Kinetic Study Of Reaction Research Articles

Water-involved tandem conversion of aryl ethers to alcohols over metal phosphide catalyst

Lignin-derived compounds provide a platform for the production of value-added chemicals. Herein, we reported metal phosphide (Pd-Ni-P) catalyzed the conversion of diphenyl ether (DPE) via a restricted pathway involving partial hydrogenation-hydrolysis-hydrogenation. Cyclohexanol, an important raw material for the polymer industry, was therefore obtained as the main product in 87% mole yield with a high production rate of 14.65 mol·g−1Pd·h−1. The results of X-ray diffraction, X-ray absorption spectroscopy and X-ray photoelectron spectroscopy confirmed that Ni and P atoms were inserted into the face-centred cubic Pd lattices, leading to the expanded Ni-Ni lattices and Pd-P covalent bonds. The electronic deficient Pd contributes to the partial hydrogenation of DPE to cyclohexyl phenyl ether (CHPE), and the inserted Ni facilitates the hydrolysis of CHPE to monocycles. Various control experiments including deuterium experiment and reaction kinetic study revealed the strong hydrolysis ability of Pd-Ni-P catalyst accounting for the high production rate of cyclohexanol. Besides, several lignin-derived aryl ethers could undergo the same reaction pathway to produce alcohol chemicals with high yields ranging from 50% to 94%.

High Cycle Stability of Hybridized Co(OH)2 Nanomaterial Structures Synthesized by the Water Bath Method as Anodes for Lithium-Ion Batteries.

Cobalt oxides have been intensely explored as anodes of lithium-ion batteries to resolve the intrinsic disadvantages of low electrical conductivity and volume change. However, as a precursor of preparing cobalt oxides, Co(OH)2 has rarely been investigated as the anode material of lithium-ion batteries, perhaps because of the complexity of hydroxides. Hybridized Co(OH)2 nanomaterial structures were synthesized by the water bath method and exhibited high electrochemical performance. The initial discharge and charge capacities were 1703.2 and 1262.9 mAh/g at 200 mA/g, respectively. The reversible capacity was 1050 mAh/g after 150 cycles. The reversible capability was 1015 mAh/g at 800 mA/g and increased to 1630 mAh/g when driven back to 100 mA/g. The electrochemical reaction kinetics study shows that the lithium-ion diffusion-controlled contribution is dominant in the energy storage mechanism. The superior electrochemical performance could result from the water bath method and the hybridization of nanosheets and nanoparticles structures. These hybridized Co(OH)2 nanomaterial structures with high electrochemical performance are promising anodes for lithium-ion batteries.

Mechanistic investigation of cellulose formate to 5-hydroxymethylfurfural conversion in DMSO-H2O

5-hydroxymethylfurfural (HMF) primary can be synthesized from monosaccharides including glucose and fructose, cost is one of barriers to realize HMF large-scale production. In this study, a high HMF yield of 69.6 mol% was obtained at 180℃ for 5 min using biomass derived cellulose formate as reactant, which was prepared by formylation of cellulose using recyclable formic acid, and sequentially catalyzed by hydrochloric acid (HCl) and aluminum chloride (AlCl3) in dimethyl sulfoxide (DMSO) and H2O system. To investigate the effect of cosolvents and formyl groups on the cellulose formate conversion, kinetics analysis and molecular dynamics simulations were conducted. Reaction kinetics study shows that the rate constant of hydrolysis of cellulose formate to glucose increased by almost three times in DMSO-H2O and the reaction rates’ constants of glucose, fructose and HMF to humins decreased with the presence of DMSO. Molecular dynamics simulations show that formyl group and DMSO increased its hydrophilicity around the reactive hydroxyl group on the carbon ring and steric hindrance of formyl group affect the distribution of water molecular and DMSO molecular around formylated glucose, resulting in facilitating the formation of a precursor to fructose and inhibiting the formation of humins during formylated glucose conversion.

Hydrodeoxygenation reactivity of the carbonyl group and carboxyl group and their interaction: taking 2-pentanone, valeric acid, and levulinic acid as examples

The interaction of different functional groups in bio-oil fuel was discussed through the study of reaction kinetics.

Quantum chemical study of the reaction paths and kinetics of acetaldehyde formation on a methanol-water ice model.

Acetaldehyde (CH3CHO) is ubiquitous in interstellar space and is important for astrochemistry as it can contribute to the formation of amino acids through reaction with nitrogen containing chemical species. Quantum chemical and reaction kinetics studies are reported for acetaldehyde formation from the chemical reaction of C(3P) with a methanol molecule adsorbed at the eighth position of a cubic water cluster. We present extensive quantum chemical calculations for total spin S = 1 and S = 0. The UωB97XD/6-311++G(2d,p) model chemistry is employed to optimize the structures, compute minimum energy paths and zero-point vibrational energies of all reaction steps. For the optimized structures, the calculated energies are refined by CCSD(T) single point computations. We identify four transition states on the triplet potential energy surface (PES), and one on the singlet PES. The reaction mechanism involves the intermediate formation of CH3OCH adsorbed on the ice cluster. The rate limiting step for forming acetaldehyde is the C–O bond breaking in CH3OCH to form adsorbed CH3 and HCO. We find two positions on the reaction path where spin crossing may be possible such that acetaldehyde can form in its singlet spin state. Using variational transition-state theory with multidimensional tunnelling we provide thermal rate constants for the energetically rate limiting step for both spin states and discuss two routes to acetaldehyde formation. As expected, quantum effects are important at low temperatures.

Reaction Pathway and Kinetic Study of 4,5-Dihydroxyimidazolidine-2-thione Synthesis by HPLC and NMR

Reaction Pathway and Kinetic Study of 4,5-Dihydroxyimidazolidine-2-thione Synthesis by HPLC and NMR

Reaction Kinetics Study of Catalytical Hydrogenation of Furfural in Liquid Phase

Reaction Kinetics Study of Catalytical Hydrogenation of Furfural in Liquid Phase

Kinetic Study of SN2 Reaction between Paranitrophenyl Benzoate and Hydrazine in the Presence of CTAB Reverse Micelles

Kinetic study of the reaction between p-Nitrophenyl benzoate (PNPB) by hydrazine (HYN) in the presence of Cetyltrimethylammonium bromide (CTAB)/Chloroform/Hexane reverse micellar medium shows that the reaction obeys first order kinetics with respect to each of the reactants. The rate of the reaction is much slower in reverse micellar medium compared to aqueous medium under identical conditions (kˈAq = 2.84×10−3 sec−1, krm =1.34×10−4 sec−1). The rate constants for the reaction in the reverse micellar medium have been determined at different values of W {W=[H2O]/[CTAB]} and at different concentrations of CTAB. It was found that the observed rate constant decreases with W. This kinetic behaviour was interpreted by using modified Berezin pseudo phase model, taking into consideration the distribution of the reactants, PNPB and hydrazine between the three pseudo phases, i.e., water pool, interface an organic phase. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Product inhibition of mammalian thiamine pyrophosphokinase is an important mechanism for maintaining thiamine diphosphate homeostasis

BackgroundThiamine diphosphate (ThDP), an indispensable cofactor for oxidative energy metabolism, is synthesized through the reaction thiamine + ATP ⇆ ThDP + AMP, catalyzed by thiamine pyrophosphokinase 1 (TPK1), a cytosolic dimeric enzyme. It was claimed that the equilibrium of the reaction is in favor of the formation of thiamine and ATP, at odds with thermodynamic calculations. Here we show that this discrepancy is due to feedback inhibition by the product ThDP. MethodsWe used a purified recombinant mouse TPK1 to study reaction kinetics in the forward (physiological) and for the first time also in the reverse direction. ResultsKeq values reported previously are strongly underestimated, due to the fact the reaction in the forward direction rapidly slows down and reaches a pseudo-equilibrium as ThDP accumulates. We found that ThDP is a potent non-competitive inhibitor (Ki ≈ 0.4 μM) of the forward reaction. In the reverse direction, a true equilibrium is reached with a Keq of about 2 × 10−5, strongly in favor of ThDP formation. In the reverse direction, we found a very low Km for ThDP (0.05 μM), in agreement with a tight binding of ThDP to the enzyme. General significanceInhibition of TPK1 by ThDP explains why intracellular ThDP levels remain low after administration of even very high doses of thiamine. Understanding the consequences of this feedback inhibition is essential for developing reliable methods for measuring TPK activity in tissue extracts and for optimizing the therapeutic use of thiamine and its prodrugs with higher bioavailability under pathological conditions.

Oxidative Cross‐Coupling Reactions between Two Nucleophiles†

Comprehensive SummaryOxidative cross‐coupling reactions between two nucleophiles have become one of the most important tools to construct chemical bonds in organic synthesis methodology. Directly using hydrocarbons to synthesize valuable chemicals is an ideal and economical process because hydrocarbons are cheap, abundant and readily available. The account covered a brief introduction about our efforts on the development of oxidative cross‐coupling reactions. We discovered this reaction model by the cross‐coupling of two organometallic reagents. Related mechanisms were revealed by the characterization of reaction intermediates and the study of reaction kinetics through operando spectroscopy, such as in‐situ IR (infrared), EPR (electron paramagnetic resonance), Raman and XAS (X‐ray absorption) spectroscopy. Representative applications, such as oxidative cross‐coupling reactions with H2 evolution, exhibited their high atom economy and step economy. What is the most favorite and original chemistry developed in your research group?Oxidative Cross‐Coupling – The chemistry between two “nucleophiles”.How do you get into this specific field? Could you please share some experiences with our readers?My first contact with palladium chemistry was the halopalladation of acetylene in 1998. Then I worked on palladium enolate and found it could initiate a transmetalation reaction. Until 2006, I found that desyl chloride (a halogenated hydrocarbon) showed different reactivity with organometallic reagents due to the halophilic and oxyphilic properties, thus we achieved the cross‐coupling between two organometallic reagents. At that moment, we started the research about “Oxidative Cross‐coupling Reactions – the chemistry between two nucleophiles.What is the most important personality for scientific research?Hard‐working, passion and ambition (安钻迷).What are your hobbies? What are your favorite book(s)?Sports. Jin Yong's martial arts novels, Morrison's Organic Chemistry, Electronic Interpretation of Organic Chemistry.

Mathematical Modeling of Urea Reaction with Sulfuric Acid and Phosphoric Acid to Produce Ammonium Sulfate and Ammonium Dihydrogen Phosphate Respectively

Urea is the final product of protein metabolism in mammals and can be found in different biological fluids. Use of mammalian urine in agricultural production as organic fertilizer requires safe handling to avoid the formation of ammonia that will decrease the fertilizer value due to the loss of nitrogen. Safe handling is also required to minimize the decomposition of urea into condensed products such as biuret and cyanuric acid, which will also have a negative impact on the potential sustainable production of crops and sanitation technologies. The study of thermodynamics and reaction kinetics of urea stabilization plays a key role in understanding the conditions under which undesirable compounds and impurities in urea-based fertilizers and urea-based selective catalytic reduction systems are formed. For this reason, we studied the reaction of urea in acid media to achieve urea stabilization by modeling the reaction of urea with sulfuric acid and phosphoric acid, and estimating the reaction enthalpy and adiabatic heat difference for control of the heat released from the neutralization step using Ca(OH)2 or MgO for the safety of the process. Numerical and simulation analyses were performed by studying the effect of the surrounding temperature, the ratio of acid reagent to urea concentration, the rate of addition, and the reaction rate to estimate the required time to achieve an optimum value of urea conversion into ammonium dihydrogen phosphate or ammonium sulfate as potential technological opportunities for by-product valorization. Full conversion of urea was achieved in about 10 h for reaction rates in the order of 1 × 10−5s−1 when the ratio of H2SO4 to CH4N2O was 1.5. When increasing the ratio to 10, the time required for full conversion was considerably reduced to 3 h.

Cp(π-Allyl)Pd-Initiated Polymerization of Diazoacetates: Reaction Development, Kinetic Study, and Chain Transfer with Alcohols

A new initiating system, (cyclopentadienyl) (π-allyl)palladium(II) [Cp(π-allyl)Pd], for the polymerization of diazoacetate monomers has been developed. Homo- and copolymers bearing an ester substituent at every main-chain carbon atom were efficiently synthesized from various alkyl and aryl diazoacetates. In particular, this polymerization system can tolerate various functional groups, which allows for effective postpolymerization functionalization of the resultant polymers. Detailed kinetic study indicates that this polymerization has the characteristics of slow initiation and rapid propagation. Furthermore, alcohols were found to function as chain transfer agents as confirmed by polymerization experiments and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) analyses of the polymer products, thus providing an effective method for controlling the molecular weight of the polymer.

Photocatalytic degradation of organic dyes by U3MnO10 nanoparticles under UV and sunlight

Herein, U3MnO10 bimetal oxide particles were prepared by co-precipitation method alongside pure metal oxides (MnO2 and U3O8). The prepared samples were characterized by XRD, SEM and FTIR techniques. The XRD and FTIR results elucidated thatU3MnO10sample was composed of a mixture of MnO2 and U3O8 crystals. The MnO2, U3O8 and U3MnO10 bimetal oxide were used as photocatalysts in the degradation of four toxic organic dyes. The photocatalytic results showed that the U3MnO10 bimetal oxide had higher photocatalytic activity than pure MnO2 and U3O8 oxides. The better activity of U3MnO10 bimetal oxide was related to its porous structure, large surface area, well crystalline structure and low band gap. The band gap value calculated by Tauc plot was found to be 2.4 eV for U3MnO10bimetal oxide. The percent degradation rate shows that bromothymol blue is degraded faster than acid black, rhodamine b and crystal voilet. The reaction kinetic studies reveal that bromothymol blue showed the faster degradation rate with a rate constant of 0.02 min−1.

Potential Biopolymer Adsorbent Functionalized with Fe3O4 Nanoparticles for the Removal of Cr(VI) From Aqueous Solution

In the present study, an adsorbent with a synergistic effect was developed from chitosan (CS) and Fe3O4 nanoparticles (Fe3O4 Nps) to remove Cr(VI) from aqueous solutions. The Fe3O4 Nps were synthesized by co-precipitation and were characterized by TEM. The CS/NPs composites were prepared by electrospinning technique and analyzed by SEM, FT-IR, DSC, and TGA. In the batch system, the influence of Fe3O4 Nps content, pH, contact time, Cr(VI) initial concentration, adsorbent dosage, and the temperature was investigated; the Cr(VI) concentration was determined using a colorimetric method by UV–Vis spectroscopy. The Fe3O4 Nps presented a quasi-spherical shape and an average size of 18 nm, with a low particle distribution. The SEM analysis reveals the presence of highly porous, interconnected micrometric structures. The optimal adsorption conditions were 1% load of Fe3O4 Nps by weight of CS, pH 3, 25 °C, and equilibrium was reached at just 9 min. Besides, the adsorption is favored by increasing Cr(VI) initial concentration and adsorbent dosage. The studies of reaction kinetics and adsorption equilibrium showed that the experimental data were better fitted to the Pseudo-second-order and Langmuir isotherm models, establishing monolayer formation and chemisorption. The maximum adsorption capacity of CS/Fe3O4 Nps was 440.75 mg/g, which indicates a high affinity of the adsorbent for Cr(VI). Finally, a kinetic diffusion study established that intraparticle diffusion, and in particular surface diffusion, are important resistances in the transport of Cr(VI) from the liquid phase to the active site.

A comprehensive study of char reaction kinetics: Does CO always promote NO reduction on char surface?

This investigation focuses on the NO reduction process over chars and quantifies the effects of CO on char-NO reactivity under different conditions. Kinetic data were measured in a lab-scale fixed-bed reactor at temperatures between 1023 K and 1223 K, involving three coal chars with coal ranks ranging from lignite to anthracite. Experimental results show that CO can promote the reduction of NO over chars at low temperatures. However, there is a significant decrease in NO conversion rate at high temperatures compared to the case without CO present in the gas. The promotion or inhibition effects of CO on char-NO reactivity will become more obvious if the CO concentration is higher. Moreover, the consumption rate of NO is about the same as the generating rate of CO2 under high-level CO conditions, while a considerable amount of CO is generated during the direct reduction of NO by carbon. Further analysis based on Langmuir adsorption theory also indicates that char plays a catalytic role in NO reduction rather than acting as a reactant when CO is added. In addition, under the same temperature and gas conditions, the reactivity of SC lignite char is roughly five times higher than that of HP bituminous char and ten times higher than that of WH anthracite char, namely, the increase of coal rank leads to the decline in char-NO reactivity. Besides, the char made from higher rank coal has a broader range of temperature at which the CO presents a positive effect on NO reduction. Finally, a simple expression was proposed to calculate the NO reduction rate on char surface based on the experimental data, which can be easily applied in the description of nitrogen chemistry for fluidized bed combustion.

Reversible Addition–Fragmentation Chain Transfer-Mediated Amphiphilic Copolymeric Composite as a Nanocarrier for Drug Delivery Application

Magnetic core–shell nanoparticle (NP)-polymer-based composite materials, in which the stimuli-responsive polymer acts as a suitable shell, become more advantageous as nanocarriers. Here, nanocomposites comprising magneto-responsive γ-Fe2O3 NPs that incorporated amphiphilic copolymers have been synthesized. At first, the copolymer [dextran grafted with poly(N-vinyl caprolactam)] has been prepared via reversible addition–fragmentation chain transfer polymerization followed by ex situ incorporation of γ-Fe2O3 NPs. The copolymerization is living in nature as apparent from molecular weight distribution (determined using advanced polymer chromatography, i.e., APC analysis) and the reaction kinetics study. The developed nanocomposite exhibits regular core–shell morphology, where the magnetic NPs have been found to behave as the core, while the copolymer represents as the shell, as obvious from field emission scanning electron microscopy and high-resolution transmission electron microscopy analyses. The nanocarrier is non-cytotoxic and has further been studied for its effectivity as an efficient carrier for a hydrophobic drug (naproxen).

Quantitative and Sensitive Mid-Infrared Frequency Modulation Detection of HCN behind Shock Waves

Despite its key role for the study and modeling of nitrogen chemistry and NOx formation in combustion processes, HCN has only rarely been detected under high-temperature conditions. Here, we demonstrate quantitative detection of HCN behind incident and reflected shock waves using a novel sensitive single-tone mid-infrared frequency modulation (mid-IR-FM) detection scheme. The temperature-dependent pressure broadening of the P(26) line in the fundamental CH stretch vibration band was investigated in the temperature range 670K≤T≤1460K, yielding a pressure broadening coefficient for argon of 2γAr296K=(0.093±0.007)cm−1atm−1 and a temperature exponent of nAr=0.67±0.07. The sensitivity of the detection scheme was characterized by means of an Allan analysis, showing that HCN detection on the ppm mixing ratio level is possible at typical shock wave conditions. In order to demonstrate the capability of mid-IR-FM spectroscopy for future high-temperature reaction kinetic studies, we also report the first successful measurement of a reactive HCN decay profile induced by its reaction with oxygen atoms.

Carbon nanotube incorporated eucalyptus derived activated carbon-based novel adsorbent for efficient removal of methylene blue and eosin yellow dyes

Carbon nanotube (CNT) incorporated eucalyptus derived activated carbon-based novel adsorbent is synthesized by a novel route. This adsorbent is investigated for the removal of two different dyes; methylene blue (MB) and eosin yellow (EY) from the waste water. The effect of pH, adsorbent dose, contact time and initial concentration, has been used to measure the dye removal efficiency of the adsorbent. Langmuir isotherm, Freundlich isotherm and D-R isotherm models were used to fit the experimental dye adsorption data, with the D-R model providing the best fit. The maximum adsorption efficiency of adsorbent for MB and EY removal is 49.61 and 49.15 mg/g, respectively. Reaction kinetics studies were also established to further investigate the dye adsorption mechanism. It is observed that pseudo second order model define the reaction kinetics involved in the reaction. This activated carbon adsorbent based on CNTs is shown to be highly promising for water decontamination applications.

Development of Three-Dimensional Nickel-Cobalt Oxide Nanoflowers for Superior Photocatalytic Degradation of Food Colorant Dyes: Catalyst Properties and Reaction Kinetic Study.

In this work, we present three-dimensional flower-like nickel-cobalt oxide (F-NCO) nanosheets developed in a facile, eco-friendly hydrothermal route to apply as photocatalysts for food colorant Allura Red AC dye removal under light illumination. Using Brunauer-Emmett-Teller analysis, it was found that the F-NCO nanosheets displayed a surface area of ∼53.65 m2/g and a Barrett-Joyner-Halenda pore size of ∼14 nm, which was also confirmed by the calculated crystallite size of ∼15 nm using powder X-ray diffraction (XRD) analysis. From Williamson-Hall analysis of XRD spectra, F-NCO nanosheets revealed a crystal-lattice strain of ∼3.42 × 10-3 and a dislocation density of ∼4.397 × 1015 lines/m2 in the crystal structure. Transmission electron microscopy analysis revealed that F-NCO nanosheets accumulated to form flower-like nanostructures of <100 nm length with a d-spacing of ∼2.6 Å, which is attributed to the (311) crystallographic plane (α = γ = β = 90°, a = b = c = 8.110 Å, JCPDS No. 00-020-0781) of the cubic phase. The F-NCO nanosheets exhibited an excellent photocatalytic efficiency of ∼94.75% in ∼10 min with sodium borohydride under UV light. The Langmuir-Hinshelwood model determined pseudo-first-order reaction kinetics of dye degradation using the versus time plot. The kinetic study produced a first-order rate constant (k) of ∼0.219 min-1, resulting in ∼3.16 min half-life (t1/2) for the F-NCO-catalyzed degradation reaction. Thus outstanding photocatalytic performance of F-NCO nanosheets would display their huge potential for organic-pollutant removal from water with exceptional recyclability for wide research applications in the future.

Rational Synthesis of Polymeric Nitrogen N8– with Ultraviolet Irradiation and Its Oxygen Reduction Reaction Mechanism Study with In Situ Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy

Polynitrogen (PN) deposited on multiwalled carbon nanotubes was synthesized by cyclic voltammetry with ultraviolet (UV) irradiation. Compared to the sample formed without UV, a larger amount of N8– was synthesized and was found to distribute more uniformly on the MWNTs with 254 nm UV irradiation, indicating that the production of more azide (N3)0 radicals as the precursors for synthesis of N8– by photoexcitation of azide (N3–) ions is a rate-limiting step for PN synthesis. An oxygen reduction reaction kinetics study indicated a four-electron reaction pathway on N8–, whereas a two-electron process occurs on N3–. Analysis by in situ shell-isolated nanoparticle-enhanced Raman spectroscopy revealed that the side-on and end-on O2 adsorption occurred at N8– and N3–, respectively, confirming the electron transfer process. A full direct-methanol fuel cell study shows that methanol crossover typically reduces the current density of Pt/C by ∼40% but has very little effect on the performance of the PN-MWNT catalyst after testing for 120 h. Moreover, the power density from the PN-MWNT cathode is at least twice that from a Pt/C cathode.