Power-law Rate Expression Research Articles

A global kinetic model for the oxidative dehydrogenation of ethane over mixed metal oxide catalysts at supra-ambient pressures

Oxidative dehydrogenation of ethane (ODHE), unlike traditional steam cracking processes, can potentially be used to produce ethene at supra-ambient pressures, thereby reducing reactor footprint and alleviating (de)compression energy requirements. Global kinetic models that capture kinetic features of both desired and undesired reactions over an extended range of reactant and product pressures are lacking despite the clear reliance of comparative reactor design assessments on such models. We report herein a global kinetic model that accounts for the rates (between 603 and 703 K) of all 6 of the prevalent reaction network steps, extends up to 6 bar total pressure, and explains a broad set of differential and integral kinetic features measured over MoVTeNbOx catalysts. H2O2-mediated dissolution procedures enable low-temperature measurements which under the extended pressure ranges used in this study evidence significant coverages of reduced sites the contributions of which can be interpreted as being determined by ethane to oxygen molar ratios. Explaining measured kinetic features require invoking an oxygen pool present in quasi-equilibrium with gas phase oxygen that is distinct in identity from lattice oxygens, only the latter of which are wholly responsible for hydrogen abstraction steps in turnovers producing ethene, not COx. We demonstrate how a simplified global kinetic model that employs power law rate expressions for undesired reactions and excludes product inhibitory effects for the entirety of the reaction network is sufficient to explain both co-feed data as well as differential and integral features evaluated in the absence of product co-feeds. The proposed kinetic model can be employed in comparative assessments of high-pressure ODHE reactor configurations operating non-isothermally, especially those carrying a high sensitivity to contributions from highly exothermic total oxidation reactions.

Deactivation kinetics of γ-Al2O3 catalyst in methanol dehydration to dimethyl ether

The kinetics of deactivation of γ-alumina catalyst in dehydration of methanol to dimethyl ether (DME) was studied using integral method of analysis. A power-law rate expression was used for dehydration reaction and an independent kinetics for catalyst deactivation. Catalytic test runs were performed in a fixed-bed integral reactor in the temperature range of 250–300 °C under kinetically controlled reaction conditions. A second-order independent deactivation kinetics was found to fit experimental conversion-time data accurately. The activation energies of the main reaction and catalyst deactivation were obtained as 121 and −85 kJ/mol, respectively. The apparent negative value of the latter was attributed to a predominant deactivation mechanism via exothermic reversible partial hydration of active γ-alumina phase to the less active boehmite. At higher reaction temperatures, however, this mechanism is ceased at the expense of irreversible sintering of alumina crystallites.

Catalytic influence of mineral compounds on the reactivity of cellulose-derived char in O2-, CO2-, and H2O-containing atmospheres

The catalytic effects of mineral compounds on the conversion of a biomass-derived char in air- and oxyfuel-related atmospheres were investigated by thermogravimetric analysis at atmospheric pressure. The applied char originated from the hydrothermal carbonization (HTC) of cellulose followed by pyrolysis at 1073 K and subsequent mixing with 20 wt% of minerals by grinding to achieve tight contact. The reactivities of the mineral-loaded HTC chars were evaluated based on isothermal experiments in O2-, CO2-, and H2O-containing atmospheres as a function of their composition applying a magnetic suspension balance. The reactivity sequence K2CO3 > Na2CO3 ≫ Fe2O3 > CaO > MgO ≥ mineral-free was derived consistently for char oxidation in O2/inert as well as for char gasification in diluted H2O and CO2 mixtures. In addition to this qualitative assessment, the kinetic experiments were first modelled based on a simple global nth-order power-law rate expression. Then, the more complex Carbon Burnout Kinetics (CBK/G) model and the PoliMi model were applied. All three modeling approaches enabled a systematic quantification of the catalytic effects and led to a comparable lowering in the apparent activation energy. In combination with the kinetic parameters determined for the mineral-free char, the lowered apparent activation energies specific for the applied mineral and atmosphere facilitate the implementation of catalytic effects on the conversion of biomass-derived char into combustion models.

Consequences of product inhibition in the quantification of kinetic parameters

While the potential for product inhibition in catalytic reactions is well known, the impact of neglected inhibition on measured kinetic parameters is often overlooked. The presence of product inhibition, most often caused by the competitive adsorption of products with reactants on catalytic active sites, is difficult to determine a priori for an arbitrary catalytic system. The significance of product inhibition relies on the concentration of the products, their adsorption thermodynamics on catalytically relevant sites, and process parameters such as temperature and pressure. When inhibition is significant, however, apparent activation energies and reaction orders vary from the differential-reactor apparent activation energy by a factor of 1/(1 − δ), where δ is the total inhibition order (e.g., the factor (1 − δ) = 1.6 for a system with product inhibition of −0.6 order). This is illustrated here with the kinetics of NO oxidation over Cu ion clusters (CuxOy) in Cu-SSZ-13, for which the product NO2 inhibits the forward reaction. Furthermore, in the presence of inhibition, when only reactants are fed to a flow reactor or placed in a batch reactor, there is often no practical conversion that is low enough to guarantee differential behavior. Inclusion of products in the feed solves this problem, allowing accurate determination of kinetic parameters such as apparent reaction orders and activation energies. We also demonstrate that evaluation of the necessity of co-feeding products to assure measurement of differential-reactor data in a given catalytic system is straightforward from a plot of the log of the rate (or conversion) versus the log of the space time in a flow reactor or elapsed time in a batch reactor. We encourage inclusion of this test in all kinetic analyses that are reasonably approximated by power law rate expressions.

Ammonia decomposition kinetics over LiOH-promoted, α-Al2O3-supported Ru catalyst

A LiOH-promoted Ru-based catalyst was recently reported to have a high TOF of 17.7 s−1 at 623 K, compared to 2.7 s−1 for an un-promoted Ru-based catalyst, and has been reproduced for this study to develop further understanding of the catalyst activity under a range of conditions. The kinetic values were calculated using a Temkin-Pyzhev-like power law rate expression model. Reaction orders, pre-exponential factors (A) and activation energies (E) were calculated for two temperature ranges, 623–748 K, and 748–873 K. The TOF of this catalyst at 623 K is not similar to that previously reported, being only 1.6 s−1 in this study. A follow-up CFD analysis supports the fact that the kinetic model effectively describes performance of the catalyst at a range of temperatures and pressures, and can be used in the future on similar catalysts. H2 partial pressure has an inhibitory effect on the rate of decomposition of NH3 at all temperatures, not just near or below 673 K as previously proposed in the literature, however equilibrium decomposition is still possible with sufficient catalyst loading.

Kinetic and mechanistic features of carbon dioxide reforming of methane over Co–Ce/ZrO2 catalysts

AbstractCarbon dioxide reforming of methane (CDRM) is an effective route to utilize CO2 and CH4, the most abundant, thermodynamically stable and hazardous greenhouse gases. To overcome the economical impediments to favor CDRM's industrial applicability, its mechanistic features need to be revealed both for developing efficient catalysts and optimizing operational conditions. In this context, this work aims to obtain power‐law type CDRM kinetic expressions over 5%Co–2%Ce/ZrO2 and 10%Co–2%Ce/ZrO2 catalysts and compare and analyze mechanistic routes to elucidate the effect of the Co:Ce ratio on kinetics. The empirical power‐law type rate expressions were estimated with the reaction orders of 1.63 and 1.12 for CH4 and 0.29 and –0.12 for CO2 for 5%Co–2%Ce/ZrO2 and 10%Co–2%Ce/ZrO2 catalysts, respectively. Limited CH4 activation and, thus, carbon formation due to low Co loading lead to accumulation of surface oxygen on ZrO2 as redox ability of Ce becomes suppressed. This causes higher CO2 activation barrier. The presence of H2 in the feed slows down mechanistic steps involving CHx. The reactions including CH4 activation, most probably reversible direct CH4 dissociation, are found to be rate determining.

Reaction mechanism and kinetics of CO oxidation over a CuO/Ce0.75Zr0.25O2-δ catalyst

The CuO/Ce0.75Zr0.25O2-δ and Ce0.75Zr0.25Oδ catalysts were prepared by the sol-gel method, and Cu0.07Ce0.75Zr0.25O2-δ was obtained by treating CuO/Ce0.75Zr0.25O2-δ with nitric acid to remove the well-dispersed CuO on the surface. Various characterizations were used to reveal the different active sites, such as surface-dispersed CuO and Cu-Ce-Zr-Oδ solid solutions in CuO/Ce0.75Zr0.25O2-δ, Cu-Ce-Zr-Oδ solid solutions in Cu0.07Ce0.75Zr0.25O2-δ and Ce-Zr-Oδ solid solutions in Ce0.75Zr0.25Oδ. The Raman and O2-TPD results showed that the concentration of oxygen vacancies in Cu-Ce-Zr-Oδ solid solutions was higher than that in Ce-Zr-Oδ solid solutions. CO oxidation testing suggested that the catalytic activity decreases in the order of CuO/Ce0.75Zr0.25O2-δ > Cu0.07Ce0.75Zr0.25O2-δ > Ce0.75Zr0.25Oδ. Combined with the in situ diffuse-reflectance Fourier transform (in situ DRIFT) results, the reaction sensitivity followed the order of CO linear chemisorption onto dispersed CuOx species (Mars-van Krevelen mechanism) > carbonate species onto a Cu-Ce-Zr-Oδ solid solution (Langmuir-Hinshelwood mechanism) > carbonate species onto a Ce-Zr-Oδ solid solution (Langmuir-Hinshelwood mechanism). Kinetic studies suggested that the power-law rate expressions and apparent activation energies were r = 6.02 × 10−7×PCO0.68PO20.03 (53 ± 3 kJ/mol) for CuO/Ce0.75Zr0.25O2-δ, r = 5.86 × 10−7×PCO0.8PO20.07 (105 ± 5 kJ/mol) for Cu0.07Ce0.75Zr0.25O2-δ and r = 5.7 × 10−7×PCO0.75PO20.12 (115 ± 6 kJ/mol) for Ce0.75Zr0.25Oδ. The Mars-van Krevelen mechanism should be the crucial reaction pathway over CuO/Ce0.75Zr0.25O2-δ in CO interfacial reactions, although the Langmuir-Hinshelwood mechanism cannot be ignored, and the Langmuir-Hinshelwood mechanism mainly occurred over the Cu0.07Ce0.75Zr0.25O2-δ and Ce0.75Zr0.25Oδ catalysts, where the contribution from the Mars-van Krevelen mechanism was negligible due to the absence of surface CuOx species.

Advantages of mesoporous silica based catalysts in methane reforming by CO2 from kinetic perspective

Nickel confined inside mesoporous silica SBA-15 (Ni5/SBA-15), and iridium supported nickel/SBA-15 catalysts (Ir0.1-Ni5/SBA-15) were tested in dry reforming of methane (DRM). Calcined samples were characterized and their structural and morphological properties were obtained and analyzed by N2-sorption, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Nickel oxide nanoparticles with estimated particle sizes of 3.3 and 4.2 nm were obtained. Their reducibility and active surface area were determined by temperature programed reduction and temperature programed desorption, respectively. Kinetic studies in DRM were then performed at 480 °C and the facile power-law rate expressions attained for Ni5/SBA-15 and Ir0.1-Ni5/SBA-15 confirmed the dependency of both rates on CO2 and CH4 partial pressures, which decreased the formation of carbon deposition due to the confinement effect of nickel inside support’s mesopores. Activation energies (Ea) of the catalysts were also calculated by varying the temperature. The values of Ea in this study (8.4 and 6 Kcal.mol−1 for CH4 and CO2 on Ni5/SBA-15 catalyst) were lower than those present in other studies, which were mainly performed on non-porous based catalysts. Such outcome stresses on the importance of mesoporous supports in improving the kinetics of DRM. Finally, long tests duration shows that the presence of Ir is beneficial at high temperature (650 °C) in order to maintain the conversion levels of reactants.

A comprehensive study of kinetics mechanism of Fischer-Tropsch synthesis over cobalt-based catalyst

A comprehensive kinetics study of Fischer-Tropsch (FT) synthesis mechanism was investigated over an in-house 37% Co-based catalyst on a SiO2 support. A series of combined FT and water gas shift (WGS) reaction mechanisms were developed in order to calibrate the model at twelve different operating conditions. Two different approaches were used to develop a model for the FT synthesis reaction network. The first was based on an empirical approach; whereas the second approach explained the novel mechanistic details of FT kinetics. In the former, the rate equations were derived by power-law rate expressions, while in the latter the rate equations were derived by the Langmuir–Hinshelwood-Hougen-Watson (LHHW) rate theory. The limitations of power-law rate model were highlighted for the applications that wider range of operating conditions has to be selected. In contrast the advantages of LHHW for predicting a wider range of operating conditions were underlined. A comprehensive plausible mechanism-derived FT kinetics models with eight elementary reaction pathways along with seven WGS kinetics models were developed. Such reaction networks were investigated to fit and validate against the newly obtained experimental results which can be used as a key tool to emphasise the most significant facts of FT synthesis catalysis and chemistry. Model validation was carried out subsequent to completion of the model calibration and the estimation of proper kinetic parameters. The overall purpose of the validation study was to ensure that the model provides a robust and realistic assessment of all the parameters. In order to ensure model is precise to an appropriate level, the model was assessed against experimental data at four different operating conditions. The results obtained from kinetic study were compared to the most recent findings that have been reported in literature. It was shown that the novel developed kinetic model based on a combination of alkyl/alkenyl mechanism for FT reactions (for production of n-paraffins and α-olefins) along with formate mechanism for WGS reaction can provide the most accurate predictions.

Sub- and super-critical water oxidation of wastewater containing organic and heavy metallic pollutants and recovery of superfine metallic particles

The wastewater containing organic and heavy metallic pollutants is studied with sub- and super-critical water oxidation. First the in situ change was obtained with the simulated wastewater containing ethanol as organic pollutant and zinc acetate as heavy metal by an optical fused silica capillary and Raman spectroscopy and it is observed that there is deposition of superfine particles up to the temperature of 523K during oxidation degradation. In the temperature range of 573–633K, the degradation kinetics based on the chemical oxygen demand (COD) by a global power-law rate expression was determined to give the apparent reaction activation energy (Ea) of 45.51KJ/mol. According to the simulated wastewater, the industrial leather wastewater containing heavy metal Cr and organic pollutants was treated. The Cr was fast converted to superfine Cr2O3 particles and the COD was easier removed with lower Ea of 36.96KJ/mol.

Kinetics of Fischer-Tropsch synthesis on supported cobalt: Effect of temperature on CO and H2 partial pressure dependencies

Kinetic data were measured for Fischer-Tropsch Synthesis (FTS) on a cobalt catalyst supported on silica-modified alumina at various partial pressures of CO and H2 and at four different temperatures (210, 220, 230, and 240°C). The data were sufficient to determine power law rate expressions at each of the four temperatures which indicate that the dependence of rate on PH2 increases with increasing temperature while the rate coefficient for PCO decreases with temperature going from positive order (+0.3) at 210°C to negative order (−0.6) at 240°C. Several mechanisms were explored and Langmuir–Hinshelwood (LH) rate models derived in an attempt to explain the data trends. Traditional FT rate expressions have a denominator term, KCO*PCO which, since the denominator is squared in LH expressions, can allow for an overall negative order PCO dependence. However, since KCO is the equilibrium constant for the adsorption of CO, its value decreases with increasing temperature which causes the overall PCO dependence to become more positive with increasing temperature instead of more negative. In this work we propose a mechanism based on parallel hydrogen-assisted mechanistic pathways that leads to a LH model with the denominator term, k’CO*PCO where k’CO is effectively an activated rate constant instead of an equilibrium constant and therefore increases with increasing temperature instead of decreasing. This model, which fits the data extremely well, also explains the presence of atomic carbon on the surface of the catalyst.

Production of CO-rich hydrogen from methane dry reforming over lanthania-supported cobalt catalyst: Kinetic and mechanistic studies

In this study, the production of CO-rich hydrogen from methane dry reforming over lanthania-supported Co catalyst was investigated. The Co/La2O3 catalyst was synthesized via wet-impregnation method and characterized using instrument techniques such as TGA, FTIR, XRD, FESEM-EDX and N2 adsorption-desorption analysis. The catalytic activity of the Co/La2O3 catalyst tested in a fixed bed stainless steel reactor yielded highest CH4 and CO2 conversion of 50% and 60% respectively at 1023 K and feed ratio of 1.0. The methane dry reforming reaction gave highest H2 and CO yield of 45% and 58% respectively. Furthermore, kinetics and mechanistic behavior of the La2O3 supported Co catalyst in methane dry reforming reaction was investigated as a function of temperature and partial pressure of reactants (CH4 and CO2). The experimental data obtained from the kinetics measurements were fitted using the empirical power-law rate expression, as well as six different Langmuir–Hinshelwood kinetics models. The six models were then statistically and thermodynamically discriminated. Consequently, the Langmuir–Hinshelwood kinetics model (dual-site associative adsorption of both CH4 and CO2 with bimolecular surface reaction) was adjudged the best representative model. Activation energy values of 96.44 and 98.11 kJ mol−1 were obtained for the CH4 consumptions from the power-law and Langmuir–Hinshelwood models, respectively. A lower activation energy of circa 72 kJ mol−1 obtained for CO2 consumption showed that the rate of consumption of CO2 consumption was speedier than CH4.

Kinetic Study on the Effect of Chromium Addition to Ni-Based Catalysts for the Steam-CO2 Reforming of Methane.

In the present work, the kinetic effects of Ni-based catalysts containing various amounts of Cr on the steam-CO2 reforming (SCR) of methane were studied. Kinetic expressions for the SCR of methane over the Ni-based catalysts have been proposed using the power-law rate expression, based on the kinetic data obtained. In addition, the Arrhenius equation was used for calculating the activation energy. Analysis of the data revealed four simple results. Firstly, the partial pressure of CH4 exerts a major influence on the CH4 conversion rates. Secondly, the CH4 conversion rate is inversely proportional to the partial pressure of CO2. Thirdly, the partial pressure of steam has a very slight effect on the reaction rates. Finally, all the catalysts studied have similar apparent activation energies.

Kinetics of CO2 Absorption into Aqueous Basic Amino Acid Salt: Potassium Salt of Lysine Solution.

Aqueous amino acid salts are considered as an attractive alternative to alkanolamine solvents (e.g., MEA) for carbon dioxide (CO2) absorption. The kinetics of CO2 into unloaded aqueous solutions of potassium lysinate (LysK) was studied using a wetted wall column at concentrations ranging from 0.25 to 2.0 M and temperatures from 298 to 333 K. Physicochemical properties of aqueous LysK solutions such as density, viscosity, and physical solubility of CO2 were measured to evaluate the reaction rate constants. The reaction pathway is described using zwitterion mechanism taking into account the effect of ionic strength on the reaction rate. Under the fast pseudo-first-order regime, the reaction rate parameters were obtained and correlated in a power-law reaction rate expression. LysK shows higher chemical reactivity toward CO2 than the industrial standard MEA and most of amino acid salts. Its reaction rate constants increase considerably with concentration and temperature. The reaction order is found to be an average value of 1.58 with respect to LysK. The forward second-order kinetic rate constant, k2 0 , are obtained as 31615 and 84822 m3 kmol−1 s−1 at 298 and 313 K, respectively with activation energy of 51.0 kJ mol−1. The contribution of water to the zwitterion deprotonation seems to be more significant than that of LysK for the above-mentioned kinetic conditions

Catalytic performance of cobalt–silica catalyst for Fischer–Tropsch synthesis: Effects of reaction rates on efficiency of liquid synthesis

A one-dimensional pseudo-homogeneous mathematical model of a fixed bed reactor for Fischer–Tropsch (FT) synthesis was developed for the flow of simulated N2-rich syngas over an in-house cobalt–silica catalyst. This study aims at improving the efficiency of FT synthesis by maximizing the liquid productivities and selectivity, as well as maximizing the syngas conversion and minimizing the methane formation. The developed model predicts the fraction of the reactants and products along the reactor bed length. The rate of syngas conversion and the rate of CO2, H2O, CH4, C2H4, C2H6, C3H8, n-C4H10, i-C4H10 and C6.05H12.36 (C5+) formation were calculated by developing advanced codes in MATLAB. The reaction equations were proposed as a number of lumped chemical reactions (8 reactions, including water gas shift reaction) by means of the molar coefficients of reaction molecules (11 reactive species). The kinetic parameters were estimated by global optimization in MATLAB using the global search method. Optimum values were achieved during the search process. The results predicted by the model were in very good agreement with those measured experimentally at different operating conditions, with respect to conversion and the FT products׳ selectivity. The rates of production and consumption were derived from a modified power-law rate expression. This study shows that the adapted rate model can deliver a better prediction of final conversion and selectivity. The accuracy of the fitted model relative to the experimental data was determined by a quantitative analysis method using the mean absolute relative residual percentage (MARR %) for the total of 35 data points. It was found that the model based on the modified equation provided a better fit to the experimental data with a MARR of 6.57%, compared to the classic equation with a MARR of 12.24%.The model predicts the influence of reaction rates on the performance of the fixed bed FT reactor using an unpromoted Co/SiO2 catalyst at 503K, 15 bar and 6Lgcat−1h−1. As a result, the conversions of 91.57% and 97.26% were achieved for CO and H2, respectively, with the FT C5+ synthesis reaction rate of 7.81×10−5molgcat−1s−1. The higher rate of C5+ formation was found by increasing FT reaction rates compared to the rate of lighter the hydrocarbons׳ formation. At the same condition, only 5.04% and 8.91% methane and C2–C4 selectivity respectively, were predicted; while the highest value of 86.05% liquid (C5+) selectivity was obtained in this case. It was concluded that the higher rate of conversion of H2 inside the pores filled with liquid products, compared to that of CO, caused an increase in the H2/CO ratio in the catalyst pores; and thus, a shift towards the formation of lighter hydrocarbons.

Modelling of a fixed bed reactor for Fischer–Tropsch synthesis of simulated N 2 -rich syngas over Co/SiO 2 : Hydrocarbon production

Abstract A numerical pseudo-homogeneous one-dimensional mathematical model of a mini-scale laboratory fixed bed reactor for Fischer–Tropsch (FT) synthesis was developed. FT synthesis was modelled for simulated N 2 -rich syngas (17%Vol CO, 33%Vol H 2 , and 50%Vol N 2 ) on a cobalt-silica (i.e. Co/SiO 2 ) catalyst/support. The performance of the reactor model for gas/liquid fuel production was studied at different operating conditions i.e. temperature of 503–543 K, pressure of 10–25 bar and gas hourly space velocity (GHSV) of 1800–3600 Nml g cat −1 h −1 . An algorithm was written in order to calculate the conservation of species, pressure drop, reaction rate equations and physicochemical and thermodynamic properties’ relationships along the axial dimension i.e. in the flow direction. The program code was executed in a MATLAB environment to describe the profiles of concentration of each individual component in the gas phase along the reactor. The model was capable of predicting the selectivity of different product species and conversion of CO and H 2 in the flow direction. The power law rate expression was chosen for the rate of reaction and the dominating FT and Water Gas Shift (WGS) reaction equations were considered in accordance with the literature. After the mechanisms and rate equations were derived, the kinetic data (e.g. rate constant ( k j ), for reaction ‘j’ ) for the proposed reaction equations were obtained as “integral reactor data” where the total conversion is measured as a function of: catalyst weight to flow rate ratio (i.e. W/F), inlet pressure, final conversion obtained by experiment, and inlet fluid temperature. The pre-exponential factors ( A j ) were calculated by the classic Arrhenius equation using the predicted k j and literature-derived activation energies ( E j ). Finally, the partial order of reactions with regard to CO ( m j ) and H 2 ( n j ) were calculated for the power law rate equation using MATLAB Global Optimization Toolbox with additional in-house procedures according to the results acquired from experiments with the Co/SiO 2 catalyst. The predicted results of the model were validated successfully against 16 experimental conditions with respect to conversion of CO and selectivity of products species such as CO 2 , CH 4 , C 2 , C 3 , C 4 , and C 5+ . The error between the predicted and experimental results was negligible. Finally, the influence of the GHSV, temperature and inlet pressure of fluid mixture on components' selectivity and conversion, were also investigated and the conclusions were in agreement with the literature.

Reactive Absorption of Carbon Dioxide in l-Prolinate Salt Solutions

Aqueous amino acid salt solutions are seen as more sustainable alternative CO2 solvents compared to conventional alkanolamines. The absorption of CO2 into aqueous solutions of potassium l-prolinate, over the temperature range of 290–303 K, was studied using a stirred cell. To compare the effect of potassium versus sodium as counterion, the absorption rates of CO2 in sodium l-prolinate solutions were also determined. The amino acid salt concentration was varied between 0.5 and 3 mol dm–3. Physicochemical properties such as density, viscosity, and physical solubility of N2O, required in the interpretation of absorption rate experiments, were determined separately. The obtained experimental reactive absorption fluxes were interpreted, using the pseudo-first-order approach, into intrinsic reaction kinetics. The potassium-based solvent showed, on average, a 32% higher reactivity toward CO2 than the sodium equivalent. The kinetic data were correlated in a power-law reaction rate expression. The reaction order with respect to the amino acid was found to be between 1.40 and 1.44 for both l-prolinate salts, and the second order kinetic rate constant, k2, was calculated for the potassium salt to be 93.7 × 103 dm3·mol–1·s–1 at 298 K with an activation energy of 43.3 kJ·mol–1. l-Prolinate salts show higher chemical reactivity toward CO2 than most of the amino-alcohols and amino acid salts.

Unpromoted and Mn‐Promoted Cobalt Catalyst Supported on Carbon Nanotubes for Fischer‐Tropsch Synthesis

AbstractLangmuir‐Hinselwood (LH) and power rate equations were applied to describe the kinetics of the Fischer‐Tropsch reaction on cobalt catalysts and manganese‐doped cobalt catalysts supported on carbon nanotubes (CNTs). LH‐based kinetics characterize the activity behavior of the unpromoted Co/CNT system satisfactorily, but fail with respect to the manganese‐promoted Co/CNT catalyst. An alternative LH equation is able to fit the experimental data, but the fitting parameters are out of the range of usual values and underrate the activity at ambient pressure regardless of manganese promotion. Application of power law rate expressions results in satisfying characterization of the kinetics in the whole CO pressure range in the promoted case and within a defined range of CO pressure in the unpromoted case.

Kinetic study of propane dehydrogenation and catalyst deactivation over Pt-Sn/Al2O3 catalyst

The kinetics of propane dehydrogenation and catalyst deactivation over Pt-Sn/Al2O3 catalyst were studied. Performance test runs were carried out in a fixed-bed integral reactor. Using a power-law rate expression for the surface reaction kinetics and independent law for deactivation kinetics, the experimental data were analyzed both by integral and a novel differential method of analysis and the results were compared. To avoid fluctuation of time-derivatives of conversion required for differential analysis, the conversion-time data were first fitted with appropriate functions. While the time-zero and rate constant of reaction were largely insensitive to the function employed, the rate constant of deactivation was much more sensitive to the function form. The advantage of the proposed differential method, however, is that the integration of the rate expression is not necessary which otherwise could be complicated or impossible. It was also found that the reaction is not limited by external and internal mass transfer limitations, implying that the employed kinetics could be considered as intrinsic ones.

Power-law type rate expression for WGS reaction over Au–Re/CeO2 catalyst under realistic fuel processor conditions

Abstract The kinetic behavior of 1Au–0.5Re/CeO 2 catalyst was investigated at 280–325 °C as a function of temperature and partial pressures of reactants and products of the forward WGS reaction under realistic feed conditions. Parameters estimated by non-linear regression analysis were found to predict the overall CO conversion rate within a 10% error margin.