Catalysts

25 pages, 1793 KiB

Open AccessReview

Recent Advances in the Application of Enzyme Processing Assisted by Ultrasound in Agri-Foods: A Review

by Andrés Córdova, Paola Henríquez, Helena Nuñez, Fabián Rico-Rodriguez, Cecilia Guerrero, Carolina Astudillo-Castro and Andrés Illanes

Catalysts 2022, 12(1), 107; https://doi.org/10.3390/catal12010107 - 17 Jan 2022

Cited by 21 | Viewed by 4570

Abstract

The intensification of processes is essential for the sustainability of the biorefinery concept. Enzyme catalysis assisted by ultrasound (US) may offer interesting opportunities in the agri-food sector because the cavitation effect provided by this technology has been shown to improve the efficiency of [...] Read more.

The intensification of processes is essential for the sustainability of the biorefinery concept. Enzyme catalysis assisted by ultrasound (US) may offer interesting opportunities in the agri-food sector because the cavitation effect provided by this technology has been shown to improve the efficiency of the biocatalysts. This review presents the recent advances in this field, focused on three main applications: ultrasound-assisted enzymatic extractions (UAEE), US hydrolysis reactions, and synthesis reactions assisted by US for the manufacturing of agri-food produce and ingredients, enabling the upgrading of agro-industrial waste. Some theoretical and experimental aspects of US that must be considered are also reviewed. Ultrasonic intensity (UI) is the main parameter affecting the catalytic activity of enzymes, but a lack of standardization for its quantification makes it unsuitable to properly compare results. Applications of enzyme catalysis assisted by US in agri-foods have been mostly concentrated in UAEE of bioactive compounds. In second place, US hydrolysis reactions have been applied for juice and beverage manufacturing, with some interesting applications for producing bioactive peptides. In last place, a few efforts have been performed regarding synthesis reactions, mainly through trans and esterification to produce structured lipids and sugar esters, while incipient applications for the synthesis of oligosaccharides show promising results. In most cases, US has improved the reaction yield, but much information is lacking on how different sonication conditions affect kinetic parameters. Future research should be performed under a multidisciplinary approach for better comprehension of a very complex phenomenon that occurs in very short time periods. Full article

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

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15 pages, 9503 KiB

Open AccessFeature PaperArticle

Synthesis of Indoles by Palladium-Catalyzed Reductive Cyclization of β-Nitrostyrenes with Phenyl Formate as a CO Surrogate

by Francesco Ferretti, Manar Ahmed Fouad and Fabio Ragaini

Catalysts 2022, 12(1), 106; https://doi.org/10.3390/catal12010106 - 17 Jan 2022

Cited by 8 | Viewed by 2875

Abstract

The reductive cyclization of suitably substituted organic nitro compounds by carbon monoxide is a very appealing technique for the synthesis of heterocycles because of its atom efficiency and easiness of separation of the only stoichiometric byproduct CO₂, but the need for [...] Read more.

The reductive cyclization of suitably substituted organic nitro compounds by carbon monoxide is a very appealing technique for the synthesis of heterocycles because of its atom efficiency and easiness of separation of the only stoichiometric byproduct CO₂, but the need for pressurized CO has hampered its diffusion. We have recently reported on the synthesis of indoles by reductive cyclization of o-nitrostyrenes using phenyl formate as a CO surrogate, using a palladium/1,10-phenanthroline complex as catalyst. However, depending on the desired substituents on the structure, the use of β-nitrostyrenes as alternative reagents may be advantageous. We report here the results of our study on the possibility to use phenyl formate as a CO surrogate in the synthesis of indoles by reductive cyclization of β-nitrostyrenes, using PdCl₂(CH₃CN)₂ + phenanthroline as the catalyst. It turned out that good results can be obtained when the starting nitrostyrene bears an aryl substituent in the alpha position. However, when no such substituent is present, only fair yield of indole can be obtained because the base required to decompose the formate also catalyzes an oligo-polymerization of the starting styrene. The reaction can be performed in a single glass pressure tube, a cheap and easily available piece of equipment. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts: Molecular Catalysis)

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19 pages, 8122 KiB

Open AccessArticle

Bimetallic Co-Rh Systems as a Prospective Base for Design of CH₄ Reforming Catalysts to Produce Syngas with a Controllable Composition

by Sholpan S. Itkulova, Kirill A. Valishevskiy and Yerzhan A. Boleubayev

Catalysts 2022, 12(1), 105; https://doi.org/10.3390/catal12010105 - 17 Jan 2022

Cited by 5 | Viewed by 2196

Abstract

Dry and bireforming (CO₂-H₂O) of methane are the most environmentally friendly routes involving two main greenhouse gases to produce syngas—an important building block for large-scale production of various commodity chemicals. The main drawback preventing their industrial application is the [...] Read more.

Dry and bireforming (CO₂-H₂O) of methane are the most environmentally friendly routes involving two main greenhouse gases to produce syngas—an important building block for large-scale production of various commodity chemicals. The main drawback preventing their industrial application is the coke formation. Developing catalysts that do not favour or are resistant to coke formation is the only way to improve the catalyst stability. Designing an economically viable catalyst may be achieved by exploiting the synergic effects of combining noble (expensive but coke-resistant) and non-noble (cheap but prone to carbonisation) metals to form highly effective catalysts. This work deals with development of highly active and stable bimetallic Co-containing catalysts modified with small amount of Rh, 0.1–0.5 mass %. The catalysts were characterised by BET, XRD, TEM, SEM, XPS, and TPR-H₂ methods and tested in dry, bi-, and for comparison in steam reforming of methane. It was revealed that the bimetallic Co-Rh systems is much more effective than monometallic ones due to Co-Rh interaction accompanied with increasing dispersion and reducibility of Co. The extents of CH₄ and CO₂ conversion over the 5%Co-Rh/Al₂O₃ are varied within 85–99%. Syngas with variable H₂/CO = 0.9–3.9 was formed. No loss of activity was observed for 100 h of long-term stability test. Full article

(This article belongs to the Special Issue Catalytic Processes of Bimetallic Nanoparticles)

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15 pages, 2790 KiB

Open AccessFeature PaperArticle

Catalytic Conversion of Glycerol to Methyl Lactate over Au-CuO/Sn-Beta: The Roles of Sn-Beta

by Ying Duan, Qianqian Luo, Renfeng Nie, Jianshe Wang, Yongsheng Zhang, Tianliang Lu and Chunbao Xu

Catalysts 2022, 12(1), 104; https://doi.org/10.3390/catal12010104 - 17 Jan 2022

Cited by 6 | Viewed by 2701

Abstract

The production of methyl lactate as a degradable polymer monomer from biomass was an important topic for a sustainable society. In this manuscript, glycerol was oxidated to methyl lactate catalyzed by the combination of Au-CuO and Sn-Beta. The influence of Sn content, Sn [...] Read more.

The production of methyl lactate as a degradable polymer monomer from biomass was an important topic for a sustainable society. In this manuscript, glycerol was oxidated to methyl lactate catalyzed by the combination of Au-CuO and Sn-Beta. The influence of Sn content, Sn source, and the preparation conditions for Sn-β was studied. The Au content in Au/CuO was also investigated by varying the Au content in Au/CuO. The catalysts were characterized by XRD, FTIR spectroscopy of pyridine adsorption, and TEM to study the role of Sn and the influence of different parameters for catalyst preparation. After the optimization of reaction parameters, the yield of methyl lactate from glycerol reached 59% at 363 K after reacting in 1.6 MPa of O₂ for 6 h. Full article

(This article belongs to the Special Issue Catalytic Conversion of Glycerol)

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13 pages, 1639 KiB

Open AccessArticle

Advanced Treatment of Phosphorus Pesticide Wastewater Using an Integrated Process of Coagulation and Ozone Catalytic Oxidation

by Shengping Cao, Lei Chen, Minyan Zhao, Ankang Liu, Mingxiu Wang and Yongjun Sun

Catalysts 2022, 12(1), 103; https://doi.org/10.3390/catal12010103 - 17 Jan 2022

Cited by 12 | Viewed by 2506

Abstract

Conventional pretreatment and secondary biochemical treatment are ineffective methods for removing phosphorus from phosphorus-containing pesticide wastewater. In this study, coagulation-coupled ozone catalytic oxidation was used to treat secondary biochemical tailwater of phosphorus-containing pesticide wastewater thoroughly. The effects of the coagulant type, coagulant dosage, [...] Read more.

Conventional pretreatment and secondary biochemical treatment are ineffective methods for removing phosphorus from phosphorus-containing pesticide wastewater. In this study, coagulation-coupled ozone catalytic oxidation was used to treat secondary biochemical tailwater of phosphorus-containing pesticide wastewater thoroughly. The effects of the coagulant type, coagulant dosage, coagulant concentration, wastewater pH, stirring rate, and stirring time on the removal efficiency of chemical oxygen demand (COD), total phosphorus (TP), and chromaticity were investigated during coagulation. When the dosage of the coagulant PAFS was equal to 100 mg/L, the concentration of the coagulant, pH, stirring rate, and stirring time were 5 wt%, 8, 100 rpm, and 5 min, respectively, and the removal rates of COD, TP, and chroma in wastewater reached the maximum value of 17.6%, 86.8%, and 50.0%, respectively. Effluent after coagulation was treated via ozone catalytic oxidation. When the respective ozone dosage, H₂O₂ dosage, catalyst dosage, and reaction time were 120 mg/L, 0.1 vt‰, 10 wt%, and 90 min, residual COD and chromaticity of the final effluent were 10.3 mg/L and 8, respectively. The coagulation-coupled ozone catalytic oxidation process has good application prospects in the treatment of secondary biochemical tailwater from phosphorus-containing pesticide wastewater. Full article

(This article belongs to the Special Issue Advanced Functional Materials for Environmental Catalysis)

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11 pages, 4760 KiB

Open AccessArticle

Island-Type Hybrid Catalysts Applied for Anion Exchange Membrane Water Electrolysis

by Hsueh-Yu Chen, Guan-Cheng Chen, Kuo-Wei Liao, Wen-Hui Wei, Hsin-Chih Huang and Chen-Hao Wang

Catalysts 2022, 12(1), 102; https://doi.org/10.3390/catal12010102 - 17 Jan 2022

Cited by 3 | Viewed by 2302

Abstract

A rapid, productive, and efficient process was invented to produce hybrid catalysts for transition metal oxide water electrolysis. The microwave-assisted hydrothermal method was applied to synthesize transition metal oxide catalysts by controlling the amount of cobalt and iron. This work solves the cracking [...] Read more.

A rapid, productive, and efficient process was invented to produce hybrid catalysts for transition metal oxide water electrolysis. The microwave-assisted hydrothermal method was applied to synthesize transition metal oxide catalysts by controlling the amount of cobalt and iron. This work solves the cracking problem for the catalytic layer during the water electrolysis. It uses Fe₂O₃ as the support and covers a catalytic layer outside it and a nanoscale gap between each catalyst, which can help to remove the gas and fill up the water. The unique structure of the catalysts can prevent them from accumulating gas and increasing their efficiency for long-term water electrolysis. By using unique catalysts in the water electrolyzer, the current density reaches higher than 200 mA cm⁻² at 2.0 V and does not show a significant decay even after 200 h. Full article

(This article belongs to the Section Catalysis for Sustainable Energy)

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13 pages, 3878 KiB

Open AccessPerspective

Horizons in Asymmetric Organocatalysis: En Route to the Sustainability and New Applications

by Sandra Ardevines, Eugenia Marqués-López and Raquel P. Herrera

Catalysts 2022, 12(1), 101; https://doi.org/10.3390/catal12010101 - 16 Jan 2022

Cited by 12 | Viewed by 4154

Abstract

Nowadays, the development of new enantioselective processes is highly relevant in chemistry due to the relevance of chiral compounds in biomedicine (mainly drugs) and in other fields, such as agrochemistry, animal feed, and flavorings. Among them, organocatalytic methods have become an efficient and [...] Read more.

Nowadays, the development of new enantioselective processes is highly relevant in chemistry due to the relevance of chiral compounds in biomedicine (mainly drugs) and in other fields, such as agrochemistry, animal feed, and flavorings. Among them, organocatalytic methods have become an efficient and sustainable alternative since List and MacMillan pioneering contributions were published in 2000. These works established the term asymmetric organocatalysis to label this area of research, which has grown exponentially over the last two decades. Since then, the scientific community has attended to the discovery of a plethora of organic reactions and transformations carried out with excellent results in terms of both reactivity and enantioselectivity. Looking back to earlier times, we can find in the literature a few examples where small organic molecules and some natural products could act as effective catalysts. However, with the birth of this type of catalysis, new chemical architectures based on amines, thioureas, squaramides, cinchona alkaloids, quaternary ammonium salts, carbenes, guanidines and phosphoric acids, among many others, have been developed. These organocatalysts have provided a broad range of activation modes that allow privileged interactions between catalysts and substrates for the preparation of compounds with high added value in an enantioselective way. Here, we briefly cover the history of this chemistry, from our point of view, including our beginnings, how the field has evolved during these years of research, and the road ahead. Full article

(This article belongs to the Special Issue Organocatalysis: Advances, Opportunity, and Challenges)

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10 pages, 1158 KiB

Open AccessArticle

Thermal Stability of Potassium-Promoted Cobalt Molybdenum Nitride Catalysts for Ammonia Synthesis

by Paweł Adamski, Wojciech Czerwonko and Dariusz Moszyński

Catalysts 2022, 12(1), 100; https://doi.org/10.3390/catal12010100 - 16 Jan 2022

Cited by 6 | Viewed by 2959

Abstract

The application of cobalt molybdenum nitrides as ammonia synthesis catalysts requires further development of the optimal promoter system, which enhances not only the activity but also the stability of the catalysts. To do so, elucidating the influence of the addition of alkali metals [...] Read more.

The application of cobalt molybdenum nitrides as ammonia synthesis catalysts requires further development of the optimal promoter system, which enhances not only the activity but also the stability of the catalysts. To do so, elucidating the influence of the addition of alkali metals on the structural properties of the catalysts is essential. In this study, potassium-promoted cobalt molybdenum nitrides were synthesized by impregnation of the precursor CoMoO₄·3/4H₂O with aqueous KNO₃ solution followed by ammonolysis. The catalysts were characterized with the use of XRD and BET methods, under two conditions: as obtained and after the thermal stability test. The catalytic activity in the synthesis of ammonia was examined at 450 °C, under 10 MPa. The thermal stability test was carried out by heating at 650 °C in the same apparatus. As a result of ammonolysis, mixtures of two phases: Co₃Mo₃N and Co₂Mo₃N were obtained. The phase concentrations were affected by potassium admixture. The catalytical activity increased for the most active catalyst by approximately 50% compared to non-promoted cobalt molybdenum nitrides. The thermal stability test resulted in a loss of activity, on average, of 30%. Deactivation was caused by the collapse of the porous structure, which is attributed to the conversion of the Co₂Mo₃N phase to the Co₃Mo₃N phase. Full article

(This article belongs to the Special Issue Applied Catalysis in Chemical Industry: Synthesis, Catalyst Design, and Evaluation)

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13 pages, 2637 KiB

Open AccessArticle

Fabrication and Characterization of a Marine Wet Solar Cell with Titanium Dioxide and Copper Oxides Electrodes

by Htoo Nay Wunn, Shinichi Motoda and Motoaki Morita

Catalysts 2022, 12(1), 99; https://doi.org/10.3390/catal12010099 - 15 Jan 2022

Cited by 3 | Viewed by 2528

Abstract

One of the effective ways of utilizing marine environments is to generate energy, power, and hydrogen via the effect of photocatalysts in the seawater. Since the ocean is vast, we are able to use its large area, but the power generation system must [...] Read more.

One of the effective ways of utilizing marine environments is to generate energy, power, and hydrogen via the effect of photocatalysts in the seawater. Since the ocean is vast, we are able to use its large area, but the power generation system must be of low cost and have high durability against both force and corrosion. In order to meet those requirements, this study focuses on the fabrication of a novel marine wet solar cell composed of a titanium dioxide photoanode and a copper oxide photocathode. These electrodes were deposited on type 329J4L stainless steel, which possesses relative durability in marine environments. This study focuses on the characterization of the photocatalytic properties of electrodes in seawater. Low-cost manufacturing processes of screen-printing and vacuum vapor deposition were applied to produce the titanium dioxide and copper oxides electrodes, respectively. We investigated the photopotential of the electrodes, along with the electrochemical properties and cell voltage properties of the cell. X-ray diffraction spectroscopy (XRD) of the copper oxides electrode was analyzed in association with the loss of photocatalytic effect in the copper oxides electrode. Although the conversion efficiency of the wet cell was less than 1%, it showed promising potential for use in marine environments with low-cost production. Electrochemical impedance spectroscopy (EIS) of the cell was also conducted, from which impedance values regarding the electrical properties of electrodes and their interfaces of charge-transfer processes were obtained. This study focuses on the early phase of the marine wet solar cell, which should be further studied for long-term stability and in actual marine environmental applications. Full article

(This article belongs to the Special Issue Application of Photocatalysts in Environmental Chemistry)

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14 pages, 4004 KiB

Open AccessArticle

A Model of Catalytic Cracking: Catalyst Deactivation Induced by Feedstock and Process Variables

by Galina Y. Nazarova, Elena N. Ivashkina, Emiliya D. Ivanchina and Maria Y. Mezhova

Catalysts 2022, 12(1), 98; https://doi.org/10.3390/catal12010098 - 14 Jan 2022

Cited by 10 | Viewed by 3048

Abstract

Changes in the quality of the feedstocks generated by involving various petroleum fractions in catalytic cracking significantly affect catalyst deactivation, which stems from coke formed on the catalyst surface. By conducting experimental studies on feedstocks and catalysts, as well as using industrial data, [...] Read more.

Changes in the quality of the feedstocks generated by involving various petroleum fractions in catalytic cracking significantly affect catalyst deactivation, which stems from coke formed on the catalyst surface. By conducting experimental studies on feedstocks and catalysts, as well as using industrial data, we studied how the content of saturates, aromatics and resins (SAR) in feedstock and the main process variables, including temperature, consumptions of the feedstock, catalyst and slops, influence the formation of catalytic coke. We also determined catalyst deactivation patterns using TG-DTA, N₂ adsorption and TPD, which were further used as a basis for a kinetic model of catalytic cracking. This model helps predict the changes in reactions rates caused by coke formation and, also, evaluates quantitatively how group characteristics of the feedstock, the catalyst-to-oil ratio and slop flow influence the coke content on the catalyst and the degree of catalyst deactivation. We defined that a total loss of acidity changes from 8.6 to 30.4 wt% for spent catalysts, and this depends on SAR content in feedstock and process variables. The results show that despite enriching the feedstock by saturates, the highest coke yields (4.6–5.2 wt%) may be produced due to the high content of resins (2.1–3.5 wt%). Full article

(This article belongs to the Special Issue Modeling of the Catalytic Cracking)

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13 pages, 3106 KiB

Open AccessFeature PaperArticle

Hydrogenation of Carboxyl Nitrile Butadiene Rubber Latex Using a Ruthenium-Based Catalyst

by Xiaodong Liu, Yunlei Fu, Defang Zhou, Hanchu Chen, Yanyan Li, Jianhui Song, Shouyan Zhang and Hui Wang

Catalysts 2022, 12(1), 97; https://doi.org/10.3390/catal12010097 - 14 Jan 2022

Cited by 4 | Viewed by 3416

Abstract

Hydrogenated carboxyl nitrile rubber (HXNBR) is endowed with superior mechanical performance and heat–oxygen aging resistance via emulsion hydrogenation of its precursor, i.e., carboxyl nitrile rubber (XNBR). Herein, a ruthenium-based catalyst was prepared to achieve the direct catalytic hydrogenation of XNBR latex. The effects [...] Read more.

Hydrogenated carboxyl nitrile rubber (HXNBR) is endowed with superior mechanical performance and heat–oxygen aging resistance via emulsion hydrogenation of its precursor, i.e., carboxyl nitrile rubber (XNBR). Herein, a ruthenium-based catalyst was prepared to achieve the direct catalytic hydrogenation of XNBR latex. The effects of a series of hydrogenation conditions, such as catalyst dosage, solid content and reaction temperature, as well as the hydrogen pressure, on the hydrogenation reaction were investigated in detail. We found that the hydrogenation rate fell upon increasing the solid content of the XNBR latex, with an XNBR conversion rate of 95.01 mol% in 7 h with 11.25 wt% solid content. As the reaction temperature was increased, the hydrogenation rate first increased and then decreased. The fastest reaction hydrogenation rate was reached at 140 °C, with an XNBR conversion of 95.10 mol% in 5 h. The hydrogenation rate was positively related with the hydrogen pressure employed in the reactor. In view of the safety and cost, a pressure rate of 1300 psi was considered optimal. Similarly, the hydrogenation rate can also be enhanced by adding more catalyst. When 0.05 wt% catalyst was added, the fastest hydrogenation rate was achieved. In summary, the following optimum hydrogenation conditions were determined by using a synthesized ruthenium-based catalyst: 11.25 wt% solid content of XNBR latex, 140 °C of reaction temperature, 1300 psi of hydrogen pressure and 0.05 wt% catalyst. The vulcanization, mechanical performance, aging resistance and oil resistance of the produced HXNBR under the above reaction conditions were systematically investigated. Full article

(This article belongs to the Special Issue Novel Catalysts for Polyolefin and Synthetic Rubber)

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16 pages, 3087 KiB

Open AccessArticle

PdAg/C Electrocatalysts Synthesized by Thermal Decomposition of Polymeric Precursors Improve Catalytic Activity for Ethanol Oxidation Reaction

by Yonis Fornazier Filho, Ana Caroliny Carvalho da Cruz, Rolando Pedicini, José Ricardo Cezar Salgado, Rodrigo Vieira Rodrigues, Priscilla Paiva Luz, Sergi Garcia-Segura and Josimar Ribeiro

Catalysts 2022, 12(1), 96; https://doi.org/10.3390/catal12010096 - 14 Jan 2022

Cited by 6 | Viewed by 2510

Abstract

An efficient ethanol oxidation reaction (EOR) is required to enhance energy production in alcohol-based fuel cells. The use of bimetallic catalysts promises decreasing reliance on platinum group metal (PGM) electrocatalysts by minimizing the use of these expensive materials in the overall electrocatalyst composition. [...] Read more.

An efficient ethanol oxidation reaction (EOR) is required to enhance energy production in alcohol-based fuel cells. The use of bimetallic catalysts promises decreasing reliance on platinum group metal (PGM) electrocatalysts by minimizing the use of these expensive materials in the overall electrocatalyst composition. In this article, an alternative method of bimetallic electrocatalyst synthesis based on the use of polymeric precursors is explored. PdAg/C electrocatalysts were synthesized by thermal decomposition of polymeric precursors and used as the anode electrocatalyst for EOR. Different compositions, including pristine Pd/C and Ag/C, as well as bimetallic Pd₈₀Ag₂₀/C, and Pd₆₀Ag₄₀/C electrocatalysts, were evaluated. Synthesized catalysts were characterized, and electrochemical activity evaluated. X-ray diffraction showed a notable change at diffraction peak values for Pd₈₀Ag₂₀/C and Pd₆₀Ag₄₀/C electrocatalysts, suggesting alloying (solid solution) and smaller crystallite sizes for Pd₆₀Ag₄₀/C. In a thermogravimetric analysis, the electrocatalyst Pd₆₀Ag₄₀/C presented changes in the profile of the curves compared to the other electrocatalysts. In the cyclic voltammetry results for EOR in alkaline medium, Pd₆₀Ag₄₀/C presented a more negative onset potential, a higher current density at the oxidation peak, and a larger electrically active area. Chronoamperometry tests indicated a lower poisoning rate for Pd₆₀Ag₄₀/C, a fact also observed in the CO-stripping voltammetry analysis due to its low onset potential. As the best performing electrocatalyst, Pd₆₀Ag₄₀/C has a lower mass of Pd (a noble and expensive metal) in its composition. It can be inferred that this bimetallic composition can contribute to decreasing the amount of Pd required while increasing the fuel cell performance and expected life. PdAg-type electrocatalysts can provide an economically feasible alternative to pure PGM-electrocatalysts for use as the anode in EOR in fuel cells. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts: Achievements in Electrocatalysis for Sustainable Energy Technologies)

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17 pages, 4937 KiB

Open AccessArticle

Coke Deposition and Structural Changes of Pellet V₂O₅/NaY-SiO₂ in Air Regeneration: The Effects of Temperature on Regeneration

by Chu-Chin Hsieh, Jyong-Sian Tsai, Hwo-Shuenn Sheu and Jen-Ray Chang

Catalysts 2022, 12(1), 95; https://doi.org/10.3390/catal12010095 - 14 Jan 2022

Cited by 1 | Viewed by 1824

Abstract

V₂O₅/NaY-SiO₂ adsorbents were prepared by soaking up vanadium oxalate precursors into pellet NaY-SiO₂. The NaY-SiO₂ supports were prepared from NaY-SiO₂ dough followed by extrusion and calcination at 450 °C. Ethanol was used as a [...] Read more.

V₂O₅/NaY-SiO₂ adsorbents were prepared by soaking up vanadium oxalate precursors into pellet NaY-SiO₂. The NaY-SiO₂ supports were prepared from NaY-SiO₂ dough followed by extrusion and calcination at 450 °C. Ethanol was used as a model adsorbate to test the performance of the adsorbents. The regeneration efficacy, defined as the ratio of the adsorption capacity of a regenerated adsorbent to that of the fresh adsorbent, was investigated through the dynamics of fixed-bed adsorption (breakthrough curve). TPO, DSC, and FT-IR were used to characterize carbonaceous species on the adsorbents; meanwhile, synchrotron XRPD, XAS, and the N₂ isotherm were used to characterize the zeolite, vanadia structure, and surface area, respectively. The results indicated that in low temperature (300 °C) regeneration, adsorption sites covered by alkylated aromatic coke formed during regeneration, causing adsorbent deactivation. In contrast, during regeneration at a high temperature (450 °C), the deactivation was caused by the destruction of the NaY framework concomitant with channel blockage, as suggested by the BET surface area combined with Rietvelt XRPD refinement results. In addition, the appearance of V-O-V contribution in the EXAFS spectra indicated the aggregation of isolated VO₄, which led to a decrease in the combustion rate of the carbonaceous species deposited on the adsorbents. For regeneration at 350 and 400 °C, only trace coke formation and minor structural destruction were observed. Long-term life tests indicated that regeneration at 400 °C presents a higher maintenance of stability. Full article

(This article belongs to the Special Issue Air Pollution Control: Catalytic Oxidation and Reduction of Gaseous Pollutants)

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35 pages, 33716 KiB

Open AccessReview

Recent Advances of Photocatalytic Hydrogenation of CO₂ to Methanol

by Gajanan Y. Shinde, Abhishek S. Mote and Manoj B. Gawande

Catalysts 2022, 12(1), 94; https://doi.org/10.3390/catal12010094 - 14 Jan 2022

Cited by 30 | Viewed by 7785

Abstract

Constantly increasing hydrocarbon fuel combustion along with high levels of carbon dioxide emissions has given rise to a global energy crisis and environmental alterations. Photocatalysis is an effective technique for addressing this energy and environmental crisis. Clean and renewable solar energy is a [...] Read more.

Constantly increasing hydrocarbon fuel combustion along with high levels of carbon dioxide emissions has given rise to a global energy crisis and environmental alterations. Photocatalysis is an effective technique for addressing this energy and environmental crisis. Clean and renewable solar energy is a very favourable path for photocatalytic CO₂ reduction to value-added products to tackle problems of energy and the environment. The synthesis of various products such as CH₄, CH₃OH, CO, EtOH, etc., has been expanded through the photocatalytic reduction of CO₂. Among these products, methanol is one of the most important and highly versatile chemicals widely used in industry and in day-to-day life. This review emphasizes the recent progress of photocatalytic CO₂ hydrogenation to CH₃OH. In particular, Metal organic frameworks (MOFs), mixed-metal oxide, carbon, TiO₂ and plasmonic-based nanomaterials are discussed for the photocatalytic reduction of CO₂ to methanol. Finally, a summary and perspectives on this emerging field are provided. Full article

(This article belongs to the Section Photocatalysis)

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19 pages, 5569 KiB

Open AccessFeature PaperArticle

Electrocatalysts Based on Novel Carbon Forms for the Oxidation of Sulphite

by George Pchelarov, Dzhamal Uzun, Sasho Vassilev, Elena Razkazova-Velkova, Ognian Dimitrov, Aleksandar Tsanev, Adriana Gigova, Nadezhda Shukova and Konstantin Petrov

Catalysts 2022, 12(1), 93; https://doi.org/10.3390/catal12010093 - 14 Jan 2022

Viewed by 2194

Abstract

Described herewith is an electrochemical method to decontaminate sulphur compounds. Studies were carried out of sulphites (SO₃²⁻) oxidation on a range of anode catalysts. The electrocatalysts were characterized by scanning electron microscopy, XRD, XPS and BET. Polarization curves were [...] Read more.

Described herewith is an electrochemical method to decontaminate sulphur compounds. Studies were carried out of sulphites (SO₃²⁻) oxidation on a range of anode catalysts. The electrocatalysts were characterized by scanning electron microscopy, XRD, XPS and BET. Polarization curves were recorded of electrodes incorporating lyophilized higher fullerenes and manganese oxides. The experiments showed that lyophilized higher fullerenes and C₆₀/C₇₀ fullerene catalysts in conjunction with manganese oxides electrochemically convert sulphites (SO₃²⁻) to sulphates (SO₄²⁻). The oxidation products do not poison the electrodes. The XPS analysis shows that the catalysts incorporating DWCNTs, MWCNTs and higher fullerenes have a higher concentration of sp³C carbon bonding leading to higher catalytic activity. It is ascertained that higher fullerenes play a major role in the synthesis of more effective catalysts. The electrodes built by incorporating lyophilized catalysts containing higher fullerenes and manganese oxides are shown as most promising in the effective electrochemical decontamination of industrial and natural wastewaters. Full article

(This article belongs to the Special Issue Design of Electrocatalysts for Green Hydrogen Production from Hydrogen Sulfide and Seawater)

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12 pages, 1991 KiB

Open AccessArticle

Application of Raw and Chemically Modified Biomasses for Heterogeneous Cu-Catalysed Conversion of Aryl boronic Acids to Phenols Derivatives

by Fernanda Guimarães Torres, Filipe Simões Teodoro, Leandro Vinícius Alves Gurgel, Flavien Bourdreux, Olfa Zayene, Anne Gaucher, Laurent Frédéric Gil and Damien Prim

Catalysts 2022, 12(1), 92; https://doi.org/10.3390/catal12010092 - 14 Jan 2022

Cited by 3 | Viewed by 2343

Abstract

This work describes the application of raw and chemically modified cellulose and sugarcane bagasse for ipso-hydroxylation of aryl boronic acids in environmentally friendly reaction conditions. The catalytic efficiency of five support-[Cu] materials was compared in forming phenols from aryl boronic acids. Our [...] Read more.

This work describes the application of raw and chemically modified cellulose and sugarcane bagasse for ipso-hydroxylation of aryl boronic acids in environmentally friendly reaction conditions. The catalytic efficiency of five support-[Cu] materials was compared in forming phenols from aryl boronic acids. Our investigation highlights that the CEDA-[Cu] material (6-deoxy-6-aminoethyleneamino cellulose loaded with Cu) leads to the best results under very mild reaction conditions. The optimized catalytic sequence, allowing a facile transformation of boronic acids to phenols, required the mandatory and joint presence of the support, Cu₂O, and KOH at room temperature. CEDA-[Cu] was characterized using ¹³C solid-state NMR, ICP, and FTIR. The use of CEDA-[Cu] accounts for the efficacious synthesis of variously substituted phenol derivatives and presents very good recyclability after five catalytic cycles. Full article

(This article belongs to the Section Biomass Catalysis)

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9 pages, 1165 KiB

Open AccessFeature PaperReview

Solid Acid Catalysts for the Hock Cleavage of Hydroperoxides

by Jan Drönner, Peter Hausoul, Regina Palkovits and Matthias Eisenacher

Catalysts 2022, 12(1), 91; https://doi.org/10.3390/catal12010091 - 14 Jan 2022

Cited by 8 | Viewed by 4632

Abstract

The oxidation of cumene and following cleavage of cumene hydroperoxide (CHP) with sulfuric acid (Hock rearrangement) is still, by far, the dominant synthetic route to produce phenol. In 2020, the global phenol market reached a value of 23.3 billion US$ with a projected [...] Read more.

The oxidation of cumene and following cleavage of cumene hydroperoxide (CHP) with sulfuric acid (Hock rearrangement) is still, by far, the dominant synthetic route to produce phenol. In 2020, the global phenol market reached a value of 23.3 billion US$ with a projected compound annual growth rate of 3.4% for 2020–2025. From ecological and economical viewpoints, the key step of this process is the cleavage of CHP. One sought-after way to likewise reduce energy consumption and waste production of the process is to substitute sulfuric acid with heterogeneous catalysts. Different types of zeolites, silicon-based clays, heteropoly acids, and ion exchange resins have been investigated and tested in various studies. For every type of these solid acid catalysts, several materials were found that show high yield and selectivity to phenol. In this mini-review, first a brief introduction and overview on the Hock process is given. Next, the mechanism, kinetics, and safety aspects are summarized and discussed. Following, the different types of heterogeneous catalysts and their performance as catalyst in the Hock process are illustrated. Finally, the different approaches to substitute sulfuric acid in the synthetic route to produce phenol are briefly concluded and a short outlook is given. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis in Green Chemistry)

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29 pages, 21117 KiB

Open AccessFeature PaperReview

Heterocycles by Consecutive Multicomponent Syntheses via Catalytically Generated Alkynoyl Intermediates

by Jonas Niedballa and Thomas J. J. Müller

Catalysts 2022, 12(1), 90; https://doi.org/10.3390/catal12010090 - 13 Jan 2022

Cited by 15 | Viewed by 2451

Abstract

Multicomponent processes are beneficial tools for the synthesis of heterocycles. As densely substituted bifunctional electrophiles, ynones are essential intermediates by applying cyclocondensations or cycloadditions in numerous heterocycle syntheses. The respective alkynoyl intermediates are generally accessible by palladium-, copper- and palladium/copper-catalyzed alkynylation. In turn, [...] Read more.

Multicomponent processes are beneficial tools for the synthesis of heterocycles. As densely substituted bifunctional electrophiles, ynones are essential intermediates by applying cyclocondensations or cycloadditions in numerous heterocycle syntheses. The respective alkynoyl intermediates are generally accessible by palladium-, copper- and palladium/copper-catalyzed alkynylation. In turn, the mild reaction conditions allow for a fast and versatile entry to functional heterocycles in the sense of consecutive multicomponent processes. This review collates and presents recent advances in accessing thirteen heterocycle classes and their applications by virtue of catalytic alkynoyl generation in diversity-oriented multicomponent syntheses in a one-pot fashion. Full article

(This article belongs to the Special Issue Metal-Catalyzed Processes in One-Pot Syntheses of Heterocycles)

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48 pages, 20444 KiB

Open AccessFeature PaperReview

Catalytic Hydrofunctionalization Reactions of 1,3-Diynes

by Victorio Cadierno

Catalysts 2022, 12(1), 89; https://doi.org/10.3390/catal12010089 - 13 Jan 2022

Cited by 10 | Viewed by 3651

Abstract

Metal-catalyzed hydrofunctionalization reactions of alkynes, i.e., the addition of Y–H units (Y = heteroatom or carbon) across the carbon–carbon triple bond, have attracted enormous attention for decades since they allow the straightforward and atom-economic access to a wide variety of functionalized olefins and, [...] Read more.

Metal-catalyzed hydrofunctionalization reactions of alkynes, i.e., the addition of Y–H units (Y = heteroatom or carbon) across the carbon–carbon triple bond, have attracted enormous attention for decades since they allow the straightforward and atom-economic access to a wide variety of functionalized olefins and, in its intramolecular version, to relevant heterocyclic and carbocyclic compounds. Despite conjugated 1,3-diynes being considered key building blocks in synthetic organic chemistry, this particular class of alkynes has been much less employed in hydrofunctionalization reactions when compared to terminal or internal monoynes. The presence of two C≡C bonds in conjugated 1,3-diynes adds to the classical regio- and stereocontrol issues associated with the alkyne hydrofunctionalization processes’ other problems, such as the possibility to undergo 1,2-, 3,4-, or 1,4-monoadditions as well as double addition reactions, thus increasing the number of potential products that can be formed. In this review article, metal-catalyzed hydrofunctionalization reactions of these challenging substrates are comprehensively discussed. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts: Molecular Catalysis)

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24 pages, 6002 KiB

Open AccessReview

Lipases as Effective Green Biocatalysts for Phytosterol Esters’ Production: A Review

by Adejanildo da S. Pereira, Aline Habibe de Souza, Jully L. Fraga, Pierre Villeneuve, Alexandre G. Torres and Priscilla F. F. Amaral

Catalysts 2022, 12(1), 88; https://doi.org/10.3390/catal12010088 - 13 Jan 2022

Cited by 31 | Viewed by 4452

Abstract

Lipases are versatile enzymes widely used in the pharmaceutical, cosmetic, and food industries. They are green biocatalysts with a high potential for industrial use compared to traditional chemical methods. In recent years, lipases have been used to synthesize a wide variety of molecules [...] Read more.

Lipases are versatile enzymes widely used in the pharmaceutical, cosmetic, and food industries. They are green biocatalysts with a high potential for industrial use compared to traditional chemical methods. In recent years, lipases have been used to synthesize a wide variety of molecules of industrial interest, and extraordinary results have been reported. In this sense, this review describes the important role of lipases in the synthesis of phytosterol esters, which have attracted the scientific community’s attention due to their beneficial effects on health. A systematic search for articles and patents published in the last 20 years with the terms “phytosterol AND esters AND lipase” was carried out using the Scopus, Web of Science, Scielo, and Google Scholar databases, and the results showed that Candida rugosa lipases are the most relevant biocatalysts for the production of phytosterol esters, being used in more than 50% of the studies. The optimal temperature and time for the enzymatic synthesis of phytosterol esters mainly ranged from 30 to 101 °C and from 1 to 72 h. The esterification yield was greater than 90% for most analyzed studies. Therefore, this manuscript presents the new technological approaches and the gaps that need to be filled by future studies so that the enzymatic synthesis of phytosterol esters is widely developed. Full article

(This article belongs to the Special Issue Biocatalysis in Lipids Modification)

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17 pages, 4692 KiB

Open AccessArticle

Bulk Co₃O₄ for Methane Oxidation: Effect of the Synthesis Route on Physico-Chemical Properties and Catalytic Performance

by Andoni Choya, Beatriz de Rivas, Jose Ignacio Gutiérrez-Ortiz and Rubén López-Fonseca

Catalysts 2022, 12(1), 87; https://doi.org/10.3390/catal12010087 - 13 Jan 2022

Cited by 12 | Viewed by 2321

Abstract

The synthesis of bulk pure Co₃O₄ catalysts by different routes has been examined in order to obtain highly active catalysts for lean methane combustion. Thus, eight synthesis methodologies, which were selected based on their relatively low complexity and easiness for [...] Read more.

The synthesis of bulk pure Co₃O₄ catalysts by different routes has been examined in order to obtain highly active catalysts for lean methane combustion. Thus, eight synthesis methodologies, which were selected based on their relatively low complexity and easiness for scale-up, were evaluated. The investigated procedures were direct calcination of two different cobalt precursors (cobalt nitrate and cobalt hydroxycarbonate), basic grinding route, two basic precipitation routes with ammonium carbonate and sodium carbonate, precipitation-oxidation, solution combustion synthesis and sol-gel complexation. A commercial Co₃O₄ was also used as a reference. Among the several examined methodologies, direct calcination of cobalt hydroxycarbonate (HC sample), basic grinding (GB sample) and basic precipitation employing sodium carbonate as the precipitating agent (CC sample) produced bulk catalysts with fairly good textural and structural properties, and remarkable redox properties, which were found to be crucial for their good performance in the oxidation of methane. All catalysts attained full conversion and 100% selectivity towards CO₂ formation at a temperature of 600 °C while operating at 60,000 h⁻¹. Among these, the CC catalyst was the only one that achieved a specific reaction rate higher than that of the reference commercial Co₃O₄ catalyst. Full article

(This article belongs to the Special Issue State-of-the-Art Catalytic Materials in Europe)

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26 pages, 14648 KiB

Open AccessFeature PaperReview

Synthesis of Conjugated Dienes in Natural Compounds

by Geoffrey Dumonteil and Sabine Berteina-Raboin

Catalysts 2022, 12(1), 86; https://doi.org/10.3390/catal12010086 - 13 Jan 2022

Cited by 18 | Viewed by 4314

Abstract

This review describes the various synthetic methods commonly used to obtain molecules possessing conjugated dienes. We focus on methods involving cross-coupling reactions using various metals such as nickel, palladium, ruthenium, cobalt, cobalt/zinc, manganese, zirconium, or iron, mainly through examples that aimed to access [...] Read more.

This review describes the various synthetic methods commonly used to obtain molecules possessing conjugated dienes. We focus on methods involving cross-coupling reactions using various metals such as nickel, palladium, ruthenium, cobalt, cobalt/zinc, manganese, zirconium, or iron, mainly through examples that aimed to access natural molecules or their analogues. Among the natural molecules covered in this review, we discuss the total synthesis of a phytohormone, Acid Abscisic (ABA), carried out by our team involving the development of a conjugated diene chain. Full article

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

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17 pages, 2074 KiB

Open AccessFeature PaperArticle

VOCs Photothermo-Catalytic Removal on MnO_x-ZrO₂ Catalysts

by Roberto Fiorenza, Roberta Agata Farina, Enrica Maria Malannata, Francesca Lo Presti and Stefano Andrea Balsamo

Catalysts 2022, 12(1), 85; https://doi.org/10.3390/catal12010085 - 13 Jan 2022

Cited by 16 | Viewed by 3248

Abstract

Solar photothermo-catalysis is a fascinating multi-catalytic approach for volatile organic compounds (VOCs) removal. In this work, we have explored the performance and the chemico-physical features of non-critical, noble, metal-free MnO_x-ZrO₂ mixed oxides. The structural, morphological, and optical characterizations of these [...] Read more.

Solar photothermo-catalysis is a fascinating multi-catalytic approach for volatile organic compounds (VOCs) removal. In this work, we have explored the performance and the chemico-physical features of non-critical, noble, metal-free MnO_x-ZrO₂ mixed oxides. The structural, morphological, and optical characterizations of these materials pointed to as a low amount of ZrO₂ favoured a good interaction and the ionic exchange between the Mn and the Zr ions. This favoured the redox properties of MnO_x increasing the mobility of its oxygens that can participate in the VOCs oxidation through a Mars-van Krevelen mechanism. The further application of solar irradiation sped up the oxidation reactions promoting the VOCs total oxidation to CO₂. The MnO_x-5 wt.%ZrO₂ sample showed, in the photothermo-catalytic tests, a toluene T₉₀ (temperature of 90% of conversion) of 180 °C and an ethanol T₉₀ conversion to CO₂ of 156 °C, 36 °C, and 205 °C lower compared to the thermocatalytic tests, respectively. Finally, the same sample exhibited 84% toluene conversion and the best selectivity to CO₂ in the ethanol removal after 5 h of solar irradiation at room temperature, a photoactivity similar to the most employed TiO₂-based materials. The as-synthetized mixed oxide is promising for an improved sustainability in both catalyst design and environmental applications. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis and Advanced Oxidation Processes (AOP) for Environmental Protection (VOCs Oxidation, Air and Water Purification))

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13 pages, 4666 KiB

Open AccessFeature PaperArticle

Enhanced Photocatalytic Activity of ZnO–CdS Composite Nanostructures towards the Degradation of Rhodamine B under Solar Light

by Thirumala Rao Gurugubelli, R. V. S. S. N. Ravikumar and Ravindranadh Koutavarapu

Catalysts 2022, 12(1), 84; https://doi.org/10.3390/catal12010084 - 12 Jan 2022

Cited by 35 | Viewed by 3165

Abstract

A simple chemical precipitation route was utilized for the synthesis of ZnO nanoparticles (NPs), CdS NPs and ZnO–CdS nanocomposites (NCs). The synthesized nanostructures were examined for the crystal structure, morphology, optical properties and photodegradation activity of rhodamine B (RhB) dye. The ZnO–CdS NCs [...] Read more.

A simple chemical precipitation route was utilized for the synthesis of ZnO nanoparticles (NPs), CdS NPs and ZnO–CdS nanocomposites (NCs). The synthesized nanostructures were examined for the crystal structure, morphology, optical properties and photodegradation activity of rhodamine B (RhB) dye. The ZnO–CdS NCs showed a mixed phase of hexagonal wurtzite structure for both ZnO NPs and CdS NPs. Pure ZnO NPs and CdS NPs possessed bandgaps of 3.2617 and 2.5261 eV, respectively. On the other hand, the composite nanostructures displayed a more narrow bandgap of 2.9796 eV than pure ZnO NPs. When compared to bare ZnO NPs, the PL intensity of near-band-edge emission at 381 nm was practically suppressed, suggesting a lower rate of photogenerated electron–hole (e⁻/h⁺) pairs recombination, resulting in enhanced photocatalytic activity. Under solar light, the composite nanostructures displayed a photodegradation efficiency of 98.16% towards of RhB dye. After four trials, the structural stability of ZnO–CdS NCs was verified. Full article

(This article belongs to the Special Issue Development of Sunlight Responsive Nanostructured-Catalysts for Environmental Applications)

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10 pages, 5320 KiB

Open AccessArticle

Modified Cellulose with BINAP-Supported Rh as an Efficient Heterogeneous Catalyst for Asymmetric Hydrogenation

by Cuiping Yu, Weilong Wu, Min Gao and Yu Liu

Catalysts 2022, 12(1), 83; https://doi.org/10.3390/catal12010083 - 12 Jan 2022

Cited by 7 | Viewed by 2513

Abstract

Asymmetric catalysis is the preferred method for the synthesis of pure chiral molecules in the fine chemical industry. Cellulose has long been sought as a support in enantioselective catalysis. Dialdehyde cellulose (DAC) is produced by the selective oxidation of cellulose and is used [...] Read more.

Asymmetric catalysis is the preferred method for the synthesis of pure chiral molecules in the fine chemical industry. Cellulose has long been sought as a support in enantioselective catalysis. Dialdehyde cellulose (DAC) is produced by the selective oxidation of cellulose and is used to bind 5,5′-diamino Binap by forming a Schiff base. Here, we report the synthesis of modified cellulose-supported Rh as a novel biomass-supported catalyst and the characterization of its morphology, composition, and thermal stability. DAC-BINAP-Rh was a very effective catalyst in the asymmetric hydrogenation of enamides and could be easily recycled. This work provides a novel supported catalyst that broadens the applications of cellulose in asymmetric catalysis. Full article

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13 pages, 496 KiB

Open AccessArticle

Continuous Production of Fumaric Acid with Immobilised Rhizopus oryzae: The Role of pH and Urea Addition

by Reuben Marc Swart, Dominic Kibet Ronoh, Hendrik Brink and Willie Nicol

Catalysts 2022, 12(1), 82; https://doi.org/10.3390/catal12010082 - 12 Jan 2022

Cited by 8 | Viewed by 2339

Abstract

Fumaric acid is widely used in the food and beverage, pharmaceutical and polyester resin industries. Rhizopus oryzae is the most successful microorganism at excreting fumaric acid compared to all known natural and genetically modified organisms. It has previously been discovered that careful control [...] Read more.

Fumaric acid is widely used in the food and beverage, pharmaceutical and polyester resin industries. Rhizopus oryzae is the most successful microorganism at excreting fumaric acid compared to all known natural and genetically modified organisms. It has previously been discovered that careful control of the glucose feed rate can eliminate the by-product formation of ethanol. Two key parameters affecting fumaric acid excretion were identified, namely the medium pH and the urea feed rate. A continuous fermentation with immobilised R. oryzae was utilised to determine the effect of these parameters. It was found that the selectivity for fumaric acid production increased at high glucose consumption rates for a pH of 4, different from the trend for pH 5 and 6, achieving a yield of

0.93 gg^{- 1}

. This yield is higher than previously reported in the literature. Varying the urea feed rate to

0.255 m g L^{- 1} h^{- 1}

improved the yield of fumaric acid but experienced a lower glucose uptake rate compared to higher urea feed rates. An optimum region has been found for fumaric acid production at pH 4, a urea feed rate of

0.625 m g L^{- 1} h^{- 1}

and a glucose feed rate of

0.329 g L^{- 1} h^{- 1}

. Full article

(This article belongs to the Special Issue Advanced Technologies for Biocatalytic Synthesis)

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12 pages, 3585 KiB

Open AccessArticle

Acetalization of Glycerol with Citral over Heteropolyacids Immobilized on KIT-6

by José Castanheiro

Catalysts 2022, 12(1), 81; https://doi.org/10.3390/catal12010081 - 12 Jan 2022

Cited by 7 | Viewed by 2234

Abstract

Glycerol acetalization with citral was studied using a heteropolyacid (tungstophosphoric acid) supported on KIT-6, as a catalyst, at 100 °C. Different catalysts were synthesized. Catalysts were characterized by scanning electron microscopy (SEM), inductively coupled plasma (ICP), X-ray diffraction (XRD), attenuated total refletion-Fourier transform [...] Read more.

Glycerol acetalization with citral was studied using a heteropolyacid (tungstophosphoric acid) supported on KIT-6, as a catalyst, at 100 °C. Different catalysts were synthesized. Catalysts were characterized by scanning electron microscopy (SEM), inductively coupled plasma (ICP), X-ray diffraction (XRD), attenuated total refletion-Fourier transform infrared spectroscopy (ATR-FTIR), and potentiometric titrations. At a fixed time, the glycerol conversion increased with the H₃PW₁₂O₄₀ (PW) on KIT-6. PW4-KIT-6 material had a higher conversion than other catalysts. The optimization of glycerol’s acetalization with citral was studied under the PW4-KIT-6 catalyst. After 5 h, it was found that, at T = 100 °C, with m = 0.3 g of solid, molar glycerol:citral = 1:2.25, the conversion of glycerol was 89%. Moreover, the PW4-KTI-6 catalyst showed good catalytic stability. Full article

(This article belongs to the Special Issue Catalytic Conversion of Glycerol)

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19 pages, 2335 KiB

Open AccessArticle

Immobilization-Stabilization of β-Glucosidase for Implementation of Intensified Hydrolysis of Cellobiose in Continuous Flow Reactors

by Celia Alvarez-Gonzalez, Victoria E. Santos, Miguel Ladero and Juan M. Bolivar

Catalysts 2022, 12(1), 80; https://doi.org/10.3390/catal12010080 - 11 Jan 2022

Cited by 11 | Viewed by 2582

Abstract

Cellulose saccharification to glucose is an operation of paramount importance in the bioenergy sector and the chemical and food industries, while glucose is a critical platform chemical in the integrated biorefinery. Among the cellulose degrading enzymes, β-glucosidases are responsible for cellobiose hydrolysis, the [...] Read more.

Cellulose saccharification to glucose is an operation of paramount importance in the bioenergy sector and the chemical and food industries, while glucose is a critical platform chemical in the integrated biorefinery. Among the cellulose degrading enzymes, β-glucosidases are responsible for cellobiose hydrolysis, the final step in cellulose saccharification, which is usually the critical bottleneck for the whole cellulose saccharification process. The design of very active and stable β-glucosidase-based biocatalysts is a key strategy to implement an efficient saccharification process. Enzyme immobilization and reaction engineering are two fundamental tools for its understanding and implementation. Here, we have designed an immobilized-stabilized solid-supported β-glucosidase based on the glyoxyl immobilization chemistry applied in porous solid particles. The biocatalyst was stable at operational temperature and highly active, which allowed us to implement 25 °C as working temperature with a catalyst productivity of 109 mmol/min/g_support. Cellobiose degradation was implemented in discontinuous stirred tank reactors, following which a simplified kinetic model was applied to assess the process limitations due to substrate and product inhibition. Finally, the reactive process was driven in a continuous flow fixed-bed reactor, achieving reaction intensification under mild operation conditions, reaching full cellobiose conversion of 34 g/L in a reaction time span of 20 min. Full article

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

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15 pages, 20008 KiB

Open AccessCommunication

Sustainable Electrochemical NO Capture and Storage System Based on the Reversible Fe²⁺/Fe³⁺-EDTA Redox Reaction

by Heesung Eum, Seokhyeon Cheong, Jiyun Kim, Seo-Jung Han, Minserk Cheong, Hyunjoo Lee, Hae-Seok Lee and Dong Ki Lee

Catalysts 2022, 12(1), 79; https://doi.org/10.3390/catal12010079 - 11 Jan 2022

Cited by 3 | Viewed by 3548

Abstract

The removal of nitric oxide (NO), which is an aggregation agent for fine dust that causes air pollution, from exhaust gas has been considered an important treatment in the context of environmental conservation. Herein, we propose a sustainable electrochemical NO removal system based [...] Read more.

The removal of nitric oxide (NO), which is an aggregation agent for fine dust that causes air pollution, from exhaust gas has been considered an important treatment in the context of environmental conservation. Herein, we propose a sustainable electrochemical NO removal system based on the reversible Fe²⁺/Fe³⁺-ethylenediamine tetraacetic acid (EDTA) redox reaction, which enables continuous NO capture and storage at ambient temperature without the addition of any sacrificial agents. We have designed a flow-type reaction system in which the NO absorption and emission can be separately conducted in the individual reservoirs of the catholyte and anolyte with the continuous regeneration of Fe²⁺-EDTA by the electrochemical reduction in Fe³⁺-EDTA. A continuous flow reaction using a silver cathode and glassy carbon anode showed that the concentrations of Fe²⁺ and Fe³⁺-EDTA in the electrolyte were successfully maintained at a 1:1 ratio, which demonstrates that the proposed system can be applied for continuous NO capture and storage. Full article

(This article belongs to the Section Environmental Catalysis)

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11 pages, 4359 KiB

Open AccessArticle

Highly Photoactive Titanium Dioxide Supported Platinum Catalyst: Synthesis Using Cleaner Ultrasound Approach

by Shital B. Potdar, Chao-Ming Huang, BVS Praveen, Sivakumar Manickam and Shirish H. Sonawane

Catalysts 2022, 12(1), 78; https://doi.org/10.3390/catal12010078 - 11 Jan 2022

Cited by 10 | Viewed by 3089

Abstract

Catalysts increase reaction rates; however, the surface area to volume ratio of catalysts has a vital role in catalytic activity. The noble metals such as platinum (Pt) and gold (Au) are expensive; despite this, they have proven their existence in catalysis, motivating the [...] Read more.

Catalysts increase reaction rates; however, the surface area to volume ratio of catalysts has a vital role in catalytic activity. The noble metals such as platinum (Pt) and gold (Au) are expensive; despite this, they have proven their existence in catalysis, motivating the synthesis of supported metal catalysts. Metal catalysts need to be highly dispersed onto the support. In this investigation, an ultrasound approach has been attempted to synthesise highly photoactive titanium dioxide (TiO₂) nanoparticles by the hydrolysis of titanium tetraisopropoxide in an acetone/methanol mixture. To enhance its photocatalytic activity, TiO₂ was doped with Pt. The synthesised photocatalyst was characterised by techniques such as particle size analysis (PSA), XRD, FE-SEM, TEM, and EDX. The enhancement in the surface characteristics of Pt-doped TiO₂ compared with bare TiO₂ support was confirmed with Brunauer–Emmett–Teller (BET) analysis. The enhanced surface area and uniformity in particle size distribution at the nanoscale level were due to the effects of ultrasonic irradiation. The obtained results corroborated the size and composition of the synthesised catalysts. The size of the catalysts is in the nanometre range, and good dispersion of Pt catalysts over the TiO₂ support was observed. The UV-Visible spectroscopy analysis was performed to study the optical properties of the synthesised TiO₂ and Pt/TiO₂ photocatalysts. An increase in the absorbance was noted when Pt was added to TiO₂, which is due to the decrease in the band gap energy. Full article

(This article belongs to the Special Issue Synthesis and Photocatalytic Activity of Composite)

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