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20 pages, 6531 KiB

Open AccessArticle

Finely Tunable Carbon Nanofiber Catalysts for the Efficient Production of HMF in Biphasic MIBK/H₂O Systems

by Charf Eddine Bounoukta, Cristina Megías-Sayago, Nuria Rendón, Fatima Ammari, Miguel Angel Centeno and Svetlana Ivanova

Nanomaterials 2024, 14(15), 1293; https://doi.org/10.3390/nano14151293 - 31 Jul 2024

Cited by 1 | Viewed by 1373

Abstract

This work proposes catalytic systems for fructose dehydration to 5-hydroxymethylfurfural using a series of functionalized carbon nanofibers. The catalysts were synthesized via finely selected covalent grafting in order to include a variety of functionalities like pure Bronsted acid, tandem Brønsted/Lewis acid, and tandem Lewis acid/Lewis base catalysts. After the characterization and evaluation of acidity strength and the amount of acid centers, the catalyst series was screened and related to the product distribution. The best-performing catalyst was also used to optimize the reaction parameters in order to achieve 5-hydroxymethylfurfural yields rounding at 60% without significant humin formation. Full article

(This article belongs to the Section 2D and Carbon Nanomaterials)

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24 pages, 2823 KiB

Open AccessArticle

Impact of Thermal Treatment of Nb₂O₅ on Its Performance in Glucose Dehydration to 5-Hydroxymethylfurfural in Water

by Katarzyna Morawa Eblagon, Anna Malaika, Karolina Ptaszynska, Manuel Fernando R. Pereira and José Luís Figueiredo

Nanomaterials 2020, 10(9), 1685; https://doi.org/10.3390/nano10091685 - 27 Aug 2020

Cited by 30 | Viewed by 4136

Abstract

The cascade dehydration of glucose to 5-hydroxymethylfurfural (HMF) was carried out in water over a series of Nb₂O₅ catalysts, which were derived from the thermal treatment of niobic acid at 300 and 550 °C, under air or inert atmosphere. Amorphous niobic acid showed high surface area (366 m²/g) and large acidity (2.35 mmol/g). With increasing the temperature of the thermal treatment up to 550 °C, the amorphous Nb₂O₅ was gradually transformed into a pseudohexagonal phase, resulting in a decrease in surface area (27–39 m²/g) and total acidity (0.05–0.19 mmol/g). The catalysts’ performance in cascade dehydration of glucose realized in pure water was strongly influenced by the total acidity of these materials. A remarkable yield of 37% HMF in one-pot reaction in water was achieved using mesoporous amorphous niobium oxide prepared by thermal treatment of niobic acid at 300 °C in air. The best-performing catalyst displayed a total acidity lower than niobic acid (1.69 mmol/g) which afforded a correct balance between a high glucose conversion and limited further conversion of the target product to numerous polymers and humins. On the other hand, the treatment of niobic acid at 550 °C, independently of the atmosphere used during the sample preparation (i.e., air or N₂), resulted in Nb₂O₅ catalysts with a high ratio of Lewis to Brønsted acid sites and poor total acidity. These materials excelled at catalyzing the isomerization step in the tandem process. Full article

(This article belongs to the Special Issue Catalysis by Metal-Oxide Nanostructures)

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15 pages, 1599 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Stable Continuous Production of γ-Valerolactone from Biomass-Derived Levulinic Acid over Zr–Al-Beta Zeolite Catalyst

by Clara López-Aguado, Marta Paniagua, Juan A. Melero, Jose Iglesias, Pablo Juárez, Manuel López Granados and Gabriel Morales

Catalysts 2020, 10(6), 678; https://doi.org/10.3390/catal10060678 - 17 Jun 2020

Cited by 36 | Viewed by 5224

Abstract

The one-pot conversion of biomass-derived platform molecules such as levulinic acid (LA) and furfural (FAL) into γ-valerolactone (GVL) is challenging because of the need for adequate multi-functional catalysts and high-pressure gaseous hydrogen. As a more sustainable alternative, here we describe the transfer hydrogenation of LA to GVL using isopropanol as a hydrogen donor over a Zr-modified beta zeolite catalyst in a continuous fixed-bed reactor. A stable sustained production of GVL was achieved from the levulinic acid, with both high LA conversion (ca. 95%) and GVL yield (ca. 90%), for over at least 20 days in continuous operation at 170 °C. Importantly, the small decay in activity can be advantageously overcome by the means of a simple in situ thermal regeneration in the air atmosphere, leading to a complete recovery of the catalyst activity. Key to this outstanding result is the use of a Zr-modified dealuminated beta zeolite with a tailored Lewis/Brønsted acid sites ratio, which can synergistically catalyze the tandem steps of hydrogen transfer and acid-catalyzed transformations, leading to such a successful and stable production of GVL from LA. Full article

(This article belongs to the Special Issue Multifunctional Heterogeneous Catalysis)

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