapours in a closed container. Chemical species in bio-oil samples were identified by a gas chromatography/mass spectrophotometry (GC/MS) analytical procedure. Results indicate that after the ionic exchange treatment, an increase of the Brønsted acid site density and strength was observed in ammonium-modified zeolites. Brønsted acids sites were associated with an increment of the composition of ketones, aldehydes, and hydrocarbons and to a decrease in the composition of the following families (esters; ethers; and acids) in obtained bio-oil samples. The Brønsted acid sites on ammonium-modified zeolite samples are responsible for the upgraded bio-oil and value-added chemicals, obtained in this research. Bio-oil chemical composition was modified when the pyrolysis-derived compounds were upgraded over a 2NHZ zeolite sample, leading to a lower quantity of oxygenated compounds and a higher composition of value-added chemicals. Full article

(This article belongs to the Special Issue Catalysis for the Production of Sustainable Fuels and Chemicals)

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16 pages, 2520 KiB

Open AccessArticle

A Case Study for the Deactivation and Regeneration of a V₂O₅-WO₃/TiO₂ Catalyst in a Tail-End SCR Unit of a Municipal Waste Incineration Plant

by Stefano Cimino, Claudio Ferone, Raffaele Cioffi, Giovanni Perillo and Luciana Lisi

Catalysts 2019, 9(5), 464; https://doi.org/10.3390/catal9050464 - 20 May 2019

Cited by 18 | Viewed by 4865

Abstract

In this work, we set out to investigate the deactivation of a commercial V₂O₅-WO₃/TiO₂ monolith catalyst that operated for a total of 18,000 h in a selective catalytic reduction unit treating the exhaust gases of a [...] Read more.

In this work, we set out to investigate the deactivation of a commercial V₂O₅-WO₃/TiO₂ monolith catalyst that operated for a total of 18,000 h in a selective catalytic reduction unit treating the exhaust gases of a municipal waste incinerator in a tail end configuration. Extensive physical and chemical characterization analyses were performed comparing results for fresh and aged catalyst samples. The nature of poisoning species was determined with regards to their impact on the DeNOx catalytic activity which was experimentally evaluated through catalytic tests in the temperature range 90–500 °C at a gas hourly space velocity of 100,000 h⁻¹ (NO = NH₃ = 400 ppmv, 6% O₂). Two simple regeneration strategies were also investigated: thermal treatment under static air at 400–450 °C and water washing at room temperature. The effectiveness of each treatment was determined on the basis of its ability to remove specific poisoning compounds and to restore the original performance of the virgin catalyst. Full article

(This article belongs to the Special Issue Catalysts Deactivation, Poisoning and Regeneration)

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10 pages, 2097 KiB

Open AccessArticle

Expression and Characterization of a Dye-Decolorizing Peroxidase from Pseudomonas Fluorescens Pf0-1

by Nikola Lončar, Natalija Drašković, Nataša Božić, Elvira Romero, Stefan Simić, Igor Opsenica, Zoran Vujčić and Marco W. Fraaije

Catalysts 2019, 9(5), 463; https://doi.org/10.3390/catal9050463 - 20 May 2019

Cited by 16 | Viewed by 4891

Abstract

The consumption of dyes is increasing worldwide in line with the increase of population and demand for clothes and other colored products. However, the efficiency of dyeing processes is still poor and results in large amounts of colored effluents. It is desired to [...] Read more.

The consumption of dyes is increasing worldwide in line with the increase of population and demand for clothes and other colored products. However, the efficiency of dyeing processes is still poor and results in large amounts of colored effluents. It is desired to develop a portfolio of enzymes which can be used for the treatment of colored wastewaters. Herein, we used genome sequence information to discover a dye-decolorizing peroxidase (DyP) from Pseudomonas fluorescens Pf-01. Two genes putatively encoding for DyPs were identified in the respective genome and cloned for expression in Escherichia coli, of which one (PfDyP B2) could be overexpressed as a soluble protein. PfDyP B2 shows some typical features known for DyPs which includes the ability to convert dyes at the expense of hydrogen peroxide. Interestingly, t-butyl hydroperoxide could be used as an alternative substrate to hydrogen peroxide. Immobilization of PfDyP B2 in calcium-alginate beads resulted in a significant increase in stability: PfDyP B2 retains 80% of its initial activity after 2 h incubation at 50 °C, while the soluble enzyme is inactivated within minutes. PfDyP B2 was also tested with aniline and ethyl diazoacetate as substrates. Based on GC-MS analyses, 30% conversion of the starting material was achieved after 65 h at 30 °C. Importantly, this is the first report of a DyP-catalyzed insertion of a carbene into an N-H bond. Full article

(This article belongs to the Special Issue Environmental Biocatalysis: From Remediation to Waste Valorization)

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12 pages, 1602 KiB

Open AccessArticle

Biotransformation with a New Acinetobacter sp. Isolate for Highly Enantioselective Synthesis of a Chiral Intermediate of Miconazole

by Yanfei Miao, Yuewang Liu, Yushu He and Pu Wang

Catalysts 2019, 9(5), 462; https://doi.org/10.3390/catal9050462 - 20 May 2019

Cited by 8 | Viewed by 2952

Abstract

(R)-2-Chloro-1-(2,4-dichlorophenyl) ethanol is a chiral intermediate of the antifungal agent Miconazole. A bacterial strain, ZJPH1806, capable of the biocatalysis of 2-chloro-1-(2,4-dichlorophenyl) ethanone, to (R)-2-chloro-1-(2,4-dichlorophenyl) ethanol with highly stereoselectivity was isolated from a soil sample. It was identified as the [...] Read more.

(R)-2-Chloro-1-(2,4-dichlorophenyl) ethanol is a chiral intermediate of the antifungal agent Miconazole. A bacterial strain, ZJPH1806, capable of the biocatalysis of 2-chloro-1-(2,4-dichlorophenyl) ethanone, to (R)-2-chloro-1-(2,4-dichlorophenyl) ethanol with highly stereoselectivity was isolated from a soil sample. It was identified as the Acinetobacter sp., according to its morphological observation, physiological-biochemical identification, and 16S rDNA sequence analysis. After optimizing the key reaction conditions, it was demonstrated that the bioreduction of 2-chloro-1-(2,4-dichlorophenyl) ethanone was effectively transformed at relatively high conversion temperatures, along with glycerol as cosubstrate in coenzyme regeneration. The asymmetric reduction of the substrate had reached 83.2% yield with an enantiomeric excess (ee) of greater than 99.9% at 2 g/L of 2-chloro-1-(2,4-dichlorophenyl) ethanone; the reaction was conducted at 40 °C for 26 h using resting cells of the Acinetobacter sp. ZJPH1806 as the biocatalyst. The yield had increased by nearly 2.9-fold (from 28.6% to 83.2%). In the present study, a simple and novel whole-cell-mediated biocatalytic route was applied for the highly enantioselective synthesis of (R)-2-chloro-1-(2,4-dichlorophenyl) ethanol, which allowed the production of a valuable chiral intermediate method to be transformed into a versatile tool for drug synthesis. Full article

(This article belongs to the Special Issue Biocatalytic Applications in Biotechnology)

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14 pages, 3431 KiB

Open AccessArticle

Development of Titanium Dioxide-Supported Pd Catalysts for Ligand-Free Suzuki–Miyaura Coupling of Aryl Chlorides

by Tsuyoshi Yamada, Hayato Masuda, Kwihwan Park, Takumu Tachikawa, Naoya Ito, Tomohiro Ichikawa, Masatoshi Yoshimura, Yukio Takagi, Yoshinari Sawama, Yutaka Ohya and Hironao Sajiki

Catalysts 2019, 9(5), 461; https://doi.org/10.3390/catal9050461 - 19 May 2019

Cited by 20 | Viewed by 5412

Abstract

The catalyst activities of various heterogeneous palladium catalysts supported by anatase-, rutile- and brookite-type titanium oxide for ligand-free Suzuki–Miyaura cross-coupling reactions of aryl chlorides were evaluated. Palladium acetate [Pd(OAc)₂], supported on anatase-type titanium oxide (TiO₂) via acetonitrile solution impregnation [...] Read more.

The catalyst activities of various heterogeneous palladium catalysts supported by anatase-, rutile- and brookite-type titanium oxide for ligand-free Suzuki–Miyaura cross-coupling reactions of aryl chlorides were evaluated. Palladium acetate [Pd(OAc)₂], supported on anatase-type titanium oxide (TiO₂) via acetonitrile solution impregnation process without reduction [Pd/TiO₂ (anatase-type)], demonstrated the highest catalyst activity in comparison to those of other titanium oxide (rutile- or brookite-type) supported Pd(OAc)₂ without reduction and reduced Pd/TiO₂ (anatase-type) [Pd(red)/TiO₂ (anatase-type)]. Various aryl chloride and bromide derivatives were smoothly coupled with arylboronic acids including heteroarylboronic acids in the presence of 5–10 mol% Pd/TiO₂ (anatase-type) without the addition of any ligands. Although the fresh Pd/TiO₂ (anatase-type) catalyst was surprisingly comprised of ca. 1:2 mixture of palladium(II) and palladium(0) species according to X-ray photoelectron spectroscopy (XPS), in spite of no reduction process, significant further increment of palladium(0) species was observed during the Suzuki–Miyaura coupling reaction, and Pd/TiO₂ (anatase-type) was converted into a catalyst, which contained palladium(0) species as the main component [ca. 1:5 mixture of palladium(II) and palladium(0) species]. Therefore, the reduction via the electron donation process to the palladium(II) species may have occurred during the reaction on anatase-type titanium oxide. Full article

(This article belongs to the Special Issue Catalysts for Suzuki–Miyaura Coupling Reaction)

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14 pages, 5290 KiB

Open AccessArticle

Fast Degradation of Monochloroacetic Acid by BiOI-Enhanced UV/S(IV) Process: Efficiency and Mechanism

by Lili Wang and Xiaowei Liu

Catalysts 2019, 9(5), 460; https://doi.org/10.3390/catal9050460 - 19 May 2019

Cited by 9 | Viewed by 3447

Abstract

Iodide (

I^{-}

) could promote ultraviolet-activated S(IV) processes (UV/S(IV)) and degrade aqueous halogenated organic compounds and hazardous oxoanions. With the interest of promoting use of this technology, this study investigated the feasibility of using bismuth oxyiodide (BiOI) as an [...] Read more.

Iodide (

I^{-}

) could promote ultraviolet-activated S(IV) processes (UV/S(IV)) and degrade aqueous halogenated organic compounds and hazardous oxoanions. With the interest of promoting use of this technology, this study investigated the feasibility of using bismuth oxyiodide (BiOI) as an

I^{-}

source to enhance UV/S(IV) where monochloroacetic acid (MCAA) was selected as a testing model compound. Degradation of MCAA by UV/S(IV) increased by 50% in presence of BiOI. Results of competitive kinetics indicated that the promotion effect brought by BiOI mainly originated from its sustainable release of

I^{-}

, and subsequent enhanced generation of hydrated electrons. Electron spin resonance detection and fluorescence characterization proved increased formation of sulfite radical, resulting from sulfite oxidation by UV-excited BiOI. However, the sulfite radical only made a small contribution (9%) to MCAA degradation due to its moderate reactivity toward MCAA (4.2 × 10⁵ M⁻¹·s⁻¹). UV/S(IV) combined with BiOI significantly decreasing the biotoxicity of MCAA solution. BiOI can be regenerated using

I^{-}

-containing solution. Our findings provide evidence that BiOI is a promising

I^{-}

source and photocatalyst, which progresses the

I^{-}

-assisted UV/S(IV) process towards practical application. Full article

(This article belongs to the Section Photocatalysis)

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11 pages, 3642 KiB

Open AccessArticle

Engineering Ternary Copper-Cobalt Sulfide Nanosheets as High-performance Electrocatalysts toward Oxygen Evolution Reaction

by Heng Luo, Hang Lei, Yufei Yuan, Yongyin Liang, Yi Qiu, Zonglong Zhu and Zilong Wang

Catalysts 2019, 9(5), 459; https://doi.org/10.3390/catal9050459 - 17 May 2019

Cited by 23 | Viewed by 5855

Abstract

The rational design and development of the low-cost and effective electrocatalysts toward oxygen evolution reaction (OER) are essential in the storage and conversion of clean and renewable energy sources. Herein, a ternary copper-cobalt sulfide nanosheets electrocatalysts (denoted as CuCoS/CC) for electrochemical water oxidation [...] Read more.

The rational design and development of the low-cost and effective electrocatalysts toward oxygen evolution reaction (OER) are essential in the storage and conversion of clean and renewable energy sources. Herein, a ternary copper-cobalt sulfide nanosheets electrocatalysts (denoted as CuCoS/CC) for electrochemical water oxidation has been synthesized on carbon cloth (CC) via the sulfuration of CuCo-based precursors. The obtained CuCoS/CC reveals excellent electrocatalytic performance toward OER in 1.0 M KOH. It exhibits a particularly low overpotential of 276 mV at current density of 10 mA cm⁻², and a small Tafel slope (58 mV decade⁻¹), which is superior to the current commercialized noble-metal electrocatalysts, such as IrO₂. Benefiting from the synergistic effect of Cu and Co atoms and sulfidation, electrons transport and ions diffusion are significantly enhanced with the increase of active sites, thus the kinetic process of OER reaction is boosted. Our studies will serve as guidelines in the innovative design of non-noble metal electrocatalysts and their application in electrochemical water splitting Full article

(This article belongs to the Special Issue Electrocatalytic Water Oxidation)

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13 pages, 4623 KiB

Open AccessArticle

Solvothermally Doping NiS₂ Nanoparticles on Carbon with Ferric Ions for Efficient Oxygen Evolution Catalysis

by Lihong Xie, Dengke Zhao, Jiale Dai, Zexing Wu and Ligui Li

Catalysts 2019, 9(5), 458; https://doi.org/10.3390/catal9050458 - 17 May 2019

Cited by 11 | Viewed by 4583

Abstract

Exploring efficient non-precious metal based electrocatalysts for the oxygen evolution reaction (OER) is a prerequisite to implement the widespread application of a water electrolyzer and metal-air batteries. Herein, Fe-doped NiS₂ nanoparticles on a carbon matrix (Fe-NiS₂/C) are facilely prepared via [...] Read more.

Exploring efficient non-precious metal based electrocatalysts for the oxygen evolution reaction (OER) is a prerequisite to implement the widespread application of a water electrolyzer and metal-air batteries. Herein, Fe-doped NiS₂ nanoparticles on a carbon matrix (Fe-NiS₂/C) are facilely prepared via a two-step solvothermal process, where Ni-containing metal organic frameworks (Ni-MOFs) are vulcanized in situ and carbonized by a solvothermal method to form abundant NiS₂ nanoparticles homogeneously distributed on a carbon matrix (NiS₂/C), followed by doping with ferric ions via a similar solvothermal treatment. The resulting Fe-NiS₂/C nanoparticle composites show a rougher surface than the NiS₂/C parent, likely due to the formation of more structural defects after ferric ion doping, which maximizes the exposure of active sites. Moreover, ferric ion doping can also regulate the surface electronic state to reduce the activation energy barrier for OER on NiS₂/C sample. With these merits, the best sample Fe-NiS₂/C-30 only requires a potential of +1.486 V (vs. RHE) to reach an OER current density of 10 mA cm⁻² and can retain 96.85% of its initial current after continuous working for about 10 h in 1.0 M KOH aqueous solution, along with a small Tafel slope of 45.66 mV/dec, outperforming a commercial RuO₂ catalyst. The results in this work enrich the method to tailor the catalytic activity of transition metal sulfides for electrochemical energy technologies. Full article

(This article belongs to the Special Issue Electrocatalytic Water Oxidation)

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