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Catalysts, Volume 11, Issue 11 (November 2021) – 163 articles

Cover Story (view full-size image): The L-amino acid oxidase from the marine bacterium Pseudoalteromonas luteoviolacea has been characterised, showing an extreme resistance to high temperatures (Tm = 84 °C), especially in conditions of high salinity that resemble the native environment. The crystal structure further disclosed details on the substrate range of this enzyme, which is mostly active on bulky hydrophobic L-amino acids. Overall, the high expression levels (200 mg/ml) reached in vitro and the exception stability make this enzyme a valuable target for biocatalysis of enantiopure amino acids and a candidate for protein engineering towards the design of more specific variants to use in biosensing. View this paper
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Article
Supported Cu/W/Mo/Ni—Liquid Metal Catalyst with Core-Shell Structure for Photocatalytic Degradation
Catalysts 2021, 11(11), 1419; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111419 - 22 Nov 2021
Viewed by 348
Abstract
Room-temperature liquid metal is a very ideal material for the design of catalytic materials. At low temperatures, the liquid metal enters the liquid state. It provides an opportunity to utilize the liquid phase in the catalysis, which is far superior to the traditional [...] Read more.
Room-temperature liquid metal is a very ideal material for the design of catalytic materials. At low temperatures, the liquid metal enters the liquid state. It provides an opportunity to utilize the liquid phase in the catalysis, which is far superior to the traditional solid-phase catalyst. Aiming at the low performance and narrow application scope of the existing single-phase liquid metal catalyst, this paper proposed a type of liquid metal/metal oxide core-shell composite multi-metal catalyst. The Ga2O3 core-shell heterostructure was formed by chemical modification of liquid metals with different nano metals Cu/W/Mo/Ni, and it was applied to photocatalytic degrading organic contaminated raw liquor. The effects of different metal species on the rate of catalytic degradation were explored. The selectivity and stability of the LM/MO core-shell composite catalytic material were clarified, and it was found that the Ni-LM catalyst could degrade methylene blue and Congo red by 92% and 79%, respectively. The catalytic mechanism and charge transfer mechanism were revealed by combining the optical band gap value. Finally, we provided a theoretical basis for the further development of liquid metal photocatalytic materials in the field of new energy environments. Full article
(This article belongs to the Topic Nanomaterials for Sustainable Energy Applications)
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Article
Ceramized Fabrics and Their Integration in a Semi-Pilot Plant for the Photodegradation of Water Pollutants
Catalysts 2021, 11(11), 1418; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111418 - 22 Nov 2021
Viewed by 300
Abstract
The use of nano-photocatalysts for the water/wastewater purifications, particularly in developing regions, offers promising advantages over conventional technologies. TiO2-based photocatalysts deposited on fabrics represent an efficient solution for obtaining heterogeneous photocatalysts, which are easily adaptable in the already installed water treatment [...] Read more.
The use of nano-photocatalysts for the water/wastewater purifications, particularly in developing regions, offers promising advantages over conventional technologies. TiO2-based photocatalysts deposited on fabrics represent an efficient solution for obtaining heterogeneous photocatalysts, which are easily adaptable in the already installed water treatment plants or air purification systems. Despite the huge effort spent to develop and characterize novel nano-photocatalysts, which are especially active under solar light, knowledge gaps still persist for their full-scale application, starting from the reactor design and scale-up and the evaluation of the photocatalytic efficiency in pre-pilot scenarios. In this study, we offered easily scalable solutions for adapting TiO2-based photocatalysts, which are deposited on different kinds of fabrics and implemented in a 6 L semi-pilot plant, using the photodegradation of Rhodamine B (RhB) as a model of water pollution. We took advantage of a multi-variable optimization approach to identify the best design options in terms of photodegradation efficiency and turnover frequency (TOF). Surprisingly, in the condition of use, the irradiation with a light-emitting diode (LED) visible lamp appeared as a valid alternative to the use of UV LED. The identification of the best design options in the semi-pilot plant allowed scaling up the technology in a 100 L pilot plant suitable for the treatment of industrial wastewater. Full article
(This article belongs to the Special Issue Heterogeneous Photocatalysis: A Solution for a Greener Earth)
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Article
Understanding of the Key Factors Determining the Activity and Selectivity of CuZn Catalysts in Hydrogenolysis of Alkyl Esters to Alcohols
Catalysts 2021, 11(11), 1417; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111417 - 22 Nov 2021
Viewed by 189
Abstract
CuZn catalysts are perspective catalysts for esters hydrogenolysis, but more knowledge is needed to optimize their catalytic performance. In this work, we consider the impact of CuZn catalysts composition on their structure, activity, selectivity, and stability in esters hydrogenolysis. Four catalysts with various [...] Read more.
CuZn catalysts are perspective catalysts for esters hydrogenolysis, but more knowledge is needed to optimize their catalytic performance. In this work, we consider the impact of CuZn catalysts composition on their structure, activity, selectivity, and stability in esters hydrogenolysis. Four catalysts with various Cu/Zn ratio were synthesized by a co-precipitation and characterized in as-prepared, calcined, reduced, and spent state by XRF, XRD, N2 physisorption, CO2-TPD, NH3-TPD, and N2O chemisorption. XRD data revealed the effect of the composition on the size of Cu and ZnO particles. The catalytic performance was investigated using an autoclave. All catalysts exhibited high methyl hexanoate conversion about 48–60% after 3 h but their activity and selectivity were found to be dependent on Cu/Zn ratio. The conversion of methyl hexanoate and hexyl hexanoate was compared to explain the observed product selectivity. Moreover, the catalysts stability was investigated in three consecutive reaction cycles and correlated with changes in the size of constituent particles. Moreover, when different esters were tested, a slight decrease in conversion and increase in alcohol selectivity with a growth in molecule size was observed. Obtained results allow making a conclusion about the optimal composition that provides the good performance of CuZn catalysts in ester hydrogenolysis. Full article
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A Study on the Characteristic and Antibacterial Activity of Ti3Ox Thin Films
Catalysts 2021, 11(11), 1416; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111416 - 22 Nov 2021
Viewed by 248
Abstract
A pure Ti target in Ar/O2 gas mixture was used to synthesize Ti3Ox thin film on a glass substrate by Reactive High-Power Impulse Magnetron Sputtering (HiPIMS) under different sputtering power (2 and 2.5 kW). The influence of HiPIMS parameters [...] Read more.
A pure Ti target in Ar/O2 gas mixture was used to synthesize Ti3Ox thin film on a glass substrate by Reactive High-Power Impulse Magnetron Sputtering (HiPIMS) under different sputtering power (2 and 2.5 kW). The influence of HiPIMS parameters on thin films’ structural, morphological, chemical composition, optical and photocatalytic, and antibacterial properties was investigated. In this study, Ti3Ox thin films can be synthesized using the HiPIMS method without the post-annealing process. Two co-existence phases (hexagonal Ti3O and base-centered monoclinic Ti3O5 phases) existed on the Ti3Ox films. It is found that the peak intensity of (006) Ti3O hexagonal slightly increased as the sputtering power increased from 2 to 2.5 kW. The Ti3Ox thin-film bandgap values were 3.36 and 3.50 eV for 2 and 2.5 kW, respectively. The Ti3Ox films deposited at 2.5 kW showed good photocatalytic activity under UV light irradiation, with a higher methylene blue dye degradation rate than TiO2 thin films. The antibacterial study on Ti3Ox thin films exhibited a high inhibition percentage against E. coli and S. aureus. This study demonstrates that Ti3Ox thin films can promote high photocatalytic and antibacterial activity. Full article
(This article belongs to the Special Issue Photocatalytic Nanomaterials for Abatement of Microorganisms)
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Article
Figures of Merit for Photocatalysis: Comparison of NiO/La-NaTaO3 and Synechocystis sp. PCC 6803 as a Semiconductor and a Bio-Photocatalyst for Water Splitting
Catalysts 2021, 11(11), 1415; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111415 - 22 Nov 2021
Viewed by 197
Abstract
While photocatalysis is considered a promising sustainable technology in the field of heterogeneous catalysis as well as biocatalysis, figures of merit (FOM) for comparing catalytic performance, especially between disciplines, are not well established. Here, photocatalytic water splitting was conducted using a semiconductor (NiO/La-NaTaO [...] Read more.
While photocatalysis is considered a promising sustainable technology in the field of heterogeneous catalysis as well as biocatalysis, figures of merit (FOM) for comparing catalytic performance, especially between disciplines, are not well established. Here, photocatalytic water splitting was conducted using a semiconductor (NiO/La-NaTaO3) and a bio-photocatalyst (Synechocystis sp. PCC 6803) in the same setup under similar reaction conditions, eliminating the often ill-defined influence of the setup on the FOMs obtained. Comparing the results enables the critical evaluation of existing FOMs and a quantitative comparison of both photocatalytic systems. A single FOM is insufficient to compare the photocatalysts, instead a combination of multiple FOMs (reaction rate, photocatalytic space time yield and a redefined apparent quantum yield) is superior for assessing a variety of photocatalytic systems. Full article
(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)
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Article
[email protected]4 {010} Constructed for Visible-Light-Assisted Peroxymonosulfate Activation
Catalysts 2021, 11(11), 1414; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111414 - 22 Nov 2021
Viewed by 200
Abstract
A visible-light-Fenton-like reaction system was constructed for the selective conversion of peroxymonosulfate to sulfate radical. [email protected], when doped on monoclinic BiVO4 {010} facets, promoted spatial charge separation due to the different energy band between the m-BiVO4 {010} and {110} facets. The [...] Read more.
A visible-light-Fenton-like reaction system was constructed for the selective conversion of peroxymonosulfate to sulfate radical. [email protected], when doped on monoclinic BiVO4 {010} facets, promoted spatial charge separation due to the different energy band between the m-BiVO4 {010} and {110} facets. The visible-light response of m-BiVO4 was enhanced, which was attributed to the SPR effect of Au. And the photogenerated electrons were transferred from the m-BiVO4 {010} facet to Au via a Schottky junction. Owing to higher work function, CoS was able to capture these photoelectrons with acceleration of the Co(Ⅱ)/Co(Ⅲ) redox, enhancing peroxymonosulfate conversion to sulfate radical (Co2+ + HSO5→ Co3+ + •SO4 + OH). On the other hand, holes accumulated on m-BiVO4 {110} facets also contributed to organics oxidation. Thus, more than 95% of RhB was degraded within 40 min, and, even after five cycles, over 80% of RhB could be removed. The radical trapping experiments and EPR confirmed that both the sulfate radical and photogenerated hole were the main species for organics degradation. UV-vis DRS, photoluminescence (PL) and photoelectrochemical analyses also confirmed the enhancement of the visible-light response and charge separation. In a pilot scale experiment (PMS = 3 mM, initial TOC = 151 mg/L, reaction time = 4 h), CoS-Au-BiVO4 loaded on glass fiber showed a high mineralization rate (>60%) of practical wastewater. Full article
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Article
Revisiting Gas to Solids Ratio for Activated Sludge Clarification by Electrolytic Hydrogen Bubbles: Theoretical and Experimental Evaluations
Catalysts 2021, 11(11), 1413; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111413 - 22 Nov 2021
Viewed by 299
Abstract
Molecular hydrogen (H2), as the green energy carrier from water electrolysis, can be utilized for separation of suspended micro-particles as electroflotation (EF). This study provides practical guidelines for the gas to solids (G/S) ratio as the governing parameter in EF, based [...] Read more.
Molecular hydrogen (H2), as the green energy carrier from water electrolysis, can be utilized for separation of suspended micro-particles as electroflotation (EF). This study provides practical guidelines for the gas to solids (G/S) ratio as the governing parameter in EF, based on theoretical estimations and experiments for clarification of activated sludge. The G/S ratio in EF was controlled linearly by current density (j), under quasi-consistent current efficiency (at j > 8 mA/cm2) for H2 (~1) and O2 (~0.4) bubble generations on Ti cathode and IrTaOx anode, respectively. Based on the measured sizes of bubbles (approximated to 35 µm) and biological flocs (discretized to mean sizes of 22.5, 40, 60, 135, and 150 µm), batch flotation experiments estimated the maximum collision-attachment efficiency of 0.057. The rise velocities of floc-bubble aggregate were computed to derive the limiting G/S ratio to overcome the given influent hydraulic loading. Consequently, the estimates (5.23 × 10−4 and 5.92 × 10−4 at hydraulic loading of 0.87 and 1.73 cm/min, respectively) were compatible with the continuous EF experiments. Full article
(This article belongs to the Special Issue Applications of Electrocatalysts for Water Treatment: Recent Advances)
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Article
Methanation of CO2 Using MIL-53-Based Catalysts: Ni/MIL-53–Al2O3 versus Ni/MIL-53
Catalysts 2021, 11(11), 1412; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111412 - 21 Nov 2021
Viewed by 246
Abstract
MIL-53 and the MIL-53–Al2O3 composite synthesized by a solvothermal procedure, with water as the only solvent besides CrCl3 and benzene-1,4-dicarboxylic acid (BDC), were used as catalytic supports to obtain the novel MIL-53-based catalysts Ni(10 wt.%)/MIL-53 and Ni(10 wt.%)/MIL-53–Al2 [...] Read more.
MIL-53 and the MIL-53–Al2O3 composite synthesized by a solvothermal procedure, with water as the only solvent besides CrCl3 and benzene-1,4-dicarboxylic acid (BDC), were used as catalytic supports to obtain the novel MIL-53-based catalysts Ni(10 wt.%)/MIL-53 and Ni(10 wt.%)/MIL-53–Al2O3. Ni nanoparticle deposition by an adapted double-solvent method leads to the uniform distribution of metallic particles, both smaller (≤10 nm) and larger ones (10–30 nm). MIL-53–Al2O3 and Ni/MIL-53–Al2O3 show superior thermal stability to MIL-53 and Ni/MIL-53, while MIL-53–Al2O3 samples combine the features of both MIL-53 and alumina in terms of porosity. The investigation of temperature’s effect on the catalytic performance in the methanation process (CO2:H2 = 1:5.2, GHSV = 4650 h−1) revealed that Ni/MIL-53 is more active at temperatures below 300 °C, and Ni/MIL-53–Al2O3 above 300 °C. Both catalysts show maximum CO2 conversion at 350 °C: 75.5% for Ni/MIL-53 (methane selectivity of 93%) and 88.8% for Ni/MIL-53–Al2O3 (methane selectivity of 98%). Stability tests performed at 280 °C prove that Ni/MIL-53–Al2O3 is a possible candidate for the CO2 methanation process due to its high CO2 conversion and CH4 selectivity, corroborated by the preservation of the structure and crystallinity of MIL-53 after prolonged exposure in the reaction medium. Full article
(This article belongs to the Special Issue Frontiers in Catalysis for CO2 Methanation)
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Article
Ethanol Dehydrogenation to Acetaldehyde over [email protected] Carbon
Catalysts 2021, 11(11), 1411; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111411 - 21 Nov 2021
Viewed by 242
Abstract
Cobalt and nitrogen co-doped carbon materials ([email protected]) have recently attracted significant attention as highly efficient noble-metal-free catalysts exhibiting a large application range. In a similar research interest, and taking into account the ever-increasing importance of bioethanol as a renewable raw material, here, we [...] Read more.
Cobalt and nitrogen co-doped carbon materials ([email protected]) have recently attracted significant attention as highly efficient noble-metal-free catalysts exhibiting a large application range. In a similar research interest, and taking into account the ever-increasing importance of bioethanol as a renewable raw material, here, we report the results on ethanol dehydrogenation to acetaldehyde over [email protected] catalysts. The catalyst samples were synthesized by a variety of affordable techniques, ensuring generation of various types of Co species incorporated in carbon, such as subnanosized cobalt sites and nano-sized particles of metallic cobalt and cobalt oxides. The catalytic activity was tested under both oxidative and non-oxidative gas-phase conditions at 200–450 °C using a fixed-bed flow reactor. The non-oxidative conditions proved to be much more preferable for the target reaction, competing, however, with ethanol dehydration to ethylene. Under specified reaction conditions, ethanol conversion achieved a level of 66% with 84% selectivity to acetaldehyde at 400 °C. The presence of molecular oxygen in the feed led mainly to deep oxidation of ethanol to COx, giving acetaldehyde in a comparatively low yield. The potential contribution of carbon itself and supported cobalt forms to the observed reaction pathways is discussed. Full article
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Article
Application Potential of Cyanide Hydratase from Exidia glandulosa: Free Cyanide Removal from Simulated Industrial Effluents
Catalysts 2021, 11(11), 1410; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111410 - 21 Nov 2021
Viewed by 262
Abstract
Industries such as mining, cokemaking, (petro)chemical and electroplating produce effluents that contain free cyanide (fCN = HCN + CN). Currently, fCN is mainly removed by (physico)chemical methods or by biotreatment with activated sludge. Cyanide hydratases (CynHs) (EC 4.2.1.66), which convert fCN [...] Read more.
Industries such as mining, cokemaking, (petro)chemical and electroplating produce effluents that contain free cyanide (fCN = HCN + CN). Currently, fCN is mainly removed by (physico)chemical methods or by biotreatment with activated sludge. Cyanide hydratases (CynHs) (EC 4.2.1.66), which convert fCN to the much less toxic formamide, have been considered for a mild approach to wastewater decyanation. However, few data are available to evaluate the application potential of CynHs. In this study, we used a new CynH from Exidia glandulosa (protein KZV92691.1 designated NitEg by us), which was overproduced in Escherichia coli. The purified NitEg was highly active for fCN with 784 U/mg protein, kcat 927/s and kcat/KM 42/s/mM. It exhibited optimal activities at pH approximately 6–9 and 40–45 °C. It was quite stable in this pH range, and retained approximately 40% activity at 37 °C after 1 day. Silver and copper ions (1 mM) decreased its activity by 30–40%. The removal of 98–100% fCN was achieved for 0.6–100 mM fCN. Moreover, thiocyanate, sulfide, ammonia or phenol added in amounts typical of industrial effluents did not significantly reduce the fCN conversion, while electroplating effluents may need to be diluted due to high fCN and metal content. The ease of preparation of NitEg, its high specific activity, robustness and long shelf life make it a promising biocatalyst for the detoxification of fCN. Full article
(This article belongs to the Special Issue Enzymes and Biocatalysis)
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Article
Synthesis and Catalytic Properties of Novel Ruthenacarboranes Based on nido-[5-Me-7,8-C2B9H10]2− and nido-[5,6-Me2-7,8-C2B9H9]2− Dicarbollide Ligands
Catalysts 2021, 11(11), 1409; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111409 - 21 Nov 2021
Viewed by 185
Abstract
The effect of methyl substituents in the lower belt of dicarbollide ligands on the redox potential of ruthenacarboranes based thereof, as well as the ability of the metallacarboranes obtained to catalyze radical polymerization with atom transfer were studied. For this purpose, a new [...] Read more.
The effect of methyl substituents in the lower belt of dicarbollide ligands on the redox potential of ruthenacarboranes based thereof, as well as the ability of the metallacarboranes obtained to catalyze radical polymerization with atom transfer were studied. For this purpose, a new approach to the synthesis of closo-ruthenacarboranes based on substituted dicarbollide ligands was developed and six new complexes 3,3-(Ph2P(CH2)4PPh2)-3-H-3-Cl-9-Me-12-X-closo-3,1,2-RuC2B9H9, 3,3,8-(Ph2P(CH2)4PPh-μ-(C6H4-o))-3-Cl-9-Me-12-X-closo-3,1,2-RuC2B9H8 and 3,3,4,8-(Ph2P(CH2)4P-μ-(C6H4-o)2)-3-Cl-9-Me-9-X-closo-3,1,2-RuC2B9H7 (X = H, Me) were synthetized and characterized by single crystal X-ray diffraction, NMR and ESR spectroscopy and MALDI TOF mass-spectrometry. Comparison of the values of the redox potentials of the synthesized ruthenium complexes in 1,2-dichloroethane with the values previously found for the corresponding ruthenacarboranes based on the parent dicarbollide anion showed that the introduction of methyl substituents into the carborane cage led to a decrease in the redox potentials of the complexes, which made them more preferable catalysts for ATRP. Test experiments on the polymerization of MMA showed that the synthesized ruthenacarboranes were effective catalysts for ATRP, the most active being the complex with two methyl groups and two ortho-phenylenecycloboronated fragments. Full article
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Article
Halide-Doping Effect of Strontium Cobalt Oxide Electrocatalyst and the Induced Activity for Oxygen Evolution in an Alkaline Solution
Catalysts 2021, 11(11), 1408; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111408 - 20 Nov 2021
Viewed by 423
Abstract
Perovskites of strontium cobalt oxyhalides having the chemical formulae Sr2CoO4-xHx (H = F, Cl, and Br; x = 0 and 1) were prepared using a solid-phase synthesis approach and comparatively evaluated as electrocatalysts for oxygen evolution in an [...] Read more.
Perovskites of strontium cobalt oxyhalides having the chemical formulae Sr2CoO4-xHx (H = F, Cl, and Br; x = 0 and 1) were prepared using a solid-phase synthesis approach and comparatively evaluated as electrocatalysts for oxygen evolution in an alkaline solution. The perovskite electrocatalyst crystal phase, surface morphology, and composition were examined by X-ray diffraction, a scanning electron microscope, and energy-dispersive X-ray (EDX) mapping. The electrochemical investigations of the oxyhalides catalysts showed that the doping of F, Cl, or Br into the Sr2CoO4 parent oxide enhances the electrocatalytic activity for the oxygen evolution reaction (OER) with the onset potential as well as the potential required to achieve a current density of 10 mA/cm2 shifting to lower potential values in the order of Sr2CoO4 (1.64, 1.73) > Sr2CoO3Br (1.61, 1.65) > Sr2CoO3Cl (1.53, 1.60) > Sr2CoO3F (1.50, 1.56) V vs. HRE which indicates that Sr2CoO3F is the most active electrode among the studied catalysts under static and steady-state conditions. Moreover, Sr2CoO3F demonstrates long-term stability and remarkably less charge transfer resistance (Rct = 36.8 ohm) than the other oxyhalide counterparts during the OER. The doping of the perovskites with halide ions particularly the fluoride-ion enhances the surface oxygen vacancy density due to electron withdrawal away from the Co-atom which improves the ionic and electronic conductivity as well as the electrochemical activity of the oxygen evolution in alkaline solution. Full article
(This article belongs to the Special Issue Advancements in Electrochemical Energy Catalysts)
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Article
A 5-(2-Pyridyl)tetrazolate Complex of Molybdenum(VI), Its Structure, and Transformation to a Molybdenum Oxide-Based Hybrid Heterogeneous Catalyst for the Epoxidation of Olefins
Catalysts 2021, 11(11), 1407; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111407 - 20 Nov 2021
Viewed by 403
Abstract
There is a considerable practical interest in discovering new ways to obtain organomolybdenum heterogeneous catalysts for olefin epoxidation that are easier to recover and reuse and display enhanced productivity. In this study, the complex salt (H2pytz)[MoO2Cl2(pytz)] ( [...] Read more.
There is a considerable practical interest in discovering new ways to obtain organomolybdenum heterogeneous catalysts for olefin epoxidation that are easier to recover and reuse and display enhanced productivity. In this study, the complex salt (H2pytz)[MoO2Cl2(pytz)] (1) (Hpytz = 5-(2-pyridyl)tetrazole) has been prepared, structurally characterized, and employed as a precursor for the hydrolysis-based synthesis of a microcrystalline molybdenum oxide/organic hybrid material formulated as [MoO3(Hpytz)] (2). In addition to single-crystal X-ray diffraction (for 1), compounds 1 and 2 were characterized by FT-IR and Raman spectroscopies, solid-state 13C{1H} cross-polarization (CP) magic-angle spinning (MAS) NMR, and scanning electron microscopy (SEM). Compounds 1 and 2 were evaluated as olefin epoxidation catalysts using the model reaction of cis-cyclooctene (Cy8) with tert-butyl hydroperoxide (TBHP), at 70 °C, which gave 100% epoxide selectivity up to 100% conversion. While 1 behaved as a homogeneous catalyst, hybrid 2 behaved as a heterogeneous catalyst and could be recovered for recycling without showing structural degradation or loss of catalytic performance over consecutive reaction cycles. The substrate scope was broadened to monoterpene DL-limonene (Lim) and biobased unsaturated fatty acid methyl esters, methyl oleate (MeOle), and methyl linoleate (MeLin), which gave predominantly epoxide products. Full article
(This article belongs to the Special Issue 10th Anniversary of Catalysts: Molecular Catalysis)
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Au-Ag/TiO2 Thin Films Preparation by Laser Ablation and Sputtering Plasmas for Its Potential Use as Photoanodes in Electrochemical Advanced Oxidation Processes (EAOP)
Catalysts 2021, 11(11), 1406; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111406 - 20 Nov 2021
Viewed by 257
Abstract
Titanium dioxide (TiO2) is widely used, studied, and synthesized using different methodologies. By a modification of the material, it can be applied to wastewater treatment. A combined sputtering-laser ablation setup was used to deposit TiO2 thin films modified, individually and [...] Read more.
Titanium dioxide (TiO2) is widely used, studied, and synthesized using different methodologies. By a modification of the material, it can be applied to wastewater treatment. A combined sputtering-laser ablation setup was used to deposit TiO2 thin films modified, individually and simultaneously, with gold (Au) and silver (Ag). To investigate the effect of the metal incorporation in titanium and its impact on the photocatalytic activity, with dye discoloration as a pollutant compound model, the deposited films were characterized by UV–Vis, photoluminescence, and Raman spectroscopies, as well as by parallel beam X-ray diffraction. The results showed that films with different Au and Ag loads, and an 18 nm average crystallite size, were obtained. These metals have an essential effect on the deposited film’s compositional, structural, and optical properties, directly reflected in its photocatalytic activity. The photocatalytic test results using UV-Vis showed that, after 1 h of applying a 4.8 V electric voltage, a discoloration of up to 80% of malachite green (MG) was achieved, using ultraviolet (UV) light. Full article
(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)
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Use of NaNO3/SiAl as Heterogeneous Catalyst for Fatty Acid Methyl Ester Production from Rapeseed Oil
Catalysts 2021, 11(11), 1405; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111405 - 20 Nov 2021
Viewed by 352
Abstract
The use of heterogeneous catalysts to produce fatty acid methyl esters (FAME) through transesterification with methanol might contribute to both green chemistry and a circular economy, as the process can be simplified, not requiring additional stages to recover the catalyst once the reaction [...] Read more.
The use of heterogeneous catalysts to produce fatty acid methyl esters (FAME) through transesterification with methanol might contribute to both green chemistry and a circular economy, as the process can be simplified, not requiring additional stages to recover the catalyst once the reaction takes place. For this purpose, different catalysts are used, including a wide range of possibilities. In this research the use of NaNO3/SiAl as a heterogeneous catalyst for FAME production through transesterification of rapeseed oil with methanol is considered. A thorough characterization of the catalyst (including XDR and XPS analysis, SEM microscopy, lixiviation and reusability tests, among others), specific optimization of transesterification by using the final catalyst (considering catalyst amount, stirring rate, methanol/oil ratio, and temperature), and quality determination of the final biodiesel (following the UNE-EN 14214 standard) were carried out. In conclusion, 20 mmolNa·gsupport−1 (that is, NaNO3/SiAl 20/1) offered the best results, with a high activity (exceeding 99% w/w of FAMEs) without requiring higher impregnation amounts. The best chemical conditions for this heterogeneous catalyst were 5% w/w catalyst, 700 rpm, 9:1 methanol/oil ratio, and 65 °C, obtaining Ea = 73.3 kJ·mol−1 and a high-quality biodiesel, similar to those obtained through homogeneous catalysis. Consequently, this catalyst could be a suitable precursor for FAME production. Full article
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Hybrids of Reduced Graphene Oxide Aerogel and CNT for Electrochemical O2 Reduction
Catalysts 2021, 11(11), 1404; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111404 - 20 Nov 2021
Viewed by 249
Abstract
Carbon nanotubes (CNTs), graphene aerogels (GAs), and their hybrid (CNT-GA) prepared by hydrothermal treatment were tested in the electrocatalytic oxygen reduction reaction (ORR). The importance of porous structure derived from the combination of mesoporosity coming from CNTs with macroporosity stemming from GAs was [...] Read more.
Carbon nanotubes (CNTs), graphene aerogels (GAs), and their hybrid (CNT-GA) prepared by hydrothermal treatment were tested in the electrocatalytic oxygen reduction reaction (ORR). The importance of porous structure derived from the combination of mesoporosity coming from CNTs with macroporosity stemming from GAs was evidenced because the hybrid carbon material exhibited synergistic performance in terms of kinetic current and onset potential. Different electrocatalysts were prepared based on these hybrids doped with nitrogen using different precursors and also supporting Fe nanoparticles. N-doped carbon hybrids showed higher electrocatalytic activity than their undoped counterparts. Nevertheless, both doped and undoped materials provided a mixed two and four electron reduction. On the other hand, the addition of a Fe precursor and phenanthroline to the CNT-GA allowed preparing an N-doped hybrid containing Fe nanoparticles which favored the 4-electron oxygen reduction to water, thus being an excellent candidate as a structured cathode in fuel cells. Full article
(This article belongs to the Special Issue Structured Materials for Catalytic Applications)
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Article
Separable Magnetic Fe3O4@MoS2 Composite for Adsorption and Piezo-Catalytic Degradation of Dye
Catalysts 2021, 11(11), 1403; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111403 - 20 Nov 2021
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Abstract
Well-designed composite catalysts are of increasing concern due to their improved performance compared to individual components. Herein, we designed and synthesized an Fe3O4@MoS2 composite via a simple hydrothermal method. As for the resultant composite, the MoS2 nanolayers [...] Read more.
Well-designed composite catalysts are of increasing concern due to their improved performance compared to individual components. Herein, we designed and synthesized an Fe3O4@MoS2 composite via a simple hydrothermal method. As for the resultant composite, the MoS2 nanolayers presented a novel piezo-catalytic effect, while the Fe3O4 core provided a magnetic separation property. The structure and properties of Fe3O4@MoS2 were determined by relevant experiments. It was found that Fe3O4@MoS2 exhibited enhanced piezo-catalytic degradation of rhodamine B and good magnetic recovery/recycling features. The kobs for rhodamine B degradation over Fe3O4@MoS2 was 0.019 min−1—a little longer than that over MoS2 (0.013 min−1). Moreover, Fe3O4@MoS2 also showed a favorable ability to adsorb rhodamine B in solution, with a saturation adsorption of 26.8 mg/g. Further studies revealed that piezo-electrons, holes, and superoxide anions were key species in the piezo-catalytic degradation of rhodamine B. Notably, the step where oxygen trapped electrons to produce superoxide anions had a significant impact on the degradation of the dye. This work, not limited to the development of a high-performance MoS2-based piezo-catalyst, is expected to provide new insights into the working mechanisms and process profiles of composite piezo-catalysts. Full article
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Article
Epoxidation of 1,5,9-Cyclododecatriene with Hydrogen Peroxide over Ti-MCM-41 Catalyst
Catalysts 2021, 11(11), 1402; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111402 - 19 Nov 2021
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Abstract
This work presents the results of our research on the epoxidation of 1,5,9-cyclododecatriene (CDT) with hydrogen peroxide over the Ti-MCM-41 catalyst. The influence of the following parameters on the course of the process was investigated: temperature, CDT:H2O2 molar ratio, solvent [...] Read more.
This work presents the results of our research on the epoxidation of 1,5,9-cyclododecatriene (CDT) with hydrogen peroxide over the Ti-MCM-41 catalyst. The influence of the following parameters on the course of the process was investigated: temperature, CDT:H2O2 molar ratio, solvent composition and its type, and catalyst content. The highest selectivity of CDT transformation to 1,2-epoxy-5,9-cyclododecadiene (ECDD)—approximately 100 mol%, the highest yet reported—was obtained at the CDT conversion of 13 mol% and with the following parameter values: a catalyst content of 5 wt%; a molar ratio of CDT:H2O2 = 2; isopropyl alcohol (i-PrOH) as the solvent, with a composition of 80 wt% in the reaction mixture; a temperature of 80 °C; and a reaction time of 240 min. The highest conversion of CDT (37 mol%) was obtained at the ECDD selectivity of 56 mol% and using the following process parameters: a catalyst content of 5 wt%; a molar ratio of CDT:H2O2 = 0.5; i-PrOH used as the solvent, with solvent composition of 80 wt%; a temperature of 80 °C; and a reaction time of 60 min. It should be emphasized that the CDT conversion obtained in the current study is higher (by 9 mol%) than that described in the literature on heterogeneous catalysts. Full article
(This article belongs to the Section Catalysis in Organic and Polymer Chemistry)
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Article
Oxy-Steam Reforming of Liquefied Natural Gas (LNG) on Mono- and Bimetallic (Ag, Pt, Pd or Ru)/Ni Catalysts
Catalysts 2021, 11(11), 1401; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111401 - 19 Nov 2021
Viewed by 236
Abstract
This work presents, for the first time, the comparative physicochemical and reactivity studies of a range of bimetallic Pt-Ni, Pd-Ni, Ru-Ni, and Ag-Ni catalysts in the oxy-steam reforming (OSR) of liquefied natural gas (LNG) reaction towards hydrogen generation. In order to achieve the [...] Read more.
This work presents, for the first time, the comparative physicochemical and reactivity studies of a range of bimetallic Pt-Ni, Pd-Ni, Ru-Ni, and Ag-Ni catalysts in the oxy-steam reforming (OSR) of liquefied natural gas (LNG) reaction towards hydrogen generation. In order to achieve the intended purpose of this work, a binary oxide CeO2·ZrO2 (1:2) support was prepared via a co-precipitation method. The catalysts’ physicochemical properties were studied using X-ray diffraction (XRD), BET, TPR-H2, TPD-NH3, SEM-EDS and XPS methods. The highest activity in the studied process was exhibited by the 1%Pt-5%Ni catalyst supported on CeO2·ZrO2 (1:2) system. The highest activity of this system is explained by the specific interactions occurring between the components of the active phase and between the components of the active phase and the carrier itself. The activity results showed that this catalytic system exhibited above 71% of the methane conversion at 600 °C and 60% yield of hydrogen formation. The results of this work demonstrate that the Pt-Ni and Ru-Ni catalytic systems hold promise to be applied in the production of hydrogen to power solid oxide fuel cells. Full article
(This article belongs to the Special Issue Recent Advances in Nickel-Based Catalysts)
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Article
An Effective Strategy to Enhance the Electrocatalytic Activity of Ruddlesden−Popper Oxides Sr3Fe2O7−δ Electrodes for Solid Oxide Fuel Cells
Catalysts 2021, 11(11), 1400; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111400 - 18 Nov 2021
Viewed by 325
Abstract
The target of this work is to develop advanced electrode materials with excellent performance compared to conventional cathodes. Cobalt-free Ruddlesden−Popper oxides Sr3Fe2−xCuxO7−δ (SFCx, x = 0, 0.1, 0.2) were successfully synthesized and [...] Read more.
The target of this work is to develop advanced electrode materials with excellent performance compared to conventional cathodes. Cobalt-free Ruddlesden−Popper oxides Sr3Fe2−xCuxO7−δ (SFCx, x = 0, 0.1, 0.2) were successfully synthesized and assessed as cathode materials for solid oxide fuel cells (SOFCs). Herein, a Cu-doping strategy is shown to increase the electrical conductivity and improve the electrochemical performance of the pristine Sr3Fe2O7−δ. Among all the cathode materials, the Sr3Fe1.9Cu0.1O7−δ (SFC10) cathode exhibits the best electrocatalytic activity for oxygen reduction reaction (ORR). The polarization resistance is 0.11 Ω cm2 and the peak power density of the single-cell with an SFC10 cathode reaches 955 mW cm−2 at 700 °C, a measurement comparable to cobalt-based electrodes. The excellent performance is owed to favorable oxygen surface exchange capabilities and larger oxygen vacancy concentrations at elevated temperatures. Moreover, the electrochemical impedance spectra and distribution of relaxation time results indicate that the charge transfer process at the triple-phase boundary is the rate-limiting step for ORR on the electrode. This work provides an effective strategy for designing novel cathode electrocatalysts for SOFCs. Full article
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Article
New Insight into the Interplay of Method of Deposition, Chemical State of Pd, Oxygen Storage Capability and Catalytic Activity of Pd-Containing Perovskite Catalysts for Combustion of Methane
Catalysts 2021, 11(11), 1399; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111399 - 18 Nov 2021
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Abstract
Elaboration of Pd-supported catalysts for catalytic combustion is, nowadays, considered as an imperative task to reduce the emissions of methane. This study provides new insight into the method of deposition, chemical state of Pd and oxygen storage capability of transition metal ions and [...] Read more.
Elaboration of Pd-supported catalysts for catalytic combustion is, nowadays, considered as an imperative task to reduce the emissions of methane. This study provides new insight into the method of deposition, chemical state of Pd and oxygen storage capability of transition metal ions and their effects on the catalytic reactivity of supported catalysts for the combustion of methane. The catalyst with nominal composition La(Co0.8Ni0.1Fe0.1)0.85Pd0.15O3 was supported on SiO2-modified/γ-alumina using two synthetic procedures: (i) aerosol assisted chemical vapor deposition (U-AACVD) and (ii) wet impregnation (Imp). A comparative analysis shows that a higher catalytic activity is established for supported catalyst obtained by wet impregnation, where the PdO-like phase is well dispersed and the transition metal ions display a high oxygen storage capability. The reaction pathway over both catalysts proceeds most probably through Mars–van Krevelen mechanism. The supported catalysts are thermally stable when they are aged at 505 °C for 120 h in air containing 1.2 vol.% water vapor. Furthermore, the experimentally obtained data on La(Co0.8Ni0.1Fe0.1)0.85Pd0.15O3—based catalyst, supported on monolithic substrate VDM®Aluchrom Y Hf are simulated by using a two-dimensional heterogeneous model for monolithic reactor in order to predict the performance of an industrial catalytic reactor for abatement of methane emissions. Full article
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Article
Effect of Adding Chelating Ligands on the Catalytic Performance of Rh-Promoted MoS2 in the Hydrodesulfurization of Dibenzothiophene
Catalysts 2021, 11(11), 1398; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111398 - 18 Nov 2021
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Abstract
Hydrodesulfurization (HDS) is a widely used process currently employed in petroleum refineries to eliminate organosulfur compounds in fuels. The current hydrotreating process struggles to remove organosulfur compounds with a steric hindrance due to the electronic nature of the current catalysts employed. In this [...] Read more.
Hydrodesulfurization (HDS) is a widely used process currently employed in petroleum refineries to eliminate organosulfur compounds in fuels. The current hydrotreating process struggles to remove organosulfur compounds with a steric hindrance due to the electronic nature of the current catalysts employed. In this work, the effects of adding chelating ligands such as ethylenediaminetetraacetic acid (EDTA), citric acid (CA) and acetic acid (AA) to rhodium (Rh) and active molybdenum (Mo) species for dibenzothiophene (DBT) HDS catalytic activity was evaluated. HDS activities followed the order of RhMo/ɣ-Al2O3 (88%) > RhMo-AA/ɣ-Al2O3 (73%) > RhMo-CA/ɣ-Al2O3 (72%) > RhMo-EDTA/ɣ-Al2O3 (68%). The observed trend was attributed to the different chelating ligands with varying electronic properties, thus influencing the metal–support interaction and the favorable reduction of the Mo species. RhMo/ɣ-Al2O3 offered the highest HDS activity due to its (i) lower metal–support interaction energy, as observed from the RhMo/ɣ-Al2O3 band gap of 3.779 eV and the slight shift toward the lower BE of Mo 3d, (ii) increased Mo-O-Mo species (NMo-O-Mo ~1.975) and (iii) better sulfidation of Rh and MoO in RhMo/ɣ-Al2O3 compared to the chelated catalysts. The obtained data provides that HDS catalytic activity was mainly driven by the structural nature of the RhMo-based catalyst, which influences the formation of more active sites that can enhance the HDS activity. Full article
(This article belongs to the Special Issue Frontiers in Heterogeneous Catalysts for Desulfurization of Fuel Oil)
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Article
Manganese Molybdenum Oxide Micro Rods Adorned Porous Carbon Hybrid Electrocatalyst for Electrochemical Determination of Furazolidone in Environmental Fluids
Catalysts 2021, 11(11), 1397; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111397 - 18 Nov 2021
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Abstract
The frequent occurrence of furazolidone (FZD) in environmental fluids reveals the ongoing increase in use and raises concerns about the need of monitoring it. To investigate the electrochemical behavior of FZD, a novel sensor of manganese molybdenum oxide (MMO) micro rods adorned three-dimensional [...] Read more.
The frequent occurrence of furazolidone (FZD) in environmental fluids reveals the ongoing increase in use and raises concerns about the need of monitoring it. To investigate the electrochemical behavior of FZD, a novel sensor of manganese molybdenum oxide (MMO) micro rods adorned three-dimensional porous carbon (PC) electrocatalyst was constructed. The crystalline structure and surface morphology of the MMO/PC composite was characterized by XRD, Raman, FESEM, and HR-TEM. Electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and amperometric(i-t) methods were used to assess the electrocatalytic activity of modified electrodes. In the presence of FZD, the as-fabricated MMO/PC modified glassy carbon electrode (GCE) performed better at lower potentials with a greater peak current than other modified GCE. These results emanate from the synergistic effect of the MMO/PC suspension on the GCE. The electrochemical behavior of the amperometric(i-t) technique was used to determine FZD. Amperometric(i-t) detection yielded linear dynamic ranges of 150 nM to 41.05 µM and 41.05 to 471.05 µM with detection limits of 30 nM. The MMO/PC hybrid sensor was also effectively used to detect FZD in environmental fluids, yielding ultra-trace level detection. Full article
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Article
Influence of Synthesis Approach on Controlled Microstructures and Photocatalytic Properties of Ag/AgBr-Activated Carbon Composites on Visible Light Degradation of Tetracycline
Catalysts 2021, 11(11), 1396; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111396 - 18 Nov 2021
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Abstract
The influence of the synthesis approach (thermal polyol and deposition–precipitation) regarding the dispersion of Ag/AgBr nanoparticles dispersed on activated carbon prepared from chemical impregnated pinecone (TP-AABR-ACK, and DP-AABR-ACK) was studied, to increase their photocatalytic efficiency on the degradation of tetracycline (TC). The physicochemical [...] Read more.
The influence of the synthesis approach (thermal polyol and deposition–precipitation) regarding the dispersion of Ag/AgBr nanoparticles dispersed on activated carbon prepared from chemical impregnated pinecone (TP-AABR-ACK, and DP-AABR-ACK) was studied, to increase their photocatalytic efficiency on the degradation of tetracycline (TC). The physicochemical characterization evidenced the significance of the ACK catalyst promoter in enhancing controlled microstructures (morphologies and particle size distributions), synergistic interface interaction between AABR NPs and the carbonaceous support, and efficient photogenerated charge carriers separation within TP-AABR-ACK, and DP-AABR-ACK composites. The results revealed 92% removal of TC within 180 min under the LED visible light irradiation, which was achieved using TP-AABR-ACK when compared to DP-AABR-ACK composite and other catalysts in this study. Such superior results achieved with TP-AABR-ACK composite were attributed to controlled morphologies, reduced particle size and agglomeration, improved absorptivity, and superior cooperative effect between the AABR and ACK catalyst promoter as evidenced from SEM, EDX, TEM, UV-DRS, and electrochemical characterizations, respectively. Furthermore, enhanced TOC removal and abundance of reactive superoxide anion generation were achieved with the TP-AABR-ACK composite in this study. Full article
(This article belongs to the Special Issue Structured Semiconductors in Photocatalysis)
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Review
Recent Advances in the Brønsted/Lewis Acid Catalyzed Conversion of Glucose to HMF and Lactic Acid: Pathways toward Bio-Based Plastics
Catalysts 2021, 11(11), 1395; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111395 - 18 Nov 2021
Viewed by 236
Abstract
One of the most trending topics in catalysis recently is the use of renewable sources and/or non-waste technologies to generate products with high added value. That is why, the present review resumes the advances in catalyst design for biomass chemical valorization. The variety [...] Read more.
One of the most trending topics in catalysis recently is the use of renewable sources and/or non-waste technologies to generate products with high added value. That is why, the present review resumes the advances in catalyst design for biomass chemical valorization. The variety of involved reactions and functionality of obtained molecules requires the use of multifunctional catalyst able to increase the efficiency and selectivity of the selected process. The use of glucose as platform molecule is proposed here and its use as starting point for biobased plastics production is revised with special attention paid to the proposed tandem Bronsted/Lewis acid catalysts. Full article
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Review
Recent Progress on Transition Metal Based Layered Double Hydroxides Tailored for Oxygen Electrode Reactions
Catalysts 2021, 11(11), 1394; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111394 - 18 Nov 2021
Viewed by 263
Abstract
The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), namely, so-called oxygen electrode reactions, are two fundamental half-cell reactions in the energy storage and conversion devices, e.g., zinc–air batteries and fuel cells. However, the oxygen electrode reactions suffer from sluggish kinetics, large [...] Read more.
The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), namely, so-called oxygen electrode reactions, are two fundamental half-cell reactions in the energy storage and conversion devices, e.g., zinc–air batteries and fuel cells. However, the oxygen electrode reactions suffer from sluggish kinetics, large overpotential and complicated reaction paths, and thus require efficient and stable electrocatalysts. Transition-metal-based layered double hydroxides (LDHs) and their derivatives have displayed excellent catalytic performance, suggesting a major contribution to accelerate electrochemical reactions. The rational regulation of electronic structure, defects, and coordination environment of active sites via various functionalized strategies, including tuning the chemical composition, structural architecture, and topotactic transformation process of LDHs precursors, has a great influence on the resulting electrocatalytic behavior. In addition, an in-depth understanding of the structural performance and chemical-composition-performance relationships of LDHs-based electrocatalysts can promote further rational design and optimization of high-performance electrocatalysts. Finally, prospects for the design of efficient and stable LDHs-based materials, for mass-production and large-scale application in practice, are discussed. Full article
(This article belongs to the Special Issue Transition Metal Catalysis)
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Article
A Study on the Applicability of NiFe2O4 Nanoparticles as the Basis of Catalysts for the Purification of Aqueous Media from Pollutants
Catalysts 2021, 11(11), 1393; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111393 - 18 Nov 2021
Viewed by 201
Abstract
The aim of this work is to evaluate the application of NiFe2O4 nanoparticles with spinel structures as the basis of catalysts for the purification of aqueous media from pollutants such as manganese and arsenic. The interest in these catalysts is [...] Read more.
The aim of this work is to evaluate the application of NiFe2O4 nanoparticles with spinel structures as the basis of catalysts for the purification of aqueous media from pollutants such as manganese and arsenic. The interest in these catalysts is due to their ease of production and high absorption efficiency, which, together with their magnetic properties, allow the use of nanoparticles for a long time. The sol–gel method, followed by thermal annealing of the samples at different temperatures, was proposed as a method for the synthesis of spinel nanoparticles. The choice of the annealing temperature range of 200–1000 °C is caused by the possibility of estimating changes in the structural properties and the degree of nanoparticles crystallinity. During the study of structural changes in nanoparticles depending on the annealing temperature, it was found that in the temperature range of 200–800 °C, there is an ordering of structural parameters, while for samples obtained at annealing temperatures above 800 °C, there is a partial disorder caused by the agglomeration of nanoparticles with a subsequent increase in their size. According to the results of the studies on the purification of aqueous media from pollutants, it was found that the greatest absorption efficiency belongs to nanoparticles annealed at 500–700 °C, with the purification efficiency of 70–85%, depending on the type of pollutant. The results obtained from the use of nanoparticles as catalysts for the purification of aqueous media show great prospects for their further application on an industrial scale. Full article
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Article
Theoretical Study on Ethylene Polymerization Catalyzed by Half-Titanocenes Bearing Different Ancillary Groups
Catalysts 2021, 11(11), 1392; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111392 - 18 Nov 2021
Viewed by 236
Abstract
Half-titanocenes are well known to show high activity for ethylene polymerization and good capability for copolymerization of ethylene with other olefins, and the ancillary ligands can crucially affect the catalytic performance. In this paper, the mechanisms of ethylene polymerization catalyzed by three half-metallocenes, [...] Read more.
Half-titanocenes are well known to show high activity for ethylene polymerization and good capability for copolymerization of ethylene with other olefins, and the ancillary ligands can crucially affect the catalytic performance. In this paper, the mechanisms of ethylene polymerization catalyzed by three half-metallocenes, (η5-C5Me5)TiCl2(O-2,6-iPr2C6H3) (1), (η5-C5Me5)TiCl2(N=CtBu2) (2) and [Me2Si(η5-C5Me4)(NtBu)]TiCl2 (3), have been investigated by density functional theory (DFT) method. At the initiation stage, a higher free energy barrier was determined for complex 1, probably due to the presence of electronegative O atom in phenoxy ligand. At the propagation stage, front-side insertion of the second ethylene is kinetically more favorable than back-side insertion for complexes 1 and 2, while both side insertion orientations are comparable for complex 3. The energy decomposition showed that the bridged cyclopentadienyl amide ligand could enhance the rigidity of the active species as suggested by the lowest deformation energy derived from 3. At the chain termination stage, β-H transfer was calculated to be a dominant chain termination route over β-H elimination, presumably owing to the thermodynamic perspective. Full article
(This article belongs to the Special Issue Advances in Ziegler-Natta Type Catalysts for Olefin Polymerization)
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Article
“Doing More with Less”: Ni(II)@ORMOSIL, a Novel Sol-Gel Pre-Catalyst for the Reduction of Nitrobenzene
Catalysts 2021, 11(11), 1391; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111391 - 18 Nov 2021
Viewed by 250
Abstract
Reduction of nitrobenzene with NaBH4 using zero-valent iron nanoparticles (ZVI-NPs) and NiCl2∙6H2O incorporated in organically modified hybrid silica matrices as [email protected] and Ni(II)@ORMOSIL catalysts is proposed as a remediation strategy. Ni(II)@ORMOSIL is prepared by ion-exchanging H+ of [...] Read more.
Reduction of nitrobenzene with NaBH4 using zero-valent iron nanoparticles (ZVI-NPs) and NiCl2∙6H2O incorporated in organically modified hybrid silica matrices as [email protected] and Ni(II)@ORMOSIL catalysts is proposed as a remediation strategy. Ni(II)@ORMOSIL is prepared by ion-exchanging H+ of the ORMOSIL matrix with NiII. Ni(II)@ORMOSIL is a pre-catalyst that undergoes reduction by NaBH4 by an in-situ reaction and promotes nitrobenzene reduction by the unconsumed NaBH4, leading to sparing use of the catalyst. Ni(II)@ORMOSIL undergoes color change from green to black in this process, returning to a green hue after washing and drying. Nitrobenzene reductions were examined in aqueous acetonitrile solvent mixtures, and the reduction cascade produced the reaction end-products with catalytic implications. Plausible mechanisms of [email protected] and Ni(II)@ORMOSIL catalyzed reductions of nitrobenzene are discussed. This work is the first to report M(II)@ORMOSIL pre-catalysts for in-situ reduction of nitrobenzene, and expands the scope of the ORMOSIL series of catalysts for the reduction of polluting compounds. This approach enables the development of catalysts that use very low concentrations of transition metal cations. Full article
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Article
Cold-Active Lipase-Based Biocatalysts for Silymarin Valorization through Biocatalytic Acylation of Silybin
Catalysts 2021, 11(11), 1390; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111390 - 17 Nov 2021
Viewed by 290
Abstract
Extremophilic biocatalysts represent an enhanced solution in various industrial applications. Integrating enzymes with high catalytic potential at low temperatures into production schemes such as cold-pressed silymarin processing not only brings value to the silymarin recovery from biomass residues, but also improves its solubility [...] Read more.
Extremophilic biocatalysts represent an enhanced solution in various industrial applications. Integrating enzymes with high catalytic potential at low temperatures into production schemes such as cold-pressed silymarin processing not only brings value to the silymarin recovery from biomass residues, but also improves its solubility properties for biocatalytic modification. Therefore, a cold-active lipase-mediated biocatalytic system has been developed for silybin acylation with methyl fatty acid esters based on the extracellular protein fractions produced by the psychrophilic bacterial strain Psychrobacter SC65A.3 isolated from Scarisoara Ice Cave (Romania). The extracellular production of the lipase fraction was enhanced by 1% olive-oil-enriched culture media. Through multiple immobilization approaches of the cold-active putative lipases (using carbodiimide, aldehyde-hydrazine, or glutaraldehyde coupling), bio-composites (S1–5) with similar or even higher catalytic activity under cold-active conditions (25 °C) have been synthesized by covalent attachment to nano-/micro-sized magnetic or polymeric resin beads. Characterization methods (e.g., FTIR DRIFT, SEM, enzyme activity) strengthen the biocatalysts’ settlement and potential. Thus, the developed immobilized biocatalysts exhibited between 80 and 128% recovery of the catalytic activity for protein loading in the range 90–99% and this led to an immobilization yield up to 89%. The biocatalytic acylation performance reached a maximum of 67% silybin conversion with methyl decanoate acylating agent and nano-support immobilized lipase biocatalyst. Full article
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