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Supported Metal and Metal Oxide Catalysts by Sol-Gel Chemistry: Synthesis and Applications

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Catalytic Materials".

Deadline for manuscript submissions: closed (28 February 2019) | Viewed by 36861

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Special Issue Editor

Dr. Serena Esposito

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Guest Editor

Department of Civil and Mechanical Engineering, University of Cassino and Southern Latium, Via G. Di Biasio 43, 03043 Cassino (FR), Italy
Interests: sol–gel synthesis; porous materials; surface chemistry; oxide-based catalysts; metal-ceramic nanomaterials; zeolite precursors
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Special Issue Information

Dear Colleagues,

Sol-gel method has been recognized as valuable procedure to design advanced catalytic formulations, based on metal and metal oxide nanostructure. Sol-gel chemistry originated with the hydrolysis and condensation of metal alkoxides, although it can also occur between hydrated metal species. By trapping the “randomness of the solution state” and thereby ensuring atomic level mixing of reagents, the sol-gel method is a unique technique for materials synthesis. Low-temperature chemistry, reproducibility and high surface to volume ratios of obtained products are features that add merit to this technology. Nowadays, the term ‘sol-gel’ is used more broadly as covering the synthesis of solid materials, such as metal oxides, from solution-state precursors. The great advantage of tailoring the physicochemical properties of these materials through mastering the synthesis parameters have triggered a progressive development of different and fascinating procedure exploring new molecular precursors, chelating agents and templates.

The upcoming Special Issue, entitled “Supported Metal and Metal Oxide Catalysts by Sol-Gel Chemistry: Synthesis and Applications” aims to cover an overview of the sol-gel synthesis of tailored and multifunctional materials and their application in the main domain of heterogeneous catalysis.

Dr. Serena Esposito
Guest Editor

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Keywords

Sol-Gel synthesis
Xerogel
Porous oxide
Aerogel
Solid acid catalyst
Ordered Mesoporous Sol–Gel Materials
Selective partial oxidation reactions
Biomass conversion
Total oxidation reaction
Green chemistry
Bio-catalysts
Nanostructure

Published Papers (7 papers)

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Research

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14 pages, 6452 KiB

Open AccessArticle

Application of Reverse Micelle Sol–Gel Synthesis for Bulk Doping and Heteroatoms Surface Enrichment in Mo-Doped TiO₂ Nanoparticles

by Roberto Nasi, Serena Esposito, Francesca S. Freyria, Marco Armandi, Tanveer A. Gadhi, Simelys Hernandez, Paola Rivolo, Nicoletta Ditaranto and Barbara Bonelli

Materials 2019, 12(6), 937; https://doi.org/10.3390/ma12060937 - 21 Mar 2019

Cited by 24 | Viewed by 3436

Abstract

TiO₂ nanoparticles containing 0.0, 1.0, 5.0, and 10.0 wt.% Mo were prepared by a reverse micelle template assisted sol–gel method allowing the dispersion of Mo atoms in the TiO₂ matrix. Their textural and surface properties were characterized by means of X-ray powder diffraction, micro-Raman spectroscopy, N₂ adsorption/desorption isotherms at −196 °C, energy dispersive X-ray analysis coupled to field emission scanning electron microscopy, X-ray photoelectron spectroscopy, diffuse reflectance UV–Vis spectroscopy, and ζ-potential measurement. The photocatalytic degradation of Rhodamine B (under visible light and low irradiance) in water was used as a test reaction as well. The ensemble of the obtained experimental results was analyzed in order to discover the actual state of Mo in the final materials, showing the occurrence of both bulk doping and Mo surface species, with progressive segregation of MoO_x species occurring only at a higher Mo content. Full article

(This article belongs to the Special Issue Supported Metal and Metal Oxide Catalysts by Sol-Gel Chemistry: Synthesis and Applications)

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10 pages, 1047 KiB

Open AccessFeature PaperArticle

Room Temperature Synthesis of V-Doped TiO₂ and Its Photocatalytic Activity in the Removal of Caffeine under UV Irradiation

by Olga Sacco, Diana Sannino, Mariantonietta Matarangolo and Vincenzo Vaiano

Materials 2019, 12(6), 911; https://doi.org/10.3390/ma12060911 - 19 Mar 2019

Cited by 18 | Viewed by 2893

Abstract

In this work, the influence of simple acids in the room temperature sol-gel synthesis of TiO₂ was investigated and the efficiency of prepared photocatalysts was evaluated in the removal of caffeine. To improve the photoactivity of TiO₂, vanadium-doped TiO₂ (VTiO₂) samples were obtained starting from different amount of vanadyl sulphate as a dopant source. The samples were centrifuged, washed and finally dried at room temperature, and no calcination step was carried out. The prepared photocatalysts were characterized by different techniques (X-ray powder diffraction (XRD), specific surface area (SSA), ultraviolet-visible diffuse reflectance spectra (UV-vis DRS) and Raman). VTiO₂ photocatalysts were tested in the photocatalytic removal of aqueous solutions containing caffeine. The photocatalytic tests were carried out in a recirculating batch cylindrical photoreactor irradiated by a UV LEDs strip (nominal power of 12 W and wavelength emission peak at about 365 nm) surrounding the external surface of the reactor. The optimized VTiO₂ photocatalyst was able to reach a caffeine degradation of about 96% after 360 min of UV light irradiation with a total organic carbon (TOC) removal of 72%. Full article

(This article belongs to the Special Issue Supported Metal and Metal Oxide Catalysts by Sol-Gel Chemistry: Synthesis and Applications)

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14 pages, 3175 KiB

Open AccessArticle

Structured Monolithic Catalysts vs. Fixed Bed for the Oxidative Dehydrogenation of Propane

by Ilenia Rossetti, Elnaz Bahadori, Antonio Tripodi and Gianguido Ramis

Materials 2019, 12(6), 884; https://doi.org/10.3390/ma12060884 - 16 Mar 2019

Cited by 3 | Viewed by 2716

Abstract

The deposition of V-based catalysts for the oxidative dehydrogenation of propane to propene on cordierite honeycomb monoliths was optimised as a strategy to decrease the contact time in a structured reactor with respect to a conventional fixed bed one. 10 wt% VO_x supported over SiO₂ or Al₂O₃ were used as catalysts, deposed over the monolith using silica or alumina as primer, respectively. Both the alumina supported catalyst and the bohemite primer precursor were effectively deposed by dip-coating from stable powder suspensions, whereas insufficient adhesion was obtained when loading pre-synthesised SiO₂ over the cordierite. A new method based on sol-gel production of SiO₂ from tetraethylortosilicate (TEOS) over the monolith surface was set up. A correlation was derived for the prevision of the amount of silica deposed depending on the amount of TEOS. Both primer and catalyst loading were optimised as for uniformity and stability of the coating and resulted 0.5–1 wt % primer and 0.15 wt % of catalyst. Activity testing confirmed the strong improvement of propene productivity by increasing the time factor (i.e. Ncm³ of flowing reactant/min g_cat), which ended in a one order of magnitude increase of productivity for the honeycomb-supported samples with respect to the fixed bed configuration. Full article

(This article belongs to the Special Issue Supported Metal and Metal Oxide Catalysts by Sol-Gel Chemistry: Synthesis and Applications)

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17 pages, 4602 KiB

Open AccessFeature PaperArticle

Behavior of Molybdenum–Vanadium Mixed Oxides in Selective Oxidation and Disproportionation of Toluene

by Gheorghita Mitran, Florentina Neaţu, Octavian D. Pavel, Mihaela M. Trandafir and Mihaela Florea

Materials 2019, 12(5), 748; https://doi.org/10.3390/ma12050748 - 05 Mar 2019

Cited by 10 | Viewed by 3315

Abstract

This study deals with the behavior of molybdenum–vanadium (Mo/V) mixed oxides catalysts in both disproportionation and selective oxidation of toluene. Samples containing different Mo/V ratios were prepared by a modified method using tetradecyltrimethylammonium bromide and acetic acid. The catalysts were characterized using several techniques: nitrogen adsorption–desorption isotherms, X-Ray diffraction (XRD), ammonia temperature-programmed desorption (TPD-NH₃), temperature-programmed reduction by hydrogen (H₂-TPR), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Fourier-transform infrared-spectroscopy (FTIR) and ultraviolet-visible spectroscopies (UV–VIS). The XRD results evidenced the presence of orthorhombic α-MoO₃ and V₂O₅ phases, as well as monoclinic β-MoO₃ and V₂MoO₈ phases, their abundance depending on the Mo to V ratio, while the TPD-NH₃ emphasized that, the total amount of the acid sites diminished with the increase of the Mo loading. The TPR investigations indicated that the samples with higher Mo/V ratio possess a higher reducibility. The main findings of this study led to the conclusion that the presence of strong acid sites afforded a high conversion in toluene disproportionation (Mo/V = 1), while a higher reducibility is a prerequisite to accomplishing high conversion in toluene oxidation (Mo/V = 2). The catalyst with Mo/V = 1 acquires the best yield to xylenes from the toluene disproportionation reaction, while the catalyst with Mo/V = 0.33 presents the highest yield to benzaldehyde. Full article

(This article belongs to the Special Issue Supported Metal and Metal Oxide Catalysts by Sol-Gel Chemistry: Synthesis and Applications)

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14 pages, 1824 KiB

Open AccessArticle

Efficient Catalytic Production of Biodiesel with Acid-Base Bifunctional Rod-Like Ca-B Oxides by the Sol-Gel Approach

by Anping Wang, Hu Li, Heng Zhang, Hu Pan and Song Yang

Materials 2019, 12(1), 83; https://doi.org/10.3390/ma12010083 - 27 Dec 2018

Cited by 27 | Viewed by 3212

Abstract

The search for acid-base bifunctional catalysts has become a hot topic in the preparation of biofuels from renewable resources. In the present work, a series of novel acid-base bifunctional metal-boron catalysts were successfully prepared by a sol-gel method and characterized by XRD, IR, SEM, TEM, TGA, BET, and TPD. Among those bifunctional solid materials, the Ca-B(700) catalyst had the highest density of both acid and base sites and showed excellent catalytic performance in the production of biodiesel from nonedible oils with high acid value. Under the optimal reaction conditions of 20/1 methanol/oil mole ratio and 4 wt % catalyst dosage at 105 °C for 2 h, a high biodiesel yield of 96.0% could be obtained from Jatropha curcas oil in one-pot. In addition, Ca-B(700) was also applicable to producing biodiesel from Firmiana platanifolia L.f. oil in a relatively low acid value, with an almost quantitative yield (98.5%) at 65 °C after 2 h. The Ca-B(700) catalyst had good stability and reusability, which is a promising acid-base bifunctional catalytic material for the preparation of biodiesel. Full article

(This article belongs to the Special Issue Supported Metal and Metal Oxide Catalysts by Sol-Gel Chemistry: Synthesis and Applications)

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12 pages, 3883 KiB

Open AccessArticle

Boosted Visible-Light Photodegradation of Methylene Blue by V and Co Co-Doped TiO₂

by Tianping Lv, Jianhong Zhao, Mingpeng Chen, Kaiyuan Shen, Dongming Zhang, Jin Zhang, Genlin Zhang and Qingju Liu

Materials 2018, 11(10), 1946; https://doi.org/10.3390/ma11101946 - 11 Oct 2018

Cited by 43 | Viewed by 3285

Abstract

In this work, TiO₂ photocatalysts, co-doped with transition metal ions vanadium (V) and cobalt (Co) ((V,Co)–TiO₂), were synthesized by the sol–gel method. The synthesized photocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption and desorption measurement, UV-Vis absorption and photoluminescence spectrum (PL) spectra. The results show that V and Co co-doping has significant effects on sample average crystalline grain size, absorption spectrum, recombination efficiency of photo-induced electron-hole pairs (EHPs), and photocatalytic degradation efficiency of methylene blue (MB). (V,Co)–TiO₂ photocatalyst exhibits an obvious red shift of the absorption edge to 475 nm. Photocatalytic degradation rate of (V,Co)–TiO₂ sample for MB in 60 min is 92.12% under a Xe lamp with a cut-off filter (λ > 400 nm), which is significantly higher than 56.55% of P25 under the same conditions. The first principles calculation results show that V and Co ions doping introduces several impurity energy levels, which can modulate the location of the valence band and conduction band. An obvious lattice distortion is produced in the meantime, resulting in the decrease in photo-generated EHP recombination. Thus, (V,Co)–TiO₂ photocatalyst performance is significantly improved. Full article

(This article belongs to the Special Issue Supported Metal and Metal Oxide Catalysts by Sol-Gel Chemistry: Synthesis and Applications)

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Review

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25 pages, 11010 KiB

Open AccessReview

“Traditional” Sol-Gel Chemistry as a Powerful Tool for the Preparation of Supported Metal and Metal Oxide Catalysts

by Serena Esposito

Materials 2019, 12(4), 668; https://doi.org/10.3390/ma12040668 - 23 Feb 2019

Cited by 207 | Viewed by 17241

Abstract

The sol-gel method is an attractive synthetic approach in the design of advanced catalytic formulations that are based on metal and metal oxide with high degree of structural and compositional homogeneity. Nowadays, though it originated with the hydrolysis and condensation of metal alkoxides, sol-gel chemistry gathers plenty of fascinating strategies to prepare materials from solution state precursors. Low temperature chemistry, reproducibility, and high surface to volume ratios of obtained products are features that add merit to this technology. The development of different and fascinating procedure was fostered by the availability of new molecular precursors, chelating agents and templates, with the great advantage of tailoring the physico-chemical properties of the materials through the manipulation of the synthesis conditions. The aim of this review is to present an overview of the “traditional” sol-gel synthesis of tailored and multifunctional inorganic materials and their application in the main domain of heterogeneous catalysis. One of the main achievements is to stress the versatility of sol-gel preparation by highlighting its advantage over other preparation methods through some specific examples of the synthesis of catalysts. Full article

(This article belongs to the Special Issue Supported Metal and Metal Oxide Catalysts by Sol-Gel Chemistry: Synthesis and Applications)

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