Frontiers of Chemical Science and Engineering最新文献

Metal-organic frameworks have a wide range of applications in the field of membrane separation, but the inherent flexible structure and the difficulty for scale-up hinder their further applications. Herein, the relatively rigid zeolitic imidazolate framework-8 particles prepared under an electric field (E-ZIF-8) were used as the fillers in polysulfone (PSF) to form series of mixed matrix membranes. It was found that the introduction of E-ZIF-8 improves both the C₃H₆ permeability and C₃H₆/C₃H₈ selectivity of the membranes. Compared with the bare PSF membrane, the C₃H₆/C₃H₈ selectivity of the 30 wt % E-ZIF-8@PSF membrane increased by ∼230%, while the C₃H₆ permeability was enhanced by ∼830%. In addition, time and pressure dependence analysis demonstrated that such E-ZIF-8@PSF membranes also exhibited good long-term stability and pressure resistance, offering significant industrialization advantages.

This study investigates the detailed mechanism of CO₂ conversion to CO using the manganese(I) diimine electrocatalyst [Mn(pyrox)(CO)₃Br], synthesized by Christoph Steinlechner and coworkers. Employing density functional theory calculations, we thoroughly explore the electrocatalytic pathway of CO₂ reduction alongside the competing hydrogen evolution reaction. Our analysis reveals the significant role of diimine nitrogen coordination in enhancing the electron density of the Mn center, thereby favoring both CO₂ reduction and hydrogen evolution reaction thermodynamically. Furthermore, we observe that triethanolamine (TEOA) stabilizes transition states, aiding in CO₂ fixation and reduction. The critical steps influencing the reaction rate involve breaking the MnC(O)–OH bond during CO₂ reduction and cleaving the MnH–H–TEOA bond in the hydrogen evolution reaction. We explain the preference for CO₂ conversion to CO over H₂ evolution due to the higher energy barrier in forming the Mn-H₂ species during H₂ production. Our findings suggest the potential for tuning the electron density of the Mn center to enhance reactivity and selectivity in CO₂ reduction. Additionally, we analyze potential competing reactions, focusing on electrocatalytic processes for CO₂ reduction and evaluating “protonation-first” and “reduction-first” pathways through density functional theory calculations of redox potentials and Gibbs free energies. This analysis indicates the predominance of the “reduction-first” pathway in CO production, especially under high applied potential conditions. Moreover, our research highlights the selectivity of [Mn(pyrox)(CO)₃Br] toward CO production over HCOO⁻ and H₂ formation, proposing avenues for future research to expand upon these findings by using larger basis sets and exploring additional functionalized ligands.

Polyolefins, widely used for packaging, construction, and electronics, facilitate daily life but cause severe environmental pollution when discarded after usage. Chemical recycling of polyolefins has received widespread attention for eliminating polyolefin pollution, as it is promising to convert polyolefin wastes to high-value chemicals (e.g., fuels, light olefins, aromatic hydrocarbons). However, the chemical recycling of polyolefins typically involves high-viscosity, high-temperature and high-pressure, and its efficiency depends on the catalytic materials, reaction conditions, and more essentially, on the reactors which are overlooked in previous studies. Herein, this review first introduces the mechanisms and influencing factors of polyolefin waste upcycling, followed by a brief overview of in situ and ex situ processes. Emphatically, the review focuses on the various reactors used in polyolefin recycling (i.e., batch/semi-batch reactor, fixed bed reactor, fluidized bed reactor, conical spouted bed reactor, screw reactor, molten metal bed reactor, vertical falling film reactor, rotary kiln reactor and microwave-assisted reactor) and their respective merits and demerits. Nevertheless, challenges remain in developing highly efficient reacting techniques to realize the practical application. In light of this, the review is concluded with recommendations and prospects to enlighten the future of polyolefin upcycling.

The oxygen vacancy formation energy and chemical looping dry reforming of methane over metal-substituted CeO₂ (111) are investigated based on density functional theory calculations. The calculated results indicate that among the various metals that can substitute for the Ce atom in the CeO₂(111) surface, Zn substitution results in the lowest oxygen vacancy formation energy. For the activation of CH₄ on CeO₂ (111) and Zn-substituted CeO₂ (111) surfaces, the calculated results illustrate that the dissociation process of CH_3(ads) is very difficult on pristine surfaces and unfavorable for CHO_(ads) on substituted surfaces. Furthermore, the dissociative adsorption of CO and H₂ on the Zn-substituted CeO₂ (111) surface requires high energy, which is unfavorable for syngas production. This work demonstrates that excessive formation of oxygen vacancy can lead to excessively high adsorption energies, thus limiting the conversion efficiency of the reaction intermediates. This finding provides important guidance and application prospects for the design and optimization of oxygen carrier materials, especially in the field of chemical looping dry methane reforming to syngas.

The trend of employing machine learning methods has been increasing to develop promising biocatalysts. Leveraging the experimental findings and simulation data, these methods facilitate enzyme engineering and even the design of new-to-nature enzymes. This review focuses on the application of machine learning methods in the engineering of polyethylene terephthalate (PET) hydrolases, enzymes that have the potential to help address plastic pollution. We introduce an overview of machine learning workflows, useful methods and tools for protein design and engineering, and discuss the recent progress of machine learning-aided PET hydrolase engineering and de novo design of PET hydrolases. Finally, as machine learning in enzyme engineering is still evolving, we foresee that advancements in computational power and quality data resources will considerably increase the use of data-driven approaches in enzyme engineering in the coming decades.

The steam reforming of bio-oil can provide a sustainable means to produce hydrogen, while tar steam reforming can significantly enhance the efficiency of the biomass gasification process. Bio-oils and tars are highly complex mixtures, and while there has been extensive research on the reforming of small oxygenates and aliphatic hydrocarbons, there have been comparatively much less studies on aromatics reforming. In the current work, we present a comparative study of the steam reforming of hydroquinone, benzyl alcohol and toluene, selected as model compounds of the aromatic fraction of bio-oils and tars with different functional groups. The effect of temperature, partial pressure of reactants, and contact time is studied over a Rh catalyst supported on γ-Al₂O₃. Across the range of conditions studied, hydroquinone is found to be more reactive, followed by benzyl alcohol, and, lastly, toluene. The differences are attributed to the presence of hydroxyl groups in the case of the former two compounds, versus a methyl group in the case of toluene, effectively correlating activity with the O/C ratio in the compounds’ molecule. Nonetheless, similar pathways are observed, with methane, benzene, naphthalene and toluene (during hydroquinone and benzyl alcohol reforming) detected as products in addition to carbon oxides and hydrogen.

This study introduces an innovative screening approach to evaluate advanced oxidation processes (AOPs) as a preliminary diagnostic tool for degrading emerging contaminants (EC). It includes the design, prototyping, and cost-benefit analysis of circular photochemical reactors with flat and spiral internal geometries. Three-dimensional (3D) printing was used for reactor prototyping, providing flexibility and economy, and this stage was assisted by the hydrodynamic analysis of the prototypes based on residence time distribution (RTD) and macromixing models. The research evaluates the degradation of a model contaminant of emerging concern, fluoxetine (FLX) hydrochloride, using the solar/persulfate (PS) process in two water matrices (i.e., ultrapure water and sewage treatment plant effluent) to optimize reactor performance. The study also proposes primary theoretical pathways for fluoxetine degradation involving hydroxyl and sulfate radicals, as well as predicting the toxicity of the parent compound and its primary metabolites using quantitative structure-activity relationship (QSAR) models. The spiral reactor exhibits improved hydrodynamic behavior, closely resembling continuous stirred and plug flow reactors in series. Despite a slightly lower specific degradation rate in real wastewater, the solar/PS process remains effective for both matrices. By-products generated via the sulfate radical pathway are expected to be less toxic than those formed by hydroxyl radicals (HO·) attack.

Investigating the thermal hysteresis and its effect on the kinetic behaviors and reaction model of vacuum residue pyrolysis is of significant importance in industry and scientific research. Effects of heating rate and heating transfer resistance on the pyrolysis process were examined with the thermogravimetric analysis. The kinetic characteristics of the vacuum residue pyrolysis were estimated using the iso-conversional method and integral master-plots method based on a three-stage reaction model through the deconvolution of Fraser-Suzuki function. Results showed that the reaction order models for the first and second stages were associated with the evaporation of vapor, while the nucleation and growth models for the third stage were linked to char formation. During the pyrolysis, the thermal hysteresis led to an increase in the reaction order in the first stage, which resulted in a delayed release of generated hydrocarbons due to high heating rate and enhanced heat transfer resistance. The reaction in the last stage primarily involved coking, where the presence of an inert solid acted as a nucleating agent, facilitating char formation and reducing the activation energy. The optimization results suggest that the obtained three-stage reaction model and kinetic triplets have the potential to effectively describe the active pyrolysis behavior of vacuum residue under high thermal hysteresis.

The loading-dispersion-reducibility dependence has always been one of the most critical issues in the development of high-performance supported metal catalysts. Herein, up to 40 wt % NiO over ordered mesoporous alumina (OMA) was prepared by co-grinding the hybrid of template-containing OMA and Ni(NO₃)₂·6H₂O. Characterization results confirmed that the OMA mesostructure was still preserved even after loading NiO at a content as high as 40 wt %. More importantly, the reduction extent, dispersion, and average particle size of the Ni/OMA catalysts were maintained at ⩾ 91.0%, ∼13.5%, and ∼4.0–5.0 nm, respectively, when the NiO loading was increased from 20 to 40 wt %. The catalysts were evaluated for the CO methanation as a model reaction, and the similarly high turnover frequency of 24.0 h⁻¹ was achieved at 300 °C for all of the Ni/OMA catalysts. For the catalyst with the highest NiO loading of 40 wt % (40Ni/OMA), the low-temperature activity at 300 °C indexed by the space-time yield of methane (over (325.8 text{mol}_{text{CH}_{4}}cdot {text{kg}_{text{cat}}}^{-1}cdot mathrm{h}^{-1})) was achieved, while the catalyst was operated without an observable deactivation for a time on stream of 120 h under severe reaction conditions of 600 °C and a very high gas hourly space velocity of 240000 mL·g⁻¹·h⁻¹. With these significant results, this work paves the way for a rational and controllable design of supported Ni catalysts by breaking the loading-dispersion-reducibility dependence and stabilizing Ni nanoparticles under harsh reaction conditions.

To date, sustainable thermosetting polymers and their composites have emerged to address recyclability issues. However, achieving mild degradation of these polymers compromises their comprehensive properties such as flame retardancy and glass transition temperature (T_g). Moreover, the reuse of degradation products after recycling for upcycling remains a significant challenge. This study introduces phosphorus-containing anhydride into tetraglycidyl methylene diphenylamine via a facile anhydride-epoxy curing equilibrium with triethanolamine as a transesterification modifier to successfully prepare flame-retardant, malleable, reprocessable, and easily hydrothermally degradable epoxy vitrimers and recyclable carbon fiber-reinforced epoxy composites (CFRECs). The composite exhibited excellent flame retardancy and a high T_g of 192 °C, while the presence of stoichiometric primary hydroxyl groups along the ester-bonding crosslinks enabled environmentally friendly degradation (in H₂O) at 200 °C without any external catalyst. Under mild degradation conditions, the fibers of the composite material were successfully recycled without being damaged, and the degradation products were reused to create a recyclable adhesive with a peel strength of 3.5 MPa. This work presents a method to produce flame retardants and sustainable CFRECs for maximizing the value of degradation products, offering a new upcycling method for high-end applications.