Kinetic Control Region Research Articles

Enhanced CO2 methanation over LaNiO3/CeO2 derivative catalyst with high activity and stability

The conversion of CO2 into synthetic natural gas offers a promising approach for the long-term storage of renewable energy, addressing the challenge of its intermittent supply. This study successfully developed a catalyst comprised of LaNiO3 supported by CeO2, synthesized via a citric acid-aided impregnation method. This catalyst demonstrated efficiency and stability as a precursor for the CO2 methanation reaction. Upon reduction, it transforms into a Ni–La2O3/CeO2 configuration, featuring dispersed Ni nanoparticles. Characterization through hydrogen temperature-programmed reduction (H2-TPR) revealed that this catalyst exhibits enhanced reducibility and smaller particle sizes, which promote hydrogen activation at lower temperatures. X-ray photoelectron spectroscopy (XPS) analysis further clarified that the increased catalytic activity results from electron transfer interactions between Ni, CeO2, and La2O3. Moreover, the catalyst displayed an augmented count of weak to medium basic sites, which, along with improved hydrogen activation, elevated the CO2 conversion rate to 83.8% within the kinetic control region. The collaborative effect of Ni, La2O3, and CeO2 substantially outperformed the conventional Ni/CeO2 catalyst in CO2 methanation efficiency. Additionally, in-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) analysis revealed that the methanation process predominantly follows the HCOO* pathway. Notably, the LaNiO3/CeO2 catalyst exceeded the performance of Ni–La/CeO2 in CO2 adsorption, HCOO* intermediate decomposition, and CHO* conversion, significantly enhancing low-temperature methanation activity.

Hierarchically porous Co@N-doped carbon fiber assembled by MOF-derived hollow polyhedrons enables effective electronic/mass transport: An advanced 1D oxygen reduction catalyst for Zn-air battery

Developing advanced oxygen reduction reaction (ORR) electrocatalysts with rapid mass/electron transport as well as conducting relevant kinetics investigations is essential for energy technologies, but both still face ongoing challenges. Herein, a facile approach was reported for achieving the highly dispersed Co nanoparticles anchored hierarchically porous N-doped carbon fibers (Co@N-HPCFs), which were assembled by core-shell MOFs-derived hollow polyhedrons. Notably, the unique one-dimensional (1D) carbon fibers with hierarchical porosity can effectively improve the exposure of active sites and facilitate the electron transfer and mass transfer, resulting in the enhanced reaction kinetics. As a result, the ORR performance of the optimal Co@N-HPCF catalysts remarkably outperforms that of commercial Pt/C in alkaline solution, reaching a limited diffusion current density (J) of 5.85 mA cm−2 and a half-wave potential (E1/2) of 0.831 V. Particularly, the prepared Co@N-HPCF catalysts can be used as an excellent air-cathode for liquid/solid-state Zn-air batteries, exhibiting great potentiality in portable/wearable energy devices. Furthermore, the reaction kinetic during ORR process is deeply explored by finite element simulation, so as to intuitively grasp the kinetic control region, diffusion control region, and mixing control region of the ORR process, and accurately obtain the relevant kinetic parameters. This work offers an effective strategy and a reliable theoretical basis for the engineering of first-class ORR electrocatalysts with fast electronic/mass transport.

Ionic Liquid-Stabilized Single-Atom Rh Catalyst Against Leaching

Ionic Liquid-Stabilized Single-Atom Rh Catalyst Against Leaching

Upgrading of Bio-Syngas via Steam-CO2 Reforming Using Rh/Alumina Monolith Catalysts

Steam-CO2 reforming of biomass derived synthesis gas (bio-syngas) was investigated with regard to the steam concentration in the feed using Rh-loaded alumina foam monolith catalysts, which was also accompanied by thermodynamic equilibrium calculation. With 40 vol % steam addition, steam methane reforming and water gas shift reaction were prevailed at the temperature below 640 °C, above which methane dry reforming and reverse-water gas shift reaction were intensified. Substantial change of activation energy based on the methane conversion was observed at 640 °C, where the reaction seemed to be shifted from the kinetic controlled region to the mass transfer controlled region. At the reduced steam of 20 vol %, the increase in the gas velocity led to the increase in the contribution of steam reforming. Comparing to the absence of steam, the addition of steam (40 vol %) resulted in the increase in the production of H2 and CO2, which in turn increased the H2/CO ratio by 95% and decreased the CO/CO2 ratio by 60%. Rh-loaded alumina monolith was revealed to have a good stability in upgrading of the raw bio-syngas.

Effect of ash removal on structure and pyrolysis/gasification reactivity of a Chinese bituminous coal

In this study, the effect of ash removal on Shenfu bituminous coal was investigated. The coal was pretreated by hydrofluoric acid (HF) pickling, and the raw/pretreated coal chars were prepared at 900 °C in a fixed bed reactor. The structure of coal and char were detected by Fourier transform infrared (FTIR) and Raman spectroscopy. The reactivity was tested in a thermogravimetric analyzer, including coal pyrolysis and char gasification. The reaction kinetics was analyzed through the Coats–Redfern method, master plots, the model-free and model-fitting method. The results show that the HF pickling can remove silicon from coal efficiently, and the macromolecular framework of coal is quite stable according to FTIR. The Raman parameters imply some carbonaceous structure on coal surface changed. For slow pyrolysis of coal, the effect of heating rate is considered. The changes of pyrolysis characteristics and kinetics are insignificant. For char gasification, the reactivity under isothermal and non-isothermal condition are discussed with an emphasis in different residence time of devolatilization process. In kinetic control region (low temperature), the activation energy (Ea) is very close (about 240 kJ/mol) for all chars. With the temperature increases, the reactivity of raw coal char is more easily suffered by diffusion. The random pore model is more suitable for the ash-free coal char, and the char with long residence time has a larger value of structural parameter ψ and smaller value of pre-exponential factor A. The Ea calculated by model-fitting and model-free method were in good agreement.

Role of Protons on Activity and Selectivity of Fe-N-C Electroctatalysts for Oxygen Reduction Reaction

As one of the most promising candidates to replace Pt-based electrocatalysts for oxygen reduction reaction (ORR) in proton exchange membrane fuel cell (PEMFC), iron-nitrogen-carbon (Fe-N-C) materials have attracted tremendous research interests in recent years. Different from platinum-group-metal (PGM) catalysts, Fe-N-C have several categories of active sites: Fe-Nx has 4-electron pathway; pyrrolic-N and hydrogenated pyridinic-N can partially reduce oxygen into peroxide; pyridinic-N can reduce peroxide into water. Due to this complicated environment and numerous synthesis approaches from various precursors, the electrocatalysis mechanism of Fe-N-C still needs intensive investigation. Here we report the proton independence/dependence of rate-determining step (RDS) for a specific Fe-N-C catalyst via kinetic isotope effect (KIE), in addition to the activity inhibition of proton-involved N active sites via two molecular inhibitors. It is found that Fe-N-C can behave proton independent RDS like conventional Pt electrocatalyst in kinetic-controlled region, but it undergoes proton-coupled electron transfer in mass transport-controlled region, probably attributed to N active sites. It is also discovered that two molecules, tris(hydroxymethyl)aminomethane and etidronic acid, can inhibit and transform two categories of N active sites respectively: tris can effectively poison Fe-Nx active sites and pyridinic-N, resulting in obvious increase of peroxide yielding and drop of half-wave potential; etridonic acid can readily inhibit pyrrolic-N as well as hydrogenated pyridinic-N but no damage to Fe-Nx active sites, leading to decrease of peroxide yielding and no change of half-wave potentials. These results elucidate that Fe-N-C catalysts could, in principle, compete with Pt-based ORR catalysts through careful optimization of structure and morphology. Figure 1

Influence of Ink Composition and Operation Parameters on the Performance of Fe-N-C

The application of proton exchange fuel cells (PEFCs) in the automotive sector is rising to be an alternative to petroleum fuel based transportation. Nevertheless, the obstacle of cost reduction of the PEFC remains, which is due to highly expensive Pt catalysts on the cathode side for oxygen reduction reaction (ORR).[1] A possible way to substitute Pt for ORR is the use of Fe-N-C-catalysts which have been shown to be a promising option.[2] For Fe-N-C-catalysts the required catalyst loading needs to be significantly higher than for Pt-based catalysts in order to achieve sufficient current densities. This leads to a change in catalyst layer thickness of roughly one order of magnitude where transport phenomena of gases and liquids become more important.[3] Based on this, the gap between Pt/C and Fe-N-C at high current densities is significantly higher compared to the kinetic controlled region. Therefore, further optimization is needed in order to enhance activity also under high current flow. In addition to this, it need to be understood to what extent problems in the transport properties affect the durability behavior of Fe-N-C catalysts in fuel cells. The ionomer distribution and loading of the catalyst layer has found to be crucial for proton transport towards the active sites, but also influences the hydrophilicity of the catalysts pores which enhances gas transport resistance. [1] In addition, it has been shown that the preparation of the membrane electrode assembly (MEA) for the fuel cell plays a key role. [3] The widely used hot-pressing technique might influence the catalyst layer pore size which is also an important parameter for species transport. In this work, different catalyst to ionomer ratios are evaluated in fuel cell tests for Fe-N-C catalysts. Furthermore, the preparation by hot-pressing is investigated in respect to the application of different compression pressures. The results are brought in relation to structural investigations of the MEAs and serve for the validation of a theoretical model. [1] S. Komini Babu, et al. ACS Appl. Mater. Infertaces 2016, 8, 32764-32777 (2016) [2] U.I. Kramm, et al. J. Am. Chem. Soc., 138 (2), 635–640 (2016) [3] X. Yin, et al. ECS Transactions, 77 (11) 1273-1281 (2017) [4] S. Komini Babu, et al. Journal of The Electrochemical Society, 164 (9), F1037-F1049 (2017)

Determination of the Apparent Carbon Oxidation Reaction Order by a Microfluidized Bed and Its Application to Kinetic Models

During carbon oxidation, the apparent reaction order n ranges from 0 to 1. Considering the importance of the value of n to the accuracy of char combustion rate prediction models and the error caused by subjective selections of its value, this study proposes a fast, simple, and accurate method to determine n, the results of which can be applied to improve the accuracy of kinetic models. In the kinetic control region, the apparent carbon oxidation reaction order n was first determined using a microfluidized bed (MFB). As an example of its application, the value of n thus determined was applied to a universal prediction model of the char combustion rate; the model was further developed using the shrinking-core model to predict the combustion rate of graphite during the entire reaction process. The result shows that the apparent reaction order is close to zero (0.178). The accuracy of predictions using the aforementioned modified model was found to be improved, and the accuracy of the model, as further developed, is nearly unaffected, indicating that this method of determining n has a broader application potential.

Electroactivity of nanoporous platinum depending on the porosity and potential for various electrode reactions

Electroactivity of nanoporous Pt (npPt) depending on the pore characteristics was studied for various electrode reactions having a range of electrode reaction kinetics: ferrocene oxidation, l-ascorbic acid (AA) oxidation, oxygen reduction reaction (ORR), H2O2 reduction, and glucose oxidation. npPts with two different degrees of the porosities (npPt-1 and npPt-2) were electrodeposited on recessed Pt microdisk electrodes (100-μm diameter), employing deposition solutions in which the composition ratios of Pt precursor, Triton X-100, and lead acetate were varied. npPt-1 has smaller microscale pores than npPt-2. The electroactivities of npPts were analyzed using amperometric sensitivities at mass-transfer-controlled and kinetic-controlled potential regions. Both npPt-1 and npPt-2 increased the sensitivities for all the reactions but reversible ferrocene oxidation remarkably compared to bare Pt. In the kinetic-controlled region, npPt-1 showed more greatly enhanced sensitivity compared to npPt-2 due to the smaller pores exerting more efficient confinement of a reactant near the Pt surface. In mass-transfer controlled region, npPt-2 was beneficial for relatively fast reactions (AA oxidation, ORR); while npPt-1 was advantageous for slower reactions (H2O2 reduction, glucose oxidation). This suggests that the particle-to-particle distance of the npPt affects the electroactivity and an optimum degree of the porosity is different depending on the reaction kinetics.

Electrochemical Oxidation of Borohydride for Direct Fuel Cells

The direct borohydride fuel cell (DBFC) is gaining more and more interest in recent years because of high energy density and the easy handling of liquid fuels. The oxidation of the borohydride anions at the anode delivers up to eight electrons per molecule at a theoretical potential of -1.24 V vs. SHE [1,2]: BH4 - + 8OH- → BO2 - + 6H2O + 8e- In combination with an oxygen cathode and an alkaline membrane or electrolyte an electrochemical cell with a nominal voltage of 1.64 V is formed. The electrochemical oxidation is investigated on various noble metal catalysts such as Pt/C, Au/C and Pd/C and bimetallic alloys thereof with first row transition metals. The electrochemical properties of the catalysts are characterized by cyclic voltammetry in alkaline electrolyte containing NaBH4 in standard three electrode configuration with a rotating disc electrode (RDE) [3]. Figure 1 : Cyclic voltammograms of Pt/C with 5mM NaBH4 on a RDE, anodic sweeps at 200, 400, 600, 900, 1200, 1600 and 2000 rpm. The borohydride oxidation on Pt/C starts at around -50 mV vs. RHE getting diffusion limited at 200 mV vs. RHE with a complete eight electron transfer. Due to diffusion limitation data processing according to Levich and Koutecky-Levich is possible. Figure 2 : Levich plot of Pt/C catalyst at 0.50 V vs. RHE (data from Fig. 1) Figure 3 : Koutecky-Levich plot of Pt/C catalyst at 0.50 V vs. RHE (data from Fig. 1) Levich and Koutecky-Levich (Fig. 2 and 3) analysis show an eight electron transfer reaction at a potential of 0.5 V vs. RHE in the diffusion controlled region and as well at 0.01 V vs. RHE in the kinetic controlled region. Although platinum shows excellent catalytic activity towards borohydride electrooxidation, the main side reaction, namely the hydrolysis reaction is also catalyzed. Besides the loss of fuel, the formation of gaseous hydrogen can harm the electrode due to mechanical stress. This issue can be addressed by replacing platinum with less active catalysts. Gold based electrocatalysts for example do not catalyze the hydrolysis side reaction. On the roadway towards a practicable application it is necessary to improve the selectivity at the anode catalyst system. Acknowledgements Support by NAWI Graz and financial support by the Austrian Federal Ministry of Transport, Innovation and Technology (BMVIT) and The Austrian Research Promotion Agency (FFG) through the program a3plus and the IEA research cooperation is gratefully acknowledged.

Enhanced electrocatalytic activity and stability of PdCo@Pt core–shell nanoparticles for oxygen reduction reaction

The carbon-supported PdCo@Pt core–shell nanoparticles for an oxygen reduction reaction (ORR) were prepared via a two-step process at room temperature. The as-prepared PdCo@Pt/C with an average particle size of ~3.5 nm exhibited a well-defined nanostructure consisting of Pd-rich core and Pt shell formed by displacing Co core with Pt. Compared to pure Pt, PdCo@Pt/C showed a higher current density in the kinetic controlled region and more positive half-wave potential for the ORR. In a cycling stability test of the PdCo@Pt/C electrocatalyst, no remarkable activity loss was seen.

Preparation and cyclic voltammetric dissolution of core–shell–shell Ag–Pt–Ag nanocubes and their comparison in oxygen reduction reaction in alkaline media

An efficient synthesis of core–shell–shell Ag–Pt–Ag nanocubes using Ag nanocubes as reactants was developed. Ag nanocubes were synthesized as seeds; after (NH3)2Pt(NO2)2 was added in situ, the nanocubes underwent epitaxial growth followed by further Ag deposition to form core–shell–shell Ag–Pt–Ag nanocubes. In this study, the successful determination of the core–shell–shell structures of the Ag–Pt–Ag nanocubes by an electrochemical dissolution process was studied. The Ag dissolution was followed by an electrochemical quartz crystal microbalance technique, and hollow Ag–Pt nanocubes were obtained after the third cycle of a cyclic voltammetric method in 0.5 M H2SO4 electrolyte. Additionally, these Ag–Pt–Ag and Ag–Pt nanocubes were used as electrocatalysts in the alkaline oxygen reduction reaction (ORR). Electrochemical measurements were performed using an ultrathin-film rotating ring-disk electrode (RRDE). The mass activities at −0.1 V (vs. Ag/AgCl; within the kinetic control region) in terms of the currents normalized to the Pt mass for the Ag–Pt–Ag and the Ag–Pt nanocubes were 1.08 × 10−3 and 3.3 × 10−3 mA μg−1, respectively. The data supported by RRDE showed approaching 4 electrons and lower HO2− production over Ag–Pt–Ag nanocubes and Ag–Pt nanocubes, implying that the four-electron pathway governed the ORRs for these two catalysts. After 1000 cyclic tests, Ag–Pt–Ag nanocubes with solid interior displayed superior stability in ORR than hollow Ag–Pt nanocubes.

New kinetic model for the rapid step of calcium oxide carbonation by carbon dioxide

Carbonation of solid calcium oxide by gaseous carbon dioxide was monitored by thermogravimetry. A kinetic model of CaO carbonation is proposed in order to interpret the first rapid step of the reaction. By taking into account, the existence of large induction period as well as the sigmoidal shape of the kinetic curves in this kinetic-controlled region, a surface nucleation and isotropic growth kinetic model based on a single nucleus per particle is proposed, and the expressions of the fractional conversion and the reaction rate versus time are detailed. The induction period is found to have a linear variation with respect to temperature and to follow a power law with respect to CO2 partial pressure. The areic reactivity of growth decreases with temperature increase, and increases with CO2 partial pressure increase. A mechanism of CaCO3 growth is proposed to account for these results and to determine a dependence of the areic reactivity of growth on the temperature and the CO2 partial pressure.

Cornered silver and silver[sbnd]platinum nanodisks: Preparation and promising activity for alkaline oxygen reduction catalysis

A simple method for the efficient synthesis of cornered Ag and AgPt nanodisks by using triangular Ag nanoplates as reactants has been developed. The triangular Ag nanoplates are heated and reshaped to spherical nanodisks; in turn, through the introduction of PtCl42− ions, the spherical nanodisks undergo sculpturing and a subsequent displacement reaction to form cornered Ag nanodisks and AgPt nanodisks with pores. The selected-area electron diffraction pattern shows that the cornered Ag nanodisks are composed of two basal Ag (111) planes, thus indicating the occurrence of selective etching on the spherical nanodisks by this method. The analyses provided by X-ray diffraction spectroscopy and line-scanned energy-dispersive spectroscopy confirm the compositions of these cornered nanodisks and the mixed alloy in the Ag–Pt nanodisks. For the investigation of the practical feasibility of the application of the proposed method, these cornered Ag and AgPt nanodisks were then used as methanol-tolerant electrocatalysts in the alkaline oxygen reduction reaction (ORR). Electrochemical measurements were performed using an ultrathin-film rotating ring-disk electrode. The two types of nanodisks are found to have high stabilities and improved activities in 1M NaOH electrolyte. In the electrolyte with free methanol, the mass activities at −0.1V (vs. Ag/AgCl; within kinetic control region) in terms of the currents normalized to Ag mass for the Ag nanodisks and AgPt nanodisks are 6.98×10−4 and 2.01×10−3mAμg−1, respectively, which are greater than the value of 2.09×10−4mAμg−1 for Ag nanoparticles. The order in terms of the ORR activity is found to be as follows: cornered AgPt nanodisks>cornered Ag nanodisks>Ag nanoparticles. Additionally, in the presence of methanol, all the cornered nanodisk catalysts experience cathodic currents, indicating that the ORR occurs despite the use of a methanol solution.

Oxygen reduction reaction catalyzed by ɛ-MnO2: Influence of the crystalline structure on the reaction mechanism

The oxygen reduction reaction (ORR) was studied in KOH electrolyte on carbon supported epsilon-manganese dioxide (ɛ-MnO2/C). The ɛ-MnO2/C catalyst was prepared via thermal decomposition of manganese nitrate and carbon powder (Vulcan XC-72) mixtures. X-ray powder diffraction (XRD) measurements were performed in order to determine the crystalline structure of the resulting composite, while energy dispersive X-ray analysis (EDX) was used to evaluate the chemical composition of the synthesized material. The electrochemical studies were conducted using cyclic voltammetry (CV) and quasi-steady state polarization measurements carried out with an ultra thin layer rotating ring/disk electrode (RRDE) configuration. The electrocatalytic results obtained for 20% (w/w) Pt/C (E-TEK Inc., USA) and α-MnO2/C for the ORR, considered as one of the most active manganese oxide based catalyst for the ORR in alkaline media, were included for comparison. The RRDE results revealed that the ORR on the MnO2 catalysts proceeds preferentially through the complete 4e− reduction pathway via a 2 plus 2e− reduction process involving hydrogen peroxide as an intermediate. A benchmark close to the performance of 20% (w/w) Pt/C (E-TEK Inc., USA) was observed for the ɛ-MnO2/C material in the kinetic control region, superior to the performance of α-MnO2/C, but a higher amount of HO2− was obtained when ɛ-MnO2/C was used as catalyst. The higher production of hydrogen peroxide on ɛ-MnO2/C was related to the presence of structural defects, typical of this oxide, while the better catalytic performance in the kinetic control region compared to α-MnO2/C was related with the higher electrochemical activity for the proton insertion kinetics, which is a structure sensitive process.

First-principles based microkinetic modeling of borohydride oxidation on a Au(1 1 1) electrode

Borohydride oxidation electrokinetics over the Au(1 1 1) surface are simulated using first-principles determined elementary rate constants and a microkinetic model. A method to approximate the potential dependent elementary step activation barriers based on density functional theory calculations is developed and applied to the minimum energy path for borohydride oxidation. Activation barriers of the equivalent non-electrochemical reactions are calculated and made potential dependent using the Butler–Volmer equation. The kinetic controlled region of the borohydride oxidation reaction linear sweep voltammogram over the Au(1 1 1) surface is simulated. The simulation results suggest that B–H bond containing species are stable surface intermediates at potentials where an oxidation current is observed. The predicted rate is most sensitive to the symmetry factor and the BH 2OH dissociation barrier. Surface-enhanced Raman spectroscopy confirms the presence of BH 3 as a stable intermediate.

Coal gasification in CO2 atmosphere and its kinetics since 1948: A brief review

Numerous coal gasification studies have been found in the literature those employed various kinds of gasifying agents such as steam and carbon dioxide. These studies are featured with wide variations in the parametric conditions and the usage of equipments. Steam is frequently employed as a gasifying agent, however, in several studies carbon dioxide has also been used as a gasifying agent either pure or in combination with other gasifying agents (H2O, O2, CO, H2). This paper is a brief review of the coal gasification with CO2 as a diluent. Different factors were studied over the coal gasification with CO2 such as coal rank, pressure, temperature, gas composition, catalyst and the minerals present inside the coal, heating rate, particle size, and diverse reactor types. It also deals with the application of the gas–solid models developed in the literature and the combustion and gasification mechanisms for O2/CO2 streams. Moreover, it reviews the kinetics and the reaction rate equations (Arrhenius and Langmuir–Hinshelwood types) for coal-char gasification both in the reaction kinetic control region (low temperature) and the diffusion control region (high temperature) and at both low and high pressures.

Exactly solvable many-particle model of bulk recombination of coupled radical pairs with allowance for singlet–triplet transitions

We have considered a many-particle problem with irreversible bulk recombination of coupled radical pair induced by arbitrary long-range reactive interaction with B reactants residing in the presence of singlet–triplet transitions caused by external magnetic field. If a coupled radical pair is at rest, while B reactants move by stochastic jumps, a many-particle description of the reaction system is given on the level of the Liouville equation for the density matrix. The propagator of the Liouville equation is reduced to that of some integro-differential equation defining all many-particle effects. For the deduced integro-differential equation describing all many-particle effects of the reaction system under discussion the solution in the form of the Neumann series is constructed. In kinetic control region the exact summation of the series has been made, and the analytical expression of the kinetics has been derived. It is shown that this expression coincides with the solution of kinetic equations of traditional approach in the context of the perturbation theory. The decay kinetics of a coupled radical pair is calculated for small concentration of B reactants by binary scaling procedure with allowance for principal order only. This kinetics is shown to coincide with the solution of the kinetic equation derived on the basis of the law of mass action of formal chemical kinetics.

Kinetics of Brassica carinata Oil Methanolysis

A study was made of the kinetics of Brassica carinata oil methanolysis. This reaction yields fatty acid methyl esters and glycerol and consists of three consecutive reversible reactions. Diglycerides and monoglycerides are intermediate products. The mechanism of B. carinata oil methanolysis involves an initial stage of mass-transfer control, followed by a second region of kinetic control. However, the initial mass transfer-controlled step is negligible using an impeller speed of at least 600 rpm. The experiments were performed in a batch reactor stirred at 600 rpm over 2 h using potassium hydroxide as the catalyst at atmospheric pressure with a 6/1 molar ratio of methanol to B. carinata oil. The resultant mixture was analyzed by gas chromatography. The effects of temperature and catalyst concentration on the reaction rates were analyzed, determining the reaction rate constants and the activation energies. The B. carinata oil methanolysis can be described as a pseudo-homogeneous catalyzed reaction system, ...

Kinetic characteristics of catalytic reactions of CO, HC and NOx on different three-way catalysts

The kinetic characteristics of CO, HC and NOx reaction on different kinds of three way catalysts (TWC) has been investigated by using a fixed bed reactor. It was concluded that the three-way reaction on noble metal catalysts is controlled by internal diffusion at high space velocity 16×104 h−1. On non-noble metal catalysts internal diffusion control prevails at space velocities (S.V.) 4×104 h−1. On non-noble metal catalysts containing a small amount of a noble metal, the kinetic control region of the three-way reaction shifts to higher space velocity.