Research

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10 pages, 3262 KiB

Open AccessArticle

Fabrication of Conjugated Porous Polymer Catalysts for Oxygen Reduction Reactions: A Bottom-Up Approach

by Sujoy Bandyopadhyay, Su Ryong Ha, M. Alam Khan, Cheongbeom Lee, Hong In Jeong, Snehal Lokhandwala, Mohaseen S. Tamboli, Bo Ram Lee, Danil W. Boukhvalov and Hyosung Choi

Catalysts 2020, 10(11), 1224; https://doi.org/10.3390/catal10111224 - 22 Oct 2020

Cited by 1 | Viewed by 2023

Abstract

The present study demonstrates the fabrication of a conjugated porous polymer (CPP-P2) through a Pd-catalyzed Suzuki–Miyaura poly-condensation reaction. ¹³C cross-polarization solid-state NMR and Fourier transform infrared (FTIR) spectroscopy were used to characterize CPP-P2. Pristine nitrogen-containing CPP was explored as a catalyst for [...] Read more.

The present study demonstrates the fabrication of a conjugated porous polymer (CPP-P2) through a Pd-catalyzed Suzuki–Miyaura poly-condensation reaction. ¹³C cross-polarization solid-state NMR and Fourier transform infrared (FTIR) spectroscopy were used to characterize CPP-P2. Pristine nitrogen-containing CPP was explored as a catalyst for the oxygen reduction reaction in 0.1 M KOH aqueous alkaline media. In the case of CPP-P2,the polymer oxygen reduction reaction occurs via a four-electron transfer mechanism. An understanding of the oxygen reduction at the molecular level and the role of molecular packing in the three-dimensional structure was proposed based on density functional theory (DFT) modeling. Full article

(This article belongs to the Special Issue Porous Materials and Catalysts)

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11 pages, 3151 KiB

Open AccessArticle

Enhanced Phenol Tert-Butylation Reaction Activity over Hierarchical Porous Silica-Alumina Materials

by Ling Xu, Fan Wang, Zhi Xiu, Limei Duan, Zongrui Liu and Jingqi Guan

Catalysts 2020, 10(9), 1098; https://doi.org/10.3390/catal10091098 - 22 Sep 2020

Cited by 1 | Viewed by 2209

Abstract

Hierarchical aluminum-silicon materials have been successfully prepared by mixing pre-crystallization of silica-alumina sol and citric acid under hydrothermal conditions. The influence of pre-crystallization time on the micro-mesoporous structure is studied using Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), N₂ physical [...] Read more.

Hierarchical aluminum-silicon materials have been successfully prepared by mixing pre-crystallization of silica-alumina sol and citric acid under hydrothermal conditions. The influence of pre-crystallization time on the micro-mesoporous structure is studied using Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), N₂ physical adsorption, and high-resolution transmission electron microscopy (HRTEM). The catalytic performance of hierarchical silica-alumina material is evaluated by alkylation of phenol with tert-butanol. The results show that the silica-alumina materials with a pre-crystallization time of 16 h show micro-mesoporous structure and excellent catalytic activity. Full article

(This article belongs to the Special Issue Porous Materials and Catalysts)

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11 pages, 4263 KiB

Open AccessArticle

The Preparation of Amorphous Aluminum Oxide Modified g-C₃N₄ to Improve Photocatalytic Performance in Contaminant Degradation Applications

by Yining Zheng, Congcong Wang, Wenjing Fu, Qi An, Cundi Wei and Lina Li

Catalysts 2020, 10(9), 1036; https://doi.org/10.3390/catal10091036 - 09 Sep 2020

Cited by 3 | Viewed by 2622

Abstract

For the first time, aluminum alloy was used as the main source to prepare aluminum oxide-modified carbon nitride with a melamine–cyanuric acid supramolecular complex. The introduction of amorphous aluminum oxide confers macroporosity to the skeletons of g-C₃N₄-AlO_x. [...] Read more.

For the first time, aluminum alloy was used as the main source to prepare aluminum oxide-modified carbon nitride with a melamine–cyanuric acid supramolecular complex. The introduction of amorphous aluminum oxide confers macroporosity to the skeletons of g-C₃N₄-AlO_x. Its surface area increased to 75.5 m²g⁻¹, about 1.5 times that of single g-C₃N₄. After modification, the visible light response range was expanded, especially at 450~500 nm, while the band structure could be adjusted. Compared with g-C₃N₄, g-C₃N₄-AlO_x has better photocatalytic performance, the adsorption rate for the dye rhodamine B (RhB) is about 2.1 times that of g-C₃N₄, and the RhB removal rate is 1.2 times that of g-C₃N₄. Full article

(This article belongs to the Special Issue Porous Materials and Catalysts)

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13 pages, 3046 KiB

Open AccessFeature PaperArticle

Fe@Hierarchical BEA Zeolite Catalyst for MW-Assisted Alcohol Oxidation Reaction: A Greener Approach

by Marta A. Andrade, Leonardo M. S. Ansari, Armando J. L. Pombeiro, Ana P. Carvalho, Angela Martins and Luísa M. D. R. S. Martins

Catalysts 2020, 10(9), 1029; https://doi.org/10.3390/catal10091029 - 08 Sep 2020

Cited by 5 | Viewed by 2392

Abstract

The aim of this study was to investigate the catalytic activity of hybrid materials of iron supported on hierarchical zeolites in the oxidation reaction of 1-phenylethanol to acetophenone. A greener approach was considered for the preparation of the catalyst and performance of the [...] Read more.

The aim of this study was to investigate the catalytic activity of hybrid materials of iron supported on hierarchical zeolites in the oxidation reaction of 1-phenylethanol to acetophenone. A greener approach was considered for the preparation of the catalyst and performance of the oxidation reaction. Hierarchical BEA zeolite samples were obtained from an alkaline and a subsequent acid treatment. The materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and nitrogen adsorption at −196 °C. An iron salt was incorporated onto the hierarchical zeolites by mechanochemical grinding and the catalytic performance of the prepared materials was evaluated towards the microwave assisted oxidation reaction of 1-phenylethanol. The catalyst obtained by Fe immobilization on sample modified by 0.2 M NaOH followed by acid treatment (Fe@BEA0.2AT) is the most promising material with 35% yield and 56% selectivity to acetophenone, allowing five reuse cycles without significant loss of activity and selectivity. Full article

(This article belongs to the Special Issue Porous Materials and Catalysts)

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15 pages, 2536 KiB

Open AccessFeature PaperArticle

Immobilization of β-Glucosidase over Structured Cordierite Monoliths Washcoated with Wrinkled Silica Nanoparticles

by Virginia Venezia, Aniello Costantini, Gianluca Landi, Almerinda Di Benedetto, Filomena Sannino and Valeria Califano

Catalysts 2020, 10(8), 889; https://doi.org/10.3390/catal10080889 - 06 Aug 2020

Cited by 12 | Viewed by 2317

Abstract

The enzymatic conversion of biomass-derived compounds represents a key step in the biorefinery flowsheet, allowing low-temperature high-efficiency reactions. β-Glucosidases are able to hydrolyze cellobiose into glucose. Wrinkled silica nanoparticles (WSNs) were demonstrated to be a good support for the immobilization of β-glucosidases, showing [...] Read more.

The enzymatic conversion of biomass-derived compounds represents a key step in the biorefinery flowsheet, allowing low-temperature high-efficiency reactions. β-Glucosidases are able to hydrolyze cellobiose into glucose. Wrinkled silica nanoparticles (WSNs) were demonstrated to be a good support for the immobilization of β-glucosidases, showing better performance than free enzymes in batch reaction; on the other hand, immobilized enzyme microreactors (IEMs) are receiving significant attention, because small quantities of reagents can be used, and favorable heat and mass transfer can be achieved with respect to conventional batch systems. In this work, we prepared, characterized, and tested structured enzymatic reactor compounds by a honeycomb monolith, a WSN washcoat, and β-glucosidases as the active phase. Powder and structured materials were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), N₂ physisorption, thermogravimetric analysis (TGA), and Fourier-transform infrared spectroscopy (FT-IR). Structured catalysts were tested under both batch and continuous flow reaction conditions and compared to powder catalysts (batch reaction). The WSN washcoat was attached well onto the monolith walls, as suggested by the negligible weight loss after ultrasound treatment; the WSNs preserved their shape, porosity, and individual nature when deposited onto the monolith walls. The immobilized enzyme microreactors proved to be very efficient in hydrolysis of cellobiose to glucose, showing a complete conversion under continuous flow reaction at a batch-equivalent contact time equal to 120 min vs. 24 h obtained in the batch experiments. The apparent K_M value showed a 20-fold decrease with respect to the batch process, due to the absence of external diffusive transport limitations. Full article

(This article belongs to the Special Issue Porous Materials and Catalysts)

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17 pages, 6675 KiB

Open AccessArticle

Studies on the Binary MgO/SiO₂ Mixed Oxide Catalysts for the Conversion of Ethanol to 1,3-Butadiene

by Wladimir Reschetilowski, Matthias Hauser, Felix Alscher, Mandy Klauck and Grit Kalies

Catalysts 2020, 10(8), 854; https://doi.org/10.3390/catal10080854 - 01 Aug 2020

Cited by 12 | Viewed by 2883

Abstract

The demand for 1,3-butadiene, one of the most important raw materials in the rubber industry, is constantly increasing. The Lebedev process is a classical method of producing 1,3-butadiene from ethanol, which is to be optimized with regard to the mixed oxide catalysts used. [...] Read more.

The demand for 1,3-butadiene, one of the most important raw materials in the rubber industry, is constantly increasing. The Lebedev process is a classical method of producing 1,3-butadiene from ethanol, which is to be optimized with regard to the mixed oxide catalysts used. In this work, the binary MgO/SiO₂ solid system was tested with regard to its optimum chemical composition for the catalytic conversion of ethanol to 1,3-butadiene. Furthermore, novel mesoporous mixed oxides were prepared to investigate their textural, structural, and surface chemical properties as well as the catalytic activity. Nitrogen physisorption, scanning electron microscopy (SEM), and temperature-programmed ammonia desorption (NH₃-TPD) measurements were carried out and evaluated. It was shown that the optimum yield of 1,3-butadiene is achieved by using MgO/SiO₂ mixed oxide catalysts with 85–95 mol% MgO and not, as suggested by Lebedev, with 75 mol% MgO. The NH₃-TPD measurements revealed that the maximum acid-site density is achieved with an equimolar up to magnesium-rich composition. During the synthesis of binary MgO/SiO₂ solid systems based on mesoporous MgO, a thermally stable and ordered structure was formed in the autoclave, depending on the carbonate used and on the duration of the treatment. Full article

(This article belongs to the Special Issue Porous Materials and Catalysts)

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10 pages, 2592 KiB

Open AccessArticle

Prediction of a Stable Organic Metal-Free Porous Material as a Catalyst for Water-Splitting

by Hengshuai Li, Haiquan Hu, Chenglin Bai, Chunjiang Bao, Cailong Liu, Qinglin Wang, Feng Guo, Zhenbao Feng, Hanwen Yu, Ming Chen and Konggang Qu

Catalysts 2020, 10(8), 836; https://doi.org/10.3390/catal10080836 - 24 Jul 2020

Cited by 14 | Viewed by 2824

Abstract

It is of practical significance to find organic metal-free catalyst materials. We propose a new graphene-like carbon nitride structure, which was able to meet these requirements well. Its primitive cell consists of eight carbon atoms and six nitrogen atoms. Hence, we called this [...] Read more.

It is of practical significance to find organic metal-free catalyst materials. We propose a new graphene-like carbon nitride structure, which was able to meet these requirements well. Its primitive cell consists of eight carbon atoms and six nitrogen atoms. Hence, we called this structure g–C₈N₆. The stability of the structure was verified by phonon spectroscopy and molecular dynamics simulations. Then its electronic structure was calculated, and its band edge position was compared with the redox potential of water. We analyzed its optical properties and electron–hole recombination rate. After the above analysis, it is predicted that it is a suitable photocatalyst material. To improve its photocatalytic performance, two methods were proposed: applied tensile force and multilayer stacking. Our research is instructive for the photocatalytic application of this kind of materials. Full article

(This article belongs to the Special Issue Porous Materials and Catalysts)

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16 pages, 36791 KiB

Open AccessArticle

Low-Temperature Selective Catalytic Reduction of NO_x on MnO₂ Octahedral Molecular Sieves (OMS-2) Doped with Co

by Laichao Li, Yusi Wang, Li Zhang, Yuxi Yu and Hanbing He

Catalysts 2020, 10(4), 396; https://doi.org/10.3390/catal10040396 - 03 Apr 2020

Cited by 11 | Viewed by 3328

Abstract

To improve NO conversion and sulfur resistance of low-temperature NO-CO selective catalytic reduction (SCR), it is urgent to seek new catalyst materials. Herein, using the pre-doping method, Co_x-OMS-2 with different ratios of cobalt (Co) was obtained during hydrothermal synthesis of OMS-2 [...] Read more.

To improve NO conversion and sulfur resistance of low-temperature NO-CO selective catalytic reduction (SCR), it is urgent to seek new catalyst materials. Herein, using the pre-doping method, Co_x-OMS-2 with different ratios of cobalt (Co) was obtained during hydrothermal synthesis of OMS-2 molecular sieves (where x represents the doping ratio of Co, i.e., x = 0.1, 0.2, 0.3, 0.4). Co was found to very efficiently intercalate into the crystal structure of OMS-2. Co and Mn work together to promote the selective reduction reaction of NO_x;; the NO conversion of Co_0.3-OMS-2 was the highest among all samples. Specifically, NO conversion at 50 °C increased from 72% for undoped OMS-2 to 90% for Co_0.3-OMS-2. Moreover, due to the incorporation of Co, the latter also showed better sulfur resistance. Full article

(This article belongs to the Special Issue Porous Materials and Catalysts)

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Review

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31 pages, 3058 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Immobilization of Cellulolytic Enzymes in Mesostructured Silica Materials

by Valeria Califano and Aniello Costantini

Catalysts 2020, 10(6), 706; https://doi.org/10.3390/catal10060706 - 23 Jun 2020

Cited by 36 | Viewed by 4661

Abstract

Mesostructured silica nanoparticles offer a unique opportunity in the field of biocatalysis thanks to their outstanding properties. The tunable pore size in the range of mesopores allows for immobilizing bulky enzyme molecules. The large surface area improves the catalytic efficiency by increasing enzyme [...] Read more.

Mesostructured silica nanoparticles offer a unique opportunity in the field of biocatalysis thanks to their outstanding properties. The tunable pore size in the range of mesopores allows for immobilizing bulky enzyme molecules. The large surface area improves the catalytic efficiency by increasing enzyme loading and finely dispersing the biocatalyst molecules. The easily tunable pore morphology allows for creating a proper environment to host an enzyme. The confining effect of mesopores can improve the enzyme stability and its resistance to extreme pH and temperatures. Benefits also arise from other peculiarities of nanoparticles such as Brownian motion and easy dispersion. Fossil fuel depletion and environmental pollution have led to the need for alternative sustainable and renewable energy sources such as biofuels. In this context, lignocellulosic biomass has been considered as a strategic fuel source. Cellulases are a class of hydrolytic enzymes that convert cellulose into fermentable sugars. This review is intended to survey the immobilization of cellulolytic enzymes (cellulases and β-glucosidase) onto mesoporous silica nanoparticles and their catalytic performance, with the aim to give a contribution to the urgent action required against climate change and its impacts, by biorefineries’ development. Full article

(This article belongs to the Special Issue Porous Materials and Catalysts)

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