Special Issue "Porous Materials and Catalysts"

A special issue of Catalysts (ISSN 2073-4344). This special issue belongs to the section "Catalytic Materials".

Deadline for manuscript submissions: 30 September 2020.

Special Issue Editors

Prof. Dr. Aniello Costantini
Website
Guest Editor
Università degli Studi di Napoli Federico II, Department of Chemical Engineering, Materials and Industrial Production DICMaPI, Naples, Italy
Interests: nanostructured materials; sol–gel synthesis; enzyme immobilization; catalysis
Dr. Valeria Califano
Website
Guest Editor
Istituto Motori (IM), Italian National Research Council CNR, Naples, Italy.
Interests: enzyme immobilization; biocatalysis; biofuels; mesoporous silica

Special Issue Information

Dear Colleagues,

Porous materials represent a broad platform for many applications in different fields, such as molecular separation, adsorption, enzyme immobilization, and heterogeneous catalysis. Both micro- and mesoporous materials (zeolites, MOFs, carbon, mesostructured silica, and silica-alumina) attract a great interest for applications in catalysis, thanks to their outstanding properties—mainly due to their large surface area and pore volume. For microporous materials, the size of the pores remains a strong limitation for applications involving bulky substrates or for hosting large biomolecules, as in enzyme immobilization. On the other hand, mesostructured materials possess poor thermal/hydrothermal stability and acid strength. They often require functionalization in order to obtain the required catalytic properties.

The aim of this Special Issue is to open a discussion forum concerning new synthesis and functionalization strategies for preparing catalysts with improved performance. The attention is focused on (but not restricted to) green pathways, both in the preparation of the catalyst and/or in the process to catalyze (i.e., biomass transformation and carbon dioxide conversion).

Prof. Dr. Aniello Costantini
Dr. Valeria Califano
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Catalysts is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • zeolites
  • MOFs
  • carbon
  • mesostructured silica
  • silica-alumina.

Published Papers (5 papers)

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Research

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Open AccessFeature PaperArticle
Immobilization of β-Glucosidase over Structured Cordierite Monoliths Washcoated with Wrinkled Silica Nanoparticles
Catalysts 2020, 10(8), 889; https://doi.org/10.3390/catal10080889 - 06 Aug 2020
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 KM 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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Open AccessArticle
Studies on the Binary MgO/SiO2 Mixed Oxide Catalysts for the Conversion of Ethanol to 1,3-Butadiene
Catalysts 2020, 10(8), 854; https://doi.org/10.3390/catal10080854 - 01 Aug 2020
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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Open AccessArticle
Prediction of a Stable Organic Metal-Free Porous Material as a Catalyst for Water-Splitting
Catalysts 2020, 10(8), 836; https://doi.org/10.3390/catal10080836 - 24 Jul 2020
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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Open AccessArticle
Low-Temperature Selective Catalytic Reduction of NOx on MnO2 Octahedral Molecular Sieves (OMS-2) Doped with Co
Catalysts 2020, 10(4), 396; https://doi.org/10.3390/catal10040396 - 03 Apr 2020
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, Cox-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, Cox-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 NOx;; the NO conversion of Co0.3-OMS-2 was the highest among all samples. Specifically, NO conversion at 50 °C increased from 72% for undoped OMS-2 to 90% for Co0.3-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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Open AccessFeature PaperReview
Immobilization of Cellulolytic Enzymes in Mesostructured Silica Materials
Catalysts 2020, 10(6), 706; https://doi.org/10.3390/catal10060706 - 23 Jun 2020
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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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Title: Immobilization of Cellulolytic Enzymes in Mesostructured Silica Materials
Authors: Valeria Califano, Aniello Costantini
Affiliation: a) Istituto Motori, CNR; b) DICMAPI, University of Naples Federico II.
Abstract: Mesostructured silica nanoparticles offer a unique opportunity in the field of biocatalysis thanks to their outstanding properties. The tuneable 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 easy tuneable 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, due to a limited exposure to environmental factors and to the increased conformational rigidity of the polypeptide chain because of the interactions with the pore walls. 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 contest lignocellulosic biomass has been considered as a strategic fuel source. Cellulases are a class of hydrolytic enzymes that convert cellulose into fermentable sugars. They consist of three enzymes that act sequentially and synergistically on the polymeric chain of cellulose: endo-β-1,4-d-glucanase (EC 3.2.1.4), exo- β-1,4-d-glucanase or cellobiohydrolase (EC 3.2.1.9) and β-Glucosidase (EC 3.2.1.21). The latter is considered to be the bottleneck of the whole process of cellulose conversion since it hydrolyzes cellobiose, a known inhibitor for both endo- and exo-glucanase activities. Furthermore, most cellulases are poor in b-glucosidase and the immobilization of b-glucosidase can be used to supplement them. Additionally, immobilized BG can find applications in other fields (i.e. the release of aromatic residues in the flavour industry and the synthesis of oligosaccharides and glycosides in the pharmaceutical industry). 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.

Title: Immobilization of β-glucosidase over structured cordierite monoliths washcoated with wrinkled silica nanoparticles
Authors: Valeria Califano1, Aniello Costantini2, Almerinda Di Benedetto2, Gianluca Landi3, Virginia Venezia2
Affiliation: 1. Istituto Motori-CNR, Naples, 80125, Italy 2. Dipartimento di Ingegneria Chimica, dei Materiali e della Produzione Industriale, University of Naples Federico II Naples, 80125, Italy 3. Institute for Researches on Combustion-CNR, Naples, 80125, Italy

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