Kinetic Modeling of Ethane Oxidative Dehydrogenation over VO

Research Note pubs.acs.org/IECR

Kinetic Modeling of Ethane Oxidative Dehydrogenation over VOx/ Al2O3 Catalyst in a Fluidized-Bed Riser Simulator Sameer A. Al-Ghamdi,†,‡ Mohammad M. Hossain,§ and Hugo I. de Lasa*,† †

Chemical Reactor Engineering Centre (CREC), Department of Chemical and Biochemical Engineering, Western University, London, Ontario, Canada N6A 5B9 ‡ Research & Development Center, Saudi Aramco Oil Company, Dhahran 31311, Saudi Arabia § Department of Chemical Engineering, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia S Supporting Information *

ABSTRACT: This study reports kinetic modeling of ethane oxidative dehydrogenation (ODH) under an oxygen-free atmosphere employing a catalyst of 10 wt % VOx supported on c-Al2O3. The 10 wt % VOx /Al2O3 catalyst is a stable catalyst over repeated reduction and oxidation cycles, having high dispersion of VOx on the support surface. Kinetic experiments are carried out in the CREC Fluidized Bed Riser Simulator at 550−600 °C and atmospheric pressure. Ethane ODH experiments are developed at 550, 575, and 600 °C, with three experimental repeats per condition; this shows that the prepared catalyst displays 6.5%−27.6% ethane conversion and 57.6%−84.5% ethylene selectivity. Under oxygen-free conditions, the oxygen from the catalyst lattice is consumed by ODH. Therefore, the oxygen availability is expressed as the extent of catalyst oxidation during the experiment. Changes in the extent of oxidation are described using an exponential decay function based on ethane feed conversion. On the basis of the data obtained, a kinetic model is proposed in which each reaction rate is related to the catalyst oxidation extent. The kinetic and decay model parameters are estimated using regression analysis. Activation energies and Arrhenius pre-exponential constants are calculated with their respective confidence intervals. The proposed series-parallel kinetic model satisfactorily predicts the ODH reaction of ethane under the selected reaction conditions.

1. INTRODUCTION Current conventional processes for olefin production (ethylene and propylene) suffer from several limitations related to their high energy requirements, coke formation, selectivity control, and thermodynamic constraints.1−7 Because of the increasing demand for olefins, many alternative technologies have been investigated for olefin production.8−24 Oxidative dehydrogenation (ODH) is an alternate method for olefin production that does not suffer from the drawbacks of traditional methods. However, selectivity control in ODH is a major challenge. Unfortunately, in ODH, undesirable carbon oxides form either by direct alkane combustion or by deep oxidation of produced olefins. Thus, a catalyst for ODH should be designed in such a way that it prevents the detrimental reactions leading to carbon oxides.25 Vanadium-based catalysts have been reported in the technical literature as active and selective catalysts for ethane ODH.2,9,11,12,26−37 This is due to the ability of vanadium oxide to provide lattice oxygen for hydrogen extraction from alkane species.25,38 This reaction step is followed by reoxidation of the reduced V cations by gas-phase molecular O2.25,39 The variations of lattice oxygen binding strength in different VOx surface species formed on the surface of metal oxide support has been proposed as the main factor affecting the catalytic performance of metal oxide-supported vanadium catalysts.28,40−45 Kinetic studies for short-chain alkane (ethane, propane, and butane) ODH have been the subject of several papers in the open literature.18,20,29,37,38,46−53 These contributions use different kinetic models such as the Langmuir−Hinshelwood, the © 2013 American Chemical Society

Eley−Rideal, or the Mars−van Krevelen type models. However, almost all the proposed kinetic models have been based on experiments involving co-feeding of hydrocarbon species and molecular oxygen to the reaction unit. Only a small number of kinetic investigations are based on alkane ODH under oxygen-free reaction conditions. In an early work by Kung et al.,54 it was reported that ODH reactions can take place in the absence of gaseous oxygen, using oxygen from the catalyst lattice. Morover, Herguido et al.55,56 investigated the kinetics of n-butane oxidation to maleic anhydride (MA) over a commercial vanadium catalyst under anaerobic conditions. A kinetic model was proposed assuming three types of oxygen: (a) adsorbed oxygen, (b) surface lattice oxygen, and (c) subsurface lattice oxygen. In the proposed kinetic model, the reaction rate was related to the oxidation degree of the catalyst. It was also found that, although the lattice oxygen makes a significant contribution to the oxidative dehydrogenation reaction, there is also a nonselective contribution from the weakly adsorbed oxygen. Several studies have considered propane oxidative dehydrogenation in the absence of gas-phase oxygen57−60 with propane ODH occurring because of the available lattice oxygen. While there is research on propane and butane ODH without gasphase oxygen, there are no reported data on the kinetic investigation of ethane ODH in an oxygen-free atmosphere. Received: Revised: Accepted: Published: 5235

November 30, 2012 February 13, 2013 March 5, 2013 March 5, 2013 dx.doi.org/10.1021/ie303305c | Ind. Eng. Chem. Res. 2013, 52, 5235−5244

Industrial & Engineering Chemistry Research

Research Note

Moreover, although there are studies on ODH catalysts,61−65 there is limited information that deals with light olefin ODH in dense fluidized beds, using riser or downer reactors. Most of the studies in “dense fluidized beds” have been confined to butane ODH.47,56,66,67 It appears, in this respect, that there is an incentive for researchers and industry to explore this area. Butane ODH is perceived as a potential industrial-scale candidate for ODH. However, we believe that ODH should involve a broader and more-integrated approach, considering ethane and propane as ODH feedstocks. All these areas offer new opportunities for innovative fluidized-bed technology, such as the case of risers and downers. In fact, not even butane ODH has been practiced in circulating fluidized-bed (CFB) units, such as riser or downer units. Regarding catalytic fluidized beds, there is the motivation of using these units for close to isothermal conditions. Hence, one circumvents with fluidized beds the potential issues with hot spots faced in fixed-bed catalytic reactors. Nonisothermal conditions in fixed-bed reactors can interfere with reactor performance and damage the catalyst. Fluidized reactors with periodic catalyst reoxidation offer the means that enable the transport of reduced catalyst species from the oxidative dehydrogenation unit (zone) to the reoxidation unit (zone). Thus, the operation of twin reactors, one for the ODH reaction and one for catalyst regeneration appears to be a requirement for the implementation of this technology at the industrial scale. Given the above-described facts, the goal of this paper is to establish the ethane ODH kinetics over a highly selective and a stable 10 wt % VOx/c-Al2O3 catalyst in a fluidized-bed reactor (CREC Riser Simulator) under an oxygen-free atmosphere. It is our understanding that such an ethane ODH catalyst, together with the demonstration of its performance in a fluidized-bed laboratory reactor, previously has not been reported. The 10 wt % VOx loading on the c-Al2O3 support was selected to ensure that a submonolayer VOx surface coverage is achieved (64.66% coverage). Several studies in the open literature have shown that supported vanadium catalysts are more active in ODH reactions with surface VOx coverage in the submonolayer region.28,40,68−71 To address these issues, a kinetic model is reported in the present study. This kinetic model considers the variations of the catalyst performance with the extent of catalyst oxidation. This allows the kinetic model to be suitable for the simulation of CFB reactors, where the ODH catalyst circulates between a reaction zone and a regeneration zone.

as well as the experimental procedure and setup, have already been described by Al-Ghamdi et al.72,74

Figure 1. Overview of the CREC Riser Simulator reactor body.72

3. KINETIC MODELING Ethane ODH involves a network of consecutive and parallel reactions; namely (a) the ODH of ethane, (b) the undesired combustion of the ethane feed, and (c) the secondary combustion of the ethylene product. The latter two reactions can limit the ethylene selectivity and ethylene yield during ethane ODH. Many studies have investigated the reaction mechanism of ethane ODH over supported vanadium oxide catalysts.37,49,75 In these studies, it is generally agreed that as the ethane conversion increases, the selectivity toward the desired ethylene decreases. Thus, a significant fraction of the ethane or/ and ethylene is unselectively converted to carbon oxides. Based on the observed dependence between conversion and product selectivities for ethane ODH in this study, a parallelseries reaction network is proposed, as described in Figure 2. In

Figure 2. Proposed reaction network for ethane ODH over a VOx/cAl2O3 catalyst in a CREC Riser Simulator.

2. EXPERIMENTAL SECTION 2.2. Catalyst Preparation and Characterization. The ODH catalyst of this study was prepared using the incipient wetness technique. The prepared sample was characterized by Brunauer−Emmett−Teller (BET) surface area, temperatureprogrammed reduction (TPR), X-ray diffraction (XRD), and NH3 temperature-programmed oxidation (NH3-TPD). Additional details about the various characterization techniques used have been reported elsewhere by Al-Ghamdi et al.72 2.2. Kinetic and Reactivity Experiments in the CREC Riser Simulator. The reactivity and kinetic experiments were established with the CREC Riser Simulator. It is a bench-scale mini-fluidized-bed reactor, invented by de Lasa,73 that has been designed for catalyst evaluation and kinetic studies under fluidized-bed (riser/downer) reactor conditions. A schematic diagram of a CREC Riser Simulator is given in Figure 1. Details of the CREC Riser Simulator developed in the present research,

the proposed reaction network, ethane feed reacts with lattice oxygen, promoting two parallel reactions. One of the possible reaction paths is the formation of the desired ethylene product via ODH, with a rate constant k1 (reaction 1, presented later in this work). Alternatively, ethane can be competitively converted, forming combustion products (COx), with a rate constant k2 (reaction 2, also presented later in this work). Finally, the formed ethylene may also follow a secondary reaction step, leading to the formation of combustion products (COx), with a rate constant k3 (reaction 3, shown later in this work). 3.1. Model Development. Several models have been proposed for ethane ODH reaction in the open literature. However, there are only a few papers in which models for ethane ODH were based on the Langmuir−Hinshelwood model.37,45,49,76 In all these models, hydrocarbon molecules 5236

dx.doi.org/10.1021/ie303305c | Ind. Eng. Chem. Res. 2013, 52, 5235−5244


Research Note

Moreover, and assuming an effectiveness factor of η = 1, the following equation applies:

react with the lattice oxygen of the supported metal oxides, giving alkenes and H2O. The reduced metal oxides are reoxidized by gas-phase molecular oxygen (O2), to regenerate the active metal oxides and replenish the lattice oxygen. However, in cases such as the one in the present study, where ethane ODH is carried out in the absence of gas-phase oxygen, a different reaction path must be envisioned. In such an oxygenfree environment, it is of great importance to consider the change of the catalyst’s oxygen content during the course of the ODH reaction. To accomplish this, catalyst oxygen content is expressed as the degree of oxidation (% oxidation) of the catalyst. The degree of oxidation (ϕ) is defined as the ratio of oxygen content left after the ODH reaction over the original oxygen content of the catalyst before the ODH. It is believed that the catalyst’s degree of oxidation will decrease during the ODH reaction. This is especially true when one does not allow catalyst reoxidation, or replenishment of the lattice oxygen by gas-phase molecular oxygen in between ODH reaction cycles to maintain a constant degree of oxidation. An approach to modeling the change in oxygen available on catalyst during oxygen-free ODH reactions can be established using an exponential decay function based on converted ethane. This type of activity decay function, similar to that initially proposed by de Lasa and Al-Khattaf77 for FCC catalytic activity decay and recently by Hossain et al.78 for ethylbenzene dehydrogenation to styrene, can be written as follows: ϕ = exp[−λ(XC2H6)]

p

( )

i V d RT ri = W dt

This equation is appropriate under the conditions of the present study, given that (a) the CREC Riser Simulator is a bench-scale isothermal well-mixed batch reactor unit with a high fluid gas recirculation and mixing times in the 20−30 ms range,81 and (b) the catalyst particles operate freely from intraparticle diffusional transport controls. This condition is met given the small size of catalyst particles (60 μm) and the porous structure of the fluidizable alumina used. By combining eqs 1, 2, and 4, the general rate of reaction for each chemical species is obtained as follows: dpi dt

(1)

r1 =

1+

(5)

k1K C2H6pC H 2

6

1 + K C2H6pC H + K C2H4pC H + K COxpCO 6

2

4

x

exp[−λ(XC2H6)] r2 =

(2)

(6)

k 2′K C2H6pC H 2

6


6

2

4

x

exp[−λ(XC2H6)]

where ri is the rate of reaction of component i (in units of mol/ (gcat min)), kki the kinetic constant for component i (in units of mol/(gcat min)), KAi the adsorption constant for component i (in units of atm−1), and P the partial pressure of component i (in units of atm). The term n denotes the number of chemical species, while the subscript j represents each component in the denominator. Knowing that the CREC Riser Simulator in which the experimental runs are carried out operates as a well-mixed batch reactor,80,81 a balance equation for each component i can be expressed as follows:

r3 =

(7)

k 3′K C2H4pC H 2

4


6

exp[−λ(XC2H6)]

2

4

x

(8)

where KCOx represents the lumped equilibrium adsorption constant for (COx = CO + CO2) and k2′ and k3′ are the observed lumped reaction rate constants, which are defined as follows:

p

( )

i V d RT ηri = W dt

WRT riϕ V

2

kikK iApi n ∑ j = 1 KjApj

=

Thus, by developing one equation as eq 5 for each component, one can obtain a set of differential equations to represent the ODH of the ethane conversion network. This set of differential equations is presented in the next section. 3.2. Kinetic Rate Equations. For the proposed reaction network, a lumped model using a Langmuir−Hinshelwood representation was developed. In this model, the products were grouped into two lumps: (a) C2 and (b) COx. The C2 lump contained the product ethylene (C2H4), whereas the COx lump included both CO2 and CO products. One should note that the postulated reaction rate model is consistent with an ODH reaction taking place in an oxygen-free environment. Thus, the following catalytic rate equations can be written based on the Langmuir−Hinshelwood formulation given in eq 2:

where ϕ is the catalyst’s degree of oxidation, λ a constant, and X the amount of converted ethane. Based on the proposed reaction network, the rate of formation and conversion of all chemical species in this study are modeled using a Langmuir−Hinshelwood-type rate equation. This equation takes into consideration the adsorption of the various chemical species on the catalyst surface and their reactions with the catalyst lattice oxygen to form the products. The general form of a Langmuir−Hinshelwood equation for this system is shown in eq 2, as given by Ollis et al.:79 ri =

(4)

(3) 3

where V is the volume of the reactor (in cm ), W the weight of the catalyst (in grams), pi the partial pressure of species i, R the gas constant (in cm3 atm K−1 mol−1), T the reactor temperature (in Kelvin), and t the time (in seconds).

k 2′ = k 2CO + k 2CO2

(9)

k 3′ = k 3CO + k 3CO2

(10)

Given that it is useful to establish the changes in partial pressure of various chemical species, this can be accomplished by the algebraic addition of the different reactions involved in the proposed reaction network. This leads as shown in eqs 11, 5237



Research Note

Table 1. Characteristics Summary of Al2O3 Support and Supported Vanadium Catalyst Samplea H2 Uptake (cm3/g) V contentb (wt %)

sample Al2O3 (activated) 10% V/Al2O3 a

SBET (m2/ g)

Cycl-1 Cycl-2

Cycl-3 Cycl-4

% Reduction Cycl-5 Cycl-1

Cycl-2 Cycl-3

Cycl-4 Cycl-5

237.9 10

205.8

NH3 uptake (cm3 /g) 14.39

38.9

37.9

38.1

38.0

38.0

88.5

86.1

86.7

86.5

86.5

6.77

Data taken from ref 72. bVanadium content, in wt % of V atoms, was determined by atomic absorption spectrometry (AAS).

4.2. Ethane ODH in the CREC Riser Simulator. The experimental results of ethane ODH over the prepared 10 wt % VOx /Al2O3 catalyst in the CREC Riser Simulator have already been reported elsewhere by Al-Ghamdi et al.72 However, a summary of those results, including more experimental data points, are given in the Supporting Information. More experimental data points are included here to give a more statically meaningful representation of the data, as well as more data points for the kinetic model validation. The extra data points include three repetitions of each experimental point and they are reflected in all reported figures. In Figure 3, the relationships between ethane conversion and ethylene selectivity with reaction temperature are given. As the

12, and 13 to the set of ordinary differential equations (ODEs) written below. These sets of ODES must be solved simultaneously to obtain the output partial pressures of each component, which are shown as follows: Rate of C2H6 disappearance: dpC H 2

6

dt

⎛ W RT ⎞ ⎟ (r + r ) = −⎜ 2 ⎝ V ⎠ 1

(11)

Rate of ethane formulation: dpC H 2

dt

4

=

⎛ W RT ⎞ ⎜ ⎟ (r − r ) 3 ⎝ V ⎠ 1

(12)

Rate of COx formulation: dpCO

x

dt

=

⎛ W RT ⎞ ⎜ ⎟(4r + 4r ) 3 ⎝ V ⎠ 2

(13)

Equations 11−13 can be solved at a selected set of initial conditions to describe the change of partial pressures of various chemical species (e.g., ethane, ethylene, COx) with reaction time. Furthermore, to obtain the intrinsic kinetic parameters (activation energies and pre-exponential factors), the kinetic parameters ki in eqs 6−8 were allowed to vary with temperature, using an Arrhenius relationship given by ⎡ −E ⎛ 1 1 ⎞⎤ ki = k 0 exp⎢ i ⎜ − ⎟⎥ ⎢⎣ R ⎝ T Tm ⎠⎥⎦

(14) Figure 3. Temperature dependence of C2H6 conversion and C2H4 selectivity (reaction time = 30 s, C2H6 injected = 20 mL, catalyst loaded = 0.76 g). Ethane conversions and ethylene selectivities are reported with three repetitions for the 10th ethane injection (consecutive pulses without catalyst regeneration in between).72

where ki° is the pre-exponential factor, Ei the activation energy, R the universal gas constant, and Tm the average temperature. To reduce the cross-correlation between the pre-exponential factors ki° and the activation energies Ei, the ki constants were reparameterized (as shown in eq 14) by centering the reaction temperature at an average value (Tm) of 575 °C, which corresponds to the average reaction temperatures used in the present study, as recommended by Hossain and de Lasa.82 Substitution of eq 14 into eqs 11−13, along with the proposed rate expressions gives a new set of ODEs with the intrinsic kinetic parameters (k°i , Ei, and λ) to be estimated.

reaction temperature increases, ethane conversion increases from 14.86% at 550 °C to 63.46% at 700 °C. On the other hand, ethylene selectivity shows a gradual decrease, from 68.12% at 550 °C to 28.86% at 700 °C. This type of relationship is expected as ethane conversion due to cracking tends to become more dominant at higher temperatures, hence favoring the formation of more byproducts at the expense of ethylene selectivity. Therefore, a careful selection of an appropriate reaction temperature is critical for meeting the objectives of both the desired yield and selectivity. In Figure 4, the selectivity of products, as a function of the ethane conversion at different reaction temperatures, is given. The decrease in ethylene selectivity with a corresponding increase in CO and CO2 selectivities indicates that ethylene is the primary reaction product of the ethane ODH, while CO and CO2 are the secondary products of the consecutive

4. RESULTS AND DISCUSSION 4.1. Catalyst Characterization. The previously reported characterization results by Al-Ghamdi et al.72 are summarized in Table 1. Consecutive temperature-programmed reduction (TPR) experiments show that the prepared 10 wt % VOx/ Al2O3 catalyst is a stable catalyst over repeated reduction and oxidation cycles. Moreover, X-ray diffraction (XRD) demonstrates the absence of V2O5 bulk surface species and the high dispersion of VOx on the support surface. 5238



Research Note

Figure 4. C2H4, CO, and CO2 selectivities, as a function of C2H6 conversion (C2H6 injected = 20 mL, catalyst loaded = 0.76 g). Ethane conversions and product selectivities are reported with three repetitions for the 10th ethane injection (consecutive pulses without catalyst regeneration in between).72

Figure 5. Ethane conversion; ethylene, CO, and CO2 selectivities; and cumulative lattice oxygen conversion using a VOx/c-Al2O3 catalyst in the CREC Riser Simulator (T = 600 °C, C2H6 injected = 20 mL, reaction time = 15 s, catalyst loaded = 0.76 g): (a) consecutive ODH runs without catalyst reoxidation between ethane pulses, and (b) consecutive ODH runs with catalyst reoxidation between ethane pulses.72

oxidation of ethylene. Based on those results, a classical “triangular” reaction network with “direct alkane combustion”, together with alkene formation and later “alkene combustion”, could be proposed for ethane ODH in this study. Further description is given in the kinetic modeling section. In Figure 5, various gas-species conversions/selectivities per ethane pulse and the percentual cumulative lattice oxygen conversion are reported for two sets of experiments of ethane ODH. In Figure 5a, the data are reported for ethane ODH experiments with consecutive ethane reaction pulses, with no catalyst regeneration in between where the catalyst supplies oxygen (lattice oxygen) to the reaction. In Figure 5b, the data are reported for ethane ODH experiments involving repeated reaction-regeneration cycles. Catalyst regeneration was conducted by flowing air at 600 °C over the catalyst after each ethane injection (pulse). It can be seen that, at 600 °C and in an oxygen-free environment, the prepared catalyst provides promising ethane conversions (11.84%−27.64%), ethylene selectivity (57.55%−79.42%), and catalyst stability during multiple reduction cycles at 550−600 °C. On the other hand, when oxygen was introduced to the reaction system through catalyst regeneration, ethane conversions of ∼50% and very low ethylene selectivity (1.39%) are obtained. So, the absence of gas-phase oxygen seems critical for the selective conversion of ethane into ethylene and this demonstrates the major role of lattice oxygen in sustaining the ODH over several reaction

cycles, where the prepared catalyst displays a stable performance, even after 10 repeated ethane pulses. 4.3. Estimation of Kinetic Parameters. The postulated rate expressions in eqs 6−8 are nonlinear, with respect to their parameters. This is due to the fact that the parameters appear both in the numerator and in the denominator of the rate expressions, such as in the case of the KAi adsorption constant. This nonlinearity in the rate expressions can lead to an overparameterized model, given the higher correlation between these parameters. This overparameterization problem was successfully addressed in the present study by decoupling adsorption constants and intrinsic kinetic parameters. In such a procedure, experimental values for the adsorption constants of each species were determined independently in the CREC Riser Simulator. Adsorption experiments in the CREC Riser Simulator involved the determination of adsorption isotherms at different temperatures. Once the adsorption constants were determined for each component, the intrinsic kinetic constants (k1°, k2°, E2, E3, and λ) were estimated using nonlinear least-squares regression. The MATLAB routine “LSQCURVEFIT” was used for the regression analysis. The numerical integration of the differential system (eqs 11−13) and the determination of the 95% confidence intervals for each estimated parameter were performed using the MATLAB functions ode45 and nlparci, respectively. 5239



Research Note

Table 2. Further insight was established on the adequacy of the estimated parameters by analyzing their physical significance. The dependence of parameters on each other is examined through the correlation matrix shown in Table 3. It is important

Experimental data at different reaction temperatures were used to evaluate reaction rate parameters. Moreover, the Arrhenius type of temperature-dependence function was used to express the specific rate constants. This was done by taking into account the temperature dependence of the experimental data. The Arrhenius plots are shown in Figure 6. It can be

Table 3. Reported Activation Energies for Main Products Formation in Ethane ODH Activation Energy of Formation (kJ/mol) catalyst

C2H4

10% VOx/c-Al2O3

88

(COx) 41a

(COx) 143b

7 wt % V2O5/SiO2 1.4 wt % VOx/γAl2O3

202 94

(CO) 322 (CO) 51c

(CO2) 251 (CO2) 118d

present study 76 49

86

a

(COx) 55

(CO2) 51c (COx) 96b

29

87

(COx) 52a

(COx) 87b

28.4 wt % VOx/ SiO2 (K + 28.4 wt % VOx)/SiO2 6.7 wt % VOx/ SiO2 4.8 wt % VOx/ SiO2

carbon oxides

reference

137 ± 10

83

140 ± 15

a c

Figure 6. Arrhenius plot showing the change in rate constant, relative to inverse temperature (1/T).

to note that parameter spans for the 95% CI display limited deviation. This is an indicator that the proposed model is not overparameterizated. Furthermore, the cross-correlation matrix, as reported in Table 3, shows that, in most cases, crosscorrelation coefficients are below 0.90, with only two of them surpassing the 0.9 value while remaining below 0.94. Thus, kinetic parameters are not correlated and one can conclude that defined parameters can be related to physicochemical properties of the catalyst under study. To check the validity of the estimated kinetic parameters, the model predictions for partial pressures of reactants and products were compared with the experimental data obtained in the 550−600 °C range. As shown in Figure 7, it is clear that, within the limits of experimental error, the model predictions compare very well with the experimental data. Thus, this comparison validates the adequacy of the proposed reaction model.

observed that the intrinsic kinetic constants show the expected Arrhenius relationship. Values of reaction rates and activation energies obtained from the linearization of Arrhenius plots are used as the initial values for the optimization routine. The optimization criteria was based on the fact that all the rate constants and all the activation energies for each reaction must be positive and established on a minimum sum of squares of errors, given by i=1

SSQ =

Formation of COx from C2H4. bFormation of COx from C2H6. Formation from C2H4. dFormation from CO.

∑ (Ci ,exp − Ci ,theo)2 N

Model discrimination was based on the correlation coefficients (R2) and the lowest sum of square (SSQ) criteria. The values of the seven estimated parameters, along with their corresponding 95% confidence intervals (CIs), are reported in

Table 2. Intrinsic Kinetic Parameters Summary of the Proposed Kinetic Model with a 95% Confidence Interval (CI) Correlation Matrix parameter

a

value −5

k°1

k°2

±9.7 × 10 ±3.1 × 10−7 ±5.2 × 10−7

1 −0.3085 0.6050

1 −0.9104

0.2782 0.1387 −0.0098 0.9397

95% CI gcat−1 gcat−1 gcat−1

−1

−7

k1° k°2 k°3

3.0 × 10 (mol 8.3 × 10−7 (mol 4.2 × 10−6 (mol

E1 E2 E3

88.3 kJ mol−1 143.3 kJ mol−1 41.6 kJ mol−1

±3.3 ±96.0 ±28.9

λ

2.9

±0.2

σa number of data points, m degrees of freedom, DOF

1.1 × 10−3 216 209

s ) s−1) s−1)

k°3

E1

E2

0.2322 −0.6205 0.4473

−0.0153 0.4643 −0.2914

1 −0.5261 0.5870

1 −0.9480

−0.0969

0.4278

0.4129

0.0230

E3

λ

0.0767

1

1

1

σ = [∑(Xexperimental − Xestimated)2]1/2/(m − p), where m is the number of data points and p is the number of model parameters. 5240



Research Note

investigation, support an ODH process using twin circulating fluidized beds with (a) one ODH reactor and (b) one reoxidation reactor. It is envisioned that, in this type of ODH process, only a small fraction of the catalyst in the reactor outlet stream is going to be treated in the reoxidation reactor; the rest (or most) of the catalyst in the ODH reactor outlet stream is going to be cooled and recycled back directly to the reactor input stream. It is expected that such a twin ODH fluidized bed process will yield higher olefin selectivities, as reported in the present study.

5. CONCLUSIONS The following conclusions are made, regarding the work reported in this article: (1) The prepared 10 wt % VOx/Al2O3 catalyst is a stable catalyst over repeated reduction and oxidation cycles, and XRD demonstrates the absence of V2O5 bulk surface species and the high dispersion of VOx on the support surface. (2) Ethane ODH runs in a fluidized-bed CREC Riser Simulator show that, in an oxygen-free environment, the prepared catalyst provides promising ethane conversions (6.47%−27.64%), ethylene selectivity (57.55%−84.51%), and catalyst stability during multiple reduction cycles at 550−600 °C. (3) Ethane ODH reaction runs also demonstrate that the absence of gas-phase oxygen is critical for the selective conversion of ethane into ethylene. The prepared catalyst displays stable performance, even after 10 repeated ethane pulses. This demonstrates the major role of lattice oxygen in sustaining the ODH over several reaction cycles. (4) The observed conversion and product selectivity dependence found in this study supports a parallel-series reaction network for ethane ODH. On this basis, a rate equation is developed, including both reactant adsorption and reaction on the catalyst surface. This rate equation considers a lumped model using Langmuir−Hinshelwood kinetics. The change in degree of oxidation of the catalyst during oxygen-free ODH reactions is modeled using a decay function based on reactant conversion. (5) The proposed rate equation for ODH is found to be consistent with the observed rates of reaction of the gathered experimental data. The kinetic and decay model parameters are estimated using regression analysis. Activation energies and Arrhenius pre-exponential constants are calculated with their respective confidence intervals. The proposed kinetic model satisfactorily predicts the ODH reaction of ethane under the selected reaction conditions.

Figure 7. Comparison between experimental data (data points) and model predictions (solid line): (a) T = 550 °C ; (b) T = 575 °C; (c) T = 600 °C; and (d) overall comparison between the experimental results and model predictions. (Data points with three repetitions. Standard deviation on repeats is 2.94%.)

On this basis, it can be concluded that the set of adsorption and kinetic parameters established, as well as the kinetic model developed, are adequate to predict ODH reaction rates in the CREC Riser Simulator in the range of the operating conditions studied. It is important to review the values of the activation energies obtained in the context of the present study and to compare them with values reported in the literature. Table 3 reports values of activation energies for ethane ODH. Differences in activation energy values versus others reported in the literature can be attributed to the dissimilarity in experimental systems, the proposed ODH reaction network, the catalysts, and the kinetic models used for the ODH reaction. However, it should be stressed that the values of activation energies for the ethane ODH of this study are quite close to those reported by Klose et al.,49 using a similar catalyst. For instance, for the ethane ODH step, Klose et al.49 reported activation energies for ethylene formation of 94 kJ/mol, using similar VOx-based catalysts. The energy of activation observed in this study for the same step was 88.4 kJ/mol. However, in the case of CO and CO2, the reported values by Klose et al.49 are different from those obtained in the context of the present study. This discrepancy between activation energies for CO and CO2 formation can be attributed to the different reaction network paths selected. Klose et al.49 assumed that CO and CO2 are formed from ethylene only. In our view, this assumption is inconsistent with the findings in the present study, because of the fact that COx species are always present in the products, even at very low ethane conversions. This makes the proposed “triangular” reaction network of the present study much more likely to be adequate. In addition, given the COx observed species, even at very low ethane conversions, it is adequate to hypothesize that (i) there is an alkene formation step, (ii) there is a competitive direct alkane combustion step, (iii) once alkene is formed, there is further possible alkene combustion. All this information provides extra support to the “triangular” kinetic description of ethane ODH, as shown in Figure 2. In summary, the catalytic runs, together with the phenomenologically based kinetic model developed in this

■

ASSOCIATED CONTENT

S Supporting Information *

Sample experimental results of ethane ODH in the CREC Riser Simulator using the prepared VOx/c-Al2O3 catalyst at various reaction temperatures; reported for the 10th consecutive ethane injection (pulse) without catalyst regeneration in between. This material is available free of charge via the Internet at http:// pubs.acs.org. 5241



■

Research Note

(20) Heracleous, E.; Lemonidou, A. A. Ni−Nb−O mixed oxides as highly active and selective catalysts for ethene production via ethane oxidative dehydrogenation. Part II: Mechanistic aspects and kinetic modeling. J. Catal. 2006, 237, 175−189. (21) Heracleous, E.; Lemonidou, A. A. Ni−Nb−O mixed oxides as highly active and selective catalysts for ethene production via ethane oxidative dehydrogenation. Part I: Characterization and catalytic performance. J. Catal. 2006, 237, 162−174. (22) Botella, P.; Dejoz, A.; López-Nieto, J. M.; Concepcion, P.; Vazquez, M. Selective oxidative dehydrogenation of ethane over MoVSbO mixed oxide catalysts. Appl. Catal., A 2006, 298, 16−23. (23) Nakagawa, K.; Miyake, T.; Konishi, T.; Suzuki, T. Oxidative dehydrogenation of ethane to ethylene over NiO loaded on high surface area MgO. J. Mol. Catal A: Chem. 2006, 260, 144−151. (24) López-Nieto, J. M.; Botella, P.; García-González, E.; Dejoz, A.; Vazquez, M.; González-Calbet, J. Selective oxidative dehydrogenation of ethane on MoVTeNbO mixed metal oxide catalysts. J. Catal. 2004, 225, 428−438. (25) Mamedov, E. A.; Corberfin, V. C. Oxidative dehydrogenation of lower alkanes on vanadium oxide-based catalysts. The present state of the art and outlooks. Appl. Catal., A 1995, 127, 1−40. (26) Grzybowska, B.; Klisińska, A.; Loridant, S.; Stoch, J.; Gressel, I. Effect of additives on properties of V2O5/SiO2 and V2O5/MgO catalysts: II. Structure and physicochemical properties of the catalysts and their correlations with oxidative dehydrogenation of propane and ethane. Appl. Catal., A 2006, 309, 17−27. (27) Grzybowska, B.; Klisińska, A.; Samson, K.; Gressel, I. Effect of additives on properties of V2O5/SiO2 and V2O5/MgO catalysts: I. Oxidative dehydrogenation of propane and ethane. Appl. Catal., A 2006, 309, 10−16. (28) Martinez-Huerta, M. V.; Gao, X.; Tian, H.; Wachs, I. E.; Fierro, J. L. G.; Bañares, M. A. Oxidative dehydrogenation of ethane to ethylene over alumina-supported vanadium oxide catalysts: Relationship between molecular structures and chemical reactivity. Catal. Today 2006, 118, 279−287. (29) Grabowski, R.; Sloczynski, J. Kinetics of oxidative dehydrogenation of propane and ethane on VOx/SiO2 pure and with potassium additive. Chem. Eng. Process. 2005, 44, 1082−1093. (30) Heracleous, E.; Machli, M.; Lemonidou, A. A.; Vasalos, I. A. Oxidative dehydrogenation of ethane and propane over vanadia and molybdena supported catalysts. J. Mol. Catal A: Chem. 2005, 232, 29− 39. (31) Reddy, E. P.; Varma, R. S. Preparation, characterization, and activity of Al2O3-supported V2O5 catalysts. J. Catal. 2004, 221, 93− 101. (32) Enache, D. I.; Bordes-Richard, E.; Ensuque, A.; Bozon-Verduraz, F. Vanadium oxide catalysts supported on titania and zirconia. II. Selective oxidation of ethane to acetic acid and ethylene. Appl. Catal., A 2004, 278, 103−110. (33) Enache, D. I.; Bordes-Richard, E.; Ensuque, A.; Bozon-Verduraz, F. Vanadium oxide catalysts supported on zirconia and titania. I. Preparation and characterization. Appl. Catal., A 2004, 278, 93−102. (34) Navarro, M. T.; Blasco, T.; Panzacchi, B.; Rey, F.; Concepción, P.; López-Nieto, J. M. Vanadium oxide supported on mesoporous Al2O3: Preparation, characterization and reactivity. Catal. Today 2004, 96, 179−186. (35) Zhao, Z.; Yamada, Y.; Ueda, A.; Sakurai, H.; Kobayashi, T. The roles of redox and acid−base properties of silica-supported vanadia catalysts in the selective oxidation of ethane. Catal. Today 2004, 93− 95, 163−171. (36) Busca, G.; Panizza, M.; Resini, C.; Raccoli, F.; Catani, R.; Rossini, S. Oxidation of ethane over vanadia−alumina-based catalysts: Co-feed and redox experiments. Chem. Eng. J. 2003, 93, 181−189. (37) Bell, A. T.; Iglesia, E.; Argyle, M. D.; Chen, K. Ethane Oxidative Dehydrogenation Pathways on Vanadium Oxide Catalysts. J. Phys. Chem. B 2002, 106, 5421−5427. (38) Bell, A. T.; Dinse, A.; Schomäcker, R. The role of lattice oxygen in the oxidative dehydrogenation of ethane on alumina-supported vanadium oxide. Phys. Chem. Chem. Phys. 2009, 11, 6119−6124.

AUTHOR INFORMATION

Corresponding Author

*Tel.: +1-519-661-2144. Fax: +1-519-850-2931. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

REFERENCES

(1) Anon, R. New Propylene Production Technologies Hold Great Promise. Oil Gas J. 2004, 102, 50−52. (2) Bhasin, M. Is true ethane oxydehydrogenation feasible? Top. Catal. 2003, 23, 145−149. (3) Resasco, D.; Haller, G. Catalytic Dehydrogenation of Lower Alkanes. Catalysis 1994, 11. (4) Chan, K. Y. G.; Inal, F.; Senkan, S. Suppression of coke formation in the steam cracking of alkanes: Ethane and propane. Ind. Eng. Chem. Res. 1998, 37, 901−907. (5) Dharia, D.; Letzsch, W.; Kim, H.; McCue, D.; Chapin, L. Increase light olefins production. Hydrocarb. Process. 2004, 83, 61−66. (6) Ren, T.; Patel, M.; Blok, K. Olefins from conventional and heavy feedstocks: Energy use in steam cracking and alternative processes. Energy 2006, 31, 425−451. (7) Farrauto, R. J.; Bartholomew, C. H. Fundamentals of Industrial Catalytic Processes, 1st Edition; Chapman & Hall: London, 1997. (8) Shen, Z.; Liu, J.; Xu, H.; Yue, Y.; Hua, W.; Shen, W. Dehydrogenation of ethane to ethylene over a highly efficient Ga2O3/HZSM-5 catalyst in the presence of CO2. Appl. Catal., A 2009, 356, 148−153. (9) Č apek, L.; Bulánek, R.; Adam, J.; Smoláková, L.; Sheng-Yang, H.; Č ičmanec, P. Oxidative dehydrogenation of ethane over vanadiumbased hexagonal mesoporous silica catalysts. Catal. Today 2009, 141, 282−287. (10) Shi, X.; Ji, S.; Wang, K. Oxidative Dehydrogenation of Ethane to Ethylene with Carbon dioxide over Cr−Ce/SBA-15 Catalysts. Catal. Lett. 2008, 125, 331−339. (11) Č apek, L.; Adam, J.; Grygar, T.; Bulánek, R.; Vradman, L.; Košová-Kučerová, G.; Č ičmanec, P.; Knotek, P. Oxidative dehydrogenation of ethane over vanadium supported on mesoporous materials of M41S family. Appl. Catal., A 2008, 342, 99−106. (12) Klose, F.; Wolff, T.; Lorenz, H.; Seidelmorgenstern, A.; Suchorski, Y.; Piorkowska, M.; Weiss, H. Active species on γalumina-supported vanadia catalysts: Nature and reducibility. J. Catal. 2007, 247, 176−193. (13) Danica, B.; Desislava, A.; Mirko, P.; Stefan, H. An experimental study of the partial oxidation of ethane to ethylene in a shallow fluidized bed reactor. J. Serb. Chem. Soc. 2007, 72, 183−192. (14) Haddad, N.; Bordes Richard, E.; Hilaire, L.; Barama, A. Oxidative dehydrogenation of ethane to ethene on alumina-supported molybdenum-based catalysts modified by vanadium and phosphorus. Catal. Today 2007, 126, 256−263. (15) Karamullaoglu, G.; Dogu, T. Oxidative Dehydrogenation of Ethane over Chromium-Vanadium Mixed Oxide and Chromium Oxide Catalysts. Ind. Eng. Chem. Res. 2007, 46, 7079−7086. (16) Tope, B.; Zhu, Y.; Lercher, J. A. Oxidative dehydrogenation of ethane over Dy2O3/MgO supported LiCl containing eutectic chloride catalysts. Catal. Today 2007, 123, 113−121. (17) Cavani, F.; Ballarini, N.; Cericola, A. Oxidative dehydrogenation of ethane and propane: How far from commercial implementation? Catal. Today 2007, 127, 113−131. (18) Lemonidou, A. A.; Heracleous, E. Reaction pathways of ethane oxidative and non-oxidative dehydrogenation on γ-Al2O3 studied by temperature-programmed reaction (TP-reaction). Catal. Today 2006, 112, 23−27. (19) Solsona, B.; Dejoz, A.; Garcia, T.; Concepcion, P.; López-Nieto, J. M.; Vazquez, M.; Navarro, M. T. Molybdenum−vanadium supported on mesoporous alumina catalysts for the oxidative dehydrogenation of ethane. Catal. Today 2006, 117, 228−233. 5242



Research Note

(39) Cavani, F. The oxidative dehydrogenation of ethane and propane as an alternative way for the production of light olefins. Catal. Today 1995, 24, 307−313. (40) Bell, A. T.; Khodakov, A.; Olthof, B.; Iglesia, E. Structure and Catalytic Properties of Supported Vanadium Oxides: Support Effects on Oxidative Dehydrogenation Reactions. J. Catal. 1999, 181, 205− 216. (41) Bañares, M. A. Supported metal oxide and other catalysts for ethane conversion: A review. Catal. Today 1999, 51, 319−348. (42) Bañares, M. A.; Martinez-Huerta, M. V.; Gao, X.; Wachs, I. E.; Fierro, J. L. G. Dynamic behavior of supported vanadia catalysts in the selective oxidation of ethane: In situ Raman, UV−Vis DRS and reactivity studies. Catal. Today 2000, 61, 295−301. (43) Wachs, I. E.; Weckhuysen, B. M. Structure and reactivity of surface vanadium oxide species on oxide supports. Appl. Catal. 1997, 157, 67−90. (44) Kung, H. Oxidative Dehydrogenation of Light (C2 to C4) Alkanes. Adv. Catal. 1994, 40, 1−38. (45) Wan, B.; Kao, C.; Huang, K. Ethane Oxydehydrogenation over Supported Vanadium Oxides. Ind. Eng. Chem. Res. 1994, 33, 2066− 2072. (46) Grabowski, R. Kinetics of Oxidative Dehydrogenation of C2−C3 Alkanes on Oxide Catalysts. Catal. Rev. 2006, 48, 199−268. (47) Lemonidou, A. A. Oxidative dehydrogenation of C4 hydrocarbons over VMgO catalystKinetic investigations. Appl. Catal., A 2001, 216, 277−284. (48) Machli, M.; Boudouris, C.; Gaab, S.; Find, J.; Lemonidou, A. A.; Lercher, J. A. Kinetic modelling of the gas phase ethane and propane oxidative dehydrogenation. Catal. Today 2006, 112, 53−59. (49) Klose, F.; Joshi, M.; Hamel, C.; Seidel-Morgenstern, A. Selective oxidation of ethane over a VOx/γ-Al2O3 catalystInvestigation of the reaction network. Appl. Catal., A 2004, 260, 101−110. (50) Rahman, F.; Loughlin, K. F.; Al-Saleh, M. A.; Saeed, M. R.; Tukur, N. M.; Hossain, M. M.; Karim, K.; Mamedov, A. Kinetics and mechanism of partial oxidation of ethane to ethylene and acetic acid over MoV type catalysts. Appl. Catal., A 2010, 375, 17−25. (51) Chen, K.; Khodakov, A.; Yang, J.; Bell, A. T.; Iglesia, E. Isotopic Tracer and Kinetic Studies of Oxidative Dehydrogenation Pathways on Vanadium Oxide Catalysts. J. Catal. 1999, 333, 325−333. (52) Chen, K.; Iglesia, E.; Bell, A. T. Isotopic Tracer Studies of Reaction Pathways for Propane Oxidative Dehydrogenation on Molybdenum Oxide Catalysts. J. Phys. Chem. B 2001, 105, 646−653. (53) Lemonidou, A. A.; Heracleous, E.; Lercher, J. A. Mechanistic features of the ethane oxidative dehydrogenation by in situ FTIR spectroscopy over a MoO3/Al2O3 catalyst. Appl. Catal., A 2004, 264, 73−80. (54) Kung, H. Oxidative dehydrogenation of light (C2 to C6) alkanes. Adv. Catal. 1995, 40, 1−38. (55) Gascón, J.; Valenciano, R.; Téllez, C.; Herguido, J.; Menéndez, M. A generalized kinetic model for the partial oxidation of n-butane to maleic anhydride under aerobic and anaerobic conditions. Chem. Eng. Sci. 2006, 61, 6385−6394. (56) Rubio, O.; Herguido, J.; Menendez, M. Oxidative dehydrogenation of n-butane on V/MgO catalysts-kinetic study in anaerobic conditions. Chem. Eng. Sci. 2003, 58, 4619−4627. (57) Balcaen, V.; Sack, I.; Olea, M.; Marin, G. B. Transient kinetic modeling of the oxidative dehydrogenation of propane over a vanadiabased catalyst in the absence of O2. Appl. Catal., A 2009, 371, 31−42. (58) Fukudome, K.; Ikenaga, N.; Miyake, T.; Suzuki, T. Oxidative dehydrogenation of propane using lattice oxygen of vanadium oxides on silica. Catal. Sci. Technol. 2011, 1, 987. (59) Zhao, R.; Wang, J.; Dong, Q.; Liu, J. Selective Oxidation of Propane by Lattice Oxygen of Vanadium−Phosphorous Oxide in a Pulse Reactor. J. Nat. Gas Chem. 2005, 14, 88−94. (60) Creaser, D.; Andersson, B.; Hudgins, R. R.; Silveston, P. L. Transient Kinetic Analysis of the Oxidative Dehydrogenation of Propane. J. Catal. 1999, 182, 264−269.

(61) Fukudome, K.; Ikenaga, N.; Miyake, T.; Suzuki, T. Oxidative dehydrogenation of propane using lattice oxygen of vanadium oxides on silica. Catal. Sci. Technol. 2011, 987−998. (62) Al-Zahrani, S. M.; Abasaeed, A. E.; Putra, M. Kinetics of oxidehydrogenation of propane over alumina-supported Sr−V−Mo catalysts. Catal. Commun. 2012, 26, 98−102. (63) Lin, X.; Poeppelmeier, K. R.; Weitz, E. Oxidative dehydrogenation of ethane with oxygen catalyzed by K−Y zeolite supported firstrow transition metals. Appl. Catal., A 2012, 381, 114−120. (64) Piumetti, M.; Bonelli, B.; Massiani, P.; Millot, Y.; Dzwigaj, S.; Gaberova, L.; Armandi, M.; Garrone, E. Novel vanadium-containing mesocellular foams (V-MCF) obtained by direct synthesis. Microporous Mesoporous Mater. 2011, 142, 45−54. (65) Piumettia, M.; Bonell, B.; Massiani, P.; Dzwigaj, S.; Rossetti, I.; Casale, S.; Armandi, M.; Thomas, C.; Garrone, E. Effect of vanadium dispersion and of support properties on the catalytic activity of Vcontaining silicas. Catal. Today 2012, 179, 140−148. (66) Soler, J.; López-Nieto, J. M.; Herguido, J.; Menendez, M.; Santamaria, J. Oxidative Dehydrogenation of n-Butane in a Two-Zone Fluidized-Bed Reactor. Ind. Eng. Chem. Res. 1999, 38, 90−97. (67) Rubio, O.; Herguido, J.; Menendez, M. Oxidative Dehydrogenation of Butane in an Interconnected Fluidized-Bed Reactor. AIChE J. 2004, 50, 1510−1522. (68) Argyle, M. D. Oxidative Dehydrogenation of Light Alkanes on Metal Oxide Catalysts. University of California−Berkeley, Berkeley, CA, 2003. (69) Bell, A. T.; Iglesia, E.; Argyle, M. D.; Chen, K. Effect of Catalyst Structure on Oxidative Dehydrogenation of Ethane and Propane on Alumina-Supported Vanadia. J. Catal. 2002, 208, 139−149. (70) Blasco, T.; Galli, A.; López-Nieto, J. M.; Trifiro, F. Oxidative Dehydrogenation of Ethane and n-Butane on VOx/Al2O3 Catalysts. J. Catal. 1997, 169, 203−211. (71) Fierro, J. L. G.; López-Nieto, J. M.; Kremenic, G. Selective Oxidation of Propene over Supported Vanadium Oxide Catalysts. Appl. Catal. 1990, 61, 235−251. (72) Al-Ghamdi, S. A.; Volpe, M.; Hossain, M. M.; De Lasa, H. I. VOx/c-Al2O3 Catalyst for Oxidative Dehydrogenation of Ethane to Ethylene: Desorption Kinetics and Catalytic Activity. Appl. Catal., A 2013, 450, 120−130. (73) (a) De Lasa, H. I. Riser Simulator, Can. Patent 1284017, 1991. (b) De Lasa, H. I. Riser Simulator, U.S. Patent 5,102,628, 1992. (74) Al-Ghamdi, S. A. Thesis: Supported Vanadium Oxide Catalyst for Ethane Oxidative Dehydrogenation to Ethylene: Catalyst Activity and Stability; Western University, 2010. (75) Huff, M. C.; Schmidt, L. D. Elementary Step Model of Ethane Oxidative Dehydrogenation on Pt-Coated Monoliths. AIChE J. 1996, 42, 3484−3497. (76) Oyama, S. T.; Middlebrook, A. M.; Somorjai, G. A. Kinetics of Ethane Oxidation on Vanadium Oxide. J. Phys. Chem. 1990, 94, 5029− 5033. (77) De Lasa, H. I.; Al-Khattaf, S. Catalytic Cracking of Cumene in a Riser Simulator: A Catalyst Activity Decay Model. Ind. Eng. Chem. Res. 2001, 5398−5404. (78) Hossain, M. M.; Atanda, L.; Al-Yassir, N.; Al-Khattaf, S. Kinetics modeling of ethylbenzene dehydrogenation to styrene over a mesoporous alumina supported iron catalyst. Chem. Eng. J. 2012, 207−208, 308−321. (79) Ollis, D. F.; Pelizzeti, E.; Serpone, N. Heterogeneous Photocatalysis in the Environment: Application to Water Purification. In Photocatalysis: Fundamentals and Applications; Wiley Interscience: New York, 1989; p 603. (80) Ginsburg, J.; De Lasa, H. I. Catalytic Gasification of Biomass in CREC Fluidized Riser Simulator. Int. J. Chem. Reactor Eng. 2005, 3, A38. (81) Pekediz, A.; Kraemer, D. W.; Chabot, J.; De Lasa, H. I. Mixing Patterns in a Novel Riser Simulator. Appl. Sci. 1992, 133−146. (82) Hossain, M. M.; De Lasa, H. I. Reduction and oxidation kinetics of Co−Ni/Al2O3 oxygen carrier involved in a chemical-looping combustion cycles. Chem. Eng. Sci. 2010, 65, 98−106. 5243



Research Note

(83) Gervasini, A.; Carniti, P.; Keränen, J.; Niinistö, L.; Auroux, A. Surface characteristics and activity in selective oxidation of o-xylene of supported V2O5 catalysts prepared by standard impregnation and atomic layer deposition. ̈ 2004, 96, 187−194. (84) Wachs, I. E.; Chen, Y.; Jehng, J.; Briand, L. E.; Tanaka, T. Molecular structure and reactivity of the Group V metal oxides. Catal. Today 2003, 78, 13−24. (85) Ballarini, N.; Cavani, F.; Cericola, A.; Cortelli, C.; Ferrari, M.; Capannelli, G.; Comite, A.; Catani, R.; Cornaro, U. Supported vanadium oxide-based catalysts for the oxidehydrogenation of propane under cyclic conditions. Catal. Today 2004, 92, 99−104. (86) Auroux, A. Acidity characterization by microcalorimetry and relationship with reactivity. Top. Catal. 1997, 4, 71−89. (87) Miyata, H.; Ono, T.; Fujii, K. Acidic Properties of Vanadium Oxide on Titania. J. Chem. Soc., Faraday Trans. 1 1988, 84, 3121− 3128. (88) Datka, J.; Turek, A. M.; Jheng, M.; Wachs, I. E. Acidic Properties of Supported Niobium Oxide Catalysts: An Infrared Spectroscopy Investigation. J. Catal. 1992, 135, 186−199. (89) Al-Ghamdi, S. A.; Volpe, M.; De Lasa, H. I. γ-Al2O3-Supported Vanadium Oxide Catalyst for Oxidative Dehydrogenation of Ethane to Ethylene: Reactivity and Stability Study. Presented at the 22nd NAM Catalysis Conference, Detroit, MI, 2011. (90) Le Bars, J.; Vedrine, J. C.; Bernard, C.; Auroux, A.; Trautmann, S.; Baerns, M. Role of surface acidity on vanadia/silica catalysts used in the oxidative dehydrogenation of ethane. Appl. Catal., A 1992, 88, 179−195.

5244


Kinetic Modeling of Ethane Oxidative Dehydrogenation over VO

Recommend Documents