Examination of electrocatalysis in the anodic O 2 evolution reaction at Pt through evaluation of the adsorption behaviour of kinetically involved intermediate states

1990 ◽  
Vol 429 (1877) ◽  
pp. 375-397 ◽  
Keyword(s):  
Oxide Film ◽  
Reaction Pathway ◽  
Surface States ◽  
Kinetic Studies ◽  
Main Reaction ◽  
Adsorption Behaviour ◽  
Heterogeneous Catalytic ◽  
Adsorption Capacitance ◽  
Intermediate States ◽  
Intermediate Surface

In regular heterogeneous catalytic reactions, evaluation of the adsorption behaviour of the ephemeral intermediates that participate kinetically in the main reaction pathway is often inaccessible experimentally. In electrocatalysis, on the other hand, electrochemical transient methods can provide such information. In the present paper, potential-relaxation transients are used to derive information on the electroactive, kinetically significant adsorbed intermediate states that are involved in the anodic O 2 evolution reaction (OER) at Pt electrodes. By means of such transients, digitally recorded over 5–6 decades of time from microseconds to seconds, the adsorption capacitance of the intermediate states in the reaction is evaluated as a function of potential over a range corresponding to appreciable current densities for O 2 evolution. Anodic O 2 evolution takes place at Pt, as at all other metal anodes, on an oxide film. A well-defined state of such a film must be established by a pre-conditioning programme to make meaningful and reproducible kinetic studies on the OER. The state of the oxide film is conveniently characterized by means of cyclic-voltammetry. The intermediate surface states in the reaction can be two or more oxidation states of Pt atoms in the oxide and OH or O species at the oxide’s surface. Two distinct types of adsorption behaviour are distinguished for potentials above and below ca . 1.85 V against the reversible H 2 electrode (RHE), and are related to the observed kinetics of the OER.

scholarly journals Self-Assembled Bimetallic Aluminum-Salen Catalyst for the Cyclic Carbonates Synthesis

Molecules ◽  
2021 ◽  
Vol 26 (13) ◽  
pp. 4097
Author(s):  
Wooyong Seong ◽  
Hyungwoo Hahm ◽  
Seyong Kim ◽  
Jongwoo Park ◽  
Khalil A. Abboud ◽  
...  
Keyword(s):  
Hydrogen Bonding ◽  
Self Assembly ◽  
Reaction Pathway ◽  
Kinetic Studies ◽  
Cyclic Carbonate ◽  
Reaction Conditions ◽  
Formation Reaction ◽  
X Ray ◽  
Carbonate Formation ◽  
Salen Aluminum

Bimetallic bis-urea functionalized salen-aluminum catalysts have been developed for cyclic carbonate synthesis from epoxides and CO2. The urea moiety provides a bimetallic scaffold through hydrogen bonding, which expedites the cyclic carbonate formation reaction under mild reaction conditions. The turnover frequency (TOF) of the bis-urea salen Al catalyst is three times higher than that of a μ-oxo-bridged catalyst, and 13 times higher than that of a monomeric salen aluminum catalyst. The bimetallic reaction pathway is suggested based on urea additive studies and kinetic studies. Additionally, the X-ray crystal structure of a bis-urea salen Ni complex supports the self-assembly of the bis-urea salen metal complex through hydrogen bonding.

THE ANODIC OXIDATION OF AMMONIA AT PLATINUM BLACK ELECTRODES IN AQUEOUS KOH ELECTROLYTE

1963 ◽  
Vol 41 (7) ◽  
pp. 1686-1694 ◽  
Author(s):  
H. G. Oswin ◽  
M. Salomon
Keyword(s):  
Anodic Oxidation ◽  
Hydrogen Oxidation ◽  
Reaction Pathway ◽  
Kinetic Scheme ◽  
Kinetic Studies ◽  
Platinum Black ◽  
Ammonia Vapor ◽  
Consecutive Reactions ◽  
Aqueous Potassium Hydroxide ◽  
Oxidation Of Ammonia

Electrochemical kinetic studies are reported on the anodic oxidation of ammonia in aqueous potassium hydroxide solutions at platinum black electrodes. A kinetic scheme of consecutive reactions is proposed; Tafel slopes are deduced for various rate-determining mechanisms and compared with the experimental behavior. The reaction pathway is correlated with that involved in the analogous catalyzed ammonia vapor decomposition. The exchange currents obtained, compared with those for hydrogen oxidation, render the system unfavorable for fuel cell applications.

scholarly journals Synthesis of acid treated carbonized mandarin peel for purification of copper

2020 ◽  
Vol 15 (2) ◽  
pp. 460-471
Author(s):  
T. Unugul ◽  
F. U. Nigiz
Keyword(s):  
Contact Time ◽  
Freundlich Isotherm ◽  
Kinetic Studies ◽  
Adsorption Kinetic ◽  
Adsorption Behaviour ◽  
Solution Ph ◽  
Copper Adsorption ◽  
Adsorbent Dosage ◽  
Mandarin Peel ◽  
Pseudo Second Order

Abstract In this study; acid treated carbonized mandarin peel (CMP) adsorbent was prepared and the adsorption behaviour of the adsorbent for copper removal was investigated. In the adsorption studies the effects of initial metal concentration, solution pH, adsorbent dosage and contact time on the removal were investigated. As a result; the highest removal of 100% was achieved when the copper concentration in water was 5 mg/L and the adsorbent dosage was 3.75 g/L at a solution pH of 7. Isotherm studies were also done and the appropriate isotherm was obtained as the Freundlich isotherm. According to the kinetic studies, the copper adsorption onto CMP adsorbent was adopted to the pseudo-second-order adsorption kinetic. After HCl regeneration, the adsorbent maintained 94% of its activity.

scholarly journals UV-Catalyzed Persulfate Oxidation of an Anthraquinone Based Dye

Catalysts ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 456 ◽  
Author(s):  
Kamil Krawczyk ◽  
Stanisław Wacławek ◽  
Edyta Kudlek ◽  
Daniele Silvestri ◽  
Tomasz Kukulski ◽  
...  
Keyword(s):  
Textile Industry ◽  
Membrane Filtration ◽  
Lemna Minor ◽  
Reaction Pathway ◽  
Main Reaction ◽  
Synthetic Dyes ◽  
Quantum Chemical Analysis ◽  
Substantial Impact ◽  
Anthraquinone Dye ◽  
Persulfate Oxidation

Wastewater from the textile industry has a substantial impact on water quality. Synthetic dyes used in the textile production process are often discharged into water bodies as residues. Highly colored wastewater causes various of problems for the aquatic environment such as: reducing light penetration, inhibiting photosynthesis and being toxic to certain organisms. Since most dyes are resistant to biodegradation and are not completely removed by conventional methods (adsorption, coagulation-flocculation, activated sludge, membrane filtration) they persist in the environment. Advanced oxidation processes (AOPs) based on hydrogen peroxide (H2O2) have been proven to decolorize only some of the dyes from wastewater by photocatalysis. In this article, we compared two very different photocatalytic systems (UV/peroxydisulfate and UV/H2O2). Photocatalyzed activation of peroxydisulfate (PDS) generated sulfate radicals (SO4•−), which reacted with the selected anthraquinone dye of concern, Acid Blue 129 (AB129). Various conditions, such as pH and concentration of PDS were applied, in order to obtain an effective decolorization effect, which was significantly better than in the case of hydroxyl radicals. The kinetics of the reaction followed a pseudo-first order model. The main reaction pathway was also proposed based on quantum chemical analysis. Moreover, the toxicity of the solution after treatment was evaluated using Daphnia magna and Lemna minor, and was found to be significantly lower compared to the toxicity of the initial dye.

scholarly journals Density Functional Theory Based Micro- and Macro-Kinetic Studies of Ni-Catalyzed Methanol Steam Reforming

Catalysts ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 349 ◽  
Author(s):  
Changming Ke ◽  
Zijing Lin
Keyword(s):  
Density Functional Theory ◽  
Steam Reforming ◽  
Density Functional ◽  
Reaction Pathway ◽  
Elementary Reaction ◽  
Main Reaction ◽  
Methanol Steam Reforming ◽  
Surface Species ◽  
Functional Theory ◽  
Microkinetic Model

The intrinsic mechanism of Ni-catalyzed methanol steam reforming (MSR) is examined by considering 54 elementary reaction steps involved in MSR over Ni(111). Density functional theory computations and transition state theory analyses are performed on the elementary reaction network. A microkinetic model is constructed by combining the quantum chemical results with a continuous stirring tank reactor model. MSR rates deduced from the microkinetic model agree with the available experimental data. The microkinetic model is used to identify the main reaction pathway, the rate determining step, and the coverages of surface species. An analytical expression of MSR rate is derived based on the dominant reaction pathway and the coverages of surface species. The analytical rate equation is easy to use and should be very helpful for the design and optimization of the operating conditions of MSR.

scholarly journals Time-dependent activation of the semicarbazide-sensitive amine oxidase (SSAO) from ox lung microsomes

2000 ◽  
Vol 351 (3) ◽  
pp. 789-794 ◽  
Author(s):  
Jose M. LIZCANO ◽  
Keith F. TIPTON ◽  
Mercedes UNZETA
Keyword(s):  
Amine Oxidase ◽  
Reaction Pathway ◽  
Substrate Inhibition ◽  
Kinetic Studies ◽  
Tryptophan Fluorescence ◽  
The Other ◽  
Time Dependent ◽  
High Substrate ◽  
Before And After ◽  
Lag Period

The activity of ox lung microsomal semicarbazide-sensitive amine oxidase (EC 1.4.3.6; SSAO) towards benzylamine increased 20-fold during incubation at 37°C. After an initial lag-period, activation was first-order with time and complete after approx. 20h. No significant changes in activity towards methylamine, histamine or 2-phenylethylamine were observed, although mixed-substrate experiments were consistent with the same enzyme being involved in the oxidation of all these substrates, both before and after time-dependent activation. The enzyme-tryptophan fluorescence increased on incubation at 37°C in parallel with the increase in activity towards benzylamine. Treatment of the activated-enzyme preparation with 6M guanidinium chloride followed by dialysis, caused both the activity towards benzylamine and the fluorescence to fall to that occurring before activation. However, incubation of this preparation at 37°C resulted in increases in fluorescence and activity similar to those seen with the unactivated enzyme. Benzylamine oxidation was inhibited, uncompetitively with respect to oxygen, by high substrate concentrations but no such inhibition was observed with the other amines. Activation resulted in an increase in Vmax for benzylamine oxidation, with no significant alterations in the Km or the Ksi for high-substrate inhibition. Kinetic studies were consistent with sequential mechanisms being followed for the oxidation of both benzylamine and methylamine but the dependence on oxygen concentration was complex. These results might indicate that benzylamine follows a different reaction pathway from the other substrates, with substrate-specific activation involving a reaction step that is rate-limiting for benzylamine oxidation but not for the others.

scholarly journals Mn/sepiolite as the heterogeneous ozonation catalysts applied to the advanced treatment of regenerated-papermaking wastewater

2016 ◽  
Vol 75 (5) ◽  
pp. 1025-1033 ◽  
Author(s):  
Zheng Cheng ◽  
Rendang Yang ◽  
Yang Wang
Keyword(s):  
Reaction Pathway ◽  
Removal Rate ◽  
Oxygen Demand ◽  
Catalytic Ozonation ◽  
Treated Wastewater ◽  
Precipitation Method ◽  
Advanced Treatment ◽  
Heterogeneous Catalytic ◽  
High Removal Rate ◽  
Papermaking Wastewater

Herein a Mn-deposited sepiolite catalyst was obtained through a facile co-precipitation method, and then used as the heterogeneous ozonation catalysts applied to the tertiary treatment of regenerated-papermaking wastewater. During the process, the as-prepared catalyst was endowed with higher Brunauer–Emmett–Teller specific surface area of 412.3 m2/g compared to 124.6 m2/g of the natural sepiolite. Hence, in the adsorption of methylene blue, the as-prepared catalyst was observed with a very high removal rate of 96.2% although a little lower than the modified sepiolite of 97.5% in 100 min. And for practical application, the catalyst was used for treating the effluent from regenerated-papermaking industry, via a heterogeneous catalytic ozonation process. Consequently, the highest color removal rate of 99.5%, and the highest chemical oxygen demand (COD) removal efficiency of 73.4% were achieved in 20 and 30 min, respectively. As a result, the treated wastewater was more biodegradable and less toxic; the biochemical oxygen demand (BOD5)/COD value could reach 0.41. Moreover, the catalyst showed superior stability at successive ozonation runs. The main possible reaction pathway is also presented. The results indicate that catalytic ozonation was proved to be effective when Mn/sepiolite was used as catalysts applied to the advanced treatment of regenerated-papermaking wastewater.

Kinetic Studies of Hydrodeoxygenation of Ethyl Ester of Decane Acid over a Ni-Cu-Mo/Al2O3 Catalyst

2019 ◽  
Vol 19 (1) ◽  
pp. 33-39
Author(s):  
R. G. Kukushkin ◽  
S. I. Reshetnikov ◽  
S. G. Zavarukhin ◽  
P. M. Eletskiy ◽  
V. A. Yakovlev
Keyword(s):  
Contact Time ◽  
Noble Metals ◽  
Flow Reactor ◽  
Experimental Studies ◽  
Kinetic Studies ◽  
Nickel Catalysts ◽  
Effective Rate ◽  
Main Reaction ◽  
Reaction Products ◽  
Fixed Catalyst

Nickel-based catalysts for hydrodeoxygenation of vegetable oils are an alternative to the systems based on noble metals and sulfide catalysts for hydrotreatment. Modification of the nickel catalysts with molybdenum and copper allows the yield of target products to be increased and the corrosion resistance of the catalytic system to be improved. The studies were aimed at establishing relationships between temperature, contact time and activity of the modified nickel-containing catalyst to hydroxygenation of esters of fatty carboxylic acids, as well as at determining effective kinetic parameters of the reactant consumption. A flow reactor with the fixed catalyst bed was used for experimental studies at РН2 = 0.25 MPa, temperatures 270, 285, 300 and 315 °C, contact time varied from 600 to 1800 s. It was shown that the selectivity to the main reaction products – nonane and decane – did not change upon varying the reaction temperature and contact time. The experimental data were used for determining the effective rate constants and activation energy of the reaction.

Design of a heterogeneous catalytic process for the continuous and direct synthesis of lactide from lactic acid

2016 ◽  
Vol 18 (22) ◽  
pp. 5978-5983 ◽  
Author(s):  
Pravin P. Upare ◽  
Ji Woong Yoon ◽  
Dong Won Hwang ◽  
U-Hwang Lee ◽  
Young Kyu Hwang ◽  
...  
Keyword(s):  
Lactic Acid ◽  
Reaction Pathway ◽  
Direct Synthesis ◽  
Catalytic Process ◽  
Heterogeneous Catalytic Process ◽  
Atmospheric Conditions ◽  
Heterogeneous Catalytic ◽  
Nanocomposite Catalyst ◽  
One Step ◽  
Optically Pure

We present a continuous one-step reaction pathway for optically pure lactide under atmospheric conditions based on a novel SnO2–SiO2 nanocomposite catalyst.

Photocatalytic Decomposition of Metoprolol and Its Intermediate Organic Reaction Products: Kinetics and Degradation Pathway

2016 ◽  
Vol 14 (3) ◽  
pp. 809-820 ◽  
Author(s):  
Alfonso Pinedo ◽  
Mariana López ◽  
Elisa Leyva ◽  
Brenda Zermeño ◽  
Benito Serrano ◽  
...  
Keyword(s):  
Uv Light ◽  
Reaction Pathway ◽  
Kinetic Studies ◽  
Initial Reaction Rate ◽  
Degradation Pathway ◽  
Photocatalytic Decomposition ◽  
Initial Reaction ◽  
Low Molecular Weight ◽  
Reaction Products ◽  
Constant Flow Rate

Abstract High purity metoprolol prepared by neutralization of an aqueous solution of metoprolol tartrate is efficiently mineralized to CO2 and water by photocatalysis with TiO2, UV light and a constant flow rate of oxygen. Since the tartrate anions were eliminated, all the HO• generated by photocatalysis reacted efficiently with the aromatic part of the medication. The reaction pathway includes two routes of degradation. The first one includes the transformation of metoprolol to hydroquinone via formation of 4-(2-methoxyethyl)phenol, 2-(4-hydroxyphenyl)ethanol and 4-hydroxybenzaldehyde. Metoprolol is also degraded directly to hydroquinone. Then, this aromatic compound is oxidized to 1,2,4-benzenetriol, which is rapidly oxidized to low molecular weight organic acids before being completely mineralized to CO2 and water. Kinetic studies indicated that the initial reaction rate of the degradation of metoprolol, 4-(2-methoxyethyl)phenol, 2-(4-hydroxyphenyl)ethanol and 4-hydroxybenzaldehyde is described by the LH-HW model.

Sign in / Sign up

Export Citation Format

Share Document