Search Results (417)

5-Hydroxymethylfurfural (HMF) is a versatile platform molecule with the potential to replace many fossil fuel derivatives. It can be obtained through the dehydration of carbohydrates. In this study, we present a simple and cost-effective microwave-assisted method for producing HMF. This method involves the use of readily available sucrose as a substrate and glucose-derived bifunctional hydrochars as carbocatalysts. These catalysts were produced via hydrothermal carbonisation using thiourea and urea as nitrogen and sulphur sources, respectively, to introduce Brønsted acidic and basic sites into the materials. Using a microwave reactor, we found that the S, N-doped hydrochars were active in sucrose dehydration in water. Catalytic results showed that HMF yield depended on the balance between acidic and basic sites as well as the types of S and N species present on the surfaces of these hydrochars. The best-performing catalyst achieved an encouraging HMF yield of 37%. The potential of N, S-co-doped biochar as a green solid catalyst for various biorefinery processes was demonstrated. A simple kinetic model was developed to elucidate the kinetics of the main reaction pathways of this cascade process, showing a very good fit with the experimental results. The calculated rate constants revealed that reactions with a 5% sucrose loading exhibited significantly higher fructose dehydration rates and produced fewer side products than reactions using a more diluted substrate. No isomerisation of glucose into fructose was observed in an air atmosphere. On the contrary, a limited rate of isomerisation of glucose into fructose was recorded in an oxygen atmosphere. Therefore, efforts should focus on achieving a high glucose-to-fructose isomerisation rate (an intermediate reaction step) to improve HMF selectivity by reducing humin formation. Full article

Carbonyl–olefin metathesis is an important reaction for the formation of new carbon–carbon bonds, specifically double bonds. This critical review presents an overview of the different possibilities of these reactions, highlighting their use in the synthesis of natural products. It features classical photochemical approaches via [2+2]-cycloadditions, early metal-mediated reports, and emerging catalytic methods through the use of organocatalysts or Lewis or Brønsted acids. Comparisons between methods are presented throughout the text, based primarily on robustness, selectivity, methodology, experimental simplicity, and utilization in the synthesis of natural products. Full article

The combustion of biomass fuels releases alkali metals, which induce severe catalyst deactivation due to alkali metal (K) poisoning in low-temperature ammonia selective catalytic reduction (NH₃-SCR) systems. To address this issue, this study developed a series of heteropoly acid (HPA)-modified Ce/AC catalysts prepared via incipient wetness impregnation. The low-temperature NH₃-SCR performance (80–200 °C) of these catalysts was systematically evaluated, with particular emphasis on their denitrification activity and K-poisoning resistance. The silicotungstic-acid (TSiA)-modified Ce/Ac (TSiA-Ce/AC) catalyst showed an improvement (>20%) in NO conversion activity under the K poisoning condition. The superior K-poisoning resistance of the TSiA-Ce/AC catalyst was attributed to the high density of Brønsted acidic sites and the strong K binding affinity of TSiA, which together protected active sites and preserved the standard SCR reaction pathway under K contaminations. This study proposes a novel strategy for enhancing catalyst K resistance in low-temperature NH₃-SCR systems. Full article

Water pollution is a global concern, especially due to iron and manganese, which, at high concentrations, affect water quality by altering taste, odor, and color. This work explores the sustainable synthesis of hydrochar from orange peel and bagasse using hydrothermal carbonization (HTC) and a 2³ factorial design to optimize Fe²⁺ and Mn²⁺ removal for water treatment polishing. HTC was performed by varying (1) temperature (100–200 °C), (2) residence time (8–14 h), and (3) activation agent (H₃PO₄ or NaOH), with a central point at 150 °C for 11 h without activation. Characterization was performed using FTIR, TGA, SEM, nitrogen adsorption (BET) for surface area determination, elemental analysis, Brønsted acidity measurements, and zeta potential analysis. The hydrochar synthesized at 100 °C for 14 h with NaOH (HC6) showed the best Fe²⁺ and Mn²⁺ removal performance. The equilibrium time was 400 min, with pseudo-first-order kinetics best fitting the Fe²⁺ adsorption data, while pseudo-second-order kinetics provided the best fit for Mn²⁺ adsorption. The adsorption process was best described by the Freundlich and Langmuir isotherms, with maximum adsorption capacities (q_max) of 21.44 and 33.67 mg g⁻¹ for Fe²⁺ and Mn²⁺, respectively. It can be concluded that HTC-derived hydrochars offer a sustainable and efficient solution for Fe²⁺ and Mn²⁺ removal. This strategy presents a potentially valuable approach for sustainable water treatment, offering advantages for industrial application by operating at lower temperatures and eliminating the need for biomass drying, thereby reducing energy consumption and environmental impact. Full article

Nitrogen oxides (NO_x), harmful pollutants primarily from fossil fuel combustion, pose significant environmental and health risks. Among mitigation technologies, NH₃-SCR is widely adopted due to its high efficiency and industrial viability. MnO₂-based catalysts, particularly α-MnO₂, have gained attention for low-temperature NH₃-SCR owing to their redox properties, low-temperature activity, and environmental compatibility. In this study, α-MnO₂ catalysts with tunable oxygen vacancy concentrations were synthesized by varying calcination atmospheres. Compared to α-MnO₂-Air, the oxygen vacancy-rich α-MnO₂-N₂ exhibited stronger acidity, enhanced redox properties, and superior NH₃/NO adsorption and activation, achieving 98% NO conversion at 125–250 °C. Oxygen vacancies promoted NH₃ adsorption on Lewis/Brønsted acid sites, facilitating -NH₂ intermediate formation, while enhancing NO oxidation to reactive nitrates. In situ DRIFTS revealed a dual E-R and L-H reaction pathway, with oxygen vacancies crucial for NO activation, intermediate formation, and N₂ generation. These findings underscore the importance of oxygen vacancy engineering in optimizing Mn-based SCR catalysts. Full article

Solid Fe catalysts supported on SiO₂ with Lewis and Brönsted acidity were synthesized using sol–gel methodology. FTIR spectroscopy, XRD, Raman spectroscopy, BET isotherms, and SEM characterized the materials. Subsequently, they were used to dehydrate xylose to obtain furfural. It was observed that increasing the metal loading from 0.5% to 1.5% by mass increases the selectivity of furfural up to 40.09%. In addition, the calcination temperature influenced the conversion because materials calcined at 450 °C presented higher xylose conversion than those calcined at 750 °C. Finally, the employed catalysts were active and effective in obtaining furfural from hydrolysates via hydrothermal treatments of a coffee crop’s residual biomass, producing an average of 9.11 mg/g of furfural per gram of biomass. Full article

Chicken manure (CM) is a nutrient-rich but environmentally problematic biomass that requires sustainable management. This study applied a three-step process consisting of hydrothermal activation (ZnCl₂ or H₃PO₄), catalytic hydrothermal carbonization (HCl or FeCl₃), and low-temperature pyrolysis (250 °C) to develop an energy-efficient method for producing biochar. The resulting biochars were systematically analyzed for their physicochemical properties, heavy metal content, and carbon sequestration potential, and compared with conventional pyrolysis-based biochars. Among the tested samples, the biochar produced via H₃PO₄ activation and HCl-catalyzed HTC [P-HTC(HCl)] exhibited the most favorable characteristics, including the highest carbon content (59.5 wt.%) and the lowest H/C ratio (0.65). As a result, it achieved the highest total potential carbon (TPC, 158.8 g_carbon/kg_biochar) and CO₂ reduction potential (CRP, 465.9 g_CO2-eq/kg_biochar), attributed to the strong dehydration and decarboxylation reactions and effective inorganic removal induced by Brønsted acid action. In contrast, conventional pyrolysis biochars showed significantly higher concentrations of heavy metals—up to 633 mg/kg of Cu and 2331 mg/kg of Zn—due to thermal concentration effects, whereas P-HTC(HCl) biochar presented a more balanced and environmentally acceptable heavy metal profile. In conclusion, the proposed low-temperature hydrothermal-assisted process demonstrates great potential for producing high-performance biochar from chicken manure with enhanced environmental safety and carbon storage efficiency. Full article

Gallium-modified Zeolite Socony Mobil-5 (ZSM-5) zeolites were synthesized using wetness impregnation and hydrothermal synthesis methods. The structural and acidic properties of the zeolites were characterized through an analytical instrument, which demonstrated that Gallium-modified HZSM-5 zeolites retain the Mobil five instructure (MFI) framework structure, but exhibit a reduction in Brønsted acid sites and a decrease in micropore size. The catalytic performance of these zeolites in the pyrolysis of cellulose biomass and polyethylene was tested. Compared with HZSM-5, Ga-modified HZSM-5 zeolites considerably increased monoaromatic yields while reducing alkanes production. In particular, gallium-impregnated HZSM-5 increased the monoaromatic yield from 37.6% for ZSM-5 to 43.2%, while hydrothermal synthesized Ga-HMFI reduced polyaromatic and alkane yields from 6.6% and 24.6% for HZSM-5 to 2.9% and 11.4%, respectively. These results indicated that Ga-modified HZSM-5 zeolites can improve the synergy between cellulose-derived oxygenates and polyethylene-derived olefins, enhancing the yield of petrochemical hydrocarbons compared to that predicted by theoretical calculations. Full article

A study systematically investigating the structural modifications and catalytic performance of IM-5 zeolite treated with hexafluorosilicic acid in pseudocumene alkylation with methanol was carried out. Characterization techniques revealed significant alterations in crystal structure, morphology, textural properties, coordination environment, and acidity induced by the modifications. Catalytic evaluations demonstrated altered pseudocumene conversion, durene selectivity, and products distribution for optimized samples, with IM-5-0.01 (treated with 0.01 M modifier) showing superior activity stability. The improved performance was attributed to two key factors: a stable framework with high-density medium-strength Brønsted acid sites facilitating complete alkylation and expanded mesoporous volume promoting efficient product diffusion to mitigate deactivation. Conversely, reduced durene selectivity in modified samples stem from intensified isomerization reactions driven by increased external surface area, resulting in higher C₉ product fractions. In contrast, the parent IM-5 zeolite exhibited rapid deactivation, with durene selectivity peaking at 40 h before declining. Mechanistic insights revealed dynamic processes including dealumination, defect formation, silicon repair, and aluminum redistribution during treatment, providing a theoretical foundation for rational catalyst design in alkylation reactions. Full article

In the quest of the pivotal origin of the very strong gas-phase proton basicity for some iminopyrrole derivatives, proposed in the literature on the basis of quantum chemical calculations, the full tautomeric and acid/base equilibria were investigated in vacuo for 2-aminopyrrole exhibiting enamino–imino tautomerism. Thermochemistry of these processes investigated at the Density Functional Theory (DFT) level indicates a lower stability for the imino than for the enamino tautomers. However, the imino N atom in the imino forms displays an exceptionally high basicity, particularly in the minor and rare tautomers containing at least one tautomeric proton at the pyrrole C atom. This explains why derivatives of CH tautomers (being free of prototropy) display exceptionally high gas-phase proton basicity. As predicted by the Maksić group using quantum chemical methods, these derivatives can be considered as good organic imino N-superbase candidates. Unfortunately, some other structures of iminopyrrole derivatives (proposed by the same group) possess labile protons, and, thus, exhibit prototropy, resulting in the transformation into the more stable but less basic aminopyrrole derivatives under synthesis conditions or acid/base equilibria measurements. Full article

In this study, a statistical analysis of results reported in the literature was conducted through a 2ⁿ experimental design on the synthesis of bifunctional catalysts used in the production of lighter fuels, aiming for optimization while considering factors such as support (bentonite and vermiculite), acidity modifier (zirconium and cerium), metal (tungsten and molybdenum), metal content (5% and 10%), promoter (nickel and cobalt), and heteropolyacids (tungstophosphoric acid and molybdophosphoric acid), identifying their influence on textural properties and catalytic performance. Regarding the textural properties, vermiculite proved to be the most favorable support due to its high porosity. It was also established that the implemented metals impart positive characteristics to the catalysts due to their various properties; however, incorporating large amounts led to an adverse effect by clogging the pores. Catalytic performance was analyzed in isomerization and cracking reactions, which were enhanced by the use of cerium due to the presence of Brønsted acid sites and molybdenum for its stability. In this way, the statistical analysis conducted in this study was crucial for identifying the influence of key factors on the textural properties and catalytic performance of bifunctional catalysts. Using a 2ⁿ experimental design allowed for a systematic evaluation of variables reported in the literature, such as support, acidity modifiers, metals, metal content, promoters, and heteropolyacids. Full article

Zeolite is increasingly recognized for its enhancement of low-frequency acoustic performance in microspeakers. The aging characteristics of zeolite have been regarded as the critical factor for the commercial viability of mobile phones products, but the mechanism remains ambiguous. Here, the low-frequency acoustic performance of hierarchically structured ZSM-5 was investigated through aging with water and acetic acid (AA). It was discovered that water vapor augmented the resonance offset as it enhanced the structure of the zeolite, resulting in a lower water content. The resonance offset of ZSM-5 significantly decreased after the adsorption of AA vapor, as excessive AA was adsorbed through both physical and chemical adsorption, causing partial destruction of supermicropore and mesopores. The performance of ZMS-5 stored with vapor of AA and water mixture did not significantly deteriorate, indicating that water effectively protected the pores of zeolite to prevent excessive adsorption of AA. This was attributed to the fact that water was adsorbed by Brønsted acid sites of ZSM-5 more preferentially than AA, thereby avoiding excessive adsorption of AA. Full article

Designing bifunctional catalysts for efficient hydroisomerization of phenanthrene to alkyl-adamantane is a great challenge for producing high-density fuels. Herein, a bifunctional Pt catalyst was fabricated by developing hierarchical H-MSY-T zeolites with an NOA-co strategy. The influence of different mesopore template agents on the hierarchical structure of H-MSY-T zeolite was investigated. Effective regulation of pore structure and acid distribution of zeolites was achieved by adjusting the templating agents. The block copolymer P123 promoted the formation of mesoporous structures via self-assembly with a large mesopore centered at 8 nm. Large mesoporous structure and suitable distribution of Bronsted acid boosted the hydroisomerization of phenanthrene. The highest alkyl-adamantane yield of 45.9 wt% was achieved on the Pt/MSY-P1 catalyst and a reaction network of hydroisomerization was proposed. This work provides guidance to design highly selective bifunctional catalysts for the one-step hydroconversion of tricyclic aromatic hydrocarbons into high-density fuels. Full article

In this study, a Brönsted–Lewis bifunctional acidic catalyst PW/UiO/CNTs-OH was synthesized via the hydrothermal method. The parameters for the esterification reaction of oleic acid with methanol catalyzed by PW/UiO/CNTs-OH were optimized using central composite design-response surface methodology (CCD-RSM). A biodiesel yield of 92.9% was achieved under the optimized conditions, retaining 82.3% biodiesel yield after four catalytic cycles. The enhanced catalytic performance of PW/UiO/CNTs-OH can be attributed as follows: the [Zr₆O₄(OH)₄]¹²⁺ anchored on the surface of multi-walled carbon nanotubes (MWCNTs) can serve as nucleation sites for UiO-66, not only encapsulating H₃[P(W₃O₁₀)₄] (HPW) but also reversing the quadrupole moment of MWCNTs to generate Lewis acid sites. In addition, introduction of HPW during synthesis of UiO-66 decreases the solution pH, inducing the protonation of p-phthalic acid (PTA) to disrupt the coordination with the [Zr₆O₄(OH)₄] cluster, thereby creating an unsaturated Zr⁴⁺ site with electron pair-accepting capability, which generates Lewis acid sites. EIS analysis revealed that PW/UiO/CNTs-OH has higher electron migration efficiency than UiO-66 and PW/UiO. Furthermore, NH₃-TPD and Py-IR analyses showed that PW/UiO/CNTs-OH possessed high densities of Lewis acidic sites of 83.69 μmol/g and Brönsted acidic sites of 9.98 μmol/g. Full article

With the rapid development of biorefinery technology, the efficient conversion of lignocellulose into high-value platform chemicals is of great significance for enhancing the value of renewable carbon resources. In this study, a hydroxyl-functionalized covalent organic framework (COF), TAPB-DHPA, was synthesized via an in situ method and innovatively applied to the catalytic conversion of xylo-oligosaccharides (XOS) into furfural. The results demonstrated that TAPB-DHPA possesses a large specific surface area, a well-developed porous structure, and excellent thermal stability, with abundant Brønsted acid (B acid) sites, exhibiting outstanding catalytic activity. Under optimal conditions, including a catalyst loading of 0.16 wt%, a reaction temperature of 180 °C, and a reaction time of 3 h, a furfural yield of up to 65.4% was achieved. The high selectivity was primarily attributed to the p-π conjugation effect between the benzene ring and the phenolic hydroxyl group, which enhanced the ionization ability of hydroxyl hydrogen, thereby effectively promoting the hydrolysis of XOS and subsequent dehydration. Furthermore, TAPB-DHPA exhibited excellent recyclability and stability, maintaining a furfural yield of over 59.9% after six cycles. This study provides new insights into the application of functionalized COF in biomass catalytic conversion and contributes to the green transformation of the pulp and paper industry into a biorefinery-based model. Full article