Catalyst Deactivation Kinetics Research Articles

Water ozone decomposition in graphitic and graphene based catalytic materials: Kinetics of catalyst deactivation

Decomposition of ozone in water in the presence of five different materials based on graphene and graphite has been studied with the aim of stablishing the catalytic reaction and catalyst deactivation kinetics of paramount importance in treatment sustainability, catalyst design optimization, risk assessment and economics. Ozone is considered as a poison of the catalytic process and, as a consequence, catalyst deactivation has been assumed to be dependent on the ozone concentration. An apparent activity property has been considered as the ratio of decomposition rates of ozone at any time and that at start of reaction. Among materials studied, commercial graphene presents the highest catalytic capacity to decompose ozone due to its high surface area and pore volume. Ozone treatment of graphene to increase surface oxygen groups does not lead to any significant advantage. Due to nearly null surface area and pore volume, commercial graphite gives rise to a slight increment of ozone decomposition rate if compared to the free catalytic decomposition run. Ball milling of graphite leads to an increase of catalytic ozone decomposition that is further increased with a subsequent ozone treatment. In both graphite-based materials, an increase of surface oxygen groups and pore volume was observed. However, catalyst activity of graphene materials was much higher. The kinetics study leads to determine rate constants of both catalytic ozone decomposition reaction and catalyst deactivation. These rate constants follow a potential relationship with catalyst concentration in the range 0.01 to 0.15 g L−1.

Dynamic coupling of reactor and heat exchanger network considering catalyst deactivation

Catalyst activity decreases with time. Identifying the variation of optimal system parameters along with the catalyst deactivation can alleviate the effects of catalyst deactivation and reduce energy consumption. A graphic method is established to integrate reactor and HEN, considering the catalyst deactivation. Based on the reaction kinetics, the catalyst deactivation kinetics, and the material and energy balances, the relations among running time, catalyst activity, reactor temperatures, and heat load are deduced for different reactors. Their influences on energy consumption are studied by pinch analysis and algebraic reasoning. The heat load variation of each heat exchanger in the path/loop is analyzed, and the load-shift laws are proposed. A Reactor-HEN coupling diagram is constructed to illustrate the variation of system parameters with running time and determine the catalyst's optimal replacement node. The proposed method can be applied to guide the operation of the practical process and evaluate the process through the catalyst replacement cycle in the design stage. An alkylation process of benzene to ethylbenzene is studied by the proposed method, and the optimal catalyst replacement node is identified to be 5.2 months.

Optimization of the catalyst service life based on the coupling of reactor and heat exchanger network

A systematic method is proposed for targeting the optimal catalyst service life, considering the catalyst deactivation and coupling integration of HEN and reactor. Relations among the reactor’s conversion, inlet/outlet temperature, energy consumption, average product cost, and catalyst activity are determined based on the catalyst deactivation kinetics, energy balance, and the migration of the composite curves. The Reactor-HEN coupling diagram is constructed to illustrate the variation curves of these indexes with catalyst activity/catalyst regeneration activity and target the optimal regeneration activity. The optimal catalyst service time is further determined considering the catalyst deactivation dynamics. A practical process with benzene hydrogenation to cyclohexene is studied. The optimal regeneration activity of the Ru-Zn-B/ZrO2 catalyst is determined to be 0.42, and the optimal service life is 1.32 y. The proposed method is efficient, and the results can guide the design and operation of the production processes.

Use of heterogeneous activated carbon supported copper catalyst for catalytic wet oxidation of biomethanated spent wash: Reaction kinetics, catalyst stability, catalyst deactivation kinetics and biochemical methane potential

In the present study, the potential of activated carbon (AC) supported copper catalyst was investigated during catalytic wet oxidation (CWO) of pretreated high strength biomethanated spent wash (BMSW) stream which is originated from alcohol distillery. Prior to wet oxidation (WO) treatment, the BMSW was centrifuged to remove suspended solids. During CWO treatment at 220 °C temperature, the chemical oxygen demand and color removals of 72% and 97%, respectively, were observed from the centrifuged BMSW (catalyst dose = 3.4 g L−1, reaction time = 3 h). The analysis of treated liquid samples confirmed the formation of acetic acid in large concentrations which is one of the major precursors of methane during post anaerobic treatment. The kinetic expressions for WO and CWO processes were also developed using initial rate method. However, the recovered and regenerated catalyst could only be reused twice in CWO runs. The biochemical methane potential (BMP) test results showed significant production of biogas from the treated BMSW. Based on the findings, it can be inferred that the CWO of BMSW can be a potential treatment method before its disposal in the environment.

Deactivation Kinetics of the Catalytic Alkylation Reaction

A kinetics theory of catalyst deactivation is presented of the solid acid-catalyzed alkylation reaction of isobutane with propylene or butene that gives alkylate, a high octane fuel, as product. The intimate relation between the kinetics network of the reaction, catalyst deactivation kinetics, and residence time distribution is analyzed. The question is addressed why the deactivation of the alkylation reaction in a continuously stirred tank reactor (CSTR) is slow compared to that in a tubular plug flow reactor (PFR). Conditions are derived where such differences will be minimum and maximum. In the reaction regime of high alkylate selectivity, linear and quadratic power law kinetics equations in propylene concentration can be deduced from microkinetics. They are used to derive analytical expressions of deactivation times for CSTR and PFR. The theoretical power law kinetics equations can be related to previously established empirical rate equations of catalyst deactivation. We show that, in the CSTR, the self-alkylation reaction path contributes substantially to the deactivation time. In the self-alkylation reaction, alkylate is formed by reaction of the isobutene reaction intermediate and isobutane. Catalysts of high proton strength can benefit catalyst deactivation times by suppressing the carbenium ion deprotonation reaction that produces alkenes as isobutene. In the PFR, selective alkylate formation occurs only when the reaction occurs in a reaction zone of the catalyst bed. Deactivation is faster than in CSTR because of the reactant profile in the reaction zone. This reaction zone has restricted mobility due to the fast deactivation of reactive protons located behind the reaction zone by alkenes formed by nonselective reactions in the reaction zone. In PFR, as long as the reaction is limited to an immobile reaction zone, deactivation time is independent of reaction site density and contact time. Contact time dependence arises when the reaction zone is mobile. Overall deactivation time then depends strongly on the degree of deactivation of the protons behind the reaction zone.

Environmentally Friendly Fuel by n-Heptane Isomerization: Kinetics of Catalyst Deactivation

Environmentally Friendly Fuel by n-Heptane Isomerization: Kinetics of Catalyst Deactivation

Deactivation Kinetics of Solid Acid Catalyst with Laterally Interacting Protons.

Differences in catalyst deactivation kinetics in solid acid catalysis are studied with catalyst models that allow for lateral interaction between protons. Deactivation of a solid acid catalyst with laterally interacting protons induces inhomogeneity of proton reactivity that develops with time. As a consequence, product selectivity changes and deactivation will accelerate. This is demonstrated by simulations of the deactivation kinetics of the alkylation reaction of propylene with isobutane. The effect of lateral interactions between protons arises because initial catalyst deactivation is not caused by pore blocking or coke deposition but by a molecular mechanism where protons are consumed due to the formation of stable nonreactive carbenium ions. High selectivity to alkylate requires a catalyst with protons of high reactivity. When protons become consumed by formation of stable deactivating carbenium ions, initially reactive protons are converted into protons of lower reactivity. The latter only catalyze deactivating oligomerization reactions. Simulations that compare the deactivation kinetics of a catalyst model with laterally interacting protons and a catalyst model that contains protons of similar but different reactivity, but that do not laterally interact, are compared. These simulations demonstrate that the lateral interaction catalyst model is initially more selective but also has a lower stability. Catalyst deactivation of the alkylation reaction occurs through two reaction channels. One reaction channel is due to oligomerization of reactant propylene. The other deactivation reaction channel is initiated by deprotonation of intermediate carbenium ions that increase alkene concentration. By consecutive reactions, this also leads to deactivation. The hydride transfer reaction competes with oligomerization reactions. It is favored by strongly acid sites that also suppress the deprotonation reaction. Within the laterally interacting proton catalyst model, when reactive protons become deactivated, weakly reactive protons are generated that only catalyze the deactivating alkene oligomerization and consecutive reactions. This rapid formation of the weakly reactive protons is the cause of decreasing selectivity with reaction time and increased rate of deactivation. Solutions of the mean field kinetic equations as well as stochastic simulations are presented. Comparative simulations with a reduced number of neighbors of the protons illustrate decreased deactivation rates when the proton density decreases. Island formation of adsorbed reaction intermediates on the catalyst surface is observed in stochastic kinetics simulations. When alkylation selectivity is high, this island formation increases the rate of catalyst deactivation in comparison to the rate of deactivation according to the mean field studies. A nonlinear dynamics model of proton dynamics is provided, which shows that the differences between stochastic and mean field simulations are due to frustrated proton state percolation.

Production of COx-free hydrogen by the thermal decomposition of methane over activated carbon: Catalyst deactivation

Hydrogen, an environment-friendly energy source, is deemed to become strongly in demand over the next decades. In this work, COx-free hydrogen was produced by the thermal catalytic decomposition (TCD) of methane by a carbon catalyst. Deactivated catalysts at four-stage of progressive were characterized by nitrogen sorption and scanning electron microscopy. TCD of methane at 820 and 940 °C was about 13- and 8-folds higher than non-catalytic decomposition, respectively. High temperatures positively affected the kinetics of hydrogen production but negatively influenced the total amount of hydrogen and carbon products. The total pore volume was a good indicator of the total amount of hydrogen product. Catalyst activity was decreased because of the changes in the catalyst's textural properties within three ranges of relative time, that is, 0 to 45, 0.45 to 0.65, and 0.65 to 1. Models for specific surface area and total pore volume as functions of catalyst deactivation kinetics were developed.

Liquid phase propylene epoxidation with H2O2on TS-1/SiO2catalyst in a fixed-bed reactor: experiments and deactivation kinetics

BACKGROUND The epoxidation of propylene with H2O2 in liquid phase catalyzed by a TS-1/SiO2 catalyst in a fixed-bed reactor has been studied. The effects of reaction temperature (313–328 K), methanol concentrations (55–70 wt%) and hydrogen peroxide concentrations (9–15 wt%) on the reaction are investigated. The fresh, deactivated and regenerated catalysts were characterized with XRD, FT-IR, UV–vis, N2 sorption and TG to study the reasons for catalyst deactivation. In addition, the kinetics of catalyst deactivation was studied by fitting the experimental data. RESULTS The rate of decrease of H2O2 conversion decreases with increasing reaction temperature and methanol concentration, but increases with increasing hydrogen peroxide concentration. The reason for catalyst deactivation is that the bulky organic matter covers the active centers. The study on deactivation kinetics shows that the deactivation reaction order is 2, and an expression for H2O2 conversion as a function of reaction time is obtained. CONCLUSION The operating conditions such as reaction temperature, methanol concentration and hydrogen peroxide concentration remarkably affect the reaction. The kinetic parameters including deactivation reaction order and activation energy are developed by fitting the experimental data based on the Wojciechowski model. © 2014 Society of Chemical Industry

Phenol methylation on acid catalysts: Study of the catalyst deactivation kinetics and mechanism

The kinetics and mechanism of coke formation and catalyst deactivation during the synthesis of cresols from phenol methylation were investigated on SiO2–Al2O3, tungstophosphoric acid (HPA) supported on silica, and zeolites HBEA, HZSM5, HMCM22 and HY. The nature, density and strength of surface acid sites were probed by temperature programmed desorption of NH3 coupled with infrared spectra of adsorbed pyridine. Coke formed on the catalysts during reaction was characterized by temperature programmed oxidation. All the samples deactivated on stream. A linear correlation was observed between the initial catalyst deactivation and the amount of coke, thereby indicating that coke formation was responsible for the activity decay. Coking kinetic studies showed that a significant part of coke was rapidly formed from the reactants. When methanol was feeding alone, significant amounts of carbon were formed on the catalysts (between 0.6% and 6.2%C), particularly on samples containing mainly strong Brønsted acid sites. Nevertheless, the coke amounts formed during phenol methylation were clearly higher (between 3.7% and 14.9%C), which showed that phenol was also responsible for coke formation. More insight on the role of phenol and methanol on coke formation was obtained by characterizing the coke nature using infrared spectroscopy. Coked samples recovered after methanol decomposition reaction exhibited IR absorption bands characteristics of olefinic species formed on Brønsted and Lewis acid sites. The IR spectra of coked samples recovered after phenol methylation showed the presence of phenolate, aromatic and polyaromatic species adsorbed mainly on Lewis acid sites.

The Effect of Alkali Metal Promoters on the Stability and Coke Formation of Platinum-Based Propane Dehydrogenation Catalysts: A Kinetic Study

The kinetics of catalyst deactivation and coke formation during dehydrogenation of propane over supported Pt-based catalysts and, in particular, the effect of alkali metal promoters on catalyst activity and stability were studied. The analysis of propane conversion data showed that there is an optimum level of alkali metal promoter loading for both catalyst activity and stability. A model based on individual site poisoning was proposed for coke deposition kinetics. The model showed fair fits for coke formation data with time on stream. While the rate constant of coke formation was slightly affected by loading of Na as the neutralizing promoter, the ultimate coke amount was strongly dependent on the Na loading. It was found that coke formation sites should be different from active sites for the main reaction.

Integrated modelling of reaction and catalyst deactivation kinetics—Hydrogenation of sitosterol to sitostanol over a palladium catalyst

Catalyst deactivation is traditionally described with semi-empirical models involving separable kinetics and time-dependent activity factors, but the rational approach is to treat catalyst deactivation as a chemisorption process among other surface processes. The catalytic process A→R along with surface poisoning P+⁎→P⁎ (⁎ is an active site) was modelled for batch and continuous reactors. Simple semi-analytical mathematical solutions were obtained, which avoid the use of surface coverage in computations. Numerical simulations revealed the behaviour of the model in the parameter space. For batch reactors, the approach to a limit conversion as well as the increase of the apparent reaction order due to catalyst poisoning was illustrated. The model was applied to batchwise hydrogenation of sitosterol to sitostanol on a dispersed platinum catalyst and in the presence of a sulphurous poison. The behaviour of the system was successfully described with a simple, mechanistic model based on the adsorption-reaction-poisoning concept.

Surface Acidity of Aluminum Phosphate and Its Catalytic Performance in Benzene Alkylation with Long Chain Olefin

The acidic properties of aluminum phosphate (AlPO4-5) solid acid catalyst were characterized by temperature programmed desorption (TPD) of ammonia (NH3), n-propylamine (n-C3H7NH2), iso-propylamine [(CH3)2CHNH2] and n-dipropylamine [(C3H7)2NH] separately, and its catalytic performance in benzene alkylation with long chain olefin was studied in a fixed-bed reactor. The characterized acid amount of catalyst increased with the basicity of adsorbates. With increase of the activation temperature of catalyst, the acid amount characterized by NH3-TPD decreased, however, it increased when characterized by TPD using three other adsorbates. The desorption kinetics of TPD process and the deactivation kinetics of catalyst were investigated. The acidity and catalytic performance of catalyst was also correlated. The results showed that the acid amount and strength are well correlated with the activity and stability using NH3 as adsorbate, respectively, which indicated NH3 was a better basic adsorbate. It was also found that the catalyst with higher acid amount and lower acid strength on the surface exhibited the better catalytic performance and stability.

Silica-supported Ni(II) complex bearing [O^N] ligand and copolymerization to afford silica hybrid polynorbornenes nanocomposites

In situ polymerization is an ideal technique to make a perfect dispersion of nanosilica into polymer matrixes. So, in this article, a novel silica-supported β-ketoamine nickel(II) dibromide precatalyst was efficiently prepared and used in in situ slurry polymerizations of norbornene (NB) to afford a highly productive NB addition polymerization system in combination with tris(pentafluorophenyl)borane (B(C6F5)3) cocatalyst. It exhibited productivity of 176.8 kg of polynorbornene (mol Ni)−1 h−1 at a mole ratio of B/Ni = 20, and the catalyst deactivation kinetics in the early stage of polymerization fitted well by the first-order deactivation kinetics up to about 60 min. The catalyst system was also effective for the copolymerization of NB and 5-norbornene-2-carboxylic acid methyl ester to produce the addition-type copolymers with high-molecular-weights (3.28–3.45 × 105 g mol−1) and incorporation rates (8.1–49.1%) as well as narrow molecular weight distributions (polydispersity index = 1.6). The nanoparticles were confirmed to be well-dispersed in the polymer matrix with each individual nanoparticle surrounded by polymer. Transparency of nanocomposites could be kept up to about 60%. The brittleness of polymer was obviously improved, and the tensile strength of polymer film could be as high as 47.8 MPa.

Catalyst deactivation kinetics: An apparent delay in decreasing of catalyst activity, “inflection point” and data interpretation

Problems of catalyst deactivation kinetics and catalyst stability testing are considered. An apparent delay of deactivation and its interpretation is discussed. The coordinates of inflection points on the curves of conversion decay are also considered. The influence of reaction and deactivation kinetics, as well as type of laboratory reactor on inflection point is analysed. Several helpful and practical equations, as well as real examples are presented.

Preparation of Nanosilica/Polynorbornene Nanocomposite by Covalently Immobilized Silica‐Supported Acetylacetonate Palladium(II) Dichloride Catalyst

AbstractCovalently immobilized silica‐supported acetylacetonate dichloride palladium(II) precatalyst is prepared by the reaction of silica particles grafted acetylacetonate ligand further exchange with [Et4N]2PdCl4. The silica‐supported catalyst is used in slurry polymerizations of norbornene (NB) to afford a highly productive NB addition polymerization system in combination with B(C6F5)3 cocatalyst. It exhibits productivity of 84 kg of PNB (mol Pd)−1 h−1 at the initial activity, and the catalyst deactivation kinetics in the early stage of polymerization are fitted well by the first‐order deactivation kinetics. The obtained vinyl‐type polynorbornene is confirmed to be nanosilica hybrid PNB nanocomposite by SEM, TEM with an energy dispersive spectrometer, TGA, and XRD.

Relationships Between Acidity and Catalytic Performance of Solid Acid in Synthesis of Linear Alkyl Benzene (LAB)

Through the benzene alkylation experiments with long chain olefin over solid acid catalysts activated at different temperature in the fixed-bed reactor, the kinetics of alkylation reaction and the deactivation kinetics of catalyst were established. The results showed that the activity and stability of catalyst decreased with increasing the activation temperature of catalysts. The reaction rate constant (k) and the deactivation rate constant (kd) of catalyst in kinetic models were also estimated through the optimization method, respectively. The acidity of catalyst was characterized by ammonia (NH3)-temperature programmed desorption (TPD), and the desorption kinetics of NH3was obtained. The characterization results showed that the acid amount or the acid density gradually decreased, while the desorption activation energy or the acid strength increased, as the activation temperature of catalyst increased. In addition, the relationships between the acidity and catalytic performance of catalysts were correlated. It was found that the catalyst with higher acid amount and the lower acid strength on the surface exhibited the better catalytic performance and stability.

A rapid and effective method for evaluating the initial activity of Mo/HZSM-5 catalyst in the methane dehydroaromatization reaction at severe conditions

Abstract The very rapid deactivation behavior of Mo/HZSM-5 catalyst in the non-oxidative CH 4 dehydroaromatization needs its cyclic or continuous regeneration operation in a practical reactor system. Design and operation of such a system requires knowledge of the kinetics of catalyst deactivation and its regeneration. The present work reports an easy, rapid and quantitative approach to follow the dynamic variation of the activity of Mo/HZSM-5 in the very initial stage of CH 4 dehydroaromatization at severe conditions. This approach comprises an on-line sampling and storing of a reacted effluent into a number of volume-known loops at intervals from seconds to minutes, and an off-line analysis of the stored samples. With it a nearly continuous dynamic variation in outlet benzene concentration was observed in the first tens of minutes of the reaction for all tested catalysts with Mo loadings ranging from 1.0 to 10 wt.%. Quantitative comparison of the variation with that in the benzene formation rate measured using conventional on-line GC analysis further revealed that the variation actually exhibited the dynamic behavior of the benzene formation activity of catalyst. The approach was subsequently applied successfully to follow the intrinsic maximum activity of Mo/HZSM-5 at severe conditions and in periodic reaction–regeneration operation mode to collect kinetic data for the reactor design.

Selective deactivation of gold catalyst

The progressive poisoning effect of different molecules on carbon supported gold catalysts has been evaluated during the aerobic oxidation of glucose. A geometrical model has been derived for describing the morphological properties of two catalysts made of carbon supported gold particles having a known size distribution centered at 3.30 and 7.89 nm respectively. The observed deactivation trend follows the order thiocyanate > cyanide ≈ cysteine > thiourea and it obeys an exponential law. The kinetics of catalyst deactivation has been interpreted by considering the important contribute of electronic factors which overlap the space shielding of active sites, due to long range poison–catalyst interaction influencing the entire metal particle. Considering the nature of the molecules showing a high poisoning effect and the promoting effect of OH −, a molecular model for electronic interactions in gold nanoparticles during the aerobic oxidation of glucose has been proposed where the dioxygen reduction step is differently influenced by soft and hard-nucleophiles.

Implementing Heterogeneous Catalytic Dechlorination Technology for Remediating TCE-Contaminated Groundwater

To transition catalytic reductive dechlorination (CRD) into practice, it is necessary to demonstrate the effectiveness, robustness, and economic competitiveness of CRD-based treatment systems. A CRD system scaled up from previous laboratory studies was tested for remediating groundwater contaminated with 500-1200 microg L(-1) trichloroethylene (TCE) at Edwards Air Force Base (AFB), California. Groundwater was pumped from a treatment well at 2 gal min(-1), amended with hydrogen to 0.35 mg L(-1) and contacted for 2.3 min with 20 kg eggshell-coated Pd on alumina beads (2% Pd by wt) packed in a fixed-bed reactor, and then returned to the aquifer. Operation was continuous for 23 h followed a 1 h regeneration cycle. After regeneration, TCE removal was 99.8% for 4 to 9 h and then declined to 98.3% due to catalyst deactivation. The observed catalyst deactivation was tentatively attributed to formation of sulfidic compounds; modeling of catalyst deactivation kinetics suggests the presence of sulfidic species equivalent to 2-4 mg L(-1) hydrogen sulfide in the reactor water. Over the more than 100 day demonstration period, TCE concentrations in the treated groundwater were reduced by >99% to an average concentration of 4.1 microg L(-1). The results demonstrate CRD as a viable treatment alternative technically and economically competitive with activated carbon adsorption and other conventional physicochemical treatmenttechnologies.