scholarly journals Cerium d-Block Element (Co, Ni) Bimetallic Oxides as Catalysts for the Methanation of CO2: Effect of Pressure

Catalysts ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 44
Author(s):  
Joaquim Miguel Badalo Branco ◽  
Ana Cristina Ferreira ◽  
Joana Filipa Martinho
Keyword(s):  
Kinetic Model ◽  
Atmospheric Pressure ◽  
Simulated Data ◽  
Reaction Rates ◽  
Block Element ◽  
Practical Application ◽  
Catalytic Behavior ◽  
Effect Of Pressure ◽  
Catalyst Recycle ◽  
Bimetallic Oxides

Nickel– and cobalt–cerium bimetallic oxides were used as catalysts for the methanation of CO2 under pressure. The catalysts’ activity increases with pressure and an increase of just 10 bar is enough to double the yield of methane and to significantly improve the selectivity. The best results were those obtained over nickel–cerium bimetallic oxides, but the effect of pressure was particularly relevant over cobalt–cerium bimetallic oxides, which yield to methane increases from almost zero at atmospheric pressure to 50–60% at 30 bar. Both catalyst types are remarkably competitive, especially those containing nickel, which were always more active than a commercial rhodium catalyst used as a reference (5wt.% Rh/Al2O3) and tested under the same conditions. For the cobalt–cerium bimetallic oxides, the existence of a synergetic interaction between Co and CoO and the formation of cobalt carbides seems to play an important role in their catalytic behavior. Correlation between experimental reaction rates and simulated data confirms that the catalysts’ behavior follows the Langmuir–Hinshelwood–Hougen–Watson kinetic model, but Le Chatelier’s principle is also important to understand the catalysts’ behavior under pressure. A catalyst recycle study was also performed. The results obtained after five cycles using a nickel–cerium catalyst show insignificant variations in activity and selectivity, which are important for any type of practical application.

Kinetic study of key species and reactions of atmospheric pressure pulsed corona discharge in humid air

2021 ◽  
Author(s):  
Yongkang Peng ◽  
Xiaoyue Chen ◽  
Yeqiang Deng ◽  
Lan Lei ◽  
Zhan Haoyu ◽  
...  
Keyword(s):  
Chemical Reactions ◽  
Chemical Reaction ◽  
Atmospheric Pressure ◽  
Discharge Plasma ◽  
Reaction Rates ◽  
Global Model ◽  
Discharge Process ◽  
Humid Air ◽  
Pressure Discharge ◽  
Atmospheric Pressure Discharge

Abstract The traditional corona discharge fluid model considers only electrons, positive and negative ions, and the discharge parameters are determined using the simplified weighting method involving the partial pressure ratio. Atmospheric pressure discharge plasma in humid air involves three main neutral gas molecule types: N2, O2, and H2O(g). However, in these conditions, the discharge process involves many types of particles and chemical reactions, and the charge and substance transfer processes are complex. At present, the databases of plasma chemical reaction equations are still expanding based on scholarly research. In this study, we examined the key particles and chemical reactions that substantially influence plasma characteristics. In summarizing the chemical reaction model for the discharge process of N2–O2–H2O(g) mixed gases, 65 particle types and 673 chemical reactions were investigated. On this basis, a global model of atmospheric pressure humid air discharge plasma was developed, with a focus on the variation of charged particles densities and chemical reaction rates with time under the excitation of a 0–200 Td pulsed electric field. Particles with a density greater than 1% of the electron density were classified as key particles. For such particles, the top ranking generation or consumption reactions (i.e., where the sum of their rates was greater than 95% of the total rate of the generation or consumption reactions) were classified as key chemical reactions On the basis of the key particles and reactions identified, a simplified global model was derived. A comparison of the global model with the simplified global model in terms of the model parameters, particle densities, reaction rates (with time), and calculation efficiencies demonstrated that both models can adequately identify the key particles and chemical reactions reflecting the chemical process of atmospheric pressure discharge plasma in humid air. Thus, by analyzing the key particles and chemical reaction pathways, the charge and substance transfer mechanism of atmospheric pressure pulse discharge plasma in humid air was revealed, and the mechanism underlying water vapor molecules’ influence on atmospheric pressure air discharge was elucidated.

Hydrogenation and Hydrogenolysis of Acetophenone

2003 ◽  
Vol 68 (10) ◽  
pp. 1969-1984 ◽  
Author(s):  
Martina Bejblová ◽  
Petr Zámostný ◽  
Libor Červený ◽  
Jiří Čejka
Keyword(s):  
Reaction Mechanism ◽  
Liquid Phase ◽  
Kinetic Model ◽  
Active Carbon ◽  
Palladium Catalysts ◽  
Reaction Rates ◽  
Zeolite Support ◽  
Dehydration Mechanism ◽  
Supported Palladium ◽  
Very High

Catalytic hydrogenation and hydrogenolysis of acetophenone was investigated on supported palladium catalysts in liquid phase at temperatures 30-130 °C and pressures 1-10 MPa. A number of supports like active carbon, alumina and zeolites Beta and ZSM-5 were employed. The effects of solvent and support on the reaction mechanism of acetophenone transformation were studied. Catalysts with acid zeolite support showed a very high activity in transformation of acetophenone to ethylbenzene. Based on a kinetic model, the reaction rates of acetophenone transformation to ethylbenzene on Pd/C and Pd/Al2O3 catalysts were discussed. The kinetic model confirmed that the transformation of acetophenone to ethylbenzene proceeds primarily via a hydrogenation-dehydration mechanism and the effect of the direct hydrogenolysis of the C=O bond of acetophenone is insignificant.

Employing Simulated Data to Illustrate an Important Cause of the ‘Steepling’ Effect in Breath Alcohol Analysis

1994 ◽  
Vol 34 (4) ◽  
pp. 321-323 ◽  
Author(s):  
Rod G. Gullberg
Keyword(s):  
Kinetic Model ◽  
Data Collection ◽  
Nonlinear Regression ◽  
Kinetic Modelling ◽  
Analytical Data ◽  
Simulated Data ◽  
Breath Alcohol ◽  
Random Samples ◽  
The Mean ◽  
Over Time

The ‘steepling’ effect (large excursions in analytical data over time) is a debated issue in forensic breath alcohol analysis with various explanations being postulated. Simulated breath alcohol data was generated according to a hypothetical kinetic model where single random samples as well as means of duplicate random samples were plotted with respect to time at 0.2 hour intervals. In addition, the simulated data was compared when both two or more digit treatment was employed. Results showed the occurrence of significant noise or ‘steepling’ when single, two-digit breath alcohol samples were employed as compared to a four-digit mean computed from three-digit duplicates. The magnitude of variability was quantified by means of nonlinear regression resulting in the residual sum of squares (RSS) = 0.00202 for the single analysis and RSS = 0.00053 for the mean of duplicates. The method of data collection and treatment appears to contribute significantly to the ‘steepling’ phenomenon. Intuitively, replicate analyses reduce variability and allow for more accurate kinetic modelling employing breath alcohol analysis.

Organic Reactions at High Pressure; The Effect of Pressure Change Upon Reaction Rates of Bimolecular Processes

Synthesis ◽  
1986 ◽  
Vol 1986 (07) ◽  
pp. 532-535 ◽  
Author(s):  
William G. Dauben ◽  
John M. Gerdes ◽  
Gary C. Look
Keyword(s):  
High Pressure ◽  
Pressure Change ◽  
Reaction Rates ◽  
Organic Reactions ◽  
Effect Of Pressure

scholarly journals Aqueous phase oxidation of sulphur dioxide by ozone in cloud droplets

2015 ◽  
Vol 15 (23) ◽  
pp. 33843-33896 ◽  
Author(s):  
C. R. Hoyle ◽  
C. Fuchs ◽  
E. Järvinen ◽  
H. Saathoff ◽  
A. Dias ◽  
...  
Keyword(s):  
Aqueous Phase ◽  
Atmospheric Pressure ◽  
Reaction Rates ◽  
Aqueous System ◽  
Excess Pressure ◽  
Cloud Droplets ◽  
Oxidation Rates ◽  
Phase Oxidation ◽  
Bulk Solutions ◽  
Seed Aerosol

Abstract. The growth of aerosol due to the aqueous phase oxidation of SO2 by O3 was measured in laboratory generated clouds created in the CLOUD chamber at CERN. Experiments were performed at 10 and −10 °C, on acidic (sulphuric acid) and on partially to fully neutralised (ammonium sulphate) seed aerosol. Clouds were generated by performing an adiabatic expansion – pressurising the chamber to 220 hPa above atmospheric pressure, and then rapidly releasing the excess pressure, resulting in a cooling, condensation of water on the aerosol and a cloud lifetime of approximately 6 min. A model was developed to compare the observed aerosol growth with that predicted by oxidation rates previously measured in bulk solutions. The model captured the measured aerosol growth very well for experiments performed at 10 and −10 °C, indicating that, in contrast to some previous studies, the oxidation rates of SO2 in a dispersed aqueous system are well represented by accepted rates, based on bulk measurements. To the best of our knowledge, these are the first laboratory based measurements of aqueous phase oxidation in a dispersed, super-cooled population of droplets. The measurements are therefore important in confirming that the extrapolation of currently accepted reaction rates to temperatures below 0 °C is correct.

scholarly journals CO2-Enabled Cyanohydrin Synthesis and Facile Homologation Reactions

2020 ◽  
Author(s):  
Martin Juhl ◽  
Allan Petersen ◽  
JIWOONG LEE
Keyword(s):  
Atmospheric Pressure ◽  
Chemical Process ◽  
Reaction Rates ◽  
Protecting Groups ◽  
Reaction Pathways ◽  
Easy Access ◽  
Kinetic Control ◽  
Direct Reaction ◽  
Fischer Synthesis ◽  
Cyanohydrin Synthesis

Thermodynamic and kinetic control of a chemical process is the key to access desired products and states. Changes are made when desired product is not accessible; one may manipulate the reaction with additional reagents, catalysts and/or protecting groups. Here we report the use of carbon dioxide to direct reaction pathways in order to selectively afford desired products in high reaction rates while avoiding the formation of byproducts. The utility of CO<sub>2</sub>-mediated selective cyanohydrin synthesis was further showcased by broadening Kiliani-Fischer synthesis to offer an easy access to variety of polyols, cyanohydrins, linear alkylnitriles, by simply starting from alkyl- and arylaldehydes, KCN and atmospheric pressure of CO<sub>2</sub>.

scholarly journals Numerical analysis of parameter identifiability for a mathematical model of a chemical reaction

2018 ◽  
pp. 282-292
Author(s):  
Л.Ф. Нурисламова ◽  
И.М. Губайдуллин
Keyword(s):  
Kinetic Model ◽  
Chemical Reaction ◽  
Atmospheric Pressure ◽  
Numerical Approach ◽  
Primary Objective ◽  
Reaction Products ◽  
Parameter Identifiability ◽  
Reaction Models ◽  
Low Temperature Pyrolysis ◽  
Reaction Processes

Авторами статьи ведутся работы, направленные на разработку численного подхода к анализу параметрической идентифицируемости модели химической реакции методами анализа чувствительности для эффективного исследования и управления процессом химической реакции. Целью настоящей работы является определение параметров, подлежащих идентификации в условиях задаваемой погрешности измерений, химической реакции на примере процесса пиролиза пропана и определение незначимых параметров модели. Выполнена редукция 157-стадийной детальной схемы пиролиза пропана к 30-стадийной схеме. Предложена кинетическая модель для анализа низкотемпературного пиролиза пропана. Модель адекватно описывает выход наблюдаемых продуктов реакции при атмосферном давлении. Идентифицированы параметры кинетической модели пиролиза пропана путем решения обратной задачи химической кинетики. The authors of this paper develop a numerical approach to analyze the parametric identifiability of chemical reaction models by the methods of sensitivity analysis for the efficient study and management of chemical reaction processes. The primary objective of this paper is to determine the parameters to be identified for the propylene pyrolysis process and to determine the insignificant parameters of the model. The 157-step detailed pyrolysis scheme of propane is reduced to the 30-step scheme. A kinetic model is proposed to analyze the low-temperature pyrolysis of propane. This model adequately describes the yield of observed reaction products at atmospheric pressure. The parameters of the kinetic model of propane pyrolysis are identified by solving the inverse problem of chemical kinetics.

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