Langmuir Hinshelwood Approach Research Articles

Redundancy-Free Models for Mathematical Descriptions of Three-Phase Catalytic Hydrogenation of Cinnamaldehyde

A new approach on how to formulate redundancy-free models for mathematical descriptions of three-phase catalytic hydrogenation of cinnamaldehyde is presented. An automatically created redundant (generalized) model is formulated according to the complete reaction network. Models based on formal kinetics and kinetics concerning the Langmuir-Hinshelwood theory for three-phase catalytic hydrogenation of cinnamaldehyde were investigated. Redundancy-free models were obtained as a result of a step-by-step elimination of model parameters using sensitivity and interval analysis. Starting with 24 parameters in the redundant model, the redundancy-free model based on the Langmuir-Hinshelwood mechanism contains 6 parameters, while the model based on formal kinetics includes only 4 parameters. Due to less degrees of freedom of molecular rotation in the adsorbed state, the probability of a direct conversion of cinnamaldehyde to 3-phenylpropanol according to the redundancy-free model based on Langmuir-Hinshelwood approach is practically negligible compared to the model based on formal kinetics.

Gas-Phase TiO2 Photosensitized Mineralization of Some VOCs: Mechanistic Suggestions through a Langmuir–Hinshelwood Kinetic Approach

A jointed experimental and theoretical investigation pointing out new insights about the microscopic mechanism of the volatile organic compounds (VOCs) photocatalytic elimination by TiO2 was done. Methane, hexane, isooctane, acetone and methanol were photomineralized in a batch reactor. Values of K (adsorption constant on TiO2) and k (mineralization rate constant) of the five VOCs (treating the kinetic data through a Langmuir–Hinshelwood approach) were determined. Recorded K (in the range of 0.74 × 10−2–1.11 × 10−2 ppm−1) and k (in the range of 1.9–9.9 ppm min−1) values and performed theoretical calculations allowed us to suggest the involvement of an electron transfer step between the VOC and the hole, TiO2(h+), as the rate-determining one.

Selective hydrogenation of oxalic acid to glycolic acid and ethylene glycol with a ruthenium catalyst

The hydrogenation of the oxalic acid was evaluated with a ruthenium micro-mesoporous catalyst (5 wt%/activated carbon, 710 m2 g−1, 0.39 cm3 g−1), at 120 °C–150 °C under 80.0 bar in a slurry reactor, for the development of glycolic acid and ethylene glycol productions. The kinetic behavior of the process based on a surface mechanism was established according to the Langmuir–Hinshelwood approach. The mass balance equations fitted to the experimental data provided orders of magnitude for the specific reaction rates, reaching 1.93 × 10–1 h−1 for the hydrogenation of oxalic acid into glycolic acid at 130 °C and 2.51 × 10–2 h−1 for the production of volatile products at 150 °C. The kinetic selectivities under these conditions, 130 °C and 150 °C, were circa 70% for the production of glycolic acid, while for the volatile compounds was reached 87%.

Catalytic reduction of U(VI) with hydrazine using Pt/SiO2 catalyst in nitric acid medium—kinetics and equilibrium

Kinetics of catalytic reduction of uranyl species, U(VI) to U(IV) with hydrazine nitrate was studied over Pt/SiO2 catalyst in nitric acid medium. Experiments were carried out in a stainless-steel autoclave as a function of mixing intensity, temperature, catalyst loading and concentration of nitric acid, hydrazine and uranium. Langmuir–Hinshelwood approach was considered to derive various model equations and each of them was evaluated. Results of the present study indicated that catalytic reduction of U(VI) can be described by surface reaction between adsorbed molecules. The activation energy of the reaction was calculated to be 74.5 kJ/mol, suggesting a chemical reaction controlled process.

Fabrication of palladium and platinum nanocatalysts stabilized by polyvinylpyrrolidone and their use in the hydrogenolysis of methyl orange

Following the thermal reductive method, the synthesis of nanoparticles stabilized by polyvinylpyrrolidone was performed using ethylene glycol as a reductant and solvent. The PVP-capped platinum and palladium were well-dispersed and stable for more than 3 months, and their average sizes were 2.53 ± 0.07 nm and 4.13 ± 0.14 nm. By means of inductively coupled plasma mass spectroscopy (ICP-MS) analysis, the amount of colloidal metal nanoparticles was found to be 6.38 wt% and 5.93 wt% for platinum and palladium, respectively. The PVP-capped Pt and Pd nanocatalysts were evaluated for the hydrogenolysis of azo dyes using methyl orange as a model compound in the presence of borohydride as a reductant. Substrates adsorption on the nanocatalysts surface constituted the rate-determining step of the catalytic reduction. The Langmuir–Hinshelwood approach was applied to interpret the interface interaction between nanocatalyst and substrates. The activation energy was 65.70 ± 4.49 kJ mol−1 and 89.27 ± 2.12 kJ mol−1 using Pt and Pd nanocatalysts, respectively.

The reaction kinetics of CO2 methanation on a bifunctional Ni/MgO catalyst

A bifunctional Ni/MgO catalyst was prepared to catalyze CO2 methanation and make use of CO2 as an abundant hydrogen storage facility. The effect of Ni loading and MgO quality on the rate of methanation was tested in a temperature range of 533–648K. The Ni loading was varied between 0 to 27wt.% on MgO. To investigate the impact of matrix elements, a MgO/CaO support was tested with 21wt.% nickel loading. Further, the role of MgO in the bifunctional catalyst was proven. The reaction kinetics was modeled with a Langmuir–Hinshelwood approach considering the bifunctional character of the catalyst. Nickel provides the adsorbent capacity for hydrogen and is highly selective for methane. MgO activates CO2 through chemisorption. Increasing Ni loading of the catalyst increased the rate of CO2 conversion. According to the results, the mechanism of CO2 methanation did not change with Ni loading. The Ni/MgO catalyst acted as a robust, active and highly selective catalyst for CO2 methanation. With CO2 conversion of 87%, the selectivity to methane was ≥99%. Besides excellent catalytic activity the catalysts suffice the necessity of simple catalyst preparation, usage and recyclability for industrial applicability of CO2 methanation.

Synthesis and Characterization of N- Doped ZnO-γAl2O3 Nanoparticles for Photo-catalytic Application

Abstract In this study, photo-catalytic degradation of methyl orange (MO) azo dye was examined by undoped and Ce2O3/ CuO/ N doped ZnO nanoparticles stabilized on γAl2O3. Highest photo-catalytic activity was observed for the N-doped 10 wt. % ZnO-γAl2O3 sample. One of the optimal points with the complete MO decomposition was determined at an initial concentration of 8.25 ppm, pH 3.25, catalyst loading of 0.36 g/L and 12.56 W UV-light irradiation after 120 min. Physical and chemical properties of materials were investigated by X-ray diffraction analysis (XRD), Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) and UV–visible diffuse reflectance spectroscopy (DRS) method. The experimental data were best fitted by a Langmuir-Hinshelwood approach photo-catalysis developed kinetic reaction rate in the form of − r = 0.2797 I 0.5 [ C a t . ] 0.5 [ D y e ] / 1 + 0.1079 [ D y e ] 0 + 0.4086 I 0.5 [ C a t . ] 0.5 $- r = 0.2797\, {I^{0.5}}\, {[Cat.]^{0.5}}\, \, [Dye]{\text{ }}/\, \, \, 1 + 0.1079\, {[Dye]_0}\, + \, 0.4086\, {I^{0.5}}\, {[Cat.]^{0.5}}$ .

A kinetic model for the photocatalytic reduction of CO2 to methanol pathways

Carbon dioxide (CO2) is one of the greenhouse gases that contribute to global warming. CO2 could be converted to valuable products such as hydrocarbons through the photocatalytic process. The aim of this research was to develop the kinetic model for the photocatalytic reduction of CO2 to methanol (CH3OH) in liquid phase reaction using cerium oxide-titanium dioxide (CeO2-TiO2) catalyst. The Langmuir-Hinshelwood approach was used in developing rate laws for the catalytic reaction using the catalytic reaction mechanism proposed. The catalytic reaction mechanism is about the adsorption of reactant (CO2 dissolved in the liquid phase), the reaction on catalyst surface and desorption of product. The experimental kinetic data were evaluated in the Polymath 6.1 software. In this study, two types of mechanism are proposed whereas one is considered the carbon monoxide (CO) oxidation while the other is not. Based on the model fitting, it was found that the model considers the CO oxidation is fitted well with the experimental data represents that the oxidation reaction of intermediate product, CO is the rate-determining step in the photocatalytic reduction of CO2 to CH3OH in liquid phase reaction.

Synthesis of Ethyl Phenol over Modified HZSM-5 Catalyst in a Fixed Bed Reactor

Abstract The selective synthesis of p-ethyl phenol in vapor phase alkylation of phenol with ethanol was investigated in a fixed bed flow reactor on cerium modified zeolite CeZSM5 at temperature 693 K. A series of cerium modified zeolite such as Ce4ZSM54, Ce6ZSM56, Ce8ZSM58, Ce10ZSM5 were prepared by modifying with 4 %, 6 %, 8 % and 10 % ceric ammonium nitrate solution respectively. HZSM-5 zeolite exchanged with 10 % cerium nitrate solution was proved to be the best of all the catalyst used. The modified catalyst was further characterized by SEM, XRD and EDS. Phenol reacted with ethanol to form ethylphenyl ether by O-alkylation, and p-ethylphenol- and o-ethylphenol isomers by C-alkylation; secondary products were m-ethylphenol and dialkylated compounds. Reactions were carried out in the temperature 623 K–693 K, reactant mole ratio 0.2–0.5 over modified HZSM-5 zeolite. The optimum operating condition for maximum selectivity of p-ethyl phenol were EtOH to phenol mole ratio, 4:1; temperature, 623 K; space-time, 10.2 kg h/kmol and 1 atm pressure. A detailed kinetic study was carried out for the ethyl phenol synthesis reaction. From the product distribution pattern, a kinetic model for the reactions was proposed following the Langmuir–Hinshelwood approach. The kinetic and adsorption parameters of the rate equation were determined by non-linear regression analysis. From the kinetic analysis of the experimental data, the apparent activation energy for the reaction was determined as 43.27 kJ/mol.

Simulation and multi‐objective optimization of a fixed bed catalytic reactor to produce hydrogen using ethanol steam reforming

A mathematical model is developed for a fixed bed catalytic reactor to produce hydrogen using ethanol steam reforming in the presence of a Ni (II)-Al (III)-LDH catalyst. The simulation of the reactor has been carried out using the ode23s module of MATLAB (version 2010a) based on a mechanistic kinetic model (Langmuir-Hinshelwood approach) with proven reaction kinetics. There is a confusion regarding the values of the kinetic parameters even though earlier workers have used the same experimental data and the same model equations. The values of the model parameters obtained using two different curve-fitting techniques, the generalized reduced gradient (GRG) algorithm and a derivative-free approach based on the simplex method, were different. This leads to differences in the agreement of model predictions vs experimental results. A more powerful and recent technique, genetic algorithm (GA), has been used to resolve this problem by minimizing a sum-of-square errors (SSE). Our tuned model parameters gave good agreement with experimental data. An SSE value of the order of 10−4 is obtained in the present study over the SSE values of the order of 10−2 obtained from earlier studies. Using this tuned model, multi-objective optimization (MOO) of an isothermal fixed bed ESR reactor has been carried out using NSGA-II to achieve the maximum hydrogen mole fraction in the product gas while simultaneously minimizing the mole fractions of the greenhouse gases, CO + CO2. The maximum theoretical mole fraction of hydrogen obtained is 0.088 at 911.86 K vs 0.080 at 923 K, as observed experimentally. The more recent jumping gene adaptation of NSGA-II, namely, NSGA-II-JG, was also tried to check if it can give more rapid convergence to the Pareto set. It is found that the present problem is far too simple, and the advantage of the JG adaptation is small.

Kinetics and Reactor Design Aspects of Selective Methanation of CO over a Ru/γ-Al2O3 Catalyst in CO2/H2 Rich Gases

Polymer electrolyte membrane fuel cells (PEMFCs) for household applications utilize H2 produced from natural gas via steam reforming followed by a water gas shift (WGS) unit. The H2-rich gas contains CO2 and small amounts of CO, which is a poison for PEMFCs. Today, CO is mostly converted by addition of O2 and preferential oxidation, but H2 is then also partly oxidized. An alternative is selective CO methanation, studied in this work. CO2 methanation is then a highly unwanted reaction, consuming additional H2. The kinetics of CO methanation in CO2/H2 rich gases were studied with a home-made Ru catalyst in a fixed bed reactor at 1 bar and 160–240 °C. Both CO and CO2 methanation can be well described by a Langmuir Hinshelwood approach. The rate of CO2 methanation is slow compared to CO. CO2 is directly converted to methane, i.e., the indirect route via reverse water gas shift (WGS) and subsequent CO methanation could be excluded by the experimental data and in combination with kinetic considerations. Pore diffusion may affect the CO conversion (>200 °C). The kinetic equations were applied to model an adiabatic fixed bed methanation reactor of a fuel cell appliance.

A Review of Dendrimer-Encapsulated Metal Nanocatalysts Applied in the Fine Chemical Transformations

In catalysis, metal nanocatalyst size and stability are crucial parameters directly connected to the catalytic activity. Dendrimers consist of one of the relevant templates capable of encapsulating smaller metal nanocatalysts with the size dimension ranging from 1 to 5 nm. Metal nanocatalysts encapsulated in dendrimer describe a long physical stability estimated to more than 2 months. The innovative physicochemical properties exhibited by metal nanocatalysts tremendously improve the rate constants of redox model reactions. The catalytic pathway by which a catalytic reaction proceeds in the presence of nanocatalysts can be detailed by the means of adsorption isotherm models. The Langmuir–Hinshelwood approach constitutes a reliable the adsorption isotherm model capable of studying the kinetic and thermodynamic parameters on the nanocatalyst surface. The use of dendrimer as a metal nanocatalyst template plays an essential role in both metal stability and shift from homogeneous to heterogeneous nanocatalysts.

CO2 methanation over Ni/Al hydrotalcite-derived catalyst: Experimental characterization and kinetic study

The catalytic performance of a Ni/Al hydrotalcite derived catalyst for CO2 methanation was analysed under different operating conditions. The as synthesized sample has been characterized through atomic adsorption spectroscopy (AAS) X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) analysis, temperature programmed reduction (TPR) and CO chemisorption. Experimental investigation was carried out at atmospheric pressure by varying the reactor bed temperature (within the range 270–390 °C), the H2/CO2 feed ratio and the reactant flow rate. The impact of methanation products on the reaction rate was also analysed by co-feeding reactants with steam and methane. Stability tests were also performed, showing a good catalytic performance of the hydrotalcite-derived catalyst over time. Different kinetic rate expressions were then developed starting from experimental results. Power law, power law with an inhibition term and Langmuir-Hinshelwood (LH) approach were tested and compared. The methanation reaction was first modelled by considering the Sabatier reaction. Then, the reverse water-gas shift (RWGS) was also added to account for the presence/formation of CO. A nonlinear regression analysis was performed with the aim of finding kinetic parameters values allowing the minimization of the discrepancy between measured and calculated values of the CH4 yield (or CO2 conversion). Results showed a better fitting of experimental data by using the LH expression and the power law (with inhibition influence of adsorbed water or hydroxyl). Main transport criteria were finally checked to evaluate whether operating conditions have been chosen properly in order to study the intrinsic reaction kinetics.

Surface Modification of Nanocrystalline Zeolite X and Its Application as Catalyst in Synthesis of Cumene in a Packed Bed Flow Reactor: A Kinetic Study

AbstractIn the present investigation, synthesis of cumene by transalkylation of 1, 4 DIPB with benzene was studied over cerium modified nano crystalline zeolite X in a fixed bed plug flow reactor. Nano crystalline zeolite X was synthesized and characterized by XRD, SEM, TPD, EDS and FTIR. A series of nanocrystalline zeolite X (MX4, MX6, MX10) modified with ceric ammonium nitrate of different concentrations (4 %, 6 %, 10 %) was used for synthesis of cumene. MX10zeolite was proved to be the most active catalyst over which 27.12 % yield of cumene was obtained at temperature 553K, benzene/1, 4 DIPB mole ratio of 7.5 and space time-10.54 kg h/kmol. Reduction of crystal size (100–500 nm) in MX10increases surface area (633m2/gm) and thereby increases cumene yield. A kinetic rate equation was developed from the product distribution pattern following Langmuir–Hinshelwood approach. Kinetic parameters were estimated by nonlinear regression analysis. The activation energy for transalkylation and isomerisation reaction was found to be 88.86 kJ/mol and 99.04 kJ/mol respectively.

Isothermic adsorption of morin onto the reducible mesoporous manganese oxide materials surface

A series of mesoporous manganese oxide materials were synthesized following the inverse micelle sol-gel method and categorized by the heat treatment. The tunable features and crystallinity of the mesoporous materials were analyzed by BET and XRD analyses. The HR-TEM and TRP analyses were conducted to analyze the meso-ordered structure and reducibility of the mesoporous manganese oxide materials. The catalytic activity of the mesoporous materials was investigated in aerobic oxidation of morin as a model reaction. The experimental data were interpreted according to the Mars-van Krevelen and Langmuir-Hinshelwood approach. The heat treatment influenced the crystallite size and the activity of the mesoporous manganese oxide materials. The activity of the lattice oxygen was a critical factor in the aerobic process. MnO2–350°C exhibited the largest lattice oxygen activity ((64.3±5.6)×kJmol−1m−2).

The Langmuir-Hinshelwood approach for kinetic evaluation of cucurbit[7]uril-capped gold nanoparticles in the reduction of the antimicrobial nitrofurantoin.

In this work, gold nanoparticles protected by the macrocycle cucurbit[7]uril were used as a catalyst in the reduction of the hazardous antimicrobial nitrofurantoin. 4-Nitrophenol was also employed as the substrate of the reduction for comparative purposes. The kinetic data were modeled to the Langmuir-Hinshelwood equation to know the affinities of the reactants for the surface and the real kinetic constants, a comparison at the molecular level that is made for the first time. From the results, it was observed that the adsorption of nitrofurantoin was stronger than that of 4-nitrophenol whilst the kinetic constant on the surface was higher for 4-nitrophenol than for nitrofurantoin. Additionally, shifts in the nanoparticle surface plasmon band permitted insights to be obtained into the adsorption rate and strength. The reaction induction times were also investigated and were highly dependent on the borohydride concentration and, due to the higher surface affinity of nitrofurantoin compared with 4-nitrophenol, an increase in nitrofurantoin concentration increased the induction time, while a lag phase was not observed for 4-nitrophenol.

SYNTHESIS OF CUMENE BY TRANSALKYLATION OVER MODIFIED BETA ZEOLITE: A KINETIC STUDY

Abstract In the present study, transalkylation of 1,4-diispropylbenzene (DIPB) with benzene in the presence of modified beta zeolite was performed to produce cumene in a fixed bed reactor. Beta zeolite was exchanged with cerium in order to modify its catalytic activity. Activity of the modified catalyst was evaluated in the range of temperature 493K-593K, space time 4.2 kg h/kmol-9.03 kg h/k mol and benzene/1,4-DIPB molar ratio 1-15 to maximize the reactant conversion and selectivity of cumene. The activity and selectivity of the modified catalyst was found to increase with increase in cerium loading. Maximum selectivity of cumene (83.82%) was achieved at 573 K, benzene/1,4-DIPB 5:1 at one atmosphere pressure. A suitable kinetic model for this reaction was proposed from the product distribution pattern following the Langmuir-Hinshelwood approach. Applying non-linear regression, the model parameters were estimated. The activation energy for the transalkylation reaction was found to be 116.53 kJ/mol.

Catalytic and kinetic investigation of the encapsulated random alloy (Pdn-Au110-n) nanoparticles

Generation six hydroxyl terminated PAMAM dendrimer was used as template for the synthesis of several palladium-gold random alloy nanoparticles. The synthesis process was monitored using UV–spectroscopy. The microscopy image of the alloy nanoparticles was captured by transmission electron microscopy and their average size was compared to the theoretical value. Catalytic oxidation of morin by hydrogen peroxide was performed to investigate the activity of the alloy nanoparticles. The Langmuir–Hinshelwood approach was used to conduct a full kinetic evaluation of the catalytic process. The catalytic activity exhibited by the alloy nanoparticles demonstrates a proportional increase with the relative palladium amount. The encapsulated alloy and mono metal nanoparticles remained narrowly dispersed after the reaction.

Mechanistic Kinetic Modeling of Oxidative Steam Reforming of Bioethanol for Hydrogen Production over Rh–Ni/CeO2–ZrO2 Catalyst

A kinetic study was carried out over Rh–Ni/CeO2–ZrO2 catalyst for the oxidative steam reforming of ethanol (OSRE). A Langmuir–Hinshelwood approach based on proposed surface reaction mechanisms was used to develop the kinetic models for the OSRE process. Oxidative steam reforming (OSRE), ethanol decomposition (ED), and water–gas shift (WGS) reactions were considered as the main reaction pathway to represent the overall OSRE process. Kinetic data were collected in a fixed bed reactor under the kinetic-control regime at three different temperatures. The kinetic parameters were estimated using a nonlinear regression method. The kinetic model was developed by considering dehydrogenation of adsorbed ethoxy species, decomposition of formate species, and decomposition of acetaldehyde as the rate-determining step for OSRE, WGS, and ED reactions, respectively. The developed model fitted well with the experimental observations at all studied temperatures and contact time. The activation energy for OSRE, WGS, and ED ...

Catalytic oxidation of methylene blue by dendrimer encapsulated silver and gold nanoparticles

The catalytic oxidation of methylene blue was investigated in the presence of dendrimer generation five terminated NH2 encapsulated silver (AgDENs), and gold (AuDENs) nanoparticles as catalyst. The synthesis process of encapsulated metal nanoparticles were monitored by UV/vis spectrophotometry and their average diameters determined by transmission electron microscopy analysis, respectively. The kinetics was monitored using UV/vis spectrophotometry, under pseudo-first order conditions, resulting in observed rate constants kobs. Langmuir–Hinshelwood approach was applied to model the kinetic process. The adsorption of methylene blue on the catalyst surface is related to the type of metal nanoparticle present, and presents the rate-determining step.