Rapid Reaction Rate Research Articles

Metal Oxides Applied to Thermochemical Water-Splitting for Hydrogen Production Using Concentrated Solar Energy

Solar thermochemical processes have the potential to efficiently convert high-temperature solar heat into storable and transportable chemical fuels such as hydrogen. In such processes, the thermal energy required for the endothermic reaction is supplied by concentrated solar energy and the hydrogen production routes differ as a function of the feedstock resource. While hydrogen production should still rely on carbonaceous feedstocks in a transition period, thermochemical water-splitting using metal oxide redox reactions is considered to date as one of the most attractive methods in the long-term to produce renewable H2 for direct use in fuel cells or further conversion to synthetic liquid hydrocarbon fuels. The two-step redox cycles generally consist of the endothermic solar thermal reduction of a metal oxide releasing oxygen with concentrated solar energy used as the high-temperature heat source for providing reaction enthalpy; and the exothermic oxidation of the reduced oxide with H2O to generate H2. This approach requires the development of redox-active and thermally-stable oxide materials able to split water with both high fuel productivities and chemical conversion rates. The main relevant two-step metal oxide systems are commonly based on volatile (ZnO/Zn, SnO2/SnO) and non-volatile redox pairs (Fe3O4/FeO, ferrites, CeO2/CeO2−δ, perovskites). These promising hydrogen production cycles are described by providing an overview of the best performing redox systems, with special focus on their capabilities to produce solar hydrogen with high yields, rapid reaction rates, and thermochemical performance stability, and on the solar reactor technologies developed to operate the solid–gas reaction systems.

Microfluidic Chip Injection Photo Solidification Molding Study on Reaction Kinetics

Microfluidic chip injection photocuring is a new method for microfluidic chip fabrication. The accuracy of microfluidic chip photocuring has an important impact on the reliability of microfluidic chip. The reaction rate of photocuring system directly affects the final quality and efficiency of microfluidic chip. The rapid reaction rate of photocuring system will lead to poor feeding effect of the reaction system. The forming accuracy is affected, and the reaction rate is too slow, which will increase the forming time and affect the forming efficiency. In this paper, the conversion rate and reaction rate of different active monomers and oligomers used in the formulation system of microfluidic chips were measured on-line. The photocuring reaction kinetics of microfluidic chips was studied, and the influence of the formulation system on the photocuring reaction was explored, which laid a foundation for optimizing the formulation of microfluidic chips.

Fenton Reaction-Modified Corn Stover To Produce Value-Added Chemicals by Ultralow Enzyme Hydrolysis and Maleic Acid and Aluminum Chloride Catalytic Conversion

Fenton reaction has been widely used for pretreatment of lignocellulose with the advantages of simple operation, a rapid reaction rate, and less pollution. In this study, batch and fed-batch Fenton...

Investigating the Effectiveness of Emulsified Acid on Sandstone Formation under High Temperature Conditions

Acid stimulation supports the oil and gas industry as a versatile mean in enhanced oil recovery to fulfil the world energy demand. Although hydrochloric acid can significantly improve the reservoir permeability, its rapid reaction rate at high temperature has created a barrier for acid penetration. Subsequently, emulsified acid has slowly gain its popularity due to its retardation effect which allows deeper penetration of acid into the formation and achieves minimal corrosion issues. Nonetheless, emulsified acid has rarely applied on sandstone formation. Since a large portion of reservoirs are made up of sandstone, the effects of emulsified acid on sandstone under high temperature conditions should be studied to unlock the effective usage of emulsified acid in restoring the hydrocarbon recovery from the potential sandstone reservoirs. Besides, it is also crucial to explore cheaper and greener substitute to formulate innovative emulsified acid in minimizing the high acidizing budget along with environmental concerns. In this project, 10 different emulsified acid combinations are prepared using hydrofluoric acid, hydrochloric acid, phosphoric acid, formic acid, acetic acid, cationic surfactant, diesel and waste oil. The pre-flush treatment (5 % CH3COOH: 10 % HCl) is followed by the main flush (emulsified acids) saturation for 3 days. The thermal stability of emulsified acids and their effect on the Berea sandstone properties are evaluated. Major outcome is that the emulsified acids have the capability to remain stable at 275 °F up to 6 hours with uniform and fine droplet size. It is also proven that most of the emulsified acids can improve the porosity and permeability of Berea sandstone core samples except for HF: H3PO4. Regardless of the types of oil used for emulsified acid formulation, HF: HCl acid combination shows the best performance enhancement for both diesel-based and waste oil-based emulsified acids. In sandstone acidizing, emulsified acid dissolves the minerals and create acid transport pathway with close connectivity between pore spaces, causing the formation of large and conductive channels within the rock. Hence, these positive results clearly reflect on the feasibility of emulsified acid application in sandstone matrix acidizing and the effectiveness of waste oil as a replacement fluid for diesel.

Shock initiation of multi-component insensitive PBX explosives: Experiments and MC-DZK mesoscopic reaction rate model.

To facilitate the pre-estimation and optimization of the prescription design of a multi-component polymer bonded explosive (PBX), a multicomponent mesoscopic reaction rate model (MC-DZK model) is developed to predicate preferably the influence of both the explosive components and the particle size of on the shock initiation. All the parameters in the model are determined directly by the parameters in the DZK model for each explosive component. Furthermore, for the multicomponent insensitive explosive PBXC10 (70% TATB, 25% HMX, and 5% Kel-F800 by weight) with different explosive particle sizes, both shock initiation experiments and corresponding numerical simulations are performed, and there is satisfactory agreement between the numerical results and the available experimental data. It is found that the pressure histories present as a shape of step increase during the whole shock initiation process, which is resulted mainly from the rapid chemical reaction rate just behind the precursory shock wave front. It is also found that the smaller the size of the explosive particulates, the faster the pressure grows on the precursory shock wave front, the shorter the run distance to detonation, and the higher the chemical reaction rate just behind the precursory shock wave front.

Melt‐synthesis of LiFePO4 over a metallic bath

AbstractCompared with large‐scale processes, the LiFePO4 (LFP) melt‐synthesis is a low‐cost method with short dwell times and rapid reaction rates. However, secondary phases and impurities remaining in the olivine structure lower the cathode's electrochemical properties. Starting from a low‐cost Fe3+ precursor, we evaluated tin and silver charged metallic baths to purify the melt‐synthesis of LiFePO4 at laboratory scale. In the tin bath exploration, an x‐ray diffraction (XRD) confirmed the olivine structure and a temperature‐dependent generation of Li3PO4 and Li4P2O7. An SEM image analysis identified tin‐rich phases (SnxPyOz) segregated from the LFP structure and FexP phases on the internal walls of the crucible. A multi‐element analysis (ICP‐AES) detected more than 0.03 g of Sn/g of LFP. The tin bath prepared samples delivered up to156 mAh/g of LFP in a carbon‐free basis, 3 % lower than the capacity of the high purity Fe2O3‐based material at 0.1 C. The silver bath‐based LFP samples produced cleaner XRD patterns (less than 160 ppm of Ag in the LFP ingots), closer to the estimated molar ratios and neither silver compounds nor silver oxides. In this case, the sample delivered 161 mAh/g of LFP, the same capacity as the cathode prepared without a metallic bath. Starting from a commodity Fe3+ source, future work should explore the silver bath roles as a reactive media, a heating source, a crucible insulator, and a potential contaminant trap for the melt‐synthesis of LiFePO4.

Synthesis of highly effective stabilized CaO sorbents via a sacrificial N-doped carbon nanosheet template

Highly macroporous MgO-stabilized CaO nanosheets with rapid reaction rates, high capacity, and good stability for high-temperature CO2 capture.

Dense Na <sub>0.5</sub>K <sub>0.5</sub>NbO <sub>3</sub> Ceramics Produced by Reactive Flash Sintering of NaNbO <sub>3</sub>-KNbO <sub>3</sub> Mixed Powders

Dense Na0.5K0.5NbO3 ceramics are successfully produced by reactive flash sintering of the NaNbO3-KNbO3 mixed powders, which enables the chemical reaction and sintering to take place simultaneously, skipping the preparation process of Na0.5K0.5NbO3 powders that is required in conventional production. The as-prepared Na0.5K0.5NbO3 ceramics exhibit the high piezoelectric coefficient d33. Besides the Joule heating, generation of high concentration of defects are proposed to explain the rapid reaction and sintering rates during the reactive flash sintering. This study presents a cost-effective way to prepare dense and pure ceramic materials from their basic constituents in one step at low temperature in short time.

Watershed-scale chemical weathering in a merokarst terrain, northeastern Kansas, USA

Carbonate weathering in the merokarst landscape at the Konza Prairie (near Manhattan, KS) is governed by kinetically rapid reaction rates, similar to other carbonate settings. The geology of the site consists of repeating couplets of shale and limestone mantled by Pleistocene loess, on which most soils are built. The headwater stream that is the subject of this study is intermittent and well connected to the secondary porosity in the limestone aquifers, such that the water chemistry is groundwater-dominated. Despite increasing in situ weathering rates shown by increasing solute concentrations, long-term (~21 of 24 years) decline in stream-water discharge has reduced chemical denudation. The current chemical denudation rate is 0.02 mm yr−1. Limestone bedrock thickness (~26.6 m) is 38% of total bedrock thickness (~70 m); the present landscape would have taken 1–4 million years to dissolve at current weathering rates. Despite paleogeographic reconstructions suggesting exposure for the past 260 Ma, estimates of the time to erode younger strata using current physical and chemical denudation rates are 80–159 Ma, still much less than the age of the rocks. An alternate source of material, dust, is proposed that may slow limestone weathering, which in turn protects shales from physical erosion, thereby slowing landscape evolution.

Managing the power grid: how myoglobin can regulate PO2 and energy distribution in skeletal muscle.

Managing the power grid: how myoglobin can regulate PO2 and energy distribution in skeletal muscle.

Enhanced capacity to CO2 sorption in humid conditions with a K-doped biocarbon

Abstract Solid sorbents with enhanced capacity and selectivity towards CO2 are crucial in the design of an efficient capture process. Among the possible alternatives, K2CO3-doped activated carbons have shown high CO2 capture capacity and rapid carbonation reaction rate. In this work, a sustainable and low-cost approach is developed with a biomass-based activated carbon or biocarbon as support. The CO2 capture performance in cyclic sorption–desorption operation and the sorption kinetics have been investigated under different scenarios in a purpose-built fixed-bed set-up. Independent of the H2O concentration in the flue gas, a constant relative humidity (∼20%) in the K2CO3-doped biocarbon bed promoted the carbonation reaction and boosted the CO2 sorption capacity (1.92 mmol/g at 50 °C and 14 kPa partial pressure of CO2). Carbonation is slower than physical adsorption of CO2 but wise process design could tune the operation conditions and balance capture capacity and sorption kinetics.

Direct Estimation of Metabolic Flux by Heavy Isotope Labeling Simultaneous with Pathway Inhibition: Metabolic Flux Inhibition Assay.

Heavy isotope labeled metabolites are readily detected by mass spectrometry and are commonly used to analyze the rates of metabolic reactions in cultured cells. The ability to detect labeled metabolites-and infer fluxes-is influenced by a number of factors that can confound simplistic comparative assays. The accumulation of labeled metabolites is strongly influenced by the pool size of the metabolite of interest and also by changes in downstream reactions, which are not always fully perceived. Here, we describe a method that overcomes some of these limitations and allows simple calculation of reaction rates under low nutrient, rapid reaction rate conditions. Acutely increasing the pool of the metabolite of interest (by adding a pulse of excess unlabeled nutrient to the cells) rapidly increases accumulation of labeled metabolite, facilitating a more accurate assessment of reaction rate.

Oxidation of amino acids by peracetic acid: Reaction kinetics, pathways and theoretical calculations

Peracetic acid (PAA) is a sanitizer with increasing use in food, medical and water treatment industries. Amino acids are important components in targeted foods for PAA treatment and ubiquitous in natural waterbodies and wastewater effluents as the primary form of dissolved organic nitrogen. To better understand the possible reactions, this work investigated the reaction kinetics and transformation pathways of selected amino acids towards PAA. Experimental results demonstrated that most amino acids showed sluggish reactivity to PAA except cysteine (CYS), methionine (MET), and histidine (HIS). CYS showed the highest reactivity with a very rapid reaction rate. Reactions of MET and HIS with PAA followed second-order kinetics with rate constants of 4.6 ± 0.2, and 1.8 ± 0.1 M−1⋅s−1 at pH 7, respectively. The reactions were faster at pH 5 and 7 than at pH 9 due to PAA speciation. Low concentrations of H2O2 coexistent with PAA contributed little to the oxidation of amino acids. The primary oxidation products of amino acids with PAA were [O] addition compounds on the reactive sites at thiol, thioether and imidazole groups. Theoretical calculations were applied to predict the reactivity and regioselectivity of PAA electrophilic attacks on amino acids and improved mechanistic understanding. As an oxidative disinfectant, the reaction of PAA with organics to form byproducts is inevitable; however, this study shows that PAA exhibits lower and more selective reactivity towards biomolecules such as amino acids than other common disinfectants, causing less concern of toxic disinfection byproducts. This attribute may allow greater stability and more targeted actions of PAA in various applications.

Relay Conjugation of Living Metathesis Polymers.

The covalent coupling of complex macromolecules is a modern challenge in both chemistry and biology. The development of efficient and chemoselective methods for polymer coupling and functionalization are increasingly important for designing new advanced materials and interfacing with biochemical systems. Herein, we present a new strategy to directly conjugate living polymers prepared using ring-opening metathesis polymerization (ROMP) to both small molecules and synthetic macromolecules. Central to this methodology is a terminal alkyne that serves as a directing group to promote a rapid, intramolecular reaction with an otherwise unreactive olefin. This highly chemoselective relay conjugation is compatible with a range of monomer families and uses a bench-stable enyne motif that can be easily introduced to functional targets. The rapid rate of the conjugation reaction paves the way for greatly streamlined construction of complex macromolecular systems derived from metathesis polymerization techniques without the need for specialized equipment.

One-step hydrogen extraction and storage in plasma generated palladium nanoparticles

This study demonstrates a novel way of hydrogen extraction from toluene and direct storage in plasma generated palladium (Pd) nanoparticles in one-step. Monodispersed Pd nanoparticles with a narrow particle-size distribution have been successfully synthesized, for the first time, by a plasma discharge between Pd electrodes in the cavitation field of toluene. The resulting well-dispersed Pd nanoparticles embedded in carbon are stabilized against agglomeration. The effect of experiment time on the particle size and the expansion of lattice spacing due to hydrogen are investigated by experimental and computational studies using density functional theory (DFT). Using X-ray diffraction and high-resolution transmission electron microscopy measurements, it was found that particle size and lattice expansion increases with experiment time. Pd nanoparticle synthesis for in situ hydrogen storage in one step using plasma discharge in an appropriate solvent emphasizes the importance of adopting this methodology which offers several advantages. These include rapid reaction rate, ability to form very small nanoparticles with narrow size distribution and hydrogen extraction from the solvent for direct storage in the Pd nanoparticle lattice.

Design of a Novel Process for Continuous Lactide Synthesis from Lactic Acid

Lactide synthesis is an energy-intensive process used to produce polylactic acid (PLA). In this study, we propose a continuous lactide synthesis process developed on the basis of a recently developed one-step reaction using a SnO2–SiO2 nanocomposite catalyst. This process enables a rapid reaction time of 40 ms for the catalyst, which achieves 94% lactide yield. To design an efficient chemical process, reaction kinetics were developed and a heterogeneous reactor model was applied to the reactor. The proposed process has advantages over commercial processes, having both a rapid reaction rate and high yield. Moreover, its rapid reaction rate significantly increases the productivity. In addition, this process operates under atmospheric pressure, which makes it more energy efficient than commercial processes that operate under a high vacuum pressure of 20 mmHg. Therefore, the overall process is an effective alternative for lactide production.

Precisely fabricating Ce-O-Ti structure to enhance performance of Ce-Ti based catalysts for selective catalytic reduction of NO with NH3

A series of Ce-Ti mixed oxides (CeaTi1−a) were successfully synthesized by a spontaneous deposition method and evaluated in selective catalytic reduction of NO with NH3 (NH3-SCR). The structures and properties of the CeaTi1−a catalysts were characterized by means of XRD, Raman, TEM, N2-sorption, XPS, H2-TPR and NH3-TPD. The results demonstrated that lots of Ce-O-Ti species were formed because of the strong synergistic interaction of gelation of TiO2 and deposition of Ce3+ during the preparation process of CeaTi1−a catalysts. As results, the CeaTi1−a catalysts exhibited excellent redox ability, enrichment of Ce3+ species, high surface adsorbed oxygen concentration, and abundant acid sites. The CeaTi1−a catalysts showed remarkable catalytic activity with broad operation temperature window, and Ce0.5Ti0.5 catalyst exhibited the best catalytic activity and extraordinary H2O/SO2 durability. The in-situ FTIR results revealed that the mechanisms of L-H and E-R existed synchronously during the NH3-SCR reaction, and the former one was predominant due to its rapid reaction rate.

Structural dynamics of the transaminase active site revealed by the crystal structure of a co-factor free omega-transaminase from Vibrio fluvialis JS17

Omega (ω)-transaminase catalyzes the transfer of an amino group from a non-α position amino acid, or an amine compound with no carboxylic group, to an amino acceptor, and has been studied intensively because of its high potential utility in industry and pharmatheutics. The ω-transaminase from Vibrio fluvialis JS17 (Vfat) is an amine:pyruvate transaminase capable of the stereo-selective transamination of arylic chiral amines. This enzyme exhibits extraordinary enantio-selectivity, and has a rapid reaction rate for chiral amine substrates. In this study, we report the crystal structure of the apo form of Vfat. The overall structure of Vfat was typical of other class III aminotransferase exhibiting an N-terminal helical domain, a small domain, and a large domain. Interestingly, the two subunits of apo Vfat in the asymmetric unit had different structures. A comparison of the overall structure to other transaminases, revealed that the structures of the N-terminal helical domain and the large domain can be affected by cofactor occupancy, but the structural rearrangement in these regions can occur independently.

Reaction mechanism of spinel CuFe2O4 with CO during chemical-looping combustion: An experimental and theoretical study

Spinel CuFe2O4 is a promising oxygen carrier due to its synergistic enhanced performance. A fundamental understanding of the reaction mechanism between oxygen carrier and fuels is important for a rational design of highly efficient oxygen carrier. The reaction mechanism of spinel CuFe2O4 with CO during chemical-looping combustion (CLC) was studied based on thermogravimetric analyses (TGA) and density functional theory (DFT) calculations. Two distinct reaction stages were clearly observed. CuFe2O4 was mainly transformed into Cu and Fe3O4 with a rapid reaction rate in the initial stage, and then product Fe3O4 was slowly reduced to FeO or even to Fe. The reactivity of CuFe2O4 is much higher than that of Fe2O3, which is ascribed to the existence of Cu. The enhanced oxygen evolution activity of CuFe2O4 at low temperature is validated by both the experimental and theoretical methods. Three types of surface oxygen coordinated with different metal atoms show different reactivity. Two kinds of reaction pathways are involved in CO oxidation over CuFe2O4. In the one-step reaction pathway, CO directly reacts with the oxygen bonding to two octahedral Cu and one octahedral Fe atoms to form a CO2 molecule without an energy barrier, which corresponds to the surface oxygen consumption observed in TGA experiments. In the possible two-step reaction pathway, CO first adsorbs on the surface, and then reacts with the oxygen bound to one octahedral Cu and two octahedral Fe atoms to generate CO2 by surmounting an energy barrier of 10.84 kJ/mol, which is the most kinetically and thermodynamically favorable pathway.

Microwave-enhanced advanced oxidation processes for the degradation of dyes in water

Contamination of water bodies with dyes has become a serious global concern affecting the whole biosphere. Microwave irradiation and advanced oxidation processes (AOP) have recently gained importance as efficient remediation methods. Indeed, microwave offers special features such as fast, uniform, selective and controlled heating that result in a rapid reaction rate, whereas advanced oxidation processes are able to mineralize any organic pollutant. Here we review microwave-enhanced advanced oxidation processes for the removal or degradation of synthetic dyes, and we compare with conventional treatment methods. We found that microwave-enhanced AOP improve the efficiency of dye degradation. However, cost analyses reveal an economic limitation of microwave-enhanced processes.