Dehydrogenation of Ethylbenzene with Carbon Dioxide in the

Subscriber access provided by HACETTEPE UNIVERSITESI KUTUPHANESI

Article

Dehydrogenation of Ethylbenzene with Carbon Dioxide in the Presence of Chromosilicate-Based Composites Maasoumeh Khatamian, Maryam Saket Oskoui, and Ebrahim Sadeghi J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.6b12376 • Publication Date (Web): 13 Mar 2017 Downloaded from http://pubs.acs.org on March 17, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry C is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Dehydrogenation of Ethylbenzene with Carbon Dioxide in the Presence of Chromosilicate-based Composites M. Khatamian1, a, M. Saket Oskoui a, E. Sadeghi a,b a.

Physical Inorganic Chemistry Research Laboratory, Department of Inorganic Chemistry,

Faculty of Chemistry, Tabriz, Iran b.

Department of Chemical Engineering, Faculty of Chemistry, University of Tabriz, Tabriz, Iran

Abstract In this work, the catalytic performance of a series of Fe2O3/Chromosilicate (Fe2O3/M[Cr]ZSM-5, M= Na or K) composites with different Fe2O3 loadings together with pure γ-Fe2O3 was investigated for the dehydrogenation of ethylbenzene (EB) to styrene (ST) in the presence of CO2 as the oxidant. The composites were prepared by a solid-state dispersion (SSD) method. These samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetry (TG), Fourier transform infrared spectroscopy (FT-IR) and N2 physical adsorption analysis. According to the results, virgin γ-Fe2O3 revealed low performance (in terms of selectivity to styrene) due to the partial reduction of Fe3+ ions in its structure. For the purpose of improving the efficiency of Fe2O3

1

Corresponding author: Email: [email protected], Tel: +98-411-3393129, Fax: +98-411-3340191.

Postal address: Physical Inorganic Chemistry Research Laboratory, Department of Inorganic Chemistry, Faculty of Chemistry, Tabriz, Iran.

1 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 42

nanoparticles in ethylbenzene dehydrogenation reaction, chromosilicate was used as a support and Fe2O3/Chromosilicate composites were prepared by introducing different amounts of Fe2O3. In this way, the effect of Fe2O3 loading on catalytic activity of pure chromosilicate samples was also investigated. The results exhibited that the 10% Fe2O3/sodium chromosilicate (10F/NCS) catalyst presented the best catalytic performance for the dehydrogenation of ethylbenzene among the synthesized composites (styrene yield of 50.87% at high styrene selectivity of 95.8%). However, the KCSBW catalyst (potassium chromosilicate before washing with distilled water) offered the highest styrene yield, 56.19% with the selectivity of 96.05%, in the presence of CO2 among the all catalysts tested. The differences of catalytic activity in ethylebenzene dehydrogenation process can be attributed to the textural properties of the composites, pH of active sites and also the synergic effect of potassium ion with Fe2O3 or Cr2O3 as well as sodium ion with Fe2O3 or Cr2O3, which is discussed in detail. In this way, it can be distinguished that the role of chromium oxide species was more critical and efficient than Fe2O3 nanoparticles in the structure of the catalysts in dehydrogenation process. 1. Introduction Styrene (ST) is one of the most essential materials in petrochemical industry for production of synthetic polymers and plastics.1 The most conventional process for the commercial production of styrene is ethylbenzene (EB) dehydrogenation by the K-Fe-based catalyst with high iron loading in the presence of a large amount of superheated steam at high temperature of 600-650 °C.2-5 However, this traditional process has many disadvantages such as high energy consumption and thermodynamic equilibrium limitations. Hence, a worldwide investigation of the alternative process is being considered. Recently, as a substitute for steam, CO2 gas has received great attention as a co-feed gas for the dehydrogenation of ethylbenzene.

6

The presence of CO2 in ethylbenzene


Page 3 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


dehydrogenation reaction suppresses the coke formation and also helps remove the carbonaceous deposits.7-9 Furthermore, Mimura et al. suggested two viable reaction paths for the dehydrogenation of ethylbenzene in the presence of CO2.10 The first path (namely one-step pathway) is represented by Eq. (1), which produces ST directly through the oxidative dehydrogenation of EB with CO2. The second possible path (namely two-step pathway) is represented by Eqs. (2) and (3) which encompasses two reactions— firstly EB converts to ST with H2 formed besides, and secondly CO2 reacts with H2 by RWGS.11 Mimura and his colleagues estimated that, in the presence of CO2, the dehydrogenation of EB progress over the catalyst could proceed via 45% of a one-step pathway and via 55% of a two-step pathway.12-13 C6H5–C2H5 + CO2 → C6H5–C2H3 + CO + H2O

(1)

C6H5–C2H5 → C6H5–C2H3 + H2

(2)

H2 + CO2 → CO + H2O

(3)

However, in spite of the fact that EB dehydrogenation process in the presence of CO2 is believed to be energy-saving and environmentally friendly, the commercial Fe–Cr–K catalysts do not work effectively for EB dehydrogenation in the presence of CO2.10, 14-15 Thus, the development of new catalysts with improved catalytic activity for the mentioned process is required. For this purpose, a variety of metal oxide catalysts, such as iron oxide zirconia

22

16-17

, vanadia

18-19

, chromia

20-21

, ceria

20

, and

have been investigated by many researchers. Several catalysts have been tested in

ethylbenzene dehydrogenation in the presence of CO2.23-27 Regarding the critical role of support in providing a uniform dispersion of the active phase, it is predictable that, supported metal or metal oxide catalysts has been attracted many interests extensively both in experimental and industrial applications. This point can be related to their widespread utility in the chemical industry compared 3 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 42

with bulk oxide catalysts.28 Thus, catalysts based on iron oxide, supported on aluminum oxide exhibit sufficient activity in the dehydrogenation reaction.17, 29-30 In addition, the catalysts of iron oxide supported on silicon oxides have appreciable activity and also selectivity in the above mentioned reactions.31 Moreover, the results of a previous study by Muhler et al.3 demonstrated that the inclusion of promoters influenced the reduction properties of the iron oxide.32 Co-promotion of K-Fe2O3 with Cr improved the reduction resistance of the iron oxide, which apparently involved some interaction between Cr and K.32 Furthermore, Kotarba et al.33 has reported that in ST production catalysts, chromium can play two important roles as a stabilizer and also as an activity enhancer. As a consequence, chromosilicate (which can be considered the supported chromium oxide in the silicon oxide matrix) can be a proper candidate for using as a support in preparation of iron oxide-based composites for utilization as efficient catalysts in EB dehydrogenation process. In this work, aiming to find alternative catalysts for this reaction, chromosilicate-supported iron oxides were prepared and evaluated in EB dehydrogenation in the presence of carbon dioxide. For this purpose, the effect of alkali-metal type (K or Na) of chromosilicate structure (as the support) as well as the amount of chromium oxide and iron oxide on their catalytic activity in the EB dehydrogenation process was evaluated. Finally, for the purpose of comparison and selecting the proper condition of the dehydrogenation process, an industrial catalyst (IC) named UCI 84C (UOP) (with similar components of the synthesized composites) has been used.

2. Experimental 2.1. Catalyst preparation 2.1.1. Preparing of M[Cr]ZSM-5 (MCS) as the support 4 ACS Paragon Plus Environment

Page 5 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


M[Cr]ZSM-5 (MCS) was synthesized according to the procedure in our previous work.34-35 In summary, the synthesis of MCS samples (for the case of sodium chromosilicate M=N and for the case of potassium chromosilicate M=K) was carried out in a non-stirred autoclave by the hydrothermal method. After crystallization, the as-synthesized samples were washed several times with distilled water and dried overnight in an oven at 120 °C. Calcination of the samples was made under air for 5 h at 550 °C. Materials that were used for the preparation of the samples were as follows: silicic acid (Merck), chromium (III) nitrate (Merck), sodium carbonate (Merck) or potassium carbonate (Merck) and tetrapropylammonium bromide (TPABr, Merck) (as template). Molar ratios of the investigated samples were Si/Cr = 15, TPABr/Si = 0.17, H2O/Si = 35, and Na or K /Si = 2. At this step, the obtained product (MCS) was washed with distilled water in order to remove chromium species. In this way, KCS samples before and after washing, were labeled as KCSBW and KCSAW, respectively. By the same way, NCS samples before and after washing were labeled as NCSBW and NCSAW, respectively. 2.1.2. Preparing of γ-Fe2O3 For the preparation of γ-Fe2O3, at first, a NaOH solution (2.5 M) was added dropwise to an aqueous solution of iron (II) sulphate until the pH of the mixture adjusted to 11. This procedure, took about 6 h under vigorous stirring, and the obtained solution (which was located in a heated water bath) separated into a two-phase solution. Afterwards, the solid phase was centrifuged and washed with distilled water for several times. Finally, the obtained sample was dried at room temperature; followed by the calcination of the obtained sample, which made for 45 min at 200°C. 2.1.3. Synthesis of Fe2O3/M[Cr]ZSM-5(F/MCS) composites



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 42

For the synthesis of the composites, different amounts of iron oxide (γ-Fe2O3) nanoparticles (2, 5, 10, and 20wt %) were introduced into chromosilicate pores using solid state dispersion (SSD) method. SSD initially involved mixing of nano iron oxide and MCS thoroughly using ethanol in agate mortar; then, the solvent was removed by evaporation while mixing. In this way, the new composites as Fe2O3/M[Cr]ZSM-5 (F/MCS) were synthesized. The prepared composites with 2, 5, 10, and 20wt % Fe2O3 were labeled 2F/MCS, 5F/MCS, 10F/MCS, and 20F/MCS, respectively. In addition, virgin γ-Fe2O3 was named as Fe2O3.

2.2. Apparatus and Procedure The fresh commercial catalysts were obtained from BASF Company. Figure 1 represents a schematic diagram of the used experimental setup for the dehydrogenation of EB process. The dehydrogenation experiments were performed over extruded catalysts with 0.5-1 mm diameter under atmospheric pressure in a tubular stainless steel reactor (4.3 mm i.d. and 500 mm length), equipped with an electrically heating system. Since the yield and selectivity of ST production can be improved by the low pressure gradients of the catalytic bed reactor, in the industry, it is better to use the catalyst in the form of pellet. Thus, our samples were stored in the form of cylindrical pellets of 1mm diameter and 0.7 cm length. Before performing of the process, 2.0 g of the catalyst per each run was placed between two inert quartz beds. The reaction was carried out at 873K for 4 h. Prior to the injection of EB into the reactor, the catalyst was activated thermally under a nitrogen flow (100 mL/min) from room temperature to 873 K at the heating rate of 145 K/h and maintained at this temperature for 30 min, but soon afterwards nitrogen flow was switched to CO2. EB was introduced to reactor by a micro pump with the feed rate of 36.64 mmol/h. The outlet stream from


Page 7 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the reactor was passed through a condenser equipped with the ice bath for GC analysis. The obtained products were analyzed by a Varian 3800 CX gas chromatograph apparatus using a flame inductivity detector (FID). Helium was used as the carrier gas, the injection temperature was 180°C, and the samples were injected into the split injection mode. For each measurement, at least three repeated injections were taken, which obtained reproducible results. ST, toluene, benzene, and unreacted EB were the main desired products. The quantitative analysis of the products was performed using the peak area normalization method. Benzene was the standard sample (sensitivity factor was set at 1).

Ethylbenzene conversion =

Styrene selectivity =

(ethylebenzenein- ethylebenzeneout) ethylebenzenein

styreneout (ethylebenzenein- ethylebenzeneout)

Where ethylbenzeneout or styreneout stands for the amount of EB or ST in the products. Reusability of the KCSBW sample (as the best catalyst) was investigated using the same condition (at 873K for 4 h). 2.3. Characterization of catalysts X-ray powder diffraction profiles were recorded in a STOE X-ray diffractometer system (Version: PKS‒2.01) employing Cu Kα radiation (λ = 1.540598 Å). The applied voltage and current were 40 kV and 40 mA, respectively. Crystal structures were determined using wide-angle diffraction patterns in the 2θ = 4–70 ° range with the step size of 0.06 ° and counting time of 1.0 sec/step.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 42

Scanning electron microscopy coupled with the energy dispersive analysis–EDX was performed to get data about the morphology and surface composition of the investigated samples. The analyses were performed using a Philips XL-30 system equipped with an EDX detector on the samples coated previously with a thin layer of gold. Adsorption–desorption isotherms of N2 were evaluated by an automatic adsorption system (BELSORP mini, BEL Japan Inc.) at 77 K (liquid nitrogen temperature). Thermo-gravimetric analysis (TGA/DTA) were conducted in TGA/STTA851 (Mettler Toledo) from 50 °C to 900°C, at heating rate of 10 °C/min under 20 ml min-1 of air flow. FTIR spectra of the samples were recorded on FTIR spectrophotometer (Tensor 27) using KBr pellets in region of 4000-400 cm-1.

3. Result and discussion 3.1. XRD analysis The XRD patterns of the investigated composites are given in Figure 2. For the comparison purpose, the patterns of unsupported Fe2O3 and pure chromosilicate samples (CS) after and before washing with distilled water are also included in this Figure (Figure 2). As shown in Figure 2, XRD patterns of the synthesized Na[Cr]ZSM-5 (NCS) and K[Cr]ZSM-5 (KCS) were in good agreement with the XRD pattern of ZSM-5 zeolite with orthorhombic symmetry in the literature 36, which was characterized by peaks at 2θ = 7.94, 8.86, 23.10, 23.9, and 24.45 representing (011), (200), (051), (033), and (313) planes of crystal structure, respectively. After loading different amounts of γ-Fe2O3, irrespective of the composition of the prepared composites, the diffraction lines of Fe2O3 (2θ = 29.9, 33.7, 57.4, and 63.01) were not observed; indicating the effective distribution of Fe2O3 species over the structure of the chromosilicate as the 8 ACS Paragon Plus Environment

Page 9 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


support (see Figure 2). In addition, in comparison with the characteristic peaks of virgin chromosilicate samples, the intensity of the corresponding peaks was slightly diminished for the obtained composites by increasing the loading amount of Fe2O3 in the structure of chromosilicate samples. Moreover the XRD pattern of the IC which has been used in this work for comparison with synthesized composites is presented in Figure 3. According to this figure, it can be identified the different crystalline phases of this catalyst using the standard JCPDS cards (33-0664 (Hematite (α-Fe2O3)), 31-1034 (K2Fe22O34) and 43-1002 (CeO2). By comparing the spent and fresh catalyst it can be well explained that during the catalyst deactivation Fe2O3, K2Fe22O34 and KFeO2 phases convert to Fe3O4 and FeO phases.

3.2. Morphology studies SEM images of the KCS and NCS samples before and also after washing with water are shown in Figure (4a-d). It can be distinguished that NCS appears as cubic particles; with a particle size ranged from 7 to 8 µm. Nevertheless, KCS has well-formed and quite uniform coffin-type crystals of relatively large sizes (about 20-21 µm). The SEM images of MCS samples exposed that the growth of crystal grains was well. Nonetheless, some amorphous grains was observed, which could be due to incomplete crystallization of some particles or can be referred to as CrO3 particles. In order to deeply understand the origin of these particles, we decided to perform SEM analysis of the mentioned samples after washing with distilled water. The goal was to understand the nature of these particles. As Figure 4 shows, a large amount of grains have been removed by distilled water, although some of them still remained unremoved. In this case, a large amount of these particles can be related to CrO3 particles and the remaining particles are the ones which cannot completely



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 42

accomplish the crystallization process. On the other hand, after introducing the Fe2O3 nanoparticles into the structure of the NCS and KCS samples (as the support) (Figure 4), the amounts of the mentioned grains on the CS samples would be increased, which can be attributed to the distribution of Fe2O3 nanoparticles over the support (CS samples). Additionally, the SEM image of the fresh and spent IC samples are shown in Figure 5 and the EDAX result of the specified points is gathered in Table 1. Indeed, the TEM image of 5F/NCS sample (Figure 6) presents the agglomeration of particles with irregular morphology, with diameter around 10–20 nm. Unfortunately, the porous structure could not be observed because of low-magnification.

3.3. Nitrogen Adsorption Isotherms and Pore Size Distribution: In order to acquire further insight into the porous structure and pore size distribution of the obtained samples Brunauer–Emmett–Teller (BET) measurements were performed to evaluate their specific textural properties37-38. The adsorption-desorption isotherms and corresponding (BJH) pore size distribution curves of all samples are shown in Figure 7 and Figure 8 respectively, and the textural properties are summarized in Table 2. As can be seen in Figure 7, and according to IUPAC Classification of Gas Adsorption Isotherms, all of the samples exhibit a type IV isotherm with a mesopore filling step, thus confirming the presence of mesoporosity.

39

The steep increasing of adsorbed amount at low relative pressure (P/P0< 0.1) (except for Fe2O3 nanoparticle), reveals the presence of micropores in these materials. At intermediate P/P0, a capillary condensation step and an H3-type hysteresis loop was distinguished, proposing the formation of slit-like pores during the synthesis process which was related to the loose assemblage of plate-like particles.40


Page 11 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The pore size distribution was obtained by applying the Barret-Joyner-Halenda method. The pore size distribution curves (obtained via BJH analysis of adsorption isotherm data) in Figure 8 show narrow distributions which were centered around 1.21nm, for all prepared samples (for all samples in pure or composite form it leads to the same result). However, the only exception is 20F/NCS composite. In contrast with other prepared samples, for the case of the mentioned sample, in spite of the simultaneous presence of micropores and mesopores, the mesoporous structure is predominant so that the pore size distribution curve shows a wide distribution which was centered around 4.03 nm. Furthermore, the pore size distribution curve of 2F/NCS sample has wider distribution than the others but possesses the similar size for majority of the pores (1.21 nm). According to the textural properties of the F/NCS composites (Table 2), it can be deduced that upon incorporation of Fe2O3 in the structure of NCS, the reorganization of the pores structure would occur and by increasing the amount of Fe2O3 to a maximum of 10% the extended pores (with larger size) can be achieved which is responsible for having higher catalytic activity for dehydrogenation of ethylebenzene in our work because of the extended active sites. However, an excess amount of Fe2O3 (more than 10% ) would cause the decreasing of the pore size and thereafter the abatement of the catalytic activity of dehydrogenation of ethylebenzene in our work. For the case of F/KCS composites, upon incorporation of Fe2O3 in the structure of KCS, the specific surface area would enhance by increasing the amount of Fe2O3 to a maximum of 5%. By more increase, the specific surface area of the composites would decrease. Herein, the increased specific surface area is responsible for having higher catalytic activity in our work. This can be due to the fact that the large surface area of the composites may facilitate the EB diffusion to active sites. As a result, it can be mentioned that enhanced pore size (for the case of



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 42

F/NCS composites) or increased specific surface area (for the case of F/KCS composites) can lead to improved catalytic activity in dehydrogenation process. 3.4. Catalytic performance of the prepared samples The dehydrogenation of EB was performed in the presence of CO2 at 600°C over CS samples (chromosilicate samples), F/CS composites (Fe2O3/Chromosilicate composites) and also a Fe-K commercial catalyst for comparison. The results are presented in Table 2 and Figure 9. As we can see, in the presence of the catalysts, EB predominantly converted into ST via an oxidative manner and ST selectivity improved at the cost of a decrease in conversion.41 According to the results (Table 2, Figure 9), the MCS-based catalysts can be ordered in terms of their selectivity toward ST production as follows: KCSBW ˃ NCSBW ˃ NCSAW ˃ KCSAW This order can be due to the critical role of potassium ion as a sufficient promoter besides with Cr2O3 as a proper co-promoter in these catalysts. After removing the significant amounts of Cr2O3, the treated sample (KCSAW) had lower selectivity even compared with its sodium analogous (NCSAW). The substitution of sodium instead of potassium as the alkali metal ion into the structure of chromosilicate can slightly increase the ST selectivity of the CSAW samples (chromosilicate samples after treatment with distilled water and removing a significant amount of Cr2O3). Appropriately, this trend approved that the synergistic effect of potassium ion and Cr2O3 for improving the catalytic activity was a little bit more critical than that of sodium ion and Cr2O3. 35 It should be mentioned that potassium or sodium ion can improve the catalytic activity cooperatively with Cr2O3 in a more efficient manner in comparison with that of acting alone.


Page 13 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Additionally, according to the obtained results (Table 2 and Figure 9), the activities of F/CS catalysts (in terms of ST selectivity) for EB dehydrogenation in the presence of CO2 as a function of Fe2O3 loading are illustrated in Figure 10. The KCS- and NCS-based catalysts can be ordered with respect to their selectivity toward ST production as follows: 5F/KCS˃10F/KCS ˃ 2F/KCS ˃ 20F/KCS 10F/NCS ˃2F/NCS ˃ 20F/NCS ˃ 5F/NCS Paying attention to Figure 10, it can be inferred that the catalytic activity of these catalysts depends upon Fe2O3 loading for both cases of KCS- and NCS-based catalysts; as Fe2O3 loading was increased, ST selectivity of EB on these samples first increased and, then, decreased. In this way, the maximum of 92.4% and 95.8% for ST selectivity appeared at the Fe2O3 loading of 5% and 10% for KCS- and NCS-based samples, respectively. It is noteworthy that the KCSAW and NCSAW samples (chromosilicate samples after washing with distilled water) were applied as the support of the composites. Regarding the literature,42-43 it is obviously predictable that, in EB dehydrogenation process over chromosilicate catalysts; in the presence of CO2, chromium can enhance catalysts’ stability against reduction and sintering, which leads to increasing the catalytic activity. Hence, it is inevitable that, among the introduced samples, KCS before washing with distilled water (KCSBW), can present the best catalytic performance in the presence of CO2, which can be related to the presence of chromium oxide species (Cr2O3 and CrO3) in the structure of the catalyst. Hence, this result confirms that adding Cr2O3 to the ST production catalysts reinforces their activity and discourages sintering, being in agreement with the literature.33 As reported by the results, in comparison with 13 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 42

pure chromosilicate (CSAW) as the support, the catalytic activity of all the synthesized composites (F/CS) was improved in terms of EB conversion percentage, whereas regarding ST selectivity, the catalytic activity just improved in the case of 2F/KCS, 5F/KCS and 10F/NCS samples. This fact clarifies the effective role for synergic effect of Fe2O3 and potassium (or sodium) for improving the EB conversion yield more than ST selectivity percentage in CS-based catalysts. Further, considering KCS-based composites, the 5F/KCN sample exhibited the best activity in terms of selectivity toward ST. By comparing the activity of the KCS-based composites with that of pure KCS sample before washing (KCSBW), the critical role of Cr2O3 as a promoter can be distinguished. As a result, the synergistic effect of Cr2O3 and potassium ion for enhancing the catalytic activity in the EB dehydrogenation process can be more important than that of Fe2O3 and potassium ion. In contrast, for the case of NCS-based composites, the importance of the synergistic effect of Fe2O3 and sodium ion (with the Fe2O3 loading of 10%) can be regarded higher. All applied catalysts exhibited low selectivity to benzene and toluene as the main byproducts of EB dehydrogenation. Regarding to the literature,44-45 the conversion and selectivity of EB to ST can be influenced by the acid–base and redox properties of the catalyst. Provided that the basic sites have enough strength to remove the β-hydrogen of EB, the cleavage of the C–C lateral bond (263.7 kJ mol−1) will be promoted and thus the selectivity to toluene will increase compared with benzene (as can be seen according to the Table 2 for some prepared catalysts including: 2F/KCS, 10F/KCS, 2F/NCS, 10F/NCS, KCSBW, NCSBW, NCSAW and Fe2O3). However, if the catalyst surface acidity is prominent, abstracting α-hydrogen of EB can be more applicable, hence the rupture of the phenyl-C bond (364.2 kJ mol−1) will be occurred with more probability, resulting in a higher selectivity to benzene compared with toluene (as can be seen according to the Table 2 for some prepared samples including: 5F/KCS, 20F/KCS, 5F/NCS, 20F/NCS and KCSAw). In general, for F/CS composites 14 ACS Paragon Plus Environment

Page 15 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


with Fe2O3 contents of 2 and 10 percent, the basicity of the samples, while for those with Fe2O3 contents of 5 and 20 percent, as similar to Fe2O3 particles in pure form, the acidity of the samples can be induced to be prominent. However, unfortunately there is not any logical trend between the content of Fe2O3 and acid-base properties of the composite surface. Moreover, among the CS catalysts basicity of CSBW samples can be inferred. However, for CSAW samples, the acid-base properties differ depending on the type of cation, which was used for CS preparation. As a consequence, if Cr2O3 is not removed from the CS structure (by washing with distilled water), the basicity of the catalyst is prominent without relating to the type of the used cation in the synthesis process of CS. Finally, it is noteworthy that, according to the results (Table 2), the ST selectivity of unsupported Fe2O3 in contrast to EB conversion could be improved by supporting the sample in the structure of chromosilicate as an efficient support, which is a good evidence for the fact that the supported form of iron oxide–based catalysts can be considered more proper candidates for EB dehydrogenation process in comparison with unsupported form. 3.4.1. Catalyst reusability Coking is considered as the principal factor responsible for deactivation of catalysts or their poor performance in EB dehydrogenation. In this study, Long-term stability of KCSBW sample (as the best catalyst) without regeneration is investigated by reusing up to 3 cycles. Moreover, the spent form of the mentioned sample after reusing for three times is regenerated by calcination at 550 °C in air atmosphere for 30 min. As shown in Figure 11, it can be seen that EB conversion of the catalyst is not affected remarkably after using for 2 cycle. However, a reduction trend can be observed in catalytic selectivity towards ST in each cycle for the spent catalyst without regeneration due to coke



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 42

formation on catalyst, which can result in the covering of active sites and obstruction of pores in catalyst.46 In spite of this result, after the regeneration of the catalyst, only a slight reduction of ST selectivity is detected, demonstrating that the catalytic selectivity can be recovered to some extent. FTIR spectrum of the spent catalyst of KCSBW after reusing for three times (Figure 12) confirms the obtained results. The spectrum presents a wide band at around 3621 cm-1 which is related to O-H stretches of the steam production throughout the reaction. The C=C bands at about 1647 cm-1 can be attributed to the vibration of polyaromatic species.47 Moreover, the peak that is observed at 1517 cm-1 can be related to carbon skeleton vibration of the aromatic ring containing compounds.48 According to the mass loss of the spent catalyst after combustion from 300 ºC up to 550 ºC,49 during the TGA experiment, the amount of coke deposition for the spent catalyst was calculated to be 2.75 wt % of the total weight of the catalyst. 3.4.2. Role of CO2 flow and CO2: EB molar ratio CO2 utilization offers several merits, such as acceleration of reaction rate, improvement in product selectivity, decrease of thermodynamic limitations, suppression of total oxidation, improving of catalyst life, prohibition of hotspots, and so many more. As reported by Ikenaga et al.,20 the role of carbon dioxide in the dehydrogenation of EB over a Cr2O3-based catalyst (activated carbon supported Cr2O3) is to keep the chromium (III) oxide phase during the reaction. They have suggested that one of the possible reaction pathways for the EB dehydrogenation to ST with the supported form of chromium species as the catalyst under carbon dioxide flow is the direct process. In this process, EB reduces chromium (III) oxide to reduced chromium oxide species on the catalyst surface, and carbon dioxide re-oxidizes it to chromium (III) oxide (Eqs. 4 and 5).


Page 17 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Based on our previous work,49 chromosilicate (which was used in this work as a support) is composed of Cr2O3 loaded silica. Thus, the obtained results of Ikenaga et al.,20 as already stated above, can be employed in our case of chromosilicate samples. Hence, chromosilicate can be considered an efficient support for the catalysts of EB dehydrogenation process in the presence of CO2. For the purpose of choosing the appropriate flow of CO2 and also the proper temperature in EB dehydrogenation process, the IC in the EB dehydrogenation process, was tested in seven different conditions, because of the component similarity between this catalyst and our synthesized composites. The results have been presented in Table 3 and Figure 13. Furthermore the similar test was performed using one of the obtained samples (5F/KCS) in three different flows of CO2. The results of this composite are summarized in Table 4.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 42

Regarding the results of the Table 3 and Table 4, it seems that enhancement of CO2 flow suppresses hydrogen production, which is formed as a product of the reaction; and thereby, it can increase ST selectivity and conversely decrease the amount of waste byproducts. Regardless of the amount of EB conversion, the objective of this work was to choose an appropriate flow for CO2, which could lead to the higher selectivity towards ST. On the other hand, the more the flow of CO2 might accompany with a slight decrease in the EB conversion. Consequently, due to the higher ST yield related to the flow of CO2 in 36.64 mL/min, this flow was chosen for all of the catalyst evaluations in EB dehydrogenation process. Moreover, according to the results of Table 3, the best temperature for the mentioned process in the presence of the catalysts of this work can be considered, 600°C. 4. Conclusion In conclusion, we have successfully prepared the Fe2O3/chromosilicate (F/CS) composites via a facile solid state dispersion method by introducing different amounts of γ-Fe2O3 in the structure of chromosilicate samples (KCS or NCS) as the support. We showed that carbon dioxide could be used as a selective oxidant in the oxidative dehydrogenation of EB to ST over chromosilicatebased catalysts. The 10% Fe2O3/sodium chromosilicate(10F/NCS) catalyst exhibited the best catalytic performance for the dehydrogenation of EB with CO2 among the synthesized composites, a much more energy-efficient process than the present commercial process using steam. A higher ST yield of 50.87% at high ST selectivity of 95.8% was achieved on this catalyst. However, the KCSBW catalyst (potassium chromosilicate before washing with distilled water) offered the highest ST yield, 56.19% with the selectivity of 96.05% in the presence of CO2. According to the results, the synergistic effect of Cr2O3 and potassium for enhancing the catalytic activity in the EB dehydrogenation process can be considered more effective than that 18 ACS Paragon Plus Environment

Page 19 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


of Fe2O3 and potassium. In contrast, for the case of NCS-based composites, the importance of the synergistic effect of Fe2O3 and sodium (with the Fe2O3 loading of 10%) can be regarded to be higher. Moreover, according to the textural properties of the prepared composites, it can be inferred that the enhanced pore size (for the case of F/NCS composites) or increased specific surface area (for the case of F/KCS composites) can provide improved catalytic activity in dehydrogenation process. Furthermore, long-term stability experiments on the best catalyst (KCSBW) exhibit that EB conversion of the catalyst is not affected remarkably after using for 2 cycle. However, a reduction trend can be observed in catalytic selectivity towards ST in each cycle for the spent catalyst without regeneration because of coke deposition on active sites of the catalyst.

Acknowledgments The authors would like to thank the University of Tabriz, Tabriz Petrochemical Company, and Iranian Nanotechnology Initiative Council for the financial support of this project.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 42

References 1. Saito, K.; Okuda, K.; Ikenaga, N.-o.; 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 2009, 114, 3845-3854. 2. Muhler, M.; Schlögl, R.; Reller, A.; Ertl, G. The Nature of the Active Phase of the Fe/KCatalyst for Dehydrogenation of Ethylbenzene. Catal. Lett. 1989, 2, 201-210. 3. Muhler, M.; Schütze, J.; Wesemann, M.; Rayment, T.; Dent, A.; Schlögl, R.; Ertl, G. The Nature of the Iron Oxide-Based Catalyst for Dehydrogenation of Ethylbenzene to Styrene: I. Solid-State chemistry and bulk characterization. J. Catal. 1990, 126, 339-360. 4. Muhler, M.; Schlögl, R.; Ertl, G. The Nature of the Iron Oxide-Based Catalyst for Dehydrogenation of Ethylbenzene to Styrene 2. Surface chemistry of the active phase. J. Catal. 1992, 138, 413-444. 5. Chunguang, L.; Changxi, M.; Yingying, N.; Yinghong, Y.; Songyuan, G.; Weimin, Y.; Weiming, H.; Zi, G. Ethylbenzene Dehydrogenation in the Presence of CO2 over MCFSupported Vanadium Oxide Catalysts. Chinese J. Catal. 2010, 31, 993-998. 6. Mimura, N.; Takahara, I.; Saito, M.; Sasaki, Y.; Murata, K. Dehydrogenation of Ethylbenzene to Styrene in the Presence of CO2 over Calcined Hydrotalcite-Like Compounds as Catalysts. Catal. Lett. 2002, 78, 125-128. 7. Freire, R. M.; de Sousa, F. F.; Pinheiro, A. L.; Longhinotti, E.; Mendes Filho, J.; Oliveira, A. C.; Paulo de Tarso, C. F.; Ayala, A. P.; Oliveira, A. C. Studies of Catalytic Activity and Coke Deactivation of Spinel Oxides during Ethylbenzene Dehydrogenation. Appl. Catal. AGen. 2009, 359, 165-179. 8. de Morais Batista, A. H.; Ramos, F. S.; Braga, T. P.; Lima, C. L.; De Sousa, F. F.; Barros, E. B.; Josue Filho, M.; De Oliveira, A. S.; De Sousa, J. R.; Valentini, A. Mesoporous MAl2O4 (M= Cu, Ni, Fe or Mg) Spinels: Characterisation and Application in the Catalytic Dehydrogenation of Ethylbenzene in the Presence of CO2. Appl. Catal. A-Gen. 2010, 382, 148157. 9. de Morais Batista, A. H.; de Sousa, F. F.; Honorato, S. B.; Ayala, A. P.; Josue Filho, M.; de Sousa, F. W.; Pinheiro, A. N.; de Araujo, J.; Nascimento, R. F.; Valentini, A. Ethylbenzene to Chemicals: Catalytic Conversion of Ethylbenzene into Styrene over Metal-Containing MCM-41. J. Mol. Catal. A: Chem. 2010, 315, 86-98. 10. Mimura, N.; Takahara, I.; Saito, M.; Hattori, T.; Ohkuma, K.; Ando, M. Dehydrogenation of Ethylbenzene over Iron Oxide-Based Catalyst in the Presence of Carbon Dioxide. Catal. Today 1998, 45, 61-64. 11. Qiao, Y.; Miao, C.; Yue, Y.; Xie, Z.; Yang, W.; Hua, W.; Gao, Z. Vanadium Oxide Supported on Mesoporous MCM-41 as New Catalysts for Dehydrogenation of Ethylbenzene with CO2. Microporous Mesoporous Mater. 2009, 119, 150-157. 12. Mimura, N.; Saito, M. Dehydrogenation of Ethylbenzene to Styrene in the Presence of CO2. Appl. Organomet. Chem. 2000, 14, 773-777. 13. Mimura, N.; Saito, M. Dehydrogenation of Ethylbenzene to Styrene over Fe2O3/Al2O3 Catalysts in the Presence of Carbon Dioxide. Catal. Lett. 1999, 58, 59-62. 14. Sato, S.; Ohhara, M.; Sodesawa, T.; Nozaki, F. Combination of Ethylbenzene Dehydrogenation and Carbon Dioxide Shift-Reaction over a Sodium Oxide/Alumina Catalyst. Appl. Catal. 1988, 37, 207-215. 20 ACS Paragon Plus Environment

Page 21 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


15. Sugino, M.-o.; Shimada, H.; Turuda, T.; Miura, H.; Ikenaga, N.; Suzuki, T. Oxidative Dehydrogenation of Ethylbenzene with Carbon Dioxide. Appl. Catal. A-Gen. 1995, 121, 125137. 16. Chen, S.; Sun, A.; Qin, Z.; Wang, J. Reaction Coupling of Diethylbenzene Dehydrogenation with Water–Gas Shift over Alumina-Supported Iron Oxide Catalysts. Catal. Commun. 2003, 4, 441-447. 17. Saito, M.; Kimura, H.; Mimura, N.; Wu, J.; Murata, K. Dehydrogenation of Ethylbenzene in the Presence of CO2 over an Alumina-Supported Iron Oxide Catalyst. Appl. Catal. A-Gen. 2003, 239, 71-77. 18. Sakurai, Y.; Suzaki, T.; Nakagawa, K.; Ikenaga, N.-o.; Aota, H.; Suzuki, T. Dehydrogenation of Ethylbenzene over Vanadium Oxide-Loaded MgO Catalyst: Promoting Effect of Carbon Dioxide. J. Catal. 2002, 209, 16-24. 19. Vislovskiy, V. P.; Chang, J.-S.; Park, M.-S.; Park, S.-E. Ethylbenzene into Styrene with Carbon Dioxide over Modified Vanadia–Alumina Catalysts. Catal. Commun. 2002, 3, 227-231. 20. Ikenaga, N.-o.; Tsuruda, T.; Senma, K.; Yamaguchi, T.; Sakurai, Y.; Suzuki, T. Dehydrogenation of Ethylbenzene with Carbon Dioxide using Activated Carbon-Supported Catalysts. Ind. Eng. Chem. Res. 2000, 39, 1228-1234. 21. Ye, X.; Yue, Y.; Miao, C.; Xie, Z.; Hua, W.; Gao, Z. Effect of Modifiers on the Activity of a Cr2O3/Al2O3 Catalyst in the Dehydrogenation of Ethylbenzene with CO2. Green Chem. 2005, 7, 524-528. 22. Park, J.-N.; Noh, J.; Chang, J.-S.; Park, S.-E. Ethylbenzene to Styrene in the Presence of Carbon Dioxide over Zirconia. Catal. Lett. 2000, 65, 75-78. 23. Liu, Y.-M.; Cao, Y.; Yan, S.-R.; Dai, W.-L.; Fan, K.-N. Highly Effective Oxidative Dehydrogenation of Propane over Vanadia Supported on Mesoporous SBA-15 Silica. Catal. Lett. 2003, 88, 61-67. 24. Badstube, T.; Papp, H.; Kustrowski, P.; Dziembaj, R. Oxidative Dehydrogenation of Ethylbenzene with Carbon Dioxide on Alkali‐Promoted Fe/Active Carbon Catalysts. Catal. Lett. 1998, 55, 169-172. 25. Park, M.-S.; Vislovskiy, V. P.; Chang, J.-S.; Shul, Y.-G.; Yoo, J. S.; Park, S.-E. Catalytic Dehydrogenation of Ethylbenzene with Carbon Dioxide: Promotional Effect of Antimony in Supported Vanadium–Antimony Oxide Catalyst. Catal. Today 2003, 87, 205-212. 26. Chang, J.-S.; Vislovskiy, V. P.; Park, M.-S.; Yoo, J. S.; Park, S.-E. Utilization of Carbon Dioxide as Soft Oxidant in the Dehydrogenation of Ethylbenzene over Supported Vanadium– Antimony Oxide Catalysts. Green Chem. 2003, 5, 587-590. 27. Burri, D. R.; Choi, K.-M.; Lee, J.-H.; Han, D.-S.; Park, S.-E. Influence of SBA-15 Support on CeO2–ZrO2 Catalyst for the Dehydrogenation of Ethylbenzene to Styrene with CO2. Catal. Commun. 2007, 8, 43-48. 28. Maity, S.; Rana, M.; Srinivas, B.; Bej, S.; Dhar, G. M.; Rao, T. P. Characterization and Evaluation of ZrO2 Supported Hydrotreating Catalysts. J. Mol. Catal. A: Chem. 2000, 153, 121127. 29. Sekine, Y.; Watanabe, R.; Matsukata, M.; Kikuchi, E. High Performance of Fe–K Oxide Catalysts for Dehydrogenation of Ethylbenzene to Styrene with an Aid of ppm-Order Pd. Catal. Lett. 2008, 125, 215-219. 30. Cavani, F.; Trifiro, F. Alternative Processes for the Production of Styrene. Appl. Catal. AGen. 1995, 133, 219-239.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

31. Oliveira, A. C.; Fierro, J. L.; Valentini, A.; Nobre, P. S. S.; do Carmo Rangel, M. Nontoxic Fe-based Catalysts for Styrene Synthesis: The Effect of Salt Precursors and Aluminum Promoter on the Catalytic Properties. Catal. Today 2003, 85, 49-57. 32. Ndlela, S. C.; Shanks, B. H. Reduction Behavior of Potassium-Promoted Iron Oxide under Mixed Steam/Hydrogen Atmospheres. Ind. Eng. Chem. Res. 2006, 45, 7427-7434. 33. Serafin, I.; Kotarba, A.; Grzywa, M.; Sojka, Z.; Bińczycka, H.; Kuśtrowski, P. Quenching of Potassium Loss from Styrene Catalyst: Effect of Cr Doping on Stabilization of the K2Fe22O34 Active Phase. J. Catal. 2006, 239, 137-144. 34. Khatamian, M.; Saket Oskoui, M.; Darbandi, M. Synthesis and Characterization of Aluminium-Free ZSM-5 type Chromosilicates in Different Alkaline Systems and Investigation of their Pore Structures. Microporous Mesoporous Mater. 2013, 182, 50-61. 35. Sadeghi, E.; Oskoui, M. S.; Khatamian, M.; Ghassemi, A. H. Oxidative Dehydrogenation of Ethylbenzene over ZSM-5 Type Chromosilicates in the Presence of CO2. Mod. Res. Catal. 2016, 5, 75. 36. Treacy, M. M.; Higgins, J. B. Collection of Simulated XRD Powder Patterns for Zeolites Fifth (5th) Revised Edition. Elsevier: 2007. 37. Do, D. D. Adsorption Analysis: Equilibria and Kinetics:(With CD Containing Computer Matlab Programs). World Scientific: 1998; Vol. 2 38. Rouquerol, J.; Rouquerol, F.; Llewellyn, P.; Maurin, G.; Sing, K. S. Adsorption by Powders and Porous Solids: Principles, Methodology and Applications. Academic press: 2013. 39. Sing, K.; Everett, D.; Haul, R.; Moscou, L.; Pierotti, R.; Rouquerol, J.; Siemieniewska, T. Physical and Biophysical Chemistry Division Commission on Colloid and Surface Chemistry Including Catalysis. Pure Appl. Chem. 1985, 57, 603-619. 40. Kruk, M.; Jaroniec, M. Gas Adsorption Characterization of Ordered Organic-Inorganic Nanocomposite Materials. Chem. Mater. 2001, 13, 3169-3183. 41. Wang, S.; Zhu, Z. Catalytic Conversion of Alkanes to Olefins by Carbon Dioxide Oxidative Dehydrogenation A Review. Energ. Fuel. 2004, 18, 1126-1139. 42. Serafin, I.; Kotarba, A.; Grzywa, M.; Sojka, Z.; Bińczycka, H.; Kuśtrowski, P. Quenching of Potassium Loss from Styrene Catalyst: Effect of Cr Doping on Stabilization of the K2Fe22O34 Active Phase. J. Catal. 2006, 239, 137-144. 43. Li, Z.; Shanks, B. H. Role of Cr and V on the Stability of Potassium-Promoted Iron Oxides Used as Catalysts in Ethylbenzene Dehydrogenation. Appl. Catal. A-Gen. 2011, 405, 101-107. 44. Dulamiţă, N.; Măicăneanu, A.; Sayle, D. C.; Stanca, M.; Crăciun, R.; Olea, M.; Afloroaei, C.; Fodor, A. Ethylbenzene Dehydrogenation on Fe2O3-Cr2O3-K2CO3 Catalysts Promoted with Transitional Metal Oxides. Appl. Catal. A-Gen. 2005, 287, 9-18. 45. do Carmo Rangel, M.; de Melo Monteiro, A. P.; Marchetti, S. G.; Lima, S. B.; de Souza Ramos, M. Ethylbenzene Dehydrogenation in the Presence of Carbon Dioxide over MagnesiaSupported Iron Oxides. J. Mol. Catal. A: Chem. 2014, 387, 147-155. 46. Baghalha, M.; Mohammadi, M.; Ghorbanpour, A. Coke Deposition Mechanism on the Pores of a Commercial Pt–Re/γ-Al2O3 Naphtha Reforming Catalyst. Fuel Process. Technol. 2010, 91, 714-722. 47. Baghalha, M.; Ebrahimpour, O. Structural Changes and Surface Activities of Ethylbenzene Dehydrogenation Catalysts during Deactivation. Appl. Catal. A-Gen. 2007, 326, 143-151.


Page 22 of 42

Page 23 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


48. Su, D. S.; Delgado, J. J.; Liu, X.; Wang, D.; Schlögl, R.; Wang, L.; Zhang, Z.; Shan, Z.; Xiao, F. S. Highly Ordered Mesoporous Carbon as Catalyst for Oxidative Dehydrogenation of Ethylbenzene to Styrene. Chem-Asian J. 2009, 4, 1108-1113. 49. Ibarra, Á.; Veloso, A.; Bilbao, J.; Arandes, J. M.; Castaño, P. Dual Coke Deactivation Pathways during the Catalytic Cracking of Raw Bio-Oil and Vacuum Gasoil in FCC Conditions. Appl. Catal. B-Environ. 2016, 182, 336-346.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 42

Tables: Table .1. EDAX results of (a) fresh and (b) spent industrial catalyst (IC) at specified points Area of EDAX analysis

Catalyst fresh used

1 2 3 4

Fe (Atomic %)

76.64 76.77 70.96 86.13

K (Atomic %)

Cr (Atomic %)

Ce (Atomic %)

Mg (Atomic %)

Ca (Atomic %)

18.09 11.2 23.78 2.90

1.06 1.31

2.84 3.43 4.21 5.4

7.12 4.26

2.43 1.38 -


Page 25 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table. 2. Specific textural properties and catalytic activity of the prepared catalysts in EB dehydrogenation at 600 °C and CO2 flow of 36.64 mL/min.

Components

IC (Industrial Catalyst)

BET Average Total pore X[%] surface area pore volume (m2 g-1) diameter (cm3 g-1) (nm)

Bz[%]

Tol[%]

S[%]

EB conversion [%]

-

-

-

41.09

11.62

9.94

65.58

62.65

2F/KCS

195.24

2.484

0.1212

46.98

2.22

3.00

90.00

52.20

5F/KCS

311.39

2.4811

0.1931

46.95

2.16

1.70

92.40

50.81

10F/KCS

311.19

2.3274

0.1811

43.51

1.48

7.11

75.46

48.10

20F/KCS

276.64

2.8134

0.1946

46.20

6.67

5.10

79.38

58.20

2F/NCS

114.03

7.4709

0.213

54.97

3.15

4.13

88.45

62.15

5F/NCS

70.75

7.385

0.1306

38.63

10.43

5.60

70.68

54.66

10F/NCS

102.28

9.8998

0.2531

50.87

0.8

1.43

95.80

53.10

20F/NCS

76.42

8.0861

0.1545

40.69

3.85

2.96

85.67

47.50

KCSAW

307.59

-

-

40.52

3.5

2.08

87.80

46.15

KCSBW

294.02

2.8656

0.2106

56.19

1.07

1.24

96.05

58.5

NCSAW

316.62

-

-

44.81

2.24

3.32

88.96

50.37

NCSBW

307.74

2.2620

0.1740

46.38

1.24

1.87

93.72

49.49

Fe2O3

36.10

17.31

-

46.85

12.29

3.67

74.59

62.81

X = Styrene yield, Bz = Benzene, Tol = Toluene, S = Styrene selectivity, EB = Ethylbenzene



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 42

Table. 3. Different catalytic activity of fresh industrial catalyst (IC) in ethylbenzene dehydrogenation at various conditions. Temperature (°C)

CO2/EB ratio

CO2 (mL/min)

X[%]

Bz[%]

Tol[%]

EB[%]

S[%]

No. 1

550

5

61.07

15.402

2.76

2.098

79.74

76

EB conversion [%] 20.26

2

550

2

24.42

15.84

5.82

2.57

75.77

65.37

24.23

3

550

3

36.64

18.72

2.23

1.61

77.44

83

22.56

4

600

3

36.64

41.09

11.62

9.94

37.35

65.58

62.65

5

610

2

24.42

34.86

20.21

13.52

31.41

50.8

68.59

6

610

5

61.07

32.45

12.62

10.45

44.46

58.44

55.54

7

610

3

36.64

39.33

6

5.48

49.19

77.4

50.81



Page 27 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table. 4. Different catalytic activity of 5F/KCS sample in ethylbenzene dehydrogenation at 600 °C in the presence of various CO2 flows. No.

CO2(mL/min)

X[%]

Bz[%]

1

20

40.79

2

25

3

36.64

Tol[%]

S[%] EB conversion [%]

8.28

6.47

73.44

55.54

48.17

1.80

2.53

91.76

52.50

46.95

2.16

1.70

92.40

50.81




1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 42

Figure Captions: Figure 1. Schematic diagram of the experimental setup used for dehydrogenation of ethylbenzene (EB) to styrene (ST). Figure 2. XRD patterns of the prepared samples. Figure 3. XRD patterns of (a) fresh, and (b) spent industrial catalyst (IC) Figure 4. SEM images of NCSBW (a), NCSAW (b), KCSAW (c) and KCSBW (d) and 20F/KCS (e), (f) samples. Figure 5. SEM images of (a) fresh, and (b) spent industrial catalyst (IC) Figure 6. TEM images of 5F/NCS composite. Figure 7. Nitrogen sorption isotherms of samples. Figure 8. Pore size distribution curves of samples. Figure 9. The performance of various Fe2O3/chromosilicate composites (F/MCS) in ethylbenzene dehydrogenation reaction in the presence of CO2 at 600 °C. Figure 10. Effects of loading level of Fe2O3 on ethylbenzene conversion, styrene yield, and selectivity of KCS(a) and NCS(b) samples, in the presence of CO2 at 600 °C.

Figure 11. Catalyst reusability of KCSBW in EB dehydrogenation process. Figure 12. FTIR spectrum of KCSBW sample before (a) and after 3 cycles (b) of EB dehydrogenation process.


Page 29 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 13. Different catalytic activity of industrial catalyst (IC) in ethylbenzene dehydrogenation at various conditions.

Figure 1



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 2


Page 30 of 42

Page 31 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 4


Page 32 of 42

Page 33 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 6


Page 34 of 42

Page 35 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 7



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 8


Page 36 of 42

Page 37 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 9



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 10


Page 38 of 42

Page 39 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 11



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 12


Page 40 of 42

Page 41 of 42

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 13



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

TOC Graphic:


Page 42 of 42

Dehydrogenation of Ethylbenzene with Carbon Dioxide in the

Recommend Documents