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

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.

Hybrid organic-inorganic nanoparticles with associated functionality for catalytic transformation of biomass substrates

We present the one-pot synthesis of functionalized organosilica nanoparticles to generate multi-functional hybrid catalysts. Octadecyl, alkyl-thiol and alkyl-amino moieties were used separately and in different combinations, to generate different hybrid spherical nanoparticles with tunable acidic, basic and amphiphilic properties, covalently incorporating up to three organic functional elements onto the surface of the nanoparticles. Several parameters were optimised such as the concentration of the base employed during the hydrolysis and condensation synthesis process that showed a strong influence on the particle size. The physico-chemical properties of the hybrid materials were fully characterized by XRD, elemental and thermogravimetric analysis, electron microscopy, nitrogen adsorption isotherms and ¹³C and ²⁹Si NMR spectroscopy. Finally, the potential uses of the prepared materials as amphiphilic catalysts, with acidic or basic properties for the conversion of biomass molecules into platform chemicals were evaluated.

Supported Poly(Ionic Liquid)-Heteropolyacid Based Materials for Heterogeneous Catalytic Fructose Dehydration in Aqueous Medium

Two sets of four different supported catalyst materials were prepared. One set was obtained by polymerization of a bis-vinylimidazolium salt, which formed a poly(ionic liquid) coating on SiO2, TiO2, boron nitride BN, and carbon nitride C3N4. The other set was, instead, obtained by immobilizing Keggin heteropolyacid H3PW12O40 onto poly-imidazolium functionalized materials. All the catalysts, including the bare supports, were subjected to physical and chemical characterization by XRD, SEM, Specific Surface Area and pore size measurements, TGA, FTIR, and acidity-basicity measurements. The catalytic activity of the materials was tested versus the fructose dehydration in water solution at two different sugar initial concentrations (0.3 and 1 M). Tests lasted 3 h with an amount of catalyst of 2 g∙L−1. The presence of the poly-imidazolium on the surface of the supports increased the catalytic conversion of fructose to 5-hydroxymethylfurfural (the most abundant compound obtained) and was further improved by the contemporary presence of the heteropolyacid, at least for the highest initial fructose concentration. In the latter conditions, the highest yield of 5-hydroxymethylfurfural (>40%) was also obtained.

Highly Efficient Photocatalytic Degradation of Hydrogen Sulfide in the Gas Phase Using Anatase/TiO2(B) Nanotubes

Hydrogen sulfide (H₂S) is a highly toxic and corrosive gas that causes a foul odor even at very low concentrations [several parts per billion (ppb)]. However, industrially discharged H₂S has a concentration range of several tens of ppb to several parts per million (ppm), which conventional methods are unable to process. Therefore, advanced and sustainable methods for treating very low concentrations of H₂S are urgently needed. TiO₂-based photocatalysts are eco-friendly and have the ability to treat environmental pollutants, such as low-concentration gases, using light energy. However, there are no reports on H₂S decomposition or oxidation at concentrations below several ppb. Therefore, in this study, we employed anatase/TiO₂(B) nanotubes, which have a high specific surface area and an efficient charge-transfer interface, to treat H₂S. We successfully reduced 10 ppm of H₂S to 1 ppb or less at a kinetic rate of 75 μmol h^-1 g^-1. The suitability of our method was further demonstrated by the generation of sulfate ions and sulfur (as detected by X-ray photoelectron spectroscopy and ion chromatography), which are industrially useful as oxidation products, whereas sulfur dioxide, a harmful substance, was not produced. This is the first study to report H₂S decomposition down to the ppb level, providing meaningful solutions for malodor problems and potential health hazards associated with H₂S.

Hazardous maize processing industrial sludge: Thermo-kinetic assessment and sulfur recovery by evaporation-condensation technique

In the present work, a detailed thermo-kinetics of hazardous sulfur-rich sludge generated from the corn processing industry was performed for acquiring the optimum parameters for the efficient recovery of sulfur using the evaporation-condensation technique. Sulfur in the sludge was found to be 79 ± 3% (wt%) as estimated by the Bureau of Indian Standards method. A weight loss of 77 ± 3% was found in the active devolatilization zone from ≈ 200-400 °C. The online FTIR confirmed the evolution of mainly sulfur vapors (S₈) along with some sulfur dioxide (SO₂) and disulfur (S₂). The thermogravimetric data (TG) was used to evaluate the kinetic parameters with the help of model-free methods, and Z-master plots determined additional insight into the reaction mechanism. Furthermore, the calculated activation energy (E_a) was used to determine the thermodynamic feasibility. The average E_a values appraised by FM, FWO, sDAEM, and ST models were 55.43, 72.04, 62.33, and 62.67 kJ mol^-1, respectively. Overall, 91.2% of sulfur was successfully recovered at 400 °C, having 99 ± 0.5% purity. The approximate cost analysis of the sulfur recovery process was also estimated to check the economic viability. Recovered sulfur could be directly used for industrial and agricultural applications without any further purification.

Assessment on the Effect of Sulfuric Acid Concentration on Physicochemical Properties of Sulfated-Titania Catalyst and Glycerol Acetylation Performance

In this research, a solid acid catalyst was synthesized to catalyse glycerol acetylation into acetins. The sulphated-titania catalysts were prepared via the wet impregnation method at different sulfuric acid concentrations (5%, 10%, 15%, and 20%) and denoted as 5SA, 10SA, 15SA, and 20SA, respectively. The synthesized catalysts were characterized using FTIR, XRD, TGA, BET, NH3-TPD, XRF, and SEM-EDX. The synthesized catalysts were tested on glycerol acetylation reaction at conditions: 0.5 g catalyst loading, 100–120 °C temperature, 1:6 glycerol/acetic acid molar ratios, and 2–4 h reaction time. The final product obtained was analysed using GC-FID. An increment in sulfuric acid concentration reduces the surface area, pore volume, and particles size. However, the increment has increased the number of active sites (Lewis acid) and strong acid strength. 15SA catalyst exhibited excellent glycerol conversion (>90%) and the highest selectivity of triacetin (42%). Besides sufficient surface area (1.9 m2 g−1) and good porosity structure, the great performance of the 15SA catalyst was attributed to its high acid site density (342.6 µmol g−1) and the high active site of metal oxide (95%).

Recent Advances in the Brønsted/Lewis Acid Catalyzed Conversion of Glucose to HMF and Lactic Acid: Pathways toward Bio-Based Plastics

One of the most trending topics in catalysis recently is the use of renewable sources and/or non-waste technologies to generate products with high added value. That is why, the present review resumes the advances in catalyst design for biomass chemical valorization. The variety of involved reactions and functionality of obtained molecules requires the use of multifunctional catalyst able to increase the efficiency and selectivity of the selected process. The use of glucose as platform molecule is proposed here and its use as starting point for biobased plastics production is revised with special attention paid to the proposed tandem Bronsted/Lewis acid catalysts.

Tuning Brønsted and Lewis acidity on phosphated titanium dioxides for efficient conversion of glucose to 5-hydroxymethylfurfural

5-Hydroxymethylfurfural (HMF) derived from cellulosic sugars has become increasingly important as a platform chemical for the biorefinery industry because of its versatility in the conversion to other chemicals. Although HMF can be produced in high yield from fructose dehydration, fructose is rather expensive because it requires multiple processing steps. On the other hand, HMF can be produced directly from highly abundant glucose, which could reduce time and cost. However, an effective and multifunctional catalyst is needed to selectively promote the glucose-to-HMF reaction. In this work, we report a bifunctional phosphated titanium dioxide as an efficient catalyst for such a reaction. The best catalyst exhibits excellent catalytic performance for the glucose conversion to HMF with 72% yield and 83% selectivity in the biphasic system. We achieve this by tuning the solvent system, controlling the amount of Brønsted and Lewis acid sites on the catalyst, and modification of the reaction setup. From the analysis of acid sites, we found that the addition of phosphate group (Brønsted acid site) onto the surface of TiO2 (Lewis acid site) significantly enhanced the HMF yield and selectivity when the optimum ratio of Brønsted and Lewis acid sites is reached. The high catalytic activity, good reusability, and simple preparation method of the catalyst show a promise for the potential use of this catalytic system on an industrial scale.

Development of a continuous-flow tubular reactor for synthesis of 5-hydroxymethylfurfural from fructose using heterogeneous solid acid catalysts in biphasic reaction medium

5-Hydroxymethylfurfural (5-HMF) is an important biomass-derived platform chemical used to produce polymers, biofuels, and other valuable industrial chemicals.