ACS Engineering Au最新文献

Inclusion of van der Waals (vdW) interactions in density functional theory (DFT) calculations improves the accuracy of the calculations of molecular structures, solid structures, and molecular adsorption configuration and energy. However, it remains unclear how vdW approximations affect calculations of activation barriers of surface reactions, which is valuable for evaluating the reaction kinetics. In this work, we choose a prototype reaction─cyclohexene hydrogenation on a Pd surface─as an example to compare different approaches to include vdW interactions in the calculation of activation barriers of surface elementary steps. We find that the adsorption of cyclohexene and desorption of the product, cyclohexane, are very sensitive to the approaches used to incorporate vdW interactions, while the intrinsic barrier of hydrogenation only varies by about 10%. As a result, the apparent activation barrier also varies to a large extent (from −1.90 to 0.28 eV). The rate-determining transition state was found to be the first hydrogenation step, independent of the vdW approximation used. These calculations indicate that the comparison of intrinsic (true) activation barriers between experimentally measured activation barriers and calculated values is more straightforward, while the comparison for the apparent activation energy may be less reliable. Therefore, simultaneous measurement of intrinsic and apparent activation barriers could serve as a potential way to benchmark the most reliable vdW approximation for molecular adsorption and reaction.

Plasma-surface coupling has emerged as a promising approach to perform chemical transformations under mild conditions that are otherwise difficult or impossible thermally. However, a few examples of inexpensive and accessible in situ/operando techniques exist for observing plasma-solid interactions, which has prevented a thorough understanding of underlying surface mechanisms. Here, we provide a simple and adaptable design for a dielectric barrier discharge (DBD) plasma cell capable of interfacing with Fourier transform infrared spectroscopy (FTIR), optical emission spectroscopy (OES), and mass spectrometry (MS) to simultaneously characterize the surface, the plasma phase, and the gas phase, respectively. The system was demonstrated using two example applications: (1) plasma oxidation of primary amine functionalized SBA-15 and (2) catalytic low temperature nitrogen oxidation. The results from application (1) provided direct evidence of a 1% O₂/He plasma interacting with the aminosilica surface by selective oxidation of the amino groups to nitro groups without altering the alkyl tether. Application (2) was used to detect the evolution of NO_X species bound to both platinum and silica surfaces under plasma stimulation. Together, the experimental results showcase the breadth of possible applications for this device and confirm its potential as an essential tool for conducting research on plasma-surface coupling.

Hydrodynamic cavitation (HC) is finding ever increasing applications in water, energy, chemicals, and materials sectors. HC generates intense shear, localized hot spots, and hydroxyl radicals, which are harnessed for realizing desired physicochemical transformations. Despite identification of HC as one of the most promising technology platforms, its potential is not yet adequately translated in practice. Lack of appropriate models for design, optimization, and scale-up of HC reactors is one of the primary reasons for this. In this work, the current status of modeling of HC reactors is presented. Various prevailing approaches covering empirical, phenomenological, and multiscale models are critically reviewed in light of personal experience of their application. Use of these approaches for different applications such as biomass pretreatment and wastewater treatment is briefly discussed. Some comments on extending these models for other applications like emulsions and crystallization are included. The presented models and discussion will be useful for practicing engineers and scientists interested in applying HC for a variety of applications. Some thoughts on further advances in modeling of HC reactors and outlook are shared, which may stimulate further research on improving the fidelity of computational models of HC reactors.

The energy required to heat, cool, and illuminate buildings continues to increase with growing urbanization, engendering a substantial global carbon footprint for the built environment. Passive modulation of the solar heat gain of buildings through the design of spectrally selective thermochromic fenestration elements holds promise for substantially alleviating energy consumed for climate control and lighting. The binary vanadium(IV) oxide VO₂ manifests a robust metal─insulator transition that brings about a pronounced modulation of its near-infrared transmittance in response to thermal activation. As such, VO₂ nanocrystals are potentially useful as the active elements of transparent thermochromic films and coatings. Practical applications in retrofitting existing buildings requires the design of workflows to embed thermochromic fillers within industrially viable resins. Here, we describe the dispersion of VO₂ nanocrystals within a polyvinyl butyral laminate commonly used in the laminated glass industry as a result of its high optical clarity, toughness, ductility, and strong adhesion to glass. To form high-optical-clarity nanocomposite films, VO₂ nanocrystals are encased in a silica shell and functionalized with 3-methacryloxypropyltrimethoxysilane, enabling excellent dispersion of the nanocrystals in PVB through the formation of siloxane linkages and miscibility of the methacrylate group with the random copolymer. Encapsulation, functionalization, and dispersion of the core─shell VO₂@SiO₂ nanocrystals mitigates both Mie scattering and light scattering from refractive index discontinuities. The nanocomposite laminates exhibit a 22.3% modulation of NIR transmittance with the functionalizing moiety engendering a 77% increase of visible light transmittance as compared to unfunctionalized core─shell particles. The functionalization scheme and workflow demonstrated, here, illustrates a viable approach for integrating thermochromic functionality within laminated glass used for retrofitting buildings.

The spatiotemporal features of the multifunctional monolithic lean hydrocarbon NO_x trap (LHCNT), for eliminating NO_x (x = 1 and 2) and ethylene (C₂H₄), are examined using spatially resolved mass spectrometry (SpaciMS), spanning the sequentially positioned passive NO_x adsorber (PNA; Pd/SSZ-13), hydrocarbon trap (HCT; Pd/BEA), and oxidation catalyst (OC; Pt/Al₂O₃–CeO₂). The overall LHCNT performance is captured in temporal trapping efficiency profiles, which show the integral NO and C₂H₄ uptake followed by delayed NO release along with NO and ethylene oxidation. Spatially resolved transient concentration profiles spanning uptake, release, and conversion of NO, H₂, and C₂H₄, alone or as mixtures in feeds containing H₂O, provide detailed insight into the transient coupling not attainable with effluent concentration monitoring alone. The PNA serves as the primary zone for NO uptake, followed by the OC and HCT. NO oxidation to NO₂ occurs during NO uptake in the PNA due to Pd(II) reduction, while more extensive oxidation occurs in the OC at higher temperature. C₂H₄ uptake and oxidation occur in each of the functions with oxidation occurring the earliest (lowest temperature) in the OC. NO uptake in the PNA and HCT is negligibly affected by H₂ but protracted oxidation of H₂ during the temperature ramp delays NO release, suggesting persistence of NO bound on Pd(I). Both the PNA and HCT exhibit excellent C₂H₄ uptake, which diminishes in the presence of NO. Spatially resolved concentration data reveal several interesting features, such as high-temperature, sequential NO oxidation (by O₂ to NO₂) and C₂H₄ oxidation (by NO₂ to NO + CO₂) in the PNA. Simulated warmup experiments reveal that the LHCNT NO trapping is enhanced with C₂H₄ addition but that a reduction in space velocity may be needed to improve performance. A previously developed PNA model predicts satisfactorily the main features of spatially resolved NO and NO + C₂H₄ data.

We examined the hydrolysis of polyethylene terephthalate (PET) with added polypropylene or cellulose and measured the yield of the terephthalic acid (TPA) monomer recovered. The TPA yield from hydrolysis at 250 °C for 30 min nearly doubled from 40 to 75% with the addition of polypropylene (PP). It increased to 55% with the addition of cellulose. There were no statistically significant increases in TPA yield from hydrolysis with the added plastic or biomass at 300 or 350 °C. The solid material recovered from the hydrolytic depolymerization, after first recovering water- and dichloromethane-soluble compounds, was largely TPA, and the amounts of the other reaction products present with it were largely the same irrespective of the presence or absence of PP or cellulose in the reactor. The TPA yield was affected strongly by the reaction time, reaction temperature, and PET type (fiber-reinforced pellet vs chips from a water bottle). The addition of PP or cellulose to the reactor reduces the influence of reaction time on TPA yield from PET hydrolysis.

The objective of this study was to optimize the pectin extraction from industrial quince biowaste using citric acid as a hydrolytic agent and assisting the process with ultrasound technology. For this, the process was modeled using the Box–Behnken design (BBD) to find the factors’ optimum values and their interactions. The quince pectin extraction was carried out by adding to the biowaste a citric acid solution at different pH values (2.0, 2.5, and 3.0) in mass volume ratios of 1/25, 1/20, and 1/15 g/mL and immersing it in an ultrasound bath for 30, 45, and 60 min at controlled temperatures of 70, 80, and 90 °C. Pectin yield, process cost, and CO₂ emission were calculated under different conditions according to the BBD model, and a polynomial function was adjusted for each dependent variable. A multiobjective optimization technique known as “Genetic algorithms” was used to find the proper extraction conditions that would maximize the pectin yield and minimize the process cost. The optimal extraction conditions obtained were as follows: pH = 2.12, mvr = 0.04 g/mL, time = 48.98 min, and temperature = 85.20 °C, with response variables of pectin yield = 12.78%, cost = 1.501 USD/kg of pectin, and calculated CO₂ emission = 0.565 kg of CO₂/kg of pectin.

CuO_x/CeO₂ is emerging as an effective catalyst for CO oxidation due to its unique redox properties; however, its activity and stability still need to be enhanced compared with supported platinum group metals. Here, an approach is demonstrated to increase the CO oxidation performance and resistance to hydrocarbon inhibition through the K⁺ modification of the CuO_x/CeO₂ catalyst. The K⁺ can improve the electron transfer at the metal–oxide interface, shifting the redox equilibrium (Cu²⁺ + Ce³⁺ ↔ Cu⁺ + Ce⁴⁺) to be right to accelerate the formation of highly active Cu⁺ species. The reaction activity of the K⁺-modified CuO_x/CeO₂ catalyst was in the same order of magnitude as the noble metal of Pt and Pd catalysts. In addition, the K⁺-modified catalyst showed significantly improved resistance to hydrocarbon inhibition. This work demonstrates a facile way to tune the redox properties of binary transition metal oxides.

Large-scale biogas plants are a viable source of CH₄ and CO₂ to be converted efficiently into high-value products. Specifically, production of liquid hydrocarbons can enhance the availability of green fuels while achieving significant CO₂ reductions on site. In this study, the production of liquid hydrocarbons is simulated by dry reforming of biogas into lean-hydrogen syngas, further converted in CO hydrogenation and oligomerization reactors. The process was modeled by using CHEMCAD based on published experimental results with the projected feed composition. A high molar feed ratio of CO₂/CH₄ (>1.7) was set for the reformer to minimize steam requirement while avoiding carbon formation and reaching an optimal H₂ to CO molar ratio (0.7). Two options were techno-economically evaluated based on a biogas plant with a capacity of 5000 N m³/h that produces between 13.8 and 15.7 million liters per year of blending stock for transportation fuels. The economics of the process depends mainly on the cost and availability of the biogas. The minimum selling price of the liquid fuels is $1.47/L and $1.37/L for options 1 (once-through conversion of syngas to liquid fuels) and 2 (recycle of tail gas from oligomerization reactor), respectively, and can be significantly reduced in case the biogas throughput is increased to >20 000 N m³/h. Recycling of the tail gas (option 2) yielded higher productivity, resulting in higher carbon yield (77.9% on the basis of methane) and energy efficiency (67.1%). The economic viability of the process can be improved by implementing CO₂ tax or other incentives to reduce capital investment. It provides a potential route for efficient conversion of biogas into liquid hydrocarbons to meet the increased demand for renewable fuels as blending stock in the transportation sector while improving the sustainability of the plant.