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.
In photocatalytic studies, tetragonal bismuth vanadate (t-BiVO4) is not promising due to its wide band gap. However, according to previous studies, the tetragonal phase is inevitable when the monoclinic bismuth vanadate (m-BiVO4) is modified. Therefore, it is necessary to find ways to improve the photoresponse and photocatalytic ability of t-BiVO4 under visible light. In this study, Yb3+ and Tm3+ co-doped BiVO4 was synthesized by a simple hydrothermal method, and its microstructure, morphology and optical properties were characterized and analyzed by scanning electron microscope, transmission electron microscopy, Brunauer-Emmett-Teller, X-ray diffraction, Raman, X-ray photoelectron spectroscopy, diffuse reflectance spectra, photoluminescence, upconversion luminescence and other means. The results show that BiVO4:Yb3+/Tm3+ (BVYT) has a high content of tetragonal phase (about 80%), showing the characteristics of t-BiVO4. BVYT shows a higher separation efficiency of photogenerated carriers, its transient photocurrent response intensity increased by about 3 times, and the photocatalytic efficiency is significantly improved compare with the undoped m-BiVO4. Under simulated sunlight, BVYT completely degraded methylene blue (MB) solution and rhodamine B solution in 45 and 90 min, respectively, and the reaction rate was significantly improved. BVYT also shows excellent photocatalytic ability under visible light, about 35% of MB solution was degraded within 45 min under visible light irradiation (> 420 nm), this is because Yb3+ effectively promotes the upconversion luminescence of Tm3+ in response to visible light, and the energy cycle mechanism of Yb-Tm-Tm is proposed. Consequently, BiVO4 with high content of tetragonal phase has excellent photoactivity, even exceeding m-BiVO4. This is a novel discovery in the field of photocatalysis, which provides a broader application prospect for BiVO4 in photocatalysis.
This perspective discusses three alternative techniques which complement conventional infrared spectroscopy for obtaining vibrational information about zeolite catalysts and adsorbed molecules: inelastic neutron scattering, infrared micro-spectroscopy, and two-dimensional infrared spectroscopy. The techniques are illustrated briefly and future prospects for their use discussed.
Owing to its uncomplicated synthetic methodology and exorbitant market demand, malachite green is widely used in numerous industries, particularly as a fungicide in aquaculture. Considering its intrinsic toxicity and potential long-term health impacts, deployable and cost-effective strategies must be developed for eliminating water-soluble malachite green. In this study, chemically activated phosphogypsum, a byproduct of fertilizer production, was used to remove malachite green from an aqueous system. Due to its low cost and abundance, the use of phosphogypsum as a sorbent material may significantly reduce the cost of adsorption-based processes. Moreover, its structural durability allows efficient recycling without significant deformation during reactivation. However, untreated phosphogypsum exhibits minimal efficiency in adsorbing synthetic dyes due to its unfavorable surface chemistry. Our investigation revealed that Zn activation induced a noticeable increase in pore volume from 0.03 to 0.06 cm3·g–1. A 60 mg·L–1 sorbent dose, pH 7, 150 r·min–1, and operational temperature of 30 °C produced 99% quantitative sorption efficiency. Response surface methodology and artificial neural network were used to optimize process parameters by validating experimental values. No detectable toxicity was observed in Escherichia coli when exposed to the treated water.
Currently, the conversion of waste plastics into high-value products via catalytic pyrolysis enables the advancement of plastics’ open-loop recycling. However, enhancing selectivity remains a critical challenge. This study introduces a novel approach to catalytic pyrolysis, utilizing a combination of MCM-41 and modified gallium-based HZSM-5 catalysts, to achieve exceptional selectivity for aromatic liquid-phase products from linear low-density polyethylene. Firstly, to enhance the probability of dehydroaromatization optimization, the type and proportion of metal active sites within the HZSM-5 catalyst are fine-tuned, which would establish equilibrium with acid sites, resulting in a remarkable 15.72% increase in the selectivity of aromatic hydrocarbons. Secondly, to enhance the accessibility of volatiles to active sites, mesoporous MCM-41 with cracking capabilities is introduced. The doping ratio of MCM-41 is meticulously controlled to facilitate the diffusion of cracked volatiles to the active centers of modified gallium-based HZSM-5, enabling efficient reforming reactions. Experimental findings demonstrate that MCM-41 significantly enhances the dehydroaromatization activity of the modified gallium-based HZSM-5 catalyst. Under the influence of MCM-41:Zr2Ga3/HZSM-5 = 1:2 catalyst, the selectivity for aromatic hydrocarbons reaches an impressive 93.11%, with a notable 60.01% selectivity for benzene, toluene, ethylbenzene, and xylene. Lastly, this study proposes a plausible pathway for the generation of high-value aromatic hydrocarbons using the combined catalyst.
With the advantages of low raw material cost and 100% atom utilization, the synthesis of high value-added chemical product cyclic carbonates by the cycloaddition of CO2 to epoxides has become one of the most prospective approaches to achieve the industrial utilization of CO2. In the reported catalytic systems, the complexity of the catalyst synthesis process, high cost, separation difficulties, and low CO2 capture limit the catalytic efficiency and its large-scale application. In this paper, Ag nanoparticles loaded on polyethyleneimine (PEI)-modified UiO-66-NH2 (Ag/PEI@UiO-66-NH2) are successfully synthesized by in situ immersion reduction. The Ag nanoparticles and the amino groups on the surfaces of PEI@UiO-66-NH2 contribute to the adsorption of CO2 and polarization of C–O bonds in epoxides, thereby boosting the conversion capability for the CO2 cycloaddition reaction. At the amount of propylene oxide of 0.25 mol and the catalyst dosage of 1% of the substrate, the yield and selectivity of propylene carbonate are up to 99%. In addition, the stability and recyclability of Ag/PEI@UiO-66-NH2 catalyst are attained. The Ag/PEI@UiO-66-NH2 catalyst also demonstrates a wide range of activity and distinctive selectivity toward cyclo-carbonates in the cycloaddition of CO2 to epoxides. This work provides a guide to designing a highly efficient catalyst for in situ capture and high-value utilization of CO2 in industrial applications.
Herein, we introduced a nitrogen-alkali lignin-doped phenolic resin (N@ALnPR) to produce palladium nanoparticles through an in situ reduction of palladium in an aqueous phase, without the need for additional reagents or a reducing atmosphere. The phenolic resin nanospheres and the resulting palladium nanoparticles were extensively characterized. Alkali lignin created a highly conducive environment for nitrogen incorporation, dispersion, reduction, and stabilization of palladium, leading to a distinct catalytic performance of palladium nanoparticles in vanillin hydrodeoxygenation. Under specific conditions of 1 mmol of vanillin, 40 mg of catalyst, 1 MPa H2, 90 °C, and 3 h, the optimized Pd/N@AL30PR catalyst exhibited a nearly complete conversion of vanillin, 98.9% selectivity toward p-creosol, and good stability for multiple reuses. Consequently, an environmentally friendly lignin-based catalyst was developed and used for the efficient hydrodeoxygenation conversion of lignin-based platform compounds.
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.
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.
Separating monomeric cycloalkanes from naphtha obtained from direct coal liquefaction not only facilitates the valuable utilization of naphtha but also holds potential for addressing China’s domestic chemical feedstock market demand for these compounds. In extractive distillation processes of naphtha, relative volatility serves as a crucial parameter for extractant selection. However, determining relative volatility through conventional vapor-liquid equilibrium experiments for extractant selection proves challenging due to the complexity of naphtha’s compound composition. To address this challenge, a prediction model for the relative volatility of n-heptane/methylcyclohexane in various extractants has been developed using machine-learning quantitative structure-property relationship methods. The model enables rapid and cost-effective extractant selection. The statistical analysis of the model revealed favorable performance indicators, including a coefficient of determination of 0.88, cross-validation coefficient of 0.94, and root mean square error of 0.02. Factors such as α, EHOMO, ρ, and logPoct/water collectively influence relative volatility. Analysis of standardized coefficients in the multivariate linear regression equation identified density as the primary factor affecting the relative volatility of n-heptane/methylcyclohexane in the different extractants. Extractants with higher densities, devoid of branched chains, exhibited increased relative volatility compared to their counterparts with branched chains. Subsequently, the process of separating cycloalkane monomers from direct coal liquefaction products via extractive distillation was optimized using Aspen Plus software, achieving purities exceeding 0.99 and yields exceeding 0.90 for cyclohexane and methylcyclohexane monomers. Economic, energy consumption, and environmental assessments were conducted. Salicylic acid emerged as the most suitable extractant for purifying cycloalkanes in direct coal liquefaction naphtha due to its superior separation effectiveness, cost efficiency, and environmental benefits. The tower parameters of the simulated separation unit provide valuable insights for the design of actual industrial equipment.
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.
The reliance on fossil fuels intensifies CO2 emissions, worsening political and environmental challenges. CO2 capture and conversion present a promising solution, influenced by industrialization and urbanization. In recent times, catalytic conversion of CO2 into fuels and chemical precursors, particularly methane, are gaining traction for establishing a sustainable, carbon-neutral economy due to methane’s advantages in renewable energy applications. Though homogeneous and heterogeneous catalysts are available for the conversion of CO2 to methane, the efficiency is found to be higher in heterogeneous catalysts. Therefore, this review focuses only on the heterogeneous catalysts. In this context, the efficient heterogeneous catalysts with optimum utility are yet to be obtained. Therefore, the quest for suitable catalyst for the catalytic conversion of CO2 to CH4 is still continuing and designing efficient catalysts requires assessing their synthetic feasibility, often achieved through computational methods like density functional theory simulations, providing insights into reaction mechanisms, rate-limiting steps, catalytic cycle, activation of C=O bonds and enhancing understanding while lowering costs. In this context, this review examines the conversion of CO2 to CH4 using seven distinct types of catalysts, including single and double atom catalysts, metal organic frameworks, metalloporphyrins, graphdiyne and graphitic carbon nitrite and alloys with some case studies. The main focus of this review is to offer a detailed and extensive examination of diverse catalyst design approaches and their utilization in CH4 production, with a specific emphasis on computational aspects. It explores the array of design methodologies used to identify reaction pathways and investigates the critical role of computational tools in their refinement and enhancement. We believe this review will help budding researchers to explore the possibilities of designing catalysts for the CO2 to CH4 conversion from computational framework.
Framework materials such as zeolites and mesoporous silicas are commonly used for many applications, especially catalysis and separation. Here zeolite-mesoporous silica composite catalysts (employing zeolite Y, ZSM-5, KIT-6, SBA-15 and MCM-41 mesoporous silica) were prepared (with different weight percent of zeolite Y and ZSM-5) and assessed for catalytic cracking (using n-heptane, as the model compound at 550 °C) with the aim to improve the selectivity/yield of light olefins of ethylene and propylene from n-heptane. Physicochemical properties of the parent zeolites and the prepared composites were characterized comprehensively using several techniques including X-ray diffraction, nitrogen physisorption, scanning electron microscopy, fourier transform infrared spectroscopy, pulsed-field gradient nuclear magnetic resonance and thermogravimetric analysis. Catalytic cracking results showed that the ZY/ZSM-5/KIT-6 composite (20:20:60 wt %) achieved a high n-heptane conversion of 85% with approximately 6% selectivity to ethylene/propylene. In contrast, the ZY/ZSM-5/SBA-15 composite achieved a higher conversion of 95% and an ethylene/propylene ratio of 8%, indicating a more efficient process in terms of both conversion and selectivity. Magnetic resonance relaxation analysis of the ZY/ZSM-5/KIT-6 (20:20:60) catalyst confirmed a micro-mesoporous environment that influences n-heptane diffusion and mass transfer. As zeolite Y and ZSM-5 have micropores, n-heptane can move and undergo hydrogen transfer reactions, whereas KIT-6 has mesopores that facilitate n-heptane’s accessibility to the active sites of zeolite Y and ZSM-5.
The photocatalytic reduction of CO2 into formic acid is a feasible approach to alleviate the effects of global climate change and achieve chemical energy storage. It is important to design highly active photocatalysts to improve the selectivity and yield of formic acid. In this study, TiO2-based catalysts were prepared and loaded with Pd nanoparticles via an impregnation process. The Pd/H-TiO2 catalyst demonstrated superior CO2 reduction activity and a high formic acid production rate of 14.14 mmolcat·g–1·h–1. The excellent catalytic performance observed in the presence of a Pd/H-TiO2 catalyst is ascribed to the synergy between Ov and Pd. The presence of Ov led to increase in CO2 adsorption while Pd loading enhanced the photogenerated electron-hole pair separation. Electron transfer from H-TiO2 to Pd also contributed to CO2 activation.
Due to the relentless exploitation of non-renewable 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.
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 (EC) and the H atom on the TM1-N4/C (EH), 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 EC (–8 to –7 eV) and weakened EH (–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.
Nowadays, although functionalized pillararenes have been widely designed to be used in drug delivery system, targeted group modified pillararenes have been seldom reported and used in tumor multimodal therapy. Herein, a functionalized pillararene with a polyethylene glycol chain and triphenylphosphonium cation WP5-PEG-TPP was designed and synthesized. Subsequently, an active targeted drug delivery system was constructed based on its host-guest interactions with a newly designed porphyrin derivative, Py-Por. The experimental results demonstrated that this drug delivery system has exhibited excellent targeting ability against tumor cells, but interestingly it could not enter normal cells. After loading the hypoxia-activated prodrug tirapazamine, the prepared nanodrugs displayed high lethality to tumor cells due to their chemo/photodynamic synergistic therapy capability, but negligible toxicity to normal cells. Preliminary therapeutic mechanism study elucidated the synergistic therapy process.
The efficient fractionation and recovery of monosaccharides (xylose and glucose) from lignocellulosic biomass facilitates subsequent sugar-based derivative production. This study introduces a one-pot γ-valerolactone/CuCl2 biphasic pretreatment system (100-mmol·L–1 CuCl2, 180 °C, 60 min) capable of achieving removal rates of 92.25% and 90.64% for xylan and lignin, respectively, while retaining 83.88% of cellulose. Compared to other metal chlorides (NaCl, LiCl, FeCl3, and AlCl3), the γ-valerolactone/CuCl2 system recovered 121.2 mg·(g eucalyptus)–1 of xylose and 55.96 mg·(g eucalyptus)–1 of glucose during the pretreatment stage and 339.2 mg·(g eucalyptus)–1 of glucose during the enzymatic hydrolysis stage (90.78% of glucose yield), achieving a total monosaccharide recovery of 86.31%. In addition, the recovery of γ-valerolactone was 79.33%, exhibiting minimal changes relative to the pretreatment performance. The method proposed in this study allows a high total monosaccharides recovery and a circular economy-oriented pretreatment approach, offering a viable pathway for biorefinery.
The Fe-Mn bimetallic catalyst is a potential candidate for the conversion of CO2 into value-added chemicals. The interaction between the two metals plays a significant role in determining the catalytic performance, however which remains controversial. In this study, we aim to investigate the impact of tuning the proximity of Fe-Mn bimetallic catalysts with similar nanoparticle size. And its effect on the physicochemical properties of the catalysts and corresponding performance were investigated. It was found that closer Fe-Mn proximity resulted in enhanced CO2 hydrogenation activity and inhibited CH4 formation. The physiochemical properties of prepared catalysts were characterized using X-ray diffraction, H2 temperature programmed reduction, and X-ray photoelectron spectroscopy, revealing that a closer Fe-Mn distance promoted electron transfer from Mn to Fe, thereby facilitating Fe carburization. The adsorption behavior of CO2 and the identification of reaction intermediates were analyzed using CO2-temperature programed desorption and in situ Fourier transform infrared spectroscopy, confirming the intimate Fe-Mn sites contributed to CO2 adsorption and the formation of HCOO* species, ultimately leading to increased CO2 conversion and hydrocarbon production. The discovery of a synergistic effect at the intimate Fe-Mn sites in this study provides valuable insights into the relationship between active sites and promoters.
