Langmuir Hinshelwood Hougen Watson Mechanism Research Articles

Kinetics, Model Discrimination, and Parameters Estimation of CO2 Methanation on Highly Active Ni/CeO2 Catalyst

The reaction kinetics of CO2 methanation over a highly active 8.5% Ni/CeO2 catalyst was determined in a fixed-bed reactor, in the absence of heat- and mass-transfer limitations. Once the catalyst activity was stabilized, more than 120 kinetic experiments (with varying values of reaction temperature, total pressure, space velocity (GHSV), and partial pressure of products and reactants) were performed. From initial reaction rates, an apparent activation energy of 103.9 kJ mol–1 was determined, as well as the effect of reactants (positive) and water partial pressures (negative) on CO2 methanation rate. Three mechanistic models reported in the literature, in which CO2 is adsorbed dissociatively (carbon and formyl routes) or directly (formate route), were explored for modeling the entire reaction kinetics. For that, the corresponding rate equations were developed through the Langmuir–Hinshelwood–Hougen–Watson (LHHW) approach. In agreement with DRIFTS experiments, formate route, in which the hydrogenation of bicarbonate to formate is considered to be the rate-determining step, reflects the kinetic data accurately, operating from differential conversion to thermodynamic equilibrium. In fact, this mechanism results in a mean deviation (D) of 10.38%. Based on previous own mechanistic studies, the participation of two different active sites has been also considered. Formate route on two active sites maintains a high fitting quality of experimental data, providing kinetics parameters with a higher physical significance. Thus, the LHHW mechanism, in which Ni0 sites as well as oxygen vacant near to Ni-CeO2 interface participate in CO2 methanation, is able to predict the kinetics of Ni/CeO2 catalyst accurately for a wide range of operational conditions.

Study of mechanism and kinetic modeling of CO hydrogenation reaction over the impregnated Co‐Ni/Al2O3 catalyst

AbstractAn investigation of the kinetic and mechanism of CO hydrogenation reaction was performed on impregnated Co‐Ni/Al2O3. Determination of kinetic parameters from the experiments was carried out in a micro fixed‐bed reactor. Kinetic evaluations were performed under various operational conditions of T = 473–673 K, p = 1–14 bar, H2/CO = 1–3, and GHSV = 4,500 hr−1. Kinetic models and rate equations for CO consumption were obtained by using two main‐type rate equations of Langmuir‐Hinshelwood‐Hougen‐Watson (LHHW) and Eley‐Rideal (ER). Estimation of various kinetic parameters was performed using a nonlinear regression method. According to the obtained experimental results and using statistical criteria, one kinetic expression based on the LHHW mechanism (‐rCO = kp.bCO.PCO. bH2. PH2/[1+ bCO.PCO + bH2.PH2]2) was chosen as the best‐fitted model. For this fitted model, the activation energy was found to be 109.2 kJ/mol. Characterization of the catalyst was also performed using X‐ray diffraction (XRD), BET, scanning electron microscopy (SEM), and energy‐dispersive x‐ray spectrometer (EDS) techniques.

Single-Step Hydrogenolysis of Furfural to 1,2-Pentanediol Using a Bifunctional Rh/OMS-2 Catalyst.

Hydrogenolysis of biomass-derived furfural (FFA) to 1,2-pentanediol (1,2-PeD) was investigated using a bifunctional catalyst with basic and metallic sites, which was synthesized by the hydrothermal method. The synthesized catalyst consisting of rhodium (Rh) supported on an octahedral molecular sieve (OMS-2) of different loadings, such as 0.5, 1, and 1.5% w/w, was studied, and 1% (w/w) loading gave the best results. This 1% w/w Rh/OMS-2 catalyst showed excellent catalytic activity and selectivity for the hydrogenolysis reaction because of better dispersion of rhodium, later revealed by characterization. Furthermore, 1% Rh/OMS-2 catalyst was well characterized in virgin and reused states using various techniques such as Fourier-transform infrared spectroscopy, NH3-temperature-programmed desorption (TPD), CO2-TPD, temperature-programmed reduction, H2 pulse chemisorption, scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, Brunauer–Emmett–Teller surface area, X-ray photoelectron spectroscopy, Raman spectroscopy, and differential scanning calorimetry–thermogravimetry analysis. The catalyst showed a higher surface area of 72 m2/g and the average size of the highly dispersed Rh metal of ∼2 nm. The studies were performed in a batch reactor; the catalyst offered almost 100% conversion of FFA with 87% selectivity to 1,2-PeD at 160 °C and 30 atm hydrogen pressure in 8 h. The reaction mechanism and kinetic model have been developed using a dual-site Langmuir–Hinshelwood–Hougen–Watson mechanism. The activation energies were 12.3 and 27.6 kcal/mol, correspondingly. The catalyst was found to be active, selective, and reusable.

Correction to: Heterogeneous cycloaddition of styrene oxide with carbon dioxide for synthesis of styrene carbonate using reusable lanthanum–zirconium mixed oxide as catalyst

Development of environmentally benign green processes for utilization of carbon dioxide to synthesize value-added compounds using heterogeneous catalysis is desirable. One such proposed process is the cycloaddition of styrene oxide with carbon dioxide to synthesize styrene carbonate, synthesis of which has been well studied using various homogenous catalysts. The aim of the current work was to develop an active, selective and reusable heterogeneous catalyst for the cycloaddition of carbon dioxide to styrene oxide. Various solid catalysts such as 0.1% Li/MgO, calcined hydrotalcite (CHT), La–Zr mixed oxide (1:3 La/Zr), 0.1% La/MgO and ZrO2 were employed for cycloaddition of carbon dioxide to styrene oxide. Carboxylation of styrene oxide with carbon dioxide is enhanced by catalysts having both strong basic sites and weak acidic sites. Lanthanum–zirconia mixed oxide was prepared by combustion method using different compositions and evaluated for this reaction. La/Zr ratio of 1:3 was found to be the best among all studied and gave 90% conversion of styrene oxide with 100% selectivity of styrene carbonate at moderate temperature and pressure conditions in 3 h. The catalyst was characterized by various techniques to understand its textural properties. The catalyst was reused over three cycles without any loss of activity. The optimum reaction conditions were obtained by studying all process parameters in a laboratory batch stirred tank reactor (speed of agitation-1000 rpm, catalyst loading-2 × 10−2 g/cm3, 0.01 mol styrene oxide, DMF as solvent (total volume 30 mL), CO2 pressure-2.5 MPa, 130 °C). A detailed mathematical model was developed using Langmuir–Hinshelwood-Hougen–Watson mechanism in the absence of any transport resistances. The activation energy was calculated as 19.1 kcal/mol. The process is green and clean.

Kinetic and reactor performance of a Ni-based catalyst during the production of ethene

ABSTRACTSteam cracking of diverse hydrocarbon sources is nowadays the main technology used to produce ethene worldwide, however, it presents energetic and environmental limitations related to the large consumption of energy and production of carbon oxides. To overcome this, industry and academy have aimed their research at developing a new technology based on the oxidative dehydrogenation (ODH) of ethane. Main challenges for its industrial implementation are yet catalyst and industrial reactor design. In this sense, Ni based catalysts have been promising materials for the production of ethene out of ethane at laboratory scale, however there is a scarce amount of researching on engineering aspects related to the evaluation of their performance at industrial scale. This work is aimed at giving insights on the performance of a Ni-loaded Y zeolite catalyst (Ni/KY) during the ethene production via ODH of ethane in an industrial-scale wall-cooled fixed bed catalytic reactor with a low dt/dp. To achieve this, an industrial reactor model that couples reaction kinetics to heat and mass transport phenomena is developed following reactor engineering fundamentals. To assess the kinetics of the ODH of ethane over the aforementioned catalyst, a detailed kinetic model is developed using published experiments [J. Catal. 265 (2009) 54–62]. Then, this kinetics is coupled to the industrial-scale reactor model, a 2D heterogeneous model accounting for heat and mass transport. The kinetic model following a Langmuir–Hinshelwood–Hougen–Watson mechanism allows an accurate description of laboratory data. Activation energy, related to the formation of ethene, and enthalpy adsorption of ethene indicate that the production ethene is favored at larger reaction temperatures, however, once it is produced, this olefin is more strongly adsorbed on the catalyst surface than the other byproducts. However, from the parametric sensitivity study applied to the industrial reactor, a larger coolant temperature brings out a significant but positive effect on the yield of ethene whereas a lower concentration of ethane in the feedstock favors the oxydehydrogenation reaction rather than total oxidation reactions. To this end, the proposed industrial reactor technology, along with the Ni/KY material, overcomes the hot spot formation and enables operations at larger temperatures, hence, favoring the production of ethene rather than carbon oxides.

Presenting a new kinetic model for methanol to light olefins reactions over a hierarchical SAPO-34 catalyst using the Langmuir–Hinshelwood–Hougen–Watson mechanism

In this study, a new kinetic model for methanol to light olefins (MTO) reactions over a hierarchical SAPO-34 catalyst using the Langmuir–Hinshelwood–Hougen–Watson (LHHW) mechanism was presented and the kinetic parameters was obtained using a genetic algorithm (GA) and genetic programming (GP). Several kinetic models for the MTO reactions have been presented. However, due to the complexity of the reactions, most reactions are considered lumped and elementary, which cannot be deemed a completely accurate kinetic model of the process. Therefore, in this study, the LHHW mechanism is presented as kinetic models of MTO reactions. Because of the non-linearity of the kinetic models and existence of many local optimal points, evolutionary algorithms (GA and GP) are used in this study to estimate the kinetic parameters in the rate equations. Via the simultaneous connection of the code related to modelling the reactor and the GA and GP codes in the MATLAB R2013a software, optimization of the kinetic models parameters was performed such that the least difference between the results from the kinetic models and experiential results was obtained and the best kinetic parameters of MTO process reactions were achieved. A comparison of the results from the model with experiential results showed that the present model possesses good accuracy.

Activity and selectivity of different base catalysts in synthesis of guaifenesin from guaiacol and glycidol of biomass origin

Guaiacol and glycidol can be obtained from biomass valorization. Guaiacol (2-methoxyphenol) and glycidol (2,3-epoxy-1-propanol) have been used for the efficient synthesis of guaifenesin ((RS)-3-(2-methoxyphenoxy) propane-1,2-diol). Different catalysts such as hydrotalcite (HT), calcined hydrotalcite (CHT), calcinated hydrotalcite supported on hexagonal mesoporous silica, magnesium oxide, alumina and, potassium promoted zirconium oxide were synthesized, out of which CHT was found to be the most active, selective and reusable catalyst. The catalyst characterization was done by different techniques. Both Oxide and hydroxide phases were observed on calcination of HT in air at 450°C for 6h. CHT possess both acidic and basic sites and basicity of CHT was the highest. Crystallite size, surface area and pore size of CHT play important role in catalytic activity and selectivity. Reaction was carried out in a batch reactor and influence of different parameters was systematically studied. The reaction mechanism involving two sites, acidic and basic, was proposed. A suitable kinetic model was developed and fitted against experimental data. A second order rate equation was derived on the basis of Langmuir–Hinshelwood–Hougen–Watson mechanism with weak adsorption of reactants, intermediates and products. Kinetics was used to predict reaction conditions to obtain guaifenesin selectively. Guaifenesin was efficiently obtained with 94.8% selectivity at guaiacol conversion of 38.2% over CHT at 80°C after 4h.

Synthesis of ethyl levulinate as fuel additives using heterogeneous solid superacidic catalysts: Efficacy and kinetic modeling

Esters of levulinic acid, which is biomass derived, are used as oxygenated additives in fuels, flavoring and fragrance industry or as blending components in biodiesel. A series of sulphated metal oxide catalysts were prepared and their activities were tested in the synthesis of ethyl levulinate as the model compound, among which UDCaT-5 (mesoporous super acidic zirconia modified catalyst) was the most active and robust catalyst. The effects of various parameters were studied in a batch reactor to establish kinetics and mechanism of reaction under optimized conditions. The reaction follows Langmuir–Hinshelwood–Hougen–Watson mechanism involving weak adsorption of the reactants and products. The apparent energy of activation was found to be 9.00kcal/mol for ethyl levulinate. Several other alkyl levulinates were produced from esterification of levulinic acid with different alcohols using UDCaT-5. The use of solid acid catalyst made the process environmentally benign. The catalyst was reused up to four runs including the fresh one. A green and effective route for conversion of biobased levulinic acid into valuable esters is established.

An investigation of the kinetics and mechanism of Fischer–Tropsch synthesis on Fe–Co–Ni supported catalyst

The kinetic of the Fischer–Tropsch synthesis over a Fe-Co-Ni catalyst was investigated in a fixed bed micro reactor. Experimental conditions were varied as follow: reaction pressure 1–12bar, H2/CO feed ratio of 1, 1.5, 2 and space velocity of 4800h−1 at the temperature range of 250–280°C. Eighteen models according to the Langmuir–Hinshelwood–Hougen–Watson (LHHW) type rate equation were derived on the basis of detailed set of possible reaction mechanisms, and the reaction rate of this study is fitted fairly well by one kinetic expression based on LHHW mechanism. The kinetic parameters were estimated with non-linear regression method and the activation energy was 82.220kJ/mol for optimal kinetic model.

KINETIC STUDY OF FISCHER TROPSCH SYNTHESIS OVER CO PRECIPITATED IRON-CERIUM CATALYST

The kinetic of Fischer-Tropsch synthesis over a co-precipitated Fe-Ce catalyst was investigated in a fixed bed micro reactor. Experimental conditions were varied as follow: reaction pressure 1-15bar, H¬¬¬2/CO feed ratio of 1-3 and space velocity of 3600-5400 h-1 at the temperature range of 270-310°C. 4 models according to the Langmuir-Hinshelwood-Hougen-Watson (LHHW) type rate equation were derived on the basis of detailed set of possible reaction mechanisms and the reaction rate of this study is fitted fairly well by one kinetic expression based on LHHW mechanism. The kinetic parameters were estimated with non-linear regression method and the MARR% values for all proposed models were obtained. The activation energy was 72kJ/mol for optimum kinetic model and this model has the lower MARR% value than the other proposed models.

Selective hydrogenation of acetophenone to 1-phenyl ethanol over nanofibrous Ag-OMS-2 catalysts

Hydrogenation of acetophenone is interesting and poses a challenge in selective conversion to 1-phenyl ethanol which is a perfumery chemical. It is a complex network of series and parallel reactions. Silver incorporated octahedral molecular sieve catalysts (Ag-OMS-2) were synthesized by precipitation method and employed in the hydrogenation of acetophenone to 1-phenyl ethanol (1-PEA). The catalysts were fully characterized by TGA, XRD, SEM, EDX, TPD, TPR and nitrogen adsorption. They show a nano fibrous structure with very high activity toward hydrogenation. Acetophenone conversion increased with an increase in silver loading from 5 to 15% by wt. 15% Ag-OMS-2 showed the highest activity and 100% selectivity to 1-PEA at hydrogen pressure of 10atm and 160°C. Effects of various parameters such as speed of agitation, type of solvent, catalyst loading, acetophenone concentration, and temperature were studied. A kinetic model was built using Langmuir–Hinshelwood–Hougen–Watson mechanism with weak adsorption of all species leading to a power law model. The activation energy was found to be 12.38kcal/mol.

Selectivity engineering of solid base catalyzed O-methylation of 2-naphthol with dimethyl carbonate to 2-methoxynaphthalene

2-Methoxynaphthalene is an important intermediate used in the production of naproxen which is widely used as a non-steroidal, anti-inflammatory, analgesic and antipyretic drug. In the current work, catalytic methylation of 2-naphthol was studied by using dimethyl carbonate as a greener agent vis-à-vis methyl halides and dimethyl sulfate. Catalysts based on calcined-hydrotalcite (CHT) supported on hexagonal mesoporous silica (HMS) were synthesized. Effect of CHT loading on HMS was systematically studied including full characterization. The activity and selectivity of CHT/HMS was examined by studying the effects of different operating parameters to deduce mechanism and kinetics. Conversion of 2-naphthol at 463K and autogenous pressure was 92% with 90% selectivity toward 2-methoxynaphthalene on 20% (w/w) CHT/HMS. The catalyst was easily recovered and reused without any significant loss in activity. A kinetic model was developed. It follows zero order kinetics based on Langmuir–Hinshelwood–Hougen–Watson mechanism with strong adsorption of reactants. The apparent activation energy is 32.3kcal/mol.

Insight into esterification of eugenol to eugenol benzoate using a solid super acidic modified zirconia catalyst UDCaT-5

Eugenol benzoate is a potent lipoxygenase inhibitor prepared by esterification of eugenol with benzoic acid. The current paper depicts synthesis of eugenol benzoate using several solid acids among which super acid catalyst UDCaT-5 was found to be the best. UDCaT-5, a zirconia-based catalyst, with high sulfur content (9%w/w) but preservation of the tetragonal phase of zirconia was synthesized and is much better than the conventional sulfated zirconia (S-ZrO2). As compared to other solid acid catalysts it gives excellent conversion under moderate conditions of 110°C. The effects of various parameters were studied in a batch reactor to establish kinetics and mechanism of reaction under optimized conditions. The reaction is intrinsic kinetically controlled. The detailed kinetics of eugenol esterification by solid super acid catalyst is studied using various parameters. The reaction follows Langmuir–Hinshelwood–Hougen–Watson mechanism involving weak adsorption of the reactants and products. The apparent energy of activation was found to be 9.36kcal/mol. The catalyst is highly active and reusable.

An investigation of the kinetics and mechanism of Fischer–Tropsch synthesis on Fe–Co–Mn supported catalyst

The kinetic of the Fischer–Tropsch synthesis over a Fe–Co–Mn catalyst was investigated in a fixed bed micro reactor. Experimental conditions were varied as follow: reaction pressure 1–10bar, H2/CO feed ratio of 1–3 and space velocity of 4500h−1 at the temperature range of 290–320°C. 18 models according to the Langmuir–Hinshelwood–Hougen–Watson (LHHW) type rate equation were derived on the basis of detailed set of possible reaction mechanisms, and the reaction rate of this study is fitted fairly well by one kinetic expression based on LHHW mechanism. The kinetic parameters were estimated with non-linear regression method and the activation energy was 82.520kJ/mol for optimal kinetic model. The catalyst characterization was carried out using different methods including powder X-Ray Diffraction (XRD) and Brunauer–Emmett–Teller (BET) surface area measurements.

Reaction kinetics and mechanism for hydration of cyclohexene over ion-exchange resin and H-ZSM-5

The kinetics of liquid-phase cyclohexene hydration over ion-exchange resin and H-ZSM-5 were, respectively, investigated in a batch autoclave reactor. In order to identify the reaction mechanism involved in the heterogeneous cyclohexene hydration, a pseudo-homogeneous (PH) model and three heterogeneous models based on the Langmuir–Hinshelwood–Hougen–Watson (LHHW) mechanism and Eley–Rideal (ER) mechanism were established to correlate the kinetic data. The results indicated that the heterogeneous models exhibited a more satisfactory agreement with the experimental data than the PH model. According to the kinetic studies and spectroscopic analysis, it is proposed that cyclohexene hydration catalyzed by H-ZSM-5 belongs to the ER mechanism, which accounts that the reaction is between adsorbed water and bulk cyclohexene, while it belongs to the LHHW mechanism over the ion-exchange resin. Nevertheless, the activation energies are similar for the two catalysts, which implies similar controlling steps are encountered in the reaction.

Kinetic studies of the partial oxidation of isooctane for hydrogen production over a nickel–alumina catalyst

The kinetics of the catalytic partial oxidation of isooctane for hydrogen ( H 2 ) production over a stable Ni / γ - Al 2 O 3 catalyst was investigated at atmospheric pressure in the temperature range of 863–913 K, ratio of weight of catalyst to the molar feed rate of isooctane ( W / F iC 8 o ) in the range of 7.09 – 30.89 kg mol - 1 , and molar feed ratio O 2 / i - C 8 H 18 of 4.0 in a 12.7 mm diameter Inconel micro-reactor housed in an electrically controlled furnace. The developed rate models were based on the Langmuir–Hinshelwood–Hougen–Watson (LHHW) and Eley–Rideal (ER) formulations. Out of the 18 models developed, 10 were eliminated due to poor predictive efficiency. A LHHW mechanism requiring the dissociative adsorption of isooctane and molecular adsorption of oxygen on a single site was the most likely pathway for the partial oxidation of isooctane. The reaction order of 1.5 indicates a strong coverage of nickel by isooctane.

Kinetics of [formula omitted]-dodecane dehydrogenation on promoted platinum catalyst

Kinetics of n -dodecane dehydrogenation over a promoted Pt–Sn–/ Al 2 O 3 catalyst between 733 and 763 K were determined. The reaction scheme includes three consecutive dehydrogenation reactions and also cracking of olefins to light paraffins. Various rate models based on Langmuir–Hinshelwood–Hougen–Watson (LHHW) and Eley Rideal mechanisms were derived for the three dehydrogenation reactions and subjected to model discrimination and parameter estimation by using Box's complex optimisation method. Of the 12 different models tested, model based on LHHW mechanism with surface reaction as rate-determining step fitted the experimental data well. The estimated rate constants of the best model are thermodynamically sound and statistically consistent.

Friedel–Crafts acylation using sulfated zirconia catalyst

Synthesis of fine chemicals and intermediates by using Friedel–Crafts acylations is an important process in organic chemical technology. In most cases, very good yield and selectivity can be obtained with aluminium chloride as catalyst in conjunction with nitrobenzene as solvent. However, with modern environmental restrictions, in consonance with green chemistry, replacement of aluminium chloride–nitrobenzene or BF3–HF with solid catalysts has great industrial relevance. Acylation of benzene with 4-chlorobenzoyl chloride was attempted with different solid acid catalysts such as dodecatungstophosphoric acid (DTPA), DTPA/K-10 clay, K-10, Amberlite, Amberlyst-15, Indion-130, Filtrol-24 clay, and sulfated zirconia. However, only sulfated zirconia was found to be effective leading to 100% selective formation of 4-chlorobenzophenone, which is useful as an organic and pharmaceutical intermediate; for instance, in the manufacture of Cytrazin—a well known drug. The kinetics of the reaction was studied to establish that the reaction obeys the Langmuir–Hinshelwood–Hougen–Watson mechanism with very weak adsorption of the reactants. The reaction is intrinsically kinetically controlled.

The Kinetics of Ammonia Synthesis over Ru-Based Catalysts: 1. The Dissociative Chemisorption and Associative Desorption of N2

The dissociative chemisorption of N2is generally accepted to be the rate-determining step of ammonia synthesis over Ru-based catalysts. The interaction of N2with the following three Ru catalysts has been studied: Ru supported on Al2O3(Ru/Al2O3) and on MgO (Ru/MgO), and Ru/MgO promoted with cesium (Cs–Ru/MgO). Temperature-programmed N2adsorption and desorption experiments and the isotopic exchange reaction14N14N+15N15N⇌214N15N were performed in a microreactor flow system. A microkinetic analysis based on the Langmuir–Hinshelwood Hougen–Watson mechanism has been applied to these kinetic experiments yielding the rate constants of dissociative chemisorption (kads) and associative desorption (kdes). The dissociation of N2was indeed found to be a slow and activated process. Ru/Al2O3was found to be rather inactive for N2dissociation. Ru/MgO turned out to be a heterogeneous system with respect to the interaction with N2due to the presence of promoted active sites which dominate the rate of N2dissociation. Promotion by cesium was observed to enhance bothkadsandkdessignificantly and rendered the Ru metal surfaces uniform toward the interaction with N2. The initial sticking coefficient and the rate of desorption of N2derived from the microkinetic models are in good agreement with results obtained with Ru single crystal surfaces under ultra-high vacuum conditions.