Shape- and size- dependent desorption kinetics and surface acidity on nano-SnO2

2022 ◽  
Author(s):  
Zixiang Cui ◽  
Yidi Xue ◽  
Yongqiang Xue ◽  
Mengying Wang ◽  
Jiaojiao Chen ◽  
...  
Keyword(s):  
Activation Energy ◽  
Kinetic Parameters ◽  
Surface Acidity ◽  
Acid Sites ◽  
Desorption Kinetics ◽  
Exponential Factor ◽  
Desorption Kinetic ◽  
Size Dependent ◽  
Desorption Activation Energy ◽  
Shape And Size

The desorption kinetic parameters (the desorption activation energy (Ed) and the desorption pre-exponential factor (A)) and the surface acidity (the strength and number of acid sites) of spherical and octahedral...

scholarly journals The kinetics of the extraction of caffeine from guarana seed under the action of ultrasonic field with simultaneous cooling

2019 ◽  
Vol 9 (1) ◽  
pp. 26-36 ◽  
Author(s):  
Biljana Koturevic ◽  
Borivoj Adnadjevic ◽  
Jelena Jovanovic
Keyword(s):  
Activation Energy ◽  
Kinetic Parameters ◽  
Reaction System ◽  
Ultrasonic Field ◽  
Conventional Heating ◽  
Isothermal Kinetics ◽  
Correlation Relationship ◽  
Exponential Factor ◽  
Caffeine Extraction ◽  
Kinetics Of

AbstractThe kinetics of isothermal extraction of caffeine from guarana seed under the action of ultrasonic field with simultaneous cooling (UESC) was investigated. The isothermal kinetics curves were measured at temperatures range T = 17-58°C. Using the model-fitting method it was determined that the kinetics of caffeine extraction can be described by a theoretical Jander three-dimensional diffusional model. The values of the rate constant were calculated for different temperatures, as well as the kinetic parameters (activation energy (Ea) and pre-exponential factor (lnA)). Based on the results obtained, it is concluded that the rate constants of caffeine extraction under UESC are about 2 times higher in comparison to the values obtained for the extraction in the conditions of conventional heating (CH). The activation energy of the caffeine extraction under the UESC $\left( E_{\text{a}}\,^{\text{UESC}}=19.4\,\text{kJ}\cdot \text{mo}{{\text{l}}^{-1}} \right)$is lower than the values are for CH $\left( E_{\text{a}}\,^{\text{CH}}=21.8\,\text{kJ}\cdot \text{mo}{{\text{l}}^{-1}} \right).$Energy consumption for UESC is four times lower than for CH conditions. It is shown that there is a linear correlation relationship between kinetic parameters obtained for UESC and CH conditions. The changes in the values of kinetic parameters are explained by the model of selective transfer of energy from the reaction system to the reactant molecules.

Thermal Cure and Ceramization Kinetics of Perhydropolysilazane

2013 ◽  
Vol 575-576 ◽  
pp. 81-86 ◽  
Author(s):  
Feng Ling Ma ◽  
Hui Min Qi ◽  
Ya Ping Zhu ◽  
Xiao Wen Ren ◽  
Fan Wang
Keyword(s):  
Activation Energy ◽  
Weight Loss ◽  
Thermogravimetric Analysis ◽  
Kinetic Parameters ◽  
Nitrogen Atmosphere ◽  
Thermal Cure ◽  
Exponential Factor ◽  
Kinetics Of

The kinetics of the thermal cure and ceramization of preceramic prehydropolysilazane (PHPS) was investigated by thermogravimetric analysis (TGA) under nitrogen atmosphere. The results indicated that the gases captured during the thermal cure and ceramization process of PHPS, which had three main weight loss events. The corresponding kinetic parameters including activation energy, pre-exponential factor and empirical order of the thermal cure and ceramization stages were evaluated by using Ozawa and Kissinger metnods, respectively.

Adsorption and Desorption Kinetics for Chlorosilanes on Si(111) 7×7

1990 ◽  
Vol 204 ◽  
Author(s):  
P. Gupta ◽  
P.A. Coon ◽  
B.G. Koehler ◽  
M.L. Wise ◽  
S.M. George
Keyword(s):  
Activation Energy ◽  
Surface Coverage ◽  
Temperature Programmed Desorption ◽  
Desorption Kinetics ◽  
Sticking Coefficient ◽  
Temperature Dependent ◽  
Adsorption And Desorption ◽  
Desorption Activation Energy ◽  
Temperature Programmed ◽  
Sticking Coefficients

ABSTRACTThe adsorption and desorption kinetics for SiCl4 and SiCl2H2 on Si(111) 7×7 were studied using laser-induced thermal desorption (LITD) and temperature programmed desorption (TPD) techniques. Both LITD and TPD experiments monitored SiCl2 as the main desorption product at 950 K at all coverages of SiCl4 and SiCl2H2 on Si(111) 7×7.HC1 desorption at 850 K and H2 desorption at 810 K were also observed following SiCl2H2 adsorption. Isothermal LITD measurements of SiCl4 and SiCl2H2) adsorption on Si(111) 7×7 revealed that the initial reactive sticking coefficient decreased with increasing surface temperature for both molecules. The temperature-dependent sticking coefficients were consistent with precursor-mediated adsorption kinetics. Isothermal LITD studies of SiC12 desorption revealed second-order SiCl2 desorption kinetics. The desorption kinetics were characterizedby a desorption activation energy of Ed = 67 kcal/mol and a preexponential of vd = 3.2 cm2/s. TPD studies observed that the HCI desorption yield decreased relative to H2 and SiCl2 desorption as a function of surface coverage following SiCl2H2 exposure. These results indicate that when more hydrogen desorbs as H2 at higher coverages, The remaining chlorine is forced to desorb as SiCl 2.

Kinetics of Carbothermic Reduction of Ilmenite

2016 ◽  
Vol 852 ◽  
pp. 315-322 ◽  
Author(s):  
Min Chen ◽  
Xuan Xiao ◽  
Xue Feng Zhang
Keyword(s):  
Activation Energy ◽  
Kinetic Parameters ◽  
Carbothermic Reduction ◽  
Reduction Process ◽  
Phase Evolution ◽  
Reduction Kinetics ◽  
Isokinetic Relationship ◽  
Exponential Factor ◽  
Morphology Change ◽  
Kinetics Of

The reduction kinetics of ilmenite was investigated. Phase evolution during the reduction process was identified by XRD and morphology change was observed using SEM. Kinetic parameters of the activation energy and pre-exponential factor were determined by Kissinger-Akahira-Sunose (KAS) method and Coast-Redfern method&artificial isokinetic relationship (IKP) respectively. Results showed that when the reaction of titanium suboxides makes a growing contribution, the conversion dependence of activation energy has an ascending trend. When the conversion exceeded 0.7, the reactants almost consumed, and the process was controlled by diffusion.

Kinetic parameters associated with self-heating of New Zealand coals under adiabatic conditions

2003 ◽  
Vol 67 (4) ◽  
pp. 665-670 ◽  
Author(s):  
B. B. Beamish ◽  
J. D. St. George ◽  
M. A. Barakat
Keyword(s):  
Activation Energy ◽  
New Zealand ◽  
Kinetic Parameters ◽  
The Self ◽  
Coal Oxidation ◽  
Initial Portion ◽  
Exponential Factor ◽  
Noticeable Increase ◽  
Self Heating ◽  
Lower Reactivity

AbstractAdiabatic self-heating tests were carried out on five New Zealand coal samples ranging in rank from lignite to high-volatile bituminous. Kinetic parameters of oxidation were obtained from the self-heating curves assuming Arrhenius behaviour. The activation energy E (kJ mol–1) and the pre-exponential factor A (s–1) were determined in the temperature range of 70–140°C. The activation energy exhibited a definite rank relationship with a minimum E of 55 kJ mol–1 occurring at a Suggate rank of ∼6.2 corresponding to subbituminous C. Either side of this rank there was a noticeable increase in the activation energy indicating lower reactivity of the coal. A similar rank trend was also observed in the R70 self-heating rate index values that were taken from the initial portion of the self-heating curve from 40 to 70°C. From these results it is clear that the adiabatic method is capable of providing reliable kinetic parameters of coal oxidation.

scholarly journals Glow curve analysis by Gauss-Lorentz function

2013 ◽  
Vol 28 (1) ◽  
pp. 45-51 ◽  
Author(s):  
Zdravko Vejnovic ◽  
Milos Pavlovic ◽  
Marina Kutin ◽  
Milorad Davidovic
Keyword(s):  
Activation Energy ◽  
Kinetic Model ◽  
Kinetic Parameters ◽  
Glow Curve ◽  
Curve Analysis ◽  
Geometric Parameters ◽  
Experimental Curve ◽  
Kinetics Model ◽  
Exponential Factor ◽  
Mixed Order

A new method for fitting glow curves, described in a mixed order kinetics model, with Gauss-Lorentz function is shown. Theoretical expressions of the mixed order kinetics model are shown in a new way, so that the values of kinetic parameters can be obtained through the geometric parameters. When the model is described in this way it is possible to calculate precisely the kinetic parameters such as activation energy, pre-exponential factor and the factor a= n0/(h + n0). At the same time, obtained values of geometric parameters of the experimental curve, which is described with the Gauss-Lorentz function, can be used to estimate the kinetic model, in which thermoluminescence relaxation occurs. This gives a possibility of a new application of Gauss-Lorentz function to be used as a criterion for assessing model of relaxation, when it is not known in advance. The accuracy of fitting is studied, for the specific cases of computer simulated thermoluminescent curves with one peak.

scholarly journals Thermal Decomposition Mechanism of GIS Basin Insulator and Kinetic Parameters-Based Lifetime Prediction Methodology

Polymers ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 653
Author(s):  
Peng Ren ◽  
Qingmin Li ◽  
Honglei Liu ◽  
Yunpeng Li ◽  
Peng Peng ◽  
...  
Keyword(s):  
Activation Energy ◽  
Reaction Mechanism ◽  
Kinetic Parameters ◽  
Thermal Decomposition Mechanism ◽  
Heating Rates ◽  
Computational Accuracy ◽  
Exponential Factor ◽  
Analysis Experiment ◽  
Mechanism Function ◽  
Pyrolysis Kinetic

To reliably detect the latent defects and accurately evaluate the remaining life of gas insulated switchgear (GIS) basin insulators, more effective detection and characterization methods need to be explored. The study of pyrolysis kinetic parameters based on the intrinsic characteristics of materials provides a new way to solve this problem. First, an integral expression model of the reaction mechanism function with four parameters is proposed in this paper, which can represent various existing reaction mechanism functions with better universality and more application fields. Then, on the basis of the temperature transformation equation, an improved method for calculating the activation energy is presented, which shows higher computational accuracy than the existing methods. Further, based on a non-isothermal kinetic equation, the structure of the experimental function is given. It is a method for solving the pyrolysis reaction mechanism function of insulating materials, which can also be used to calculate the pre-exponential factor simultaneously. The thermogravimetric analysis experiment is carried out on a certain basin insulator sample at different heating rates. The pyrolysis kinetic state parameters, including the activation energy, reaction mechanism function and pre-exponential factor of the basin insulator, are calculated. Finally, the life prediction method of basin insulators is established, and the key factors affecting the life of insulators are discussed.

scholarly journals Eriobotrya japonica Lindl. Kernels: Kinetics of Thermal Degradation under Inert Atmosphere Using Model-Free and Fitting Methods

2020 ◽  
Vol 11 (4) ◽  
pp. 11357-11379
Keyword(s):  
Activation Energy ◽  
Thermal Degradation ◽  
Mass Loss ◽  
Kinetic Parameters ◽  
Inert Atmosphere ◽  
Eriobotrya Japonica ◽  
Heating Rates ◽  
Noticeable Effect ◽  
Exponential Factor ◽  
Model Free

A kinetic study of the pyrolysis process of raw Eriobotrya japonica Lindl. Kernels (RLK) was investigated using a thermogravimetric analyzer. The weight loss was measured in a nitrogen atmosphere. The samples were heated over a range of temperature from 298 K to 873 K with four different heating rates of 5, 10, 15, 20 K min-1. Mass loss (TGA) and derivative mass loss (DTG) measurements indicate that the increase in heating rate has no noticeable effect on the thermal degradation of the RLK. The results obtained from the thermal decomposition process indicate that there are three main stages such as dehydration, active, and passive pyrolysis. TGA curves indicate that active pyrolysis of RLK is between 160 and 450 °C. In this interval, a shoulder followed by a peak exists on the DTG plots. The shoulder corresponds to the decomposition of hemicelluloses, the first peak to that of cellulose. Lignin decomposes through all temperature range. The kinetic parameters such as activation energy and pre-exponential factor were obtained for two degradation steps by isoconversional model-free methods proposed by FWO, KAS, Kissinger, Tang, MKN, and FR, with degradation mode being: f(α)=(1-α)n with n = 1 for FR and g(α)=-Ln(1- α) for the other methods. The activation energy and pre-exponential factor obtained by the Kissinger method are 173 kJ/mol and 1.9×1016 min-1. While for free model methods, the average kinetic parameters calculated are 172-248 kJ.mol-1 and 5,30×1020 for integral methods (FWO, KAS, Tang and MKN) and 190-271 kJ.mol-1 and 1.77×1022 min-1 for differential Fr method. The activation energy decreases in the final stages of the process. The energy required for hemicellulose degradation is lower than that of cellulose. The most probable reaction functions have thus been determined for these two stages by Coats-Redfern and Criado method, leading to greatly improved calculation performance over the entire conversion range. The reaction, second-order F2, describes the pyrolysis reaction models of RLK. With the Arrhenius parameters obtained from the fitting model of CR, we attempt to reconstruct the temperature-dependent mass conversion curves and have resulted in generally acceptable results. Based on the Arrhenius parameter values obtained by Kissinger equation, the changes in entropy, enthalpy and Gibbs free energy, and lifetime predictions have been estimated concerning the thermal degradation processes of RLK.

scholarly journals Parameter kinetika reaksi dekomposisi katalitik metana menjadi karbon nanotube dengan katalis Ni-Cu-Al

2018 ◽  
Vol 11 (1) ◽  
pp. 34
Author(s):  
Praswasti PDK Wulan ◽  
Widodo W Purwanto ◽  
Yuswan Muharam ◽  
Anindya Adiwardhana
Keyword(s):  
Activation Energy ◽  
Carbon Nanotubes ◽  
Kinetic Model ◽  
Kinetic Parameters ◽  
Kinetic Data ◽  
Catalytic Decomposition ◽  
Experimental Result ◽  
Precipitation Method ◽  
Exponential Factor ◽  
Co Precipitation

Kinetic Parameter of Methane catalytic Decomposition Reaction into Nanotube Carbon with Ni-Cu-Al Catalyst. Development of production technology of nanotubes carbon through catalytic conversion of hydrocarbons will be efficient and effective if based on knowledge of the nucleation and growth mechanism of carbon nanotubes. Most of the research that focused on identifying the main products of reaction and estimate the activation energy. Growth kinetics and mechanism data of carbon nanotubes not completely available, so that process kinetics models are always based on experimental kinetic data. The objective of this research is to obtain kinetic parameters of catalytic decomposition of methane using the catalyst Ni-Cu-Al with composition of 2:1:1 which was prepared by co-precipitation method using natrium carbonate solution precipitant. Experimental kinetic data were taken in the temperature range of 650-750 °C and pressure of 1 atmosphere. Kinetic data were tested by micro-kinetic model derived from the catalytic surface reaction mechanism. The most appropriate kinetic model with experimental result is the adsorption stage which shows that consumption of intermediate (reaction surface) faster than the formation of intermediate (adsorption of methane). Kinetic parameters obtained are activation energy of 40,6 kJ/mole and pre-exponential factor of 8,625 x 106. Keywords: methane decomposition, hydrogen, carbon nanotubes, co-precipitation, kinetics of reactionAbstrak Pengembangan teknologi produksi karbon nanotube melalui konversi katalitik hidrokarbon akan efisien dan efektif jika didasarkan pada pengetahuan mekanisme nukleasi dan pertumbuhan karbon nanotube. Sebagian besar studi melakukan riset yang difokuskan pada identifikasi produk utama reaksi dan estimasi energi aktivasi. Data kinetika dan mekanisme pertumbuhan karbon nanotube tidak tersedia dengan lengkap sehingga model kinetika proses selalu didasarkan pada data kinetika eksperimen. Pada penelitian ini, dilakukan studi untuk memperoleh parameter kinetika reaksi dekomposisi katalitik metana menggunakan katalis Ni-Cu-Al dengan target komposisi 2:1:1 yang dipreparasi dengan metode kopresipitasi menggunakan presipitan larutan natrium karbonat. Data kinetika eksperimen diambil pada rentang temperatur 650-750 oC dan tekanan 1 atmosfer. Data kinetika diuji dengan model kinetika mikro yang diturunkan dari mekanisme reaksi permukaan katalis. Model kinetika yang paling sesuai dengan hasil percobaan adalah tahap adsorpsi yang menunjukkan bahwa konsumsi intermediate (reaksi permukaan) lebih cepat dari pembentukan intermediate (adsorpsi metana). Parameter kinetika yang diperoleh berupa Energi aktivasi sebesar 40,6 kJ/mol dan faktor pre-eksponensial 8,625 x 106.Kata kunci: dekomposisi metana, hidrogen, karbon nanotube, kopresipitasi, kinetika reaksi

Comparison of H2 Desorption Kinetics from Si(111)7×7 and Si(100)2×l

1990 ◽  
Vol 204 ◽  
Author(s):  
M. L. Wise ◽  
B. G. Koehler ◽  
P. Gupta ◽  
P. A. Coon ◽  
S. M. George
Keyword(s):  
Activation Energy ◽  
Preexponential Factor ◽  
Desorption Kinetics ◽  
Bond Energies ◽  
First Order ◽  
First Order Kinetics ◽  
Upper Limits ◽  
Desorption Activation Energy ◽  
Temperature Programmed ◽  
Kinetics Of

ABSTRACTThe desorption kinetics of hydrogen from the β1 H2 -TPD state on Si(111)7×7 and Si(100)2×l were studied using laser-induced thermal desorption (LITD) and temperature programmed desorption (TPD) techniques. Isothermal LITD studies of H2 desorption from Si(111)7×7 revealed second-order kinetics with a desorption activation energy of Ed = 62 ±4 kcal/mol and a preexponential factor of Vd = 92 ±10 cm2 /s. In contrast, H2 desorption from Si(100)2×l revealed first-order kinetics with an activation energy of Ed = 58 ±2 kcal/mol and a preexponential factor of Vd = 5.5 ±0.5 × 1015 s−1. The desorption kinetics yield similar upper limits for the Si-H bond energies but different desorption mechanisms on Si(lll)7×7 and Si(100)2×l.

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