Oxidative Dehydrogenation of Propane to Propylene over VOx on

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Article Cite This: Ind. Eng. Chem. Res. 2019, 58, 10785−10792

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Oxidative Dehydrogenation of Propane to Propylene over VOx on Mixed θ‑Al2O3/Alkaline Earth Metal Oxide Supports Idris A. Bakare,‡ Sagir Adamu,† Muhammad Qamaruddin,‡ Saad A. Al-Bogami,§ Sameer Al-Ghamdi,§ and Mohammad M. Hossain*,†,‡ Department of Chemical Engineering and ‡Center of Research Excellence in Nanotechnology, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia § Research & Development Center, Saudi Aramco Oil Company, Dhahran 31261, Saudi Arabia Downloaded via GUILFORD COLG on July 19, 2019 at 08:46:28 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

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ABSTRACT: The oxidative dehydrogenation of propane to propylene with solid-phase oxygen of VOx-based mixed-oxide catalysts is investigated. The catalysts are prepared by depositing VOx species on alkaline-oxide-modified θ-Al2O3 supports. Xray diffraction and X-ray photoelectron spectroscopy reveal the nature and variations of the crystalline phases. The surface area, acidity, and reduction properties of the catalysts are functions of the innate properties of bare θ-Al2O3 and the characteristic properties of each alkaline oxide. The multistage reduction of VOx on mixed-oxide supports indicates the reduction of various VOx species. The catalysts are evaluated in a fluidized CREC Riser Simulator by injecting a known amount of propane at different reaction temperatures. All catalysts show excellent propane conversion and plausible selectivity to olefins. VOx on θAl2O3/CaO minimizes the formation of COx species, whereas VOx θ-Al2O3/BaO displays the highest olefin yields (49%). catalyst lifetime, and so on.9−11 In this study, we have focused on developing an improved catalyst for propylene production via the ODH of propane. Although the ODH of propane is a favorable route for light olefin production, it has some inherent limitations. For example, the low selectivity of propylene and coking and the formation of COx are among the major challenges that limit the scale-up of the whole process.12−14 To improve the selectivity of propylene, which is drastically decreased by its recombustion during the ODH15 process, reactor design and catalyst development have been pursued.12 In this light, fluidized bed reactors have been found to offer some advantages over conventional reactor systems. Unlike the

1. INTRODUCTION The industrial need for light olefins has soared over the past decade because they are considered to be key components of the chemical industry. The global production of ethylene and propylene, which are the most desirable light olefins, has been estimated to be about 150 and 80 MT/year, respectively.1 As part of the ongoing efforts of the industries to meet this high demand, various technologies for olefin production have been established. These include steam catalytic cracking, which accounts for ∼70% of olefins produced,2 paraffin dehydrogenation,3 as well as fluid catalytic cracking of naphtha.4,5 Further advances in the field of technological research have led to the development of oxidative dehydrogenation (ODH) of light alkanes to olefins, which is an energy-efficient process, utilizing a cost-effective catalyst with low carbon emissions.6−8 The merits of the ODH process over other techniques for olefin production include a low operating temperature, less coke formation due to the presence of oxygen, a prolonged © 2019 American Chemical Society

Received: Revised: Accepted: Published: 10785

March 3, 2019 May 26, 2019 May 29, 2019 May 29, 2019 DOI: 10.1021/acs.iecr.9b01144 Ind. Eng. Chem. Res. 2019, 58, 10785−10792

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Industrial & Engineering Chemistry Research

Figure 1. (a) Pictorial view of the main parts of the CREC Riser Simulator. (b) Schematic diagram of the CREC Riser Simulator experimental setup.11

reaction and catalyst regeneration) presented by the fluidized bed reactor will further ease the operation of this technology on an industrial level.16,17 In the ODH process, mainly vanadium-supported catalysts and molybdenum-supported catalysts are employed.13 Specifically, the vanadium-based catalyst is the most widely used due

conventional reactors, fluidized bed reactors have the following distinct advantages, namely, uniform residence time distribution, elimination of mass-transfer limitations, and controlled isothermal conditions. Hence the problems of hot spots in fixed-bed reactors could be avoided. In addition, the periodic reoxidation of the catalyst using the twin reactor system (i.e., 10786

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sample was initially oxidized in a gaseous mixture of 5 vol % oxygen in 95 vol % helium for 1 h at 800 °C. Subsequently, the samples were cooled with Ar gas to room temperature. Following this, a 10.2% H2−Ar mixture at a flow rate of 50 mL· min−1 was introduced. Simultaneously, the whole system was heated from ambient temperature to 800 °C at rate of 10 °C min−1. Lastly, the volumes of hydrogen consumed were measured using a thermal conductivity detector (TCD). 2.2.4. Temperature-Programmed Desorption. Ammonia temperature-programmed desorption (NH3-TPD) is an important technique employed in probing the acid strength of metal-supported catalyst systems. NH3-TPD analysis was done following the procedure of our previous report.19 In a typical analysis, ∼0.28 g of newly prepared catalyst sample was placed in a quartz tube and degassed under helium flow (30 mL/min for 2 h at 500 °C) and then cooled to 100 °C. Thereafter, a gaseous stream containing 4.55% NH3 balanced with helium was introduced (at a flow rate of 50 mL min−1) for 1 h. Then, excessive physisorbed NH3 molecules were removed by purging with helium gas for 1 h. Finally, the NH3 desorbed was recorded using a TCD as the system temperature was ramped at 10 °C min−1 to 800 °C. 2.3. ODH of Propane Using a Fluidized CREC Riser Simulator. The ODH catalytic activity of the V, VM, VC, and VB catalyst systems was evaluated using a fluidized CREC Riser Simulator.9,11,18 Detailed information on the fluidized bed CREC reactor has been reported in our previous reports.20 Succinctly, the fluidized bed reactor (capacity of 53 mL) is a batch unit that mimics the fluidized bed reactor operation condition. The CREC riser simulator consists of lower and upper shells, which aids the effortless loading and removal of catalyst samples into the reactor chamber. The upper shell constitutes an impeller (with speed of ∼7000 rpm), which facilitates the fluidization of catalyst in the reactor’s basket located in the lower shell. The 3D diagram of the CREC Riser Simulator reactor body is shown in Figure 1a. Figure 1b shows the schematic diagram of the CREC Riser Simulator experimental setup, including the GC analysis. The ODH experiments were done using a fixed amount of catalyst. Prior to purging the reactor basket and the vacuum box, an initial leak test was conducted. Thereafter, the reactor was heated in an oxygen-free environment (argon gas environment) to the desired temperature. After the desired temperature was attained, the vacuum pump was then evacuated to 20.7 kPa (3.75 psi) to prepare the whole setup for the reaction. At this point, the catalyst was then fluidized by the impeller, and propane feed was injected into the reactor by using a leak-free syringe. Afterward, the reaction was conducted for a specified time. After the reaction was completed, the isolation valve linking the reactor and vacuum box opened automatically. The products and all of the unreacted feed went into the vacuum box and were then analyzed using an online Agilent 7890A GC equipped with a TCD and flame ionization detector (FID). The product analysis for each reaction run was done three times to ensure accuracy. Thermal experiments were also conducted to determine whether there would be some noncatalytic thermal cracking under the operating conditions. Finally, feed conversion and product selectivity were calculated based on integrated GC data. The feed conversion and the product selectivity have been calculated using eqs 1 and 2, respectively

to its characteristic lattice oxygen that enhances the dehydrogenation of alkanes.9,18 In this study, we compare the ODH of propane using VOx supported on CaO/θ-Al2O3, MgO/θ-Al2O3, and BaO/θ-Al2O3. It is ubiquitous knowledge that θ-Al2O3 favors the overoxidation of the reactant to COx species and coke. Therefore, employing a mixed acidic (θAl2O3) and basic support (BaO, CaO, and MgO) will produce a catalytic system with mild acidic properties that will, in turn, reduce the overoxidation of reactants to COx and coke. In addition, we expect a synergic effect due to the addition of CaO, MgO, or BaO and an overall more stable and durable catalyst system. To achieve these objectives, we have developed the targeted catalyst series employing the wet impregnation technique. X-ray diffraction (XRD), Fouriertransform infrared spectroscopy (FTIR), Brunauer−Emmett− Teller (BET), temperature-programmed desorption (TPD), Xray photoelectron spectroscopy (XPS), and temperatureprogrammed reduction (TPR) characterization techniques were employed to understand the nature of the prepared samples. The catalytic ODH of propane experiments was conducted using a fluidized CREC Riser Simulator in the absence of gas-phase oxygen. In this approach, the ODH of propane is achieved with the solid-phase oxygen of the catalysts. The main benefit of this proposed process is the opportunity to attain higher propylene yields by the proper control of the catalyst acidity and oxygen-carrying capacity.

2. EXPERIMENTAL SECTION 2.1. Catalyst Preparation. The VOx/mixed-support catalyst species were prepared by impregnating vanadyl acetyl acetate on a 1:1 mol ratio of θ-Al2O3 and alkaline earth oxide (MgO, CaO, or BaO). Typically, to prepare 10 wt % V2O5 on 2.0 g of support (bare theta alumina or a 1:1 ratio of theta alumina with MgO, CaO, or BaO), 0.3 g of vanadyl acetyl acetanoate was dissolved in toluene. Thereafter, the θ-Al2O3 and alkaline earth oxide supports were introduced into the toluene solution, which was left under constant stirring for 24 h. The resulting mixture was filtered, and the solid was washed with a copious amount of fresh solvent. The sample was then dried at 150 °C for 12 h before calcination under a gaschromatography (GC)-quality air stream for a period of 6 h at 600 °C. To simplify the nomenclature, we have designated the prepared catalyst systems as V, VC, VB, and VM, where V represents vanadium-impregnated θ-Al2O3 (i.e., V/θ-Al2O3), VC is vanadium impregnated on mixed θ-Al2O3/CaO support, VB is vanadium impregnated on mixed θ-Al2O3/BaO support, and VM is vanadium impregnated on mixed θ-Al2O3/MgO support. 2.2. Catalyst Characterization. 2.2.1. X-ray Diffraction. The XRD patterns of prepared V, VB, VC, and VM catalyst systems were analyzed using a Rigaku MiniFlex diffractometer machine. Samples were measured in the 2θ range of 10−75° using a step size of 0.02°. 2.2.2. N2 Adsorption Isotherms. To determine the BET surface areas and pore volumes of the synthesized catalysts and support, N2 adsorption was done using a Micromeritics model ASAP 2010 analyzer. During the course of analysis, ∼0.2 g of prepared catalyst was pretreated for 3 h at 350 °C under the flow of nitrogen gas. Thereafter, N2 adsorption was carried out in liquid nitrogen at 77 K in the relative pressure range of 10−6 to 1. 2.2.3. Temperature-Programmed Reduction. TPR was performed to determine the reducibility of the catalysts. Each 10787

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Industrial & Engineering Chemistry Research propane conversion, XC3H8 (%) =

∑j zjnj 3npropane + ∑j zjnj

constituent phases were θ-Al2O3, BaCO3, and BaO matched with Powder Diffraction File (PDF) database references 01086-1410, 01-078-4342, and 01-085-0418, respectively. The content in wt % of θ-Al2O3, BaCO3, and BaO in VB is 50, 43, and 7%, respectively. In the case of VC, the constituent phases were θ-Al2O3, CaCO3, and CaO matched with PDF database references 01-086-1410, 01-070-5490, and 01-085-0849, respectively. Also, the content in wt % of θ-Al2O3, CaCO3, and CaO in VC is 67, 26, and 7%, respectively. XPS analysis of prepared samples further corroborated the presence of carbonate species in samples VM, VC, and VB. XPS plots (Figure 3) for carbon in samples VM, VC, and VB

× 100 (1)

selectivity to a product, Sj (%) =

zjnj ∑j zjnj

× 100 (2)

where zj and nj are the number of atoms of carbon and moles of gaseous carbon containing product j, respectively. npropane is the moles of unconverted propane in the product stream.

3. RESULTS AND DISCUSSION 3.1. Chemical Composition of Prepared Catalyst Systems. Understanding the exact nature of a catalyst system would give a clear understanding of its activity. To properly comprehend the nature of our catalyst systems, we have characterized them using X-ray analysis, XPS analysis, and Raman spectroscopy. Figure 2a,b presents the XRD patterns of the bare θ-Al2O3 support, V, VB, VC, and VM. It is clear that the addition of

Figure 3. XPS spectra of C for prepared catalyst systems.

clearly show two distinct peaks of C. The first peak at 284.8 relates to the inherent adventitious carbon peak, whereas the peak at ∼290 eV corresponds to the carbonate species present in VM, VC, and VB, respectively. It is worth mentioning that our initial materials for the synthesis of VB, VC, and VM were BaO, CaO, and MgO, respectively, mixed in an equimolar ratio with alumina; however, during the synthesis, the acetate ion from the vanadium precursor used during the sample preparation oxidizes to CO2. This CO2 coupled with atmospheric CO2 then reacts with the alkaline earth metal oxides to form their respective carbonates. In sample VM, the MgCO3 formed is easily reconverted to MgO during calcination, whereas in samples VB and VC, the BaCO3 and CaCO3 formed remain stable even after calcination at 550 °C. Furthermore, the vanadium species present in the synthesized catalyst systems were not identifiable by XRD analysis; however, XPS analysis confirms the presence of vanadium species. The XPS plot in Figure 4 shows the presence of VOx Figure 2. (a) XRD spectra of (a) θ-Al2O3, (b) V, and (c) VM. (b) XRD spectra of (a) θ-Al2O3, (b) VC, and (c) VB.

VOx species to the bare θ-Al2O3 support (that is sample V) led to a reduction in the peak intensities of the support. In addition, no VOx species peak was observed after impregnation with vanadium precursor. The absence of VOx species peaks implies that the VOx species formed were unidentifiable by Xray. Also, the XRD pattern of the sample VM showed peaks of θ-Al2O3 and MgO supports and no peaks corresponding to vanadium species. Interestingly, in the XRD pattern of samples VB and VC, we not only found peaks corresponding to BaO and CaO species, respectively, but also found peaks corresponding to their respective carbonates. The XRD patterns of prepared sample were matched using PDXL software. For Sample VB, the

Figure 4. XPS spectra to identify vanadium species in the prepared catalyst systems. 10788

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Industrial & Engineering Chemistry Research species, as clearly indicated by V 2p peaks at ∼517 eV.21 This is also consistent with the results of Hryha et al.,22 who applied XPS to study the oxidation states of stoichiometric amounts of vanadium oxides. 3.2. N2 Sorption Properties of Prepared Catalyst Systems. Table 1 shows the N2 sorption properties of the

Table 2. Acidity of Catalyst Systems

Table 1. N2 Sorption Properties of Prepared Catalyst Systems samples

SBET (m2/g)

SExt (m2/g)

SMicro (m2/g)

VM (cm3/g)

VT (cm3/g)

θ-Al2O3 V VM VC VB

77 75 48 39 19

66 67 42 33 15

11 8 6 6 4

0.0045 0.0032 0.0023 0.0025 0.0019

0.317 0.325 0.167 0.138 0.108

a

samples

NH3 desorbed at LT (mmol/g)a

NH3 desorbed at HT (mmol/g)b

total NH3 desorbed (mmol/g)

LT/HT

θ-Al2O3 V VM VC VB

0.710 0.178 0.139 0.634 0.443

0.61 0.28 0.42 0.57 0.28

1.32 0.45 0.56 1.20 0.72

1.16 0.64 0.33 1.11 1.58

LT: Low temperature. bHT: High temperature.

sample VC, the TPD peak was of a broadening type (merging of two peaks) as opposed to two distinct peaks, as in the bare θ-Al2O3 support. These broadenings suggest the presence of mainly medium strength acidity in sample VC. Furthermore, sample VB had three peaks, which could be classified as weak, medium, and strong acidities, respectively, whereas sample VM had two main peaks, one at low temperature corresponding to weak/medium acid sites and one at high temperature corresponding to strong acid sites. Interestingly, we observed that VM had the strongest acid sites because its hightemperature peak exhibits the highest value of temperature maxima, as clearly evident in Figure 5. The acidities measured in VC and VB are apparently higher than those of V and VM catalysts. This is possibly inflated by the CO2 generated from the decomposition of the carbonates in VB and VC samples, as observed in the XRD analyses. Moreover, the TCD cannot distinguish NH3 from CO2 molecules. It should be noted, however, that NH3 TPD of alumina-supported metal oxides proceeds beyond 500 °C (see Mohan et al.,23 Ayandiran et al.,6 Khan et al.,24 etc.). Therefore, it is also possible that in the present work, NH3 desorption from the catalyst surface might have taken place throughout the entire temperature range (i.e., up to 800 °C). Figure 6 shows the TPR profiles of V, VM, VC, and VB. The TPR profile shows that the reduction of V2O5 to V2O3 occurred in a multistage manner. Low-temperature peaks are assigned to the reduction of the isolated monomeric units, whereas high-temperature peaks are assigned to the reduction of oligomeric units. The peaks having a temperature maximum around 700 °C connote the presence of V2O5 bulk-like species. Sample V exhibits three peaks with peak maxima at ∼298,

prepared catalyst systems. The surface areas and pore volumes of the catalyst systems are dependent on the initial surface area of the constituent support. As shown in Table 1, θ-Al2O3 has a surface area of 77 m2/g. It should be noted that the alkaline metal oxide modifiers (i.e., Mg, Ca, Ba) belong to the group in the periodic table (i.e., Group IIA). The decrease in the BET surface area of the catalysts, as shown in Table 1, follows from the fact that the atomic diameter of the species increases in the order Mg < Ca < Ba. 3.3. Acidity of Prepared Catalyst Systems. The NH3TPD profiles of the bare θ-Al2O3 support and the prepared catalyst samples are shown in Figure 5 and Table 2. The order of acidity of the samples is found to be θ-Al2O3 > VC > VB > VM > V. The acidity distribution in each catalyst system was quite different. θ-Al2O3 has primarily two peaks, one at a low temperature and the other at a higher temperature, corresponding to weak/medium and strong acid sites, respectively. After incorporating vanadium into θ-Al2O3 (i.e., sample “V”), we observed an apparent reduction in these peaks. This reduction of acidity resulted from the neutralization of some acid sites by VOx species and was also due to the blockage of the θ-Al2O3 pore by VOx species, which prevent access to some acid sites in the θ-Al2O3 support. Furthermore, the acidity in VC, VB, and VM is a function of the contributory effect from both θ-Al2O3 and alkaline oxide. For instance, in

Figure 5. NH3 TPD profiles of prepared catalysts systems. 10789

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Figure 6. TPR profiles of the prepared catalyst systems.

∼476, and 699 °C. This means that it contains the monomeric, oligomeric, and bulk V2O5 species. Furthermore, the figure shows that as the ODH temperature is increased from 600 to 650 °C, more vanadium species will get reduced by providing additional lattice oxygen for the reaction. Therefore, increasing the reaction temperature does increase the excitation of the propane molecules as well as enhance the propane ODH by facilitating the catalyst reduction. Similarly, for sample VM, we observed two peak maxima at ∼343 and ∼618 °C. Furthermore, in sample VC, we have peak maxima at ∼414, 621, and 707 °C. Finally, in VB, we have peak maxima at ∼358, ∼507, and 681 °C. From these peak maxima positions, it can be inferred that the catalysts contain vanadium species in the monomeric, oligomeric, and bulk states. 3.4. ODH of Propane-Fluidized CREC Riser Simulator. The highest ODH temperature (i.e., 650 °C) was selected for thermal runs (i.e., without any catalyst) to measure the effect of anaerobic dehydrogenation during a period of 30 s. Product analyses indicate mainly unconverted propane and small amounts of ethane and methane. This is consistent with a previous report on propane ODH by our research group.6,25 Therefore, the results that will be discussed shortly are mainly due to the activities of the catalyst under the given operating conditions. ODH of propane over V/θ-Al2O3 in the riser simulator is shown in Figure 7. Propane conversion increased from 57 to 86% when the temperature was increased from 600 to 625 °C. This is partly ascribed to the increase in the average kinetic energy of the reactant molecules (i.e., propane and lattice oxygen of the metal catalyst) to interact with the surface of the catalyst. Furthermore, there is higher tendency of CO2 reoxidation of the reduced VOx species during the reaction period.26 At 650 °C, the conversion decreased slightly, probably due to the competing side reactions, which limit the extent of CO2 reoxidation of the reduced VOx species. This, in turn, limited

Figure 7. Catalytic activity of V in the ODH of propane.

the total amount of available lattice oxygen from the various VOx species present in the V/θ-Al2O3 catalyst. Therefore, a reaction temperature of 625 °C seems to be an optimum for the ODH of propane over the newly prepared V/θ-Al2O3 catalyst. The olefin yield and selectivity increased with the reaction temperature. This is consistent with the reports on the effect of temperature on propane ODH in the literature.27,28 Comparing Figures 6 (TPR profile of sample V) and 7, we see that the selectivity for olefins correlates very well with the available lattice oxygen, as it increases over the temperature range from 600 to 650 °C. This is consistent with the previous VOx/Al2O3 studies on propane ODH.11,12 The catalytic activities of samples VM, VC, and VB for the ODH of propane are as shown in Figures 8−10, respectively. It is quite clear that the activity of each catalyst varies at different studied temperatures owing to the makeup of each catalyst systems. In VM, we observed that propane conversion, olefin 10790

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the temperature was increased to 650 °C to enhance the propane conversion, olefin selectivity, and yield. This is consistent with the findings of Kondratenko et al.26 that the reaction rate of propane ODH is dependent on the reoxidation of reduced sites over the VOx catalyst. For instance, the conversion was ∼94% at 600 °C, then it dropped to ∼91% at 625 °C and finally increased to ∼97% at 650 °C. It is worth mentioning that there are two prevalent side reactions during the ODH of alkanes, especially the higher ones. These are cracking and overoxidation (or combustion) processes. Selectivity to paraffins (ethane and methane) and selectivity to COx are the indicators of the extent of cracking or overoxidization during the ODH of propane. All prepared catalyst systems exhibited low selectivity to COx, indicating that the combustion side reaction was suppressed. The low selectivity to COx was most prevalent in sample VC, which exhibited only ∼2% selectivity to COx at 650 °C. Furthermore, each catalyst system showed preference to the type of olefin generated during the ODH process. Finally, it is proposed that the relatively higher low-temperature/high-temperature (LT/ HT) acidity ratio in sample VB could be another reason for its best performance. From Figures 7−10, it is notably evident that propane conversion did not always follow the expected trend of increasing as the temperature is increased from 600 to 650 °C. In Figure 9 (i.e., catalyst VC), for instance, the initial conversion at 600 °C was already very high and probably close to the equilibrium. Therefore, the observed decrease in propane conversion when the temperature was increased to 650 °C could be due to competing coke oxidation or partial olefin reoxidation, as favored by the incremental temperature difference.

Figure 8. Catalytic activity of VM in the ODH of propane.

4. CONCLUSIONS All samples showed good activity in the ODH of propane. In particular, VB showed better selectivity and yields to olefins when compared with V, VC, and VM. The following salient points can be deduced from the present study. (1) XRD and XPS analyses showed that the catalyst samples VB and VC contain some carbonate forms that are certainly from the acetate moiety of the vanadium precursor. Furthermore, the carbonate in VB was found to be stable beyond the calcination temperature of 550 °C. This route of carbonate formation might have contributed to the distinctive properties of the VB and VC catalysts as compared with VM. (2) The presence of MgO, CaO, or BaO decreased the catalyst specific surface areas (i.e., 48 m2/g for MgO-modified catalyst and the lowest, 19 m2/g, for BaO-modified catalyst) due to increase in the atomic radius of the alkaline metal oxide as well as the surface carbonates in VC and VB catalysts. (3) The incorporation of MgO, CaO, or BaO has indeed produced ODH catalysts with mild acidic properties that regulate the overoxidation of reactants to COx and suppress coke formation. (4) The unpromoted VOx/θ-Al2O3 catalyst showed a sharp increase in propane conversion from 600 to 625 °C (i.e., 57 to 86%) due to the increase in the average kinetic energy of the reactant species (i.e., propane and lattice oxygen) and the CO2 reoxidation of the reduced vanadium species. At 650 °C, the catalyst showed slightly lower conversion (i.e., ∼83%) due to some side reactions that ensue at higher temperature. However, the selectivity and the yield of olefins consistently increased.

Figure 9. Catalytic activity of VC in the ODH of propane.

Figure 10. Catalytic activity of VB in the ODH of propane.

selectivity, and olefin yield followed similar trend with respect to the reaction temperature. Each of these variables showed the highest conversion, selectivity for olefins, and yield at 650 °C and the lowest values at 625 °C. This means that the increase in the amount of reducible VOx species at 650 °C outweighs the excessive coking or possible reoxidation of the olefins. It is also possible that some reduced VOx species could have reoxidized by abstracting an oxygen atom from CO229 when 10791

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(14) Yusuf, S.; Neal, L. M.; Li, F. Effect of Promoters on ManganeseContaining Mixed Metal Oxides for Oxidative Dehydrogenation of Ethane via a Cyclic Redox Scheme. ACS Catal. 2017, 7, 5163. (15) Chaturbedy, P.; Ahamed, M.; Eswaramoorthy, M. Oxidative Dehydrogenation of Propane over a High Surface Area Boron Nitride Catalyst: Exceptional Selectivity for Olefins at High Conversion. ACS Omega 2018, 3, 369. (16) Elbadawi, A. H.; Ba-Shammakh, M. S.; Al-Ghamdi, S.; Razzak, S. A.; Hossain, M. M. Reduction Kinetics and Catalytic Activity of VOx/γ-Al2O3-ZrO2 for Gas Phase Oxygen Free ODH of Ethane. Chem. Eng. J. 2016, 284, 448. (17) Adamu, S.; Xiong, Q.; Bakare, I. A.; Hossain, M. M. Ni/CeAl2O3 for Optimum Hydrogen Production from Biomass/Tar Model Compounds: Role of Support Type and Ceria Modification on Desorption Kinetics. Int. J. Hydrogen Energy 2019, 44, 15811. (18) Wang, C.; Chen, J.-G.; Xing, T.; Liu, Z.-T.; Liu, Z.-W.; Jiang, J.; Lu, J. Vanadium Oxide Supported on Titanosilicates for the Oxidative Dehydrogenation of N-Butane. Ind. Eng. Chem. Res. 2015, 54, 3602. (19) Adamu, S.; Razzak, S. A.; Hossain, M. M. Fluidizable Ni/CeMeso-Al2O3 for Gasification of Glucose: Effect of Catalyst Reduction on Hydrogen Selectivity. J. Ind. Eng. Chem. 2018, 64, 467. (20) Adamu, S.; Hossain, M. M. Kinetics of Steam Gasification of Glucose as a Biomass Surrogate over Ni/Ce−Mesoporous Al2O3 in a Fluidized Bed Reactor. Ind. Eng. Chem. Res. 2018, 57, 3128. (21) Qiao, A. L.; Kalevaru, V. N.; Radnik, J.; Martin, A. Oxidative Dehydrogenation of Ethane to Ethylene over Ni-Nb-M-O Catalysts: Effect of Promoter Metal and CO2-Admixture on the Performance. Catal. Today 2016, 264, 144. (22) Hryha, E.; Rutqvist, E.; Nyborg, L. Stoichiometric Vanadium Oxides Studied by XPS. Surf. Interface Anal. 2012, 44, 1022. (23) Mohan, V.; Venkateshwarlu, V.; Pramod, C. V.; Raju, B. D.; Rao, K. S. R. Vapour Phase Hydrocyclisation of Levulinic Acid to γValerolactone over Supported Ni Catalysts. Catal. Sci. Technol. 2014, 4, 1253. (24) Khan, M. Y.; Al-Ghamdi, S.; Razzak, S. A.; Hossain, M. M.; de Lasa, H. Fluidized Bed Oxidative Dehydrogenation of Ethane to Ethylene over VOx/Ce-ΓAl2O3 Catalysts: Reduction Kinetics and Catalyst Activity. Mol. Catal. 2017, 443, 78. (25) Hossain, M. M. Kinetics of Oxidative Dehydrogenation of Propane to Propylene Using Lattice Oxygen of VOx/CaO/γAl2O3. Ind. Eng. Chem. Res. 2017, 56, 4309. (26) Kondratenko, E. V.; Sinev, M. Y. Effect of Nature and Surface Density of Oxygen Species on Product Distribution in the Oxidative Dehydrogenation of Propane over Oxide Catalysts. Appl. Catal., A 2007, 325, 353. (27) Mitra, B.; Wachs, I. E.; Deo, G. Promotion of the Propane ODH Reaction over Supported V2O5/Al2O3 Catalyst with Secondary Surface Metal Oxide Additives. J. Catal. 2006, 240, 151. (28) Asghari, E.; Haghighi, M.; Rahmani, F. CO2-Oxidative Dehydrogenation of Ethane to Ethylene over Cr/MCM-41 Nanocatalyst Synthesized via Hydrothermal/Impregnation Methods: Influence of Chromium Content on Catalytic Properties and Performance. J. Mol. Catal. A: Chem. 2016, 418−419, 115. (29) Saito, K.; Okuda, K.; Ikenaga, N.; Miyake, T.; Suzuki, T. Role of Lattice Oxygen of Metal Oxides in the Dehydrogenation of Ethylbenzene under a Carbon Dioxide Atmosphere. J. Phys. Chem. A 2010, 114, 3845.

(5) The incorporation of magnesium in VOx/θ-Al2O3 resulted in a catalyst system (i.e., sample VM) with a similar trend in propane conversion, olefin selectivity, and olefin yield with respect to the reaction temperature. For instance, conversion was ∼94% at 600 °C, then it dropped to ∼91% at 625 °C and finally increased to ∼97% at 650 °C.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +966-13-860-1478. Fax: +966-13-860-4234. E-mail: [email protected]. ORCID

Mohammad M. Hossain: 0000-0002-7780-5910 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We acknowledge the support provided by Research & Development Center, Saudi Aramco Oil Company for funding this work through project CENT2210. We thank the Center of Research Excellence in Nanotechnology (CENT) at KFUPM for some catalyst characterizations.

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DOI: 10.1021/acs.iecr.9b01144 Ind. Eng. Chem. Res. 2019, 58, 10785−10792