Catalytic Reaction Rate Constant Research Articles

Significantly optimized piezoelectric catalytic properties of surface functionalized Nano-BaTiO3

In piezoelectric catalysis, the interaction between reaction molecules and the catalyst surface is of great significance for designing highly selective reaction processes. In this study, chemically functionalized BaTiO3 nanoparticles were fabricated using the hydrothermal method, and the piezoelectric catalytic activity was evaluated for degradation dye reactants by ultrasonic vibration. Due to surface modification of BaTiO3 nanoparticles, the carboxyl groups will be applied on the surface of BaTiO3 nanoparticles, resulting in the reduction in particle size and an increase in specific surface area. The adsorption of the carboxyl groups on the surface can also improve the ability of the BaTiO3 nanoparticles to capture the organic dyes. A high piezoelectric catalytic reaction rate constant of 0.0716 min−1, together with a degradation efficiency of >90 % was achieved within 30 min under 60 kHz and 100 W ultrasonic conditions. These results show that the surface modification of BaTiO3 nanoparticles brought excellent performance of piezoelectric catalysis by controlling the precursor and hydrothermal parameters. This study provides a new method for the preparation of chemically functionalized piezoelectric catalysts and design of other new highly selective catalysts.

Biogenic synthesis of silver, gold, and palladium nanoparticles using moringa oleifera seeds: exploring photocatalytic, catalytic, and antimicrobial activities

In this study, we explored the green synthesis of metal nanoparticles (Ag-NPs, Au-NPs, and Pd-NPs) using Moringa oleifera seed (MOS) extract, which is known for its nutrient density, antioxidant properties, anti-inflammatory effects, and potential benefits in managing cholesterol, blood sugar levels, as well as promoting digestion, skin, and hair health. The nanoparticles’ size was controlled by varying the concentration of MOS extract. The successful formation of Au-NPs and Ag-NPs was confirmed through surface plasmon resonance (SPR), while the absence of absorption at 420 nm indicated the reduction of Pd2+ ions to Pd0, affirming the synthesis of Pd-NPs. The nanoparticles exhibited mono-dispersed, spherical shapes with confirmed crystallinity. Sizes were determined as 28 nm for Pd-NPs, 5 nm for Au-NPs, and 19 nm for Ag-NPs. The MOS extract’s phenols and proteins played a crucial role in reducing and stabilising Ag-NPs, Au-NPs, and Pd-NPs. Notably, the synthesised nanoparticles demonstrated strong antimicrobial activity, particularly against Salmonella typhi, making them potential antibacterial agents. The catalytic efficiency of Au-NPs, Ag-NPs and Pd-NPs was studied using the reduction of 4-Nitrophenol (4-NP) by NaBH4 to 4-Aminophenol. Additionally, Au-NPs showed enhanced photocatalytic degradation rate constant and catalytic reaction rate constant of 0.0038/min and 0.261/min respectively, due to their small size and increased surface area. By combining a green synthesis approach with an in-depth analysis of properties and diverse applications, this study provides valuable insights into the immense potential of MOS-assisted metal nanoparticles for various technological and environmental advancements.

CATECHOLASE ACTIVITY AND SUBSTITUENT EFFECT OF NEW HOMOLEPTIC COPPER(II) CHALCONE COMPLEXES

<p>Three new neutral complexes of copper(II) containing chalcone ligands derived from 2'-hydoxyacetophenone and 4-substituted benzaldehydes were synthesized. Complexes were prepared by solution synthesis and characterized by spectroscopy. The catalytic activity of complexes was examined in the reaction of 3,5-di-tertbutylcatehcol (DTBC) oxidation. The kinetics of DTBC catalytic oxidation by copper(II) complexes (1 – 3) was investigated spectrophotometrically under pseudo-first-order conditions. Catalytic parameters, the maximum reaction rate (vmax), Michaelis-Menten constant (KM), catalytic efficiency, catalytic reaction rate constant (kcat), turnover number (TON), and turnover frequencies (TOF) for complexes 1 – 3 in DTBC oxidation were collected. The studied complexes 1 and 2 were found to have moderate catalytic activity, while complex 3 does not show catalytic properties.</p>

Silver-loaded tannic acid modified Ti3C2 catalyst to efficiently catalyze the degradation of dyes

Ag@Ti3C2-TA nanocomposite catalyst was elaborately constructed by a simple and green method with Ti3C2 as the carrier, tannic acid (TA) as the modifier, and silver nitrate as the precious metal precursor. A series of characterizations were used to analyze morphology and microstructure of the resulting catalyst. The degradation behaviors of the catalyst were studied with rhodamine B (RB) and methyl orange (MO) as the model dyes. The result demonstrated that Ag@Ti3C2-TA exhibited efficient catalytic degradation performance toward both RB and MO, and the degradation percentage increased with the growth of TA content in the catalyst. The catalytic degradation process conformed to the quasi-level kinetic model, and catalytic reaction rate constants of Ag@Ti3C2-TA for RB and MO were 0.972 and 1.478 min−1, respectively. The catalytic degradation percentage of Ag@Ti3C2-TA toward RB and MO still remained above 80% even after 10 catalytic cycles, indicating high degradation percentage and considerable catalytic stability.

Novel decorated aluminium(iii) phthalocyanine complex with the application of MWCNTs on electrodes: electrochemical non-enzymatic oxidation and reduction of glucose and hydrogen peroxide.

In this study, we performed the physicochemical and electrochemical characterization of a decorated macrocyclic aluminium(iii) phthalocyanine complex (AlTMQNCAPc). Subsequently, the AlTMQNCAPc@MWCNT/GC electrode was used for the electrochemical detection of glucose and hydrogen peroxide (H2O2) by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and chronoamperometry (CA). Moreover, the limit of detection, linear range, and sensitivity for glucose and H2O2 were investigated (CV: 2.5 nM L-1 and 25 nM L-1, 50-500 μM, 0.052 and 0.072 μA μmol cm-2; DPV: 3.1 nM L-1 and 18 nM L-1, 50-500 μM, 0.062 and 0.066 μA μmol cm-2 and CA: 10 nM L-1 and 20 nM L-1, 50-500 μM, 0.098 and 0.07 μA μmol cm-2, respectively). In addition, the AlTMQNCAPc@MWCNT/GC electrode showed good selectivity for the detection of glucose and H2O2 in the presence of common interfering substances, such as AA, DA, UA, glycine, l-cysteine, nitrite, Pb(ii), Cd(ii), Cu(ii), Co(ii), Hg(ii), Zn(ii), and glucose. For the detection of glucose and H2O2, the kinetic parameters, including the electron transfer coefficient and catalytic reaction rate constant, were also established. Finally, for usage in practical applications, the modified electrode was employed to achieve the quantitative detection of glucose and H2O2 in human urine and commercial samples of 3% H2O2, respectively.

Chemical engineering kinetics of p-xylene chlorination in a gas-liquid agitated reactor

This study aims at determining both the rate constants of chlorination of p-xylene with molecular chlorine and FeCl3 as a catalyst at 70 °C and 90 °C and the related chemical engineering parameters to be used in the design of an effective chemical reactor.This was accomplished by a novel approach of constructing a linear mathematical function for a gas–liquid semi-batch agitated reactor correlating all engaged physical and chemical factors. Collecting values for all the necessary parameters for the application of the function, or in the absence of them calculating them, and exploiting the intercept and slope of the linear function became possible the apparent and the catalytic reaction rate constants to be calculated. It was found that the calculated values were of the same order of magnitude as values obtained by other researchers.The parameters needed to be calculated were Henry’s constant, the diffusion coefficient of the solute A (chlorine) to the solvent B (p = xylene), DAB, and the mean liquid phase mass transfer coefficient, kl. Other parameters of chemical engineering interest were also determined, namely, the interface per unit volume of liquid, a, the thickness of the liquid film, δl, and the Hatta number, MH.Evaluating the Hatta number estimated, it was concluded that the chlorination of p-xylene with molecular chlorine is very slow at both temperatures investigated, and almost no reaction occurs in the film compared to the bulk of the liquid. Thus, to increase the overall reaction rate, a large volume of liquid is needed while the increase of agitation intensity is of no value here.Combining the rate constant ratios obtained recently for the four consecutive second-order irreversible chlorinations of p-xylene with molecular chlorine with FeCl3 as a catalyst at 70 °C and under identical conditions it was possible to determine the values of all rate constants up to the fourth chlorinated product.

Autocatalytic Hydrolysis of Palm Oil for Fatty Acid Production by Using Hydrothermolysis Process

As the world major leader in the palm oil production, Indonesia need to develop a new efficient technology to replace the conventional production process of fatty acid from palm oil. Auto catalytic hydrolysis reaction of palm oil in a hydrothermal reactor offers several benefits in fatty acid production. This research objective was to determine the rate constant of hydrothermal auto catalytic hydrolysis reaction of palm oil in fatty acid production. The Auto catalytic hydrolysis reaction of palm oil was conducted in several reaction temperatures (130- 150°C) at a different time (5-30 minutes). The research results show that at all the temperature applied, along with the increasing of reaction time, the fatty acid obtained were increasing also, while the highest fatty acid concentration was obtained from the auto catalytic hydrolysis reaction of palm oil performed at temperature of 130°C.

Preparation of Ag foam catalyst based on in-situ thermally induced redox reaction between polyvinyl alcohol and silver nitrate with supercritical CO2 foaming technology

The preparation process of a traditional metal foam catalyst is cumbersome, energy-intensive, and difficult to scale production, which restricts its development. In this work, the potential of polyvinyl alcohol (PVA) as a polyhydroxy reductant was explored. We used the thermally induced redox reaction between PVA and silver nitrate (AgNO3), combining with supercritical carbon dioxide (ScCO2) foaming technology, proposing an innovative idea for preparing the micron-sized Ag foam catalyst. Firstly, through the compound plasticizing effect of H2O and AgNO3, using CO2 as foam agent, the PVA/AgNO3 composite foams with uniform structure could be prepared below 100 °C. The maximum cell density could reach 5.39*109 cells/cm3 and the average cell size could reach 8.27 μm. Then, using the PVA matrix as a reductant and self-sacrifice template, silver ions could be quickly in-situ reduced at lower temperature (160–210 °C), the resulting silver particles could self-assemble into a foam-like skeleton structure. The Ag foams have an adjustable porous structure with a cell size of 4.01–16.30 μm and a ligament size of 1.08–2.82 μm. Applying it as a catalyst to promote the reduction of 4-nitrophenol (4-NP), the catalytic reaction rate constant is 10 times that of existing commercial Ag foam. The prepared Ag foam catalyst has the advantages of less dosage, easy recovery and good stability. Also, it has great application potential in the sensing, biomedicine, heat conduction and other fields.

Characterization of Au-Ag nanoparticles biosynthesized by fungus Mariannaea sp. HJ

Biosynthesis of gold-silver alloy nanoparticles (Au-AgNPs) is a simple operation and ecological friendly, but with limited reports on the availability of fungal resources. In this study, cell-free extracts of Mariannaea sp. HJ was used to synthesize Au-AgNPs, and the effects of the different ratios of Au and Ag ion concentrations on the synthesis of Au-AgNPs were also studied. The results clearly showed that the ratio of Au and Ag ion concentrations had an impact on the composition of Au-AgNPs. With the Ag ion increasing, the color of culture supernatant changed from light purple to brown and an obvious blue shift of characteristic absorption peak was observed in UV-vis spectra, indicating an increase of the percentage of Ag in the Au-AgNPs. Transmission electron microscope showed that the morphologies of the Au-AgNPs were mainly spherical and pseudo spherical, and the average particle sizes of the Au-AgNPs at three different ion concentrations, including 0.5:0.5, 0.5:1.5 and 0.5:3.0, were 19.24 nm, 15.99 nm and 19.33 nm, respectively. X-ray diffraction results showed that the Au-AgNPs had a surface-centered cubic structure. Fourier transform infrared spectroscopy was used to characterize and speculate the involvement of -OH, -NH₃ and -COOH functional groups in the reduction and stability process of Au-AgNPs. Furthermore, 4-nitrophenol (4-NP) was used to explore catalytic activity of Au-AgNPs. Catalytic experiments demonstrated that the Au-AgNPs had a good catalytic activity on 4-NP reduction with a catalytic reaction rate constant of 7.85×10⁻³ s⁻¹. In brief, the present study suggested that Mariannaea sp. HJ could synthesize Au-AgNPs with good dispersity, and had a potential application in the catalytic reduction of nitro aromatic hydrocarbons.

Construction of detachable core/shell Fe3O4@C supported noble metal catalysts and their catalytic performance

In this article, magnetically responsive catalysts were successfully synthesized by host-guest chemistry and self-assembly strategy. Firstly, β-cyclodextrin (β-CD) was bound directly to the surface of core/shell magnetic Fe3O4@C (MFC) using chemical bonding methods. Then, in view of the host-guest recognition, p-aminothiophenol (pATP) was captured by β-CD to form inclusion complex on the surface of MFC. Lastly, pre-synthesized gold, silver, platinum nanoparticles (AuNPs, AgNPs, PtNPs) could be adsorbed on the surface of MFC@β-CD-pATP through self-assembly strategy to fabricate ternary composites MFC@β-CD-pATP@metal nanoparticles. Catalytic reduction reaction of methylene blue using NaBH4 as reducing agent evaluates the catalytic performance of three as-prepared magnetic nanocomposites. MFC@β-CD-pATP@AuNPs catalyst showed the fast catalytic reaction rate constant. Significantly, we have explored the separation of magnetic supports and novel metal nanoparticles under mild conditions. This strategy will become a green and environmental way for highly efficient separation of precious metals catalysts, and recycle and reuse of catalyst carriers.

A novel non-precious catalyst containing transition metal in nanoporous cobalt based metal-organic framework (ZIF-67) for electrooxidation of methanol

In present work, Ni catalysts doped in zeolitic imidazolate framework (ZIF-67) as conductive support were used for electrocatalytic oxidation of methanol. For this purpose, the nanosized ZIF-67 crystals were synthesized using a straightforward non-template method. The as-synthesized nanocrystal was characterized using FE-SEM, TEM, XRD, FT-IR, TGA and BET. Then, a carbon paste electrode (CPE) was modified by ZIF-67 nanoparticles doped with Ni species (Ni-ZIF-67/CPE). Cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) were employed for methanol electrooxidation. The CV exhibited remarkable oxidation current due to the increase of Ni species doped porous ZIF-67 support. EIS data showed that the activation process increases the charge transfer rate and conductivity of modified electrode. Also, the value of rate constant of catalytic redox reaction was obtained using CA. As a result, the Ni species supported on ZIF-67/CPE showed significant catalytic activity and good stability toward methanol oxidation reaction (MOR) in comparison with non-modified CPE. This work can open a new window for application of various Metal-organic frameworks (MOFs)/platinum-free metals as electrocatalysts in fuel cells.

Tris functionalized Cu-centered cyclohexamolybdate molecular armor as a bimetallic catalyst for rapid p-nitrophenol hydrogenation

An organic ligand triol protected and inorganic-ligand cyclohexamolybdate ring supported single atom Cu molecular hybrid material for rapid p-nitrophenol hydrogenation.

Behavior of epichlorohydrin catalytic acidolysis reaction with the variation of solvent polarity

The kinetics of the reaction of epichlorohydrin ((2-chloromethyl)oxirane) with acetic acid at 60 °C was studied in the presence of the catalyst—tetrabutylammonium iodide either in epichlorohydrin, or a binary solvent epichlorohydrin:tetrahydrofuran. The ratios of the binary solvent components were selected in order to preserve the excess of epichlorohydrin as the condition for pseudoorder with respect to the oxirane reactant. As the order of the reaction with respect to acid may differ depending on the reaction series, it was determined by kinetic and modelling methods. The correlation between solvent permittivity and observed and catalytic reaction rate constants was established. The equation for predicting tetrabutylammonium iodide catalytic reactivity in the binary solvent was obtained. The effect of solvent polarity on the rate and mechanism of oxirane ring opening reaction in the presence of a base catalyst was estimated via Laidler–Eyring equation. It was shown that the decrease of solvent polarity increases the reaction rate and its regioselectivity.

Size Does Matter—Mediation of Electron Transfer by Gold Clusters in Bioelectrocatalysis

AbstractMetal nanostructures are often used in bioelectrocatalytic systems to increase the electrode surface area or to improve the conductivity of biofilms. We demonstrate, that decreasing the size of gold nanoparticles below 2 nm may result in a change of the mechanism of electron transfer (ET) between the enzyme active site and the electrode from direct to mediated ET. Clusters with diameters smaller than 2 nm exhibited molecule‐like behavior reflected in the appearance of oxidation and reduction peaks separated by a clearly developed HOMO—LUMO gap. The redox activity of the nanoparticles was found to contribute to the ET mechanism of fructose dehydrogenase switching it to gold cluster mediated electron transfer instead of direct ET. In the presence of gold clusters at the electrode, the overpotential of the catalyzed fructose oxidation reaction was 100 mV lower and the catalytic reaction rate constant was 2.5 times larger confirming the unique mediating role of the Au clusters.

Medium effect (water versus MeCN) on reactivity and reaction pathways for the SNAr reaction of 1-aryloxy-2,4-dinitrobenzenes with cyclic secondary amines

A kinetic study on SNAr reactions of 1-aryloxy-2,4-dinitrobenzenes (1a–1h) with a series of cyclic secondary amines in 80 mol% water – 20 mol% DMSO at 25.0 ± 0.1 °C is reported. The plots of kobsd versus amine concentration curve upward except for the reactions of substrates possessing a strong electron-withdrawing group in the leaving aryloxide with strongly basic piperidine. The curved plots indicate that the reactions proceed through both uncatalytic and catalytic routes. Linear Brønsted-type plots have been obtained for the uncatalyzed and catalyzed reactions of 1-(4-nitrophenoxy)-2,4-dinitrobenzene (1a) with βnuc = 0.84 and 0.78, respectively. The Yukawa–Tsuno plot for the uncatalyzed reactions of 1a–1h with piperidine results in an excellent linear correlation with ρ = 1.66 and r = 0.31. In contrast, rate constants for catalyzed reactions are independent of the electronic nature of the substituent in the leaving group. The current SNAr reactions have been proposed to proceed via a zwitterionic intermediate (MC±) that partitions to products through uncatalytic and catalytic routes. The catalyzed reaction from MC± has been concluded to proceed through a concerted mechanism with a six-membered cyclic transition state (TScycl) rather than via a stepwise pathway with a discrete anionic intermediate (MC−), the traditionally accepted mechanism. Medium effects on the reactivity and reaction mechanism are discussed. Particularly, hydrogen bonding of the amines to water precludes formation of kinetically significant dimers found in some aprotic solvents; no explicit role for water in the catalytic transition state is required or proposed. The specific stabilization of the leaving aryloxides substituted with strong electron-withdrawing groups accounts for the lack of the catalytic pathway in these systems (1a–1c) with piperidine nucleophile.

Voltammetric Determination of Penicillamine Using a Carbon Paste Electrode Modified with Multiwall Carbon Nanotubes In the Presence of Methyldopa as a Mediator.

A multiwall carbon nanotubes-modified carbon paste electrode (MWCNTs/MCPE) was fabricated and used to study the electrooxidation of penicillamine (PA) by electrochemical methods in the presence of methyldopa (MDOP) as a homogeneous mediator. The electrochemical oxidation of PA on the new sensor has been carefully studied. The kinetic parameters such as electron transfer coefficient, α, and catalytic reaction rate constant, K/h, were also determined using electrochemical approaches. The electrocatalytic oxidation peak current of PA showed a linear dependent on the PA concentrations and linear calibration curves were obtained in the ranges of 0.2-250.0 µM of PA concentration with square wave voltammetry (SWV) method. The detection limit (3σ) was determined as 0.1 µM. This sensor was also examined as a fast, selective, simple and precise new sensor for voltammetric determination of PA in real samples such as drug and urine.

Mechanistic investigation on the electropolymerization of phenol red by cyclic voltammetry and the catalytic reactions toward acetaminophen and dopamine using poly(phenol red)-modified GCE

The electrochemical properties of phenol red were investigated and the fabrication of poly(phenol red) film on glassy carbon electrode was achieved by the technique of cyclic voltammetry. The sector of quinone methide in the structure of phenol red was found electroactive in aqueous solution and is the center of redox reactions for polymerization. Cyclic voltammograms of phenol red and FTIR spectra of both phenol red and poly(phenol red) suggest that the radical cations which were generated from the scans in anodic direction first coupled to a dimer and propagated further into polymers. The modified electrode was exploited in electrochemical studies such as chronoamperometry, linear sweep voltammetry, and differential pulse voltammetry for the evaluation of the rate constant of heterogeneous catalytic reaction along with the diffusion coefficients and transfer coefficients of acetaminophen and dopamine, and simultaneous determination of the analytes of interest. Heterogeneous rate constant of 1.29×103 and 8.45×102M−1s−1 was each evaluated for the oxidative reaction of acetaminophen and dopamine by the modified electrode, respectively. The linear range for acetaminophen was evaluated to be in the range of 0.4–1.8mM with the sensitivity of 0.026μAμM−1 and that for dopamine is 20–160μM with the sensitivity of 0.16μAμM−1.

Electrochemically mediated reduction of epichlorohydrin pollutant by Ni(I)(hexamethylcyclam) in aqueous media

Epichlorohydrin (ECH) is a volatile organic compound and toxic to human health. Here we investigated clean mediated electrocatalytic dechlorination of ECH in aqueous solutions using electrogenerated [Nickel(I)(hexamethylcyclam)]+ ([Ni(I)(hmc)]+) at glassy carbon cathode. Ni(II)/Ni(I) redox behavior of [Ni(II)(hmc)]2+, examined first by cyclic voltammetry in ECH free-aqueous solutions of various anions (Cl−, Br−, ClO4−, SO42−, phosphate, NO3−), showed only Cl− could provide most stable and reactive low-valent nickel species with highest versatility toward activation of ECH dechlorination. Cyclic voltammetry experiments over a range of scan rates and ECH concentrations elucidated rate limiting mechanism for Ni(I) catalyzed ECH dechlorination, and estimated catalytic reaction rate constant (kcat). ECH concentration-dependent kcat and icat results revealed ECH dechlorination by Ni(I) followed Michaelis-Menten type inner-sphere electron transfer kinetics at low ECH concentrations (< 20mM), but outer-sphere mechanism at higher concentrations. Interestingly, GC/MS showed complete destruction of ECH and production of three non-chloro products within 3-h bulk electrolysis. A possible mechanism was proposed for the overall Ni(I)(hmc)-catalyzed ECH dechlorination. Fast mediation kinetics, total removal of ECH, non-chloro organics as the only dechlorination products, and highly stable [Ni(I)(hmc)]+ mediator indicate electrocatalytic mediation using [Ni(I)(hmc)]+ in aqueous NaCl solution may be feasible for dechlorination of other organic chloro compounds.

Application of novel Ni(II) complex and ZrO2 nanoparticle as mediators for electrocatalytic determination of N-acetylcysteine in drug samples

The electrooxidation of N-acetylcysteine (N-AC) was studied by a novel Ni(II) complex modified ZrO2 nanoparticle carbon paste electrode [Ni(II)/ZrO2/NPs/CPE] using voltammetric methods. The results showed that Ni(II)/ZrO2/NPs/CPE had high electrocatalytic activity for the electrooxidation of N-AC in aqueous buffer solution (pH = 7.0). The electrocatalytic oxidation peak currents increase linearly with N-AC concentrations over the concentration ranges of 0.05–600μM using square wave voltammetric methods. The detection limit for N-AC was equal to 0.009μM. The catalytic reaction rate constant, kh, was calculated (7.01 × 102 M−1 s−1) using the chronoamperometry method. Finally, Ni(II)/ZrO2/NPs/CPE was also examined as an ultrasensitive electrochemical sensor for the determination of N-AC in real samples such as tablet and urine.

Method of solving the inverse problem of chemical kinetics for catalytic reactions in which each step involves main reactants

A new method is suggested for solving the inverse problem of chemical kinetics. This method provides means to derive, from unsteady-state experimental data, the rate constants of catalytic reactions in which each step involves at least one main reactant. Examples of applying this method to two- and three-step reactions are presented.