Frontiers of Chemical Science and Engineering最新文献

Alkali metals (AMs) play an important role in biomass pyrolysis, and it is important to explore their catalytic effects so to better utilize biomass pyrolysis. This study analyzed the catalytic influence of K and Na with different anions (Cl⁻, SO₄²⁻, and CO₃²⁻) on biomass pyrolysis, and explored the influence on the pyrolytic mechanism. AM chlorides (NaCl and KCl), sulfates (Na₂SO₄ and K₂SO₄) and carbonates (Na₂CO₃ and K₂CO₃) were mixed with cellulose and bamboo feedstocks at a mass ratio of 20 wt %, in order to maximize their potential on in situ upgrading of the pyrolysis products. AM chlorides had little effect on the pyrolysis products, whereas sulfates slightly promoted the yields of char and gas, and had a positive effect on the composition of the gaseous and liquid products. Carbonates noticeably increased the yields of the char and gases, and improved the C content of the char. Besides, AM salt catalysis is an effective method for co-production of bio-oil and porous char.

Exploring effective transition metal single-atom catalysts for selective oxidation of benzene to phenol is still a great challenge due to the lack of a comprehensive mechanism and mechanism-driven approach. Here, robust 4N-coordinated transition metal single atom catalysts embedded within graphene (TM₁-N₄/C) are systematically screened by density functional theory and microkinetic modeling approach to assess their selectivity and activity in benzene oxidation reaction. Our findings indicate that the single metal atom triggers the dissociation of H₂O₂ to form an active oxygen species (O*). The lone-electronic pair character of O* activates the benzene C-H bond by constructing C-O bond with C atom of benzene, promoting the formation of phenol products. In addition, after benzene captures O* to form phenol, the positively charged bare single metal atom activates the phenol O-H bond by electron interaction with the O atom in the phenol, inducing the generation of benzoquinone by-products. The activation process of O-H bond is accompanied by H atom falling onto the carrier. On this basis, it can be inferred that adsorption energy of the C atom on the O* atom (E_C) and the H atom on the TM₁-N₄/C (E_H), which respectively represent activation ability of benzene C-H bond and phenol O-H bond, could be labeled as descriptors describing catalytic activity and selectivity. Moreover, based on the as-obtained volcano map, appropriate E_C (−8 to −7 eV) and weakened E_H (−1.5 to 0 eV) contribute to the optimization of catalytic performance for benzene oxidation to phenol. This study offers profound opinions on the rational design of metal single-atom catalysts that exhibit favorable catalytic behaviors in hydrocarbon oxidation.

The characterization of bio-aviation fuel composition is paramount for assessing biomass conversion processes and its suitability to meet international standards. Compared with one-dimensional gas chromatography mass spectrometry (1DGC-MS), comprehensive two-dimensional gas chromatography with mass spectrometry (GC × GC-MS) emerges as a promising analytical approach for bio-aviation fuel, offering enhanced separation, resolution, selectivity, and sensitivity. This study addresses the qualitative and quantitative analysis methods for both bulk components and trace fatty acid methyl ester (FAME) in bio-aviation fuel obtained by hydrogenation at 400 °C with Ni-Mo/γ-Al₂O₃&Meso-SAPO-11 as catalyst using GC × GC-MS. In bulk composition analysis, C₁₂ concentration was highest at 25.597%. Based on GC × GC-MS analysis platform, the quality control method of FAME in bio-aviation fuel was established. At the split ratio of 10:1, limits of detections of six FAMEs were 0.011–0.027 mg·kg⁻¹, and limits of quantifications were 0.036–0.090 mg·kg⁻¹, and the GC × GC-MS research platform had the ability to detect FAME from 2 to 5 mg·kg⁻¹. The results showed that this bioaviation fuel did not contain FAME.

Over the past few decades, significant progress has been made in thin-film optoelectronic devices based on transition metal dichalcogenides. However, the exciton states’ sensitivity to the environment presents challenges for device applications. This study reports the evolution of photoinduced exciton states in monolayer tungsten disulfide in a low-pressure environment to help elucidate the physical mechanism of the transition between neutral and charged excitons. At 222 mTorr, the transition rate between excitons comprises two components: 0.09 s⁻¹ and 1.68 s⁻¹. Based on this phenomenon, we developed a pressure-tuning method that allows for a tuning range of approximately 40% of exciton weight. Our study demonstrates that the intensity of neutral exciton emission from monolayer tungsten disulfide follows a power-law distribution in relation to pressure, indicating a highly sensitive pressure dependence. We provide a nondestructive and highly sensitive method for exciton conversion through in situ optical manipulation. This highlights the potential development of monolayer tungsten disulfide for pressure sensors and explains the impact of environmental factors on the product quality in photovoltaic devices. In addition, it demonstrates the promising future of monolayer transition metal dichalcogenides in applications such as photovoltaic devices and miniature biochemical sensors.

Two-dimensional porous nanosheets such as metal-organic frameworks, covalent organic frameworks, fluorides of light lanthanide, and perforated graphene oxide are a class of nanomaterials with sheet-like morphologies and defined pore structures. Due to their porous structure and large lateral sizes, these materials exhibit excellent molecular transport properties in separation processes. This review focuses on the pore formation strategies for two-dimensional porous nanosheets and applications of these nanosheets and their constructed membranes in gas separation processes and separation processes applicable to water treatment and the humidity control of gas permeation. A brief discussion of challenges and future developments of separation applications with two-dimensional porous nanosheets and their constructed membranes is included in this review.

Supercritical water gasification is a clean technology for biomass conversion and utilization. In supercritical water gasification systems, H₂O is often used as the transport medium. Decreases in the reaction temperature at the gasification area and in the heating rate of biomass may limit the gasification rate and efficiency. In this paper, CO₂ is used as the transport medium due to its relatively low critical point and specific heat capacity. Moreover, a corn stalk gasification system with different transport media is established in this paper, and the influences of various operating parameters, such as temperature, pressure and feedstock concentration, are investigated. The results show that the gas yield in the CO₂-transport system decreases by no more than 5 wt %. In addition, thermodynamic analysis reveals that a system with CO₂ as transport medium consumes approximately 25% less electricity than a system with H₂O as the transport medium. In addition, the reaction heat absorption decreases. The results show the superiority of CO₂ to H₂O as a transport medium.

Due to the relentless exploitation of nonrenewable resources, humanity is faced with a resource depletion crisis in the coming decades and serious environmental issues. Achieving efficient removal and upcycling of pollutants (ERUP) may become a potential strategy to address these issues. Wastewater, characterized by its large production volume and fluidity, can easily cause widespread environmental pollution through natural water networks. Due to solubility constraints, pollutants in wastewater typically exhibit low concentrations and complex compositions, thereby impeding effective recovery. Therefore, achieving ERUP in wastewater is both highly significant and extremely challenging. Unlike conventional wastewater treatment strategies that are focused on removing pollutants, ERUP strategies can not only realize the efficient removal of pollutants from water but also convert pollutants into valuable and functional products. Herein, we enumerated the latest research progress on ERUP in wastewater and highlighted studies that demonstrate the simultaneous achievement of pollutant removal and the direct conversion of these contaminants into high-efficiency catalysts, hydrogen energy, electrical energy, and other high-value chemicals. Finally, we identified the problems and challenges in the development of ERUP in wastewater and outlined potential research directions for future studies.

The reduced mechanism based on the minimized reaction network method can effectively solve the rigidity problem in the numerical calculation of turbulent internal combustion engine. The optimization of dynamic parameters of the reduced mechanism is the key to reproduce the experimental data. In this work, the experimental data of ignition delay times and laminar flame speeds were taken as the optimization objectives based on the machine-learning model constructed by radial basis function interpolation method, and pre-exponential factors and activation energies of H₂ combustion mechanism were optimized. Compared with the origin mechanism, the performance of the optimized mechanism was significantly improved. The error of ignition delay times and laminar flame speeds was reduced by 24.3% and 26.8%, respectively, with 25% decrease in total mean error. The optimized mechanism was used to predict the ignition delay times, laminar flame speeds and species concentrations of jet stirred reactor, and the predicted results were in good agreement with experimental results. In addition, the differences of the key reactions of the combustion mechanism under specific working conditions were studied by sensitivity analysis. Therefore, the machine-learning model is a tool with broad application prospects to optimize various combustion mechanisms in a wide range of operating conditions.

In light of the challenges associated with catalyst separation and recovery, as well as the low production efficiency resulting from intermittent operation for titanium silicalite-1 (TS-1) catalyzed phenol hydroxylation to dihydroxybenzene in the slurry bed, researchers keep on exploring the use of a continuous fixed bed to replace the slurry bed process in recent years. This study focuses on preparing a TS-1 coated structured catalyst on SiC foam, which exhibits significant process intensification in performance. We investigated the kinetics of this structured catalyst and compared it with those of extruded TS-1 catalyst; the dynamic equations of the two catalysts were obtained. It was observed that both catalysts followed E-R adsorption mechanism model, with an effective internal diffusion factor ratio between structured and extruded TS-1 of approximately 7.71. It was confirmed that the foamed SiC-based structured TS-1 catalyst exhibited significant improvements in phenol hydroxylation in fixed-bed reactor due to its well-developed pore structure, good thermal conductivity, excellent internal mass transfer performance, and short reactant diffusion distance, leading to higher utilization efficiency of active components. This finding also provides a foundation for designing and developing phenol hydroxylation processes in fixed-bed using structured catalysts through computational fluid dynamics calculations.

This study investigated the interaction between the furfural residue and polyvinyl chloride co-pyrolysis using an infrared heating method. Various analytical techniques including production distribution analysis, thermal behavior, pyrolysis kinetic, simulated distillation and gas chromatography-mass spectrography (GCMS), and X-ray photoelectron spectroscopy were utilized to elucidate the pyrolysis characterization and reaction mechanism during the co-pyrolysis. Initially, the yield of co-pyrolysis oil increased from 35.12% at 5 °C·s⁻¹ to 37.70% at 10 °C·s⁻¹, but then decreased to 32.07% at 20 °C·s⁻¹. Kinetic and thermodynamic parameters suggested non-spontaneous and endothermic behaviors. GCMS analysis revealed that aromatic hydrocarbons, especially mono- and bi-cyclic ones, are the predominant compounds in the oil due to the presence of H radicals in polyvinyl chloride, suggesting an enhancement in oil quality. Meanwhile, the fixed chlorine content increased to 65.11% after co-pyrolysis due to the interaction between inorganic salts in furfural residues and chlorine from polyvinyl chloride.