Steam Catalytic Cracking of n-Hexane over Modified MTW Zeolites

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Steam catalytic cracking of n-hexane over modified MTW zeolites impregnated by extra-framework elements Mohammed A Sanhoob, Oki Muraza, Taichi Taniguchi, Teruoki Tago, Gaku Watanabe, and Takao Masuda Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b00857 • Publication Date (Web): 19 Sep 2016 Downloaded from http://pubs.acs.org on September 25, 2016

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Steam catalytic cracking of n-hexane over modified MTW zeolites impregnated by extra-framework elements

Mohammed A. Sanhoob1, Oki Muraza*1, Taichi Taniguchi2, Teruoki Tago3, Gaku Watanabe2, Takao Masuda2 1

Chemical Engineering Department and Center of Research Excellence in Nanotechnology, King Fahd University of Petroleum & Minerals, Dhahran, Saudi Arabia 2 Division of Chemical Process Engineering, Faculty of Engineering, Hokkaido University, N13 W8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan 3 Department of Chemical Engineering, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1, Ookayama, Meguro-Ku, Tokyo, 152-8552, Japan

Abstract One of the most interesting processes in energy-related catalysis is steam-assisted catalytic cracking. Herein, ZSM-12 (MTW) zeolite was modified by impregnation to improve the selectivity to olefins in the presence of steam. ZSM-12 zeolite was synthesized hydrothermally and modified by incorporating ZSM-12 zeolite with lanthanum (La), cerium (Ce) and boron (B). Two different ammonium solutions were used in the ion-exchange of the synthesized ZSM-12 zeolite; namely ammonium nitrate and ammonium fluoride. Each group was impregnated with 2 wt.% of lanthanum, cerium or boron. Catalytic performance was evaluated using steam catalytic cracking of n-hexane. H-ZSM-12 zeolite exchanged with ammonium nitrate and impregnated with lanthanum and cerium has conversion above 50 C-mole%. However, impregnation with boron reduced the active sites and the conversion was 20 C-mole%. On the other hand, exchanging the samples with ammonium fluoride led to the loss of the active sites and the conversion was around 20 C-mole% in the presence of lanthanum, cerium and boron.

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Keywords: Impregnation; ZSM-12 (MTW); Steam; Cracking; n-hexane; Extraframework elements. *Corresponding Author (OM) E-mail: [email protected], Phone: +966 13 860 7612

1. Introduction

Catalytic cracking of naphtha is one of the most important processes in energy-related catalysis due to the high demands on light hydrocarbons such as light olefins. Light olefins such as ethylene and propylene are aimed to be produced with high selectivity among other light hydrocarbons. However, since these reactions are mostly accomplished in the presence of heterogeneous catalysts to enhance the catalytic performance, the product distribution also depends on the physical properties of these heterogeneous catalysts as shown in acid-catalyzed chemical processes such as isomerization, alkylation and cracking 1-6. In refinery and petrochemical industries, zeolites are one of the most important heterogeneous catalysts due its importance in shape selectivity 7. Moreover, they have exchangeable cations, which enable the zeolite to be modified with different properties, for instance, if the cations exchanged to H+, number of strong acid sites increases 7. The normal procedure to get H+ is to exchange the sodium zeolite with ammonium nitrate to form NH4-zeolite and after calcination at elevated temperature, it will form H-zeolite. In some cases, another compound is used to donate protons to the zeolite in such way the physical properties of the zeolite can be modified. Ammonium fluoride can be one of these chemical compounds. Zeolites properties can strongly affect the selectivity towards either the desired or undesired products. Extensive studies are essential to produce zeolites with different characteristics to favor a particular reaction route. By different modification 2 ACS Paragon Plus Environment

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strategies, changes on Lewis or Brønsted sites, active sites, pore volume and surface area can be controlled to enhance the catalytic properties such as conversion and selectivity

8, 9

. One of the modification strategies is the post-treatment

10, 11

by the

addition of extra-frameworks such as rare-earth metals and metalloid via impregnation or ion-exchange to obtain co-catalysts material 12-14. MTW is one of the 200 frameworks which can be synthesized in laboratories 15

with excellent acitivity and stability for long reaction time

16-18

. The first synthesis

of ZSM-12 (MTW) zeolite was in 1974 by Mobil Research and Development scientists

19-21

. Its framework has a one-dimensional pore system and 12 membered-

rings (MR) 22, with the pore size of 0.56 x 0.60 nm in the [010] plane, which is larger than MFI zeolites

15

. ZSM-12 zeolite is also known as a crystalline microporous

aluminosilicates with low aluminum content. To further modify the properties of ZSM-12 zeolite in steam cracking of hexane, expecially to enhance the selectivity to olefins, Na-ZSM-12 zeolite was exchanged with ammonium nitrate and ammonium fluoride. Furthermore, the effect of impregnation was studied in both exchanged zeolites. In our studies, lanthanum (La), cerium (Ce) and boron (B) were used as extra-framework elements and the resulted co-catalysts. 2. Experimental MTW zeolite was synthesized and the silica to aluminum (SiO2/Al2O3) ratio was designed to be 160. The gel mixture was containing colloidal silica (40 wt. % in water, Snowtex 40, Nissan Chemicals) and aluminum sulfate octahydrate Al2 (SO4)3.18H2O (Acros) as silica source and aluminum source, respectively. As the synthesis required organic structure directing agent (OSDA), tetraethyl ammonium


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bromide (TEABr) was utilized. Sodium hydroxide was used to adjust phase purity and mineralizer agent source. According to our previous recipe 23, the gel mixture was prepared as follows: sodium hydroxide (NaOH, 1.18 g) was added to 14.05 g of deionized water (DI). After sodium hydroxide was dissolved in DI water, 0.79 g of aluminum sulfate octahydrate was added to the mixture followed by 5.02 g of TEABr. In another beaker, 11.39 g of DI water was mixed with 28.47 g of colloidal silica. At the end, the solution of the first beaker was added gradually to the solution in the second beaker and the whole mixture was stirred for 90 min without heating. The mixture then was transferred to a PTFE-lined stainless steel autoclaves with a volume of 100 ml and then heated in a static oven at 145 oC for 120 h. After 120 h, the product was washed thoroughly with DI water, then it was dried and calcined for 21 h under air flow at 550oC. The calcined zeolite (Na-ZSM-12) was ion-exchanged under microwave irradiation. Two kinds of ion-exchange were performed. We used two different ammonium sources which have different properties to exchange the sodium (Na) ions. The first source was ammonium nitrate (NH4NO3) and the second source was ammonium fluoride (NH4F). In all cases, 1 g of zeolite was mixed with 20 g of ammonium solution. Ions were exchanged at 85 oC for 10 min. After first ion-exchange, the powder was centrifuged once with deionized water and then the second ion-exchange was performed again with similar procedure. The product was washed systematically after the second ion-exchange and then dried and re-calcined at 550 oC for 5 h. After calcination, samples were divided into two groups; group (I) exchanged with ammonium nitrate (NH4(NO3)) and group (II) exchanged with ammonium fluoride (NH4F). Each group was divided into three 4 ACS Paragon Plus Environment

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parts. Each part was impregnated with different precursors. We impregnated ZSM-12 zeolite with 2 wt.% of lanthanum (La), cerium (Ce) or boron (B). The sources of these elements were lanthanum nitrate hexahydrate, ammonium cerium (IV) nitrate and boric acid, respectively. The impregnation procedure was performed by dissolving each compound in 5 ml of ethanol (C2H5OH). Dissolving these compounds were easy at ambient temperature except boric acid, which requires heating source (75 oC). After dissolving each compound in ethanol, zeolite sample was added to the solution and mixed vigorously to ensure the uniform distribution of the solution on the zeolite sample. After impregnation, samples were dried and re-calcined at 550 oC for 5 h. The samples in group I were assigned as X1 (Parent), X2 for La-ZSM-12, X3 for Ce-ZSM-12 and X4 for B-ZSM-12. Similarly, The samples in group II were assigned as Y1 (Parent), Y2 for La-ZSM-12, Y3 for Ce-ZSM-12 and Y4 for BZSM-12. Different instrumental techniques were used to study the physical and chemical properties of the samples. The zeolite phase before and after impregnation was identified using X-ray diffractometer (XRD) with CuKα radiation in the period of 2θ = 5o to 50o. Morphology and crystal size were determined using field-emission scanning electronic microscopy (FE-SEM, LYRA 3 Dual Beam from Tescan Company). FTIR was utilized to study the structure vibrarion of the ion-exchanged zeolite in the range of 1300-400 cm-1. Zeolites acidities were determined using temperature-programmed desorption (TPD). Solid-state

27

Al and

29

Si NMR spectrometer were used to identify the

coordination of both silicon and aluminum. The performance of modified MTW zeolites was evaluated by steamassisted catalytic cracking of n-hexane in a fixed-bed flow reactor system. The 5 ACS Paragon Plus Environment

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experimental setup of the steam catalytic cracking is shown in Figure 1. Zeolite pellet (0.06 g) was packed in a reactor tube. The catalytic performance was evaluated at 650 oC (923 K) in the presence of nitrogen flow of 29.3 ml/min, H2O flow of 0.47 ml/h and n-hexane flow of 3.6 ml/h and the residence time was 0.33 s-1. The reaction products were analyzed by gas chromatography (GC).

Please insert Figure 1 here (SCC).

3. Results and Discussion ZSM-12 zeolite was synthesized in a hydrothermal oven for 120 h at 145 oC and the silica to alumina (SiO2/Al2O3) ratio in sol-gel mixture was set at 160. However, the main target of this manuscript is to find the effect of ammonium compounds in ion-exchange and the effect of impregnation in the catalytic activity. Since the modification is post-treatment, then the zeolite sample is one in all experiments and the effective parameters is fixed to be only one parameter. The produced phase was confirmed to be a pure MTW zeolite as confirmed by the XRD patterns. After calcination at 550 oC, two different precursors were used in the ionexchange to investigate their effect on the zeolite acidity as well as the catalytic activity for steam catalytic cracking of n-hexane. In the first set, Na-ZSM-12 zeolite was exchanged with ammonium nitrate. Each chemical source was dissolved in deionized water followed by the addition of the zeolite samples. An endothermic reaction occurs when ammonium nitrate is added to deionized water which suggest


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the dissociation of ammonium nitrate to ammonium cations and nitrate anions

24

as

follows:

() () + () Analogously, if ammonium fluoride used for the ion exchange, ammonium fluoride dissociates in water to ammonium cations and fluoride anions

25

as follows:

() () + () When the Na-zeolite exchange the ions with the dissociated ammonium species, NH4-zeolite will form in both cases, which further produce the proton form of the zeolite (H-zeolite) by the calcination step 26. In the case of fluoride, we expect that fluoride will be exchanged with oxygen by using the hard and soft acid base (HSAB) theory and it will be connected to the positively charged aluminum

27, 28

. However, the confirmation of this expectation

which is related to the HSAB principle should be confirmed to be valid in the ionexchanged zeolite samples. The confirmation will be mentioned in the FTIR part later. Nevertheless, the effect of metallic substitution in the modified zeolitic samples need further exploration to study the influence of metals in affecting the catalytic performance. In this work, we concentrated in studing the effect of impregnation rather than ion-exchanged methods. Each sample was impregnated with 2 wt.% of lanthanum, cerium or boron by using lanthanum nitrate hexahydrate, ammonium cerium (IV) nitrate or boric acid, as an extra framework element, respectively. After ion-exchange and impregnation, it was observed that the zeolites phases were preserved as shown in Figure 2A (ZSM-12 zeolite exchanged with ammonium nitrate) and Figure 2B (ZSM-12 zeolite exchanged with ammonium fluoride). In the samples


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which were ion exchanged with ammonium nitrate, it was observed that the crystallinity was reduced when the samples were impregnated with lanthanum and cerium and the crystallinity was increased after boron impregnation. We suggest that this decrease or increase in the crystallinity depends on how the additive ions locate themselves on the zeolite framework and the trend of the atomic arrangements after calcination step. Moreover, the radii size of these hosted ions can affect the crystallinity due to the replacement of the space among the cages and we expect that the crystallinity decreases with increasing of the size of the radii. However, it is expected that multi ions may occupy the cage which further affect the crystallinity of the zeolite. The crystallinity was less affected by impregnation when the sample ionexchanged with ammonium fluoride as shown in Figure 2B, which suggest that ammonium fluoride has larger influence on atoms exchanges and arrangements on the ZSM-12 zeolite framework due to the large electronegativity of fluoride 29. Please insert Figure 2 here (XRD). The influence of ion-exchange and impregnation on partical size and morphology of the parent and modified ZSM-12 zeolite was studied using field emission scanning electron microscopy (FE-SEM). As shown in Figure 3, the ion exchange with ammonium nitrate and ammonium fluoride did not affect the crystal size and morphology. Furthermore, the impregnation with different extra-framework elements has no effect on the morphology and crystal size. Since the extra framework element was incorporated by impregnation method, the crystal size was not affected by impregnation as there was no re-crystallization. From Figure 3, it was observed that the average crystal size of H-ZSM-12 zeolite was ca. 800 nm. However, these agglomerates composed of numerous nano-particles with an average size of 80 nm.


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Please insert Figure 3 here (SEM).

Nevertheless, it is important to observe the effect of ion-exchange and impregnation on the zeolitic acidity. In order to evaluate the acidity, temperature-programmed desorption of ammonia (NH3-TPD) was utilized to evaluate the acid sites of the two sets of modified MTW zeolite. In the first set, where Na-ZSM-12 zeolite were exchanged with ammonium nitrate, it was observed that they have higher weak and strong acid site as compared with the second set which Na-ZSM-12 zeolite was exchanged with ammonium fluoride. As shown from Figure 4, each TPD profile consists of two strong peaks. One of these peaks appeared at low temperature (weak acid), which mostly refer to the weak Bronsted and weak Lewis acid sites and other peaks appeared at high temperature (strong acid). Both strong and weak acids were evaluated by integrating the area under each peak as shown in Table 1. In the first set, it was observed that the weak acid of X2 and X3 is identical to the parent zeolite (X1). While the presence of boron in the framework enhanced the strength of weak acid sites by enhancing the adsorption of ammonia. As shown in Table 4, the sequence of the weak acid strength is as follows: B-ZSM-12 (X4) > LaZSM-12 (X2) > Ce-ZSM-12 (X3) > H-ZSM-12 (X1). On the other hand, it was observed that boron has lower strong acidity, while the other samples were almost identical. However, small shift to lower temperature was observed in the case of zeolite impregnated with cerium. In the second set, where the parent zeolite was ion-exchanged with ammonium fluoride, it was observed that the electronegativity of fluoride resest the absorption of ammonia on the samples due to the high electronegativity nature of fluoride.


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Please insert Figure 4 here (TPD).

NMR was applied to investigate the effect of impregnation on zeolite structure as shown in Figure 5. When the sample was ion exchanged with ammonium nitrate, Solid state

27

Al MAS NMR spectra of calcined ZSM-12

zeolites was performed and it was observed that the chemical shift in all samples is absent. The results prior to and after the treatment in 27Al NMR showed that the peaks were located around 54.5 ppm, which suggest that all aluminium is located in the framework of zeolite and it represents the tetrahedral coordinate of aluminium while extra framework aluminium was absent. On the other hand, 29

Si MAS NMR was evaluated and it was observed a single broad peak located

between -105 and 120. This range is mainly covering three individual peaks which located at -112, -108 and -105 ppm. Where the peak at -105 is correspond to Si(1Al) specie. While the other two peaks which are located at 108 and -112 ppm corresponds to Si(0Al) species. Furthermore, we can observe a poorly separated peaks located at -102 ppm which it is common for Si(2Al) and SiOH sites. It can be observed that impregnation did not affect the chemical structure.

Please insert Figure 5 here (NMR).

Nevertheless, it is important to see the effect of ammonium nitrate on the zeolitic structure. Furthermore, it is worthy to confirm the HSAB principle in


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replacing the oxygen by fluoride. As shown in Figure 6, several bands can be observed in the range between 1300-400 cm-1. In this region, peaks can be classified to two peaks which is related to internal tetrahedra vibration and external linkage vibration. In the band between 500-420 cm-1, the band is related to the internal tetrahedra vibration which is related to T-O bend (where T can be Si or Al). However, as can be seen from Figure 6, samples exchanged with ammonium fluoride has less absorbance on the band 500-420 cm-1, which suggest the replacement of ooxygen ions with fluoride. This also can be observed clearly from the band at 1250-1000 cm-1, which is attributed to Internal tetrahedra of asymmetric stretch of TO4. After we observed the effect of the achieved modifications on the physical properties of the modified zeolites, we evaluated the effect of these modifications in the steam catalytic cracking of n-hexane. The modified zeolite samples were evaluated at 650 oC with residence time of 0.33 s-1. In the first case, when Na-ZSM-12 zeolite was exchanged with ammonium nitrate, it was observed that the initial conversions were 56%, 52%, 55%, and 20% for X1, X2, X3 and X4, respectively as shown in Table 2A. However, after the initial conversion, the catalytic conversion decreased with time for all samples due to deactivation of MTW catalysts as shown in Figure 7A. Another observation that the impregnated samples have lower conversion as compared to the parent zeolite (X1) due to the reduction of some active site. However, by considering the percentage decrease in reactant converted (PDRC), we observed that the impregnated samples have lower PDRC as compared to the parent X1. Using Equation 1, it was calculated that PDRC values were 34%, 23%, 28% and 5% for X1, X2, X3 and X4, respectively. This means that impregnated samples are


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more stable than the parent sample. By comparing all impregnated samples, it was observed that the parent sample impregnated with 2 wt.% of lanthanum (X2) has reasonable conversion and lower PDRC as compared to X1 and X3. However, sample impregnated with 2 wt.% of boron (X4), showed the lowest conversion. The reason behind the variation of catalytic stability in the presence of different additive could be explained by the nature of these elements. In the presence of La as an example, La is characterized by strongly basic oxide. While, on the other hand Ce, characterized by mildly basic oxide. The stability of the steam catalytic cracking seems to be more stable as the surface basicity increases. While boron, which characterized by mildly acidic oxide, has lower catalytic activity due to the weak acidity.

= ( !"# − !"# "# %")&100 (1) In the second case, when Na-ZSM-12 zeolite was exchanged with ammonium fluoride, it was observed that the initial conversions were 19%, 18%, 20%, and 6% for Y1, Y2, Y3 and Y4, respectively as shown in Table 2B and Figure 7B. This low conversion is due to low active site as corroborated from acidity studies (see TPD results). Product selectivities of the first set and second set of samples are shown in Figure 8 and 9, respectively. All samples are shown high selectivity towards light olefins. Among these light olefins, propylene was the highest. In addition to that, it is noticeable that BTX is quite small as shown in Table 3. When samples were ion exchanged with ammonium nitrate and modified by impregnation, it is clear that the initial product selectivity towards light olefins was in the range of 51-55 % which is higher that the selectivity towards 12 ACS Paragon Plus Environment

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paraffin as shown in Table 3. Furthermore, the selectivity towards both ethylene and propylene was higher over the parent sample (X1) at the initial time. But on the other hand, lanthanum and cerium enhanced the stable selectivity towards ethylene and propylene as shown in Table 3 and Figure 8. The amounts of coke formed as measured by TGA analysis for spent catalysts are shown in Table 4. It was observed that zeolite impregnated with 2 wt% of cerium has lower coke than the ones for lanthanum (X2) and the parent (X1).

4. Conclusions MTW zeolite was synthesized under hydrothermal synthesis condition. Samples were ion exchanged with two different ammonium solutions; ammonium nitrate and ammonium fluoride. It was observed that ammonium fluoride affected the acidity of the zeolite and it reduced both strong and weak acid. This was explained by the HSAB theory and the influence of the high electronegativity fluoride on the aluminum species. MAS NMR clarified that the structural changes were not observed over the impregnated samples and the extra framework aluminum was absent. It was observed that ammonium fluoride negatively affected the conversion of steam catalytic cracking of n-hexane. On the other hand, samples ion exchanged with ammonium nitrate and impregnated with lanthanum and cerium showed an improvement on the percentage decrease in reactant converted. The selectivity towards both ethylene and propylene was higher in the parent sample (X1) at the initial time. But on the other hand, lanthanum and cerium maintained stable selectivity towards ethylene and propylene.


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Acknowledgements The author would like to acknowledge the financial support provided by Saudi Aramco through contract number 6600011900.

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15. Baerlocher, C.; McCusker, L. B.; Olson, D. H., Atlas of Zeolite Framework Types. Elsevier Science: 2007. 16. Martens, J. A.; Tielen, M.; Jacobs, P. A.; Weitkamp, J., Estimation of the void structure and pore dimensions of molecular sieve zeolites using the hydroconversion of ndecane. Zeolites 1984, 4, (2), 98-107. 17. Chiche, B. H.; Dutartre, R.; Di Renzo, F.; Fajula, F.; Katovic, A.; Regina, A.; Giordano, G., Study of the sorption and acidic properties of MTW-type zeolite. Catalysis Letters 1995, 31, (4), 359-366. 18. Katovic, A.; Chiche, B. H.; Di Renzo, F.; Giordano, G.; Fajula, F., Influence of the aluminium content on the acidity and catalytic activity of MTW-type zeolites. In Studies in Surface Science and Catalysis, Avelino Corma, F. V. M. S. M.; José Luis, G. F., Eds. Elsevier: 2000; Vol. Volume 130, pp 857-862. 19. E.J. Rosinski, M. K. R., US Patent 3,832,449 1974. 20. Trewella, J. C.; Schlenker, J. L.; Woessner, D. E.; Higgins, J. B., The silicon-29 MASn.m.r. spectrum of ZSM—12. Zeolites 1985, 5, (3), 130-131. 21. Fyfe, C. A.; Strobl, H.; Kokotailo, G. T.; Pasztor, C. T.; Barlow, G. E.; Bradley, S., Correlations between lattice structures of zeolites and their 29Si MAS n.m.r. spectra: zeolites KZ-2, ZSM-12, and Beta. Zeolites 1988, 8, (2), 132-136. 22. LaPierre, R. B.; Rohrman jr, A. C.; Schlenker, J. L.; Wood, J. D.; Rubin, M. K.; Rohrbaugh, W. J., The framework topology of ZSM-12: A high-silica zeolite. Zeolites 1985, 5, (6), 346-348. 23. Sanhoob, M.; Muraza, O.; Yamani, Z. H.; Al-Mutairi, E. M.; Tago, T.; Merzougui, B.; Masuda, T., Synthesis of ZSM-12 (MTW) with different Al-source: Towards understanding the effects of crystallization parameters. Microporous and Mesoporous Materials 2014, 194, (0), 31-37. 24. Mukhopadhyay, S., Smart Sensing Technology for Agriculture and Environmental Monitoring. Springer Berlin Heidelberg: 2012. 25. Kapoor, V. J.; Brown, W. D.; Science, E. S. D.; Division, T., Proceedings of the Third Symposium on Silicon Nitride and Silicon Dioxide Thin Insulating Films. Electrochemical Society: 1994. 26. Jacobs, P. A.; van Santen, R. A., Zeolites: Facts, Figures, Future. Elsevier Science: 1989. 27. Islam, N., Theoretical and Computational Research in the 21st Century. Apple Academic Press: 2014. 28. Pearson, R. G., Hard and Soft Acids and Bases. Journal of the American Chemical Society 1963, 85, (22), 3533-3539. 29. Clugston, M.; Flemming, R., Advanced Chemistry. OUP Oxford: 2000.


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Figure Captions Figure 1. The experimental setup for the steam catalytic cracking process. Figure 2. XRD patterns of modified MTW zeolites, (A) Na-ZSM-12 zeolite exchanged with ammonium nitrate, (B) Na-ZSM-12 zeolite exchanged with ammonium fluoride. Figure 3. FE-SEM micrographs of modified MTW zeolites. Figure 4. TPD of calcined ZSM-12 zeolite prior to and after impregnation. Figure 5. Solid-state of calcined ZSM-12 zeolite prior to and after alkaline treatment (A) 27Al MAS NMR spectra, (B) Solid-state 29Si MAS NMR spectra. Figure 6. FTIR spectra of calcined ZSM-12 zeolite, (A) MTW zeolite exchanged with ammonium nitrate, (B) MTW zeolite exchanged with ammonium fluoride. Figure 7. Steam catalytic conversion of n-hexane over (A) MTW zeolite exchanged with ammonium nitrate, (B) MTW zeolite exchanged with ammonium fluoride. Figure 8. Selectivity of modified MTW zeolite exchanged with ammonium nitrate in steam catalytic cracking of n-hexane. Figure 9. Selectivity of modified MTW zeolite exchanged with ammonium fluoride in steam catalytic cracking of n-hexane.

Table captions Table 1: Acidity derived from NH3-TPD for modified ZSM-12 zeolite. Table 2: Change in conversion of modified MTW zeolite with time. (A) Samples exchanged with ammonium nitrate, (B) Samples exchanged with ammonium fluoride. Table 3: Product selectivity over modified MTW zeolite exchanged with ammonium nitrate. (A) at time= 20 min (B) at time= 260 min. Table 4: Amount of coke deposited on catalyst after reaction (A) MTW zeolite exchanged with ammonium nitrate, (B) MTW zeolite exchanged with ammonium fluoride.


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Fixed bed reactor Flow meter N2 H2O Feed

Thermo Couple

Tape heater Temp 145℃

Electrical Furnace

Purge GC

◎Experimental condition Reactant : n-hexane Reaction temp. : 650[ degree C] Reaction time : 4.5 [h] W/F : 0.025[h] Residence time τ : 0.33 [s-1] Partial pressure n-hexane : 22.1 [kPa] H2O : 21.1 [kPa] Feed rate Carrier gas N2 : 29.3[cc/min] n-hexane : 3.6 [cc/h] H2 O : 0.47 [cc/h] Steam/Oil : 0.2 [wt/wt] Catalyst weight : 0.06[g]

Tape heater Temp 145℃ ACS Paragon Plus Environment

Figure 1. The experimental setup for the steam catalytic cracking process.

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Intensity [a.u.]

(A) (A) X4 (B) X3 (C) X2 (D) X1 5

15

25

35

45

2q [o] (B) (A) Y4

Intensity [a.u.]

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

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(B) Y3 (C) Y2 (D) Y1 5

15

25

35

45

2q [o]

Paragon Plus Environment Figure 2. XRD patterns of modifiedACS MTW zeolites, (A) Na-ZSM-12 zeolite exchanged with ammonium nitrate, (B) Na-ZSM-12 zeolite exchanged with ammonium fluoride.

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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

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1 mm

X1

1 mm

X2

1 mm

X3

1 mm

X4

1 mm

Y1

1 mm

Y2

1 mm

Y3

1 mm

Y4

ACS Paragon Plus Environment

Figure 3. FE-SEM micrographs of modified MTW zeolites.

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10

8

-dq/dT [mmol/(kg・K)]

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

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X1 X2 X3 X4 Y1 Y2 Y3 Y4

6

4

2

0 300

400

500 600 Temperature [K]

700

800


Figure 4. TPD of calcined ZSM-12 zeolite prior to and after impregnation.

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(A)

150

(B)

100

50

(ppm)

0

-50

X4

X4

X3

X3

X2

X2

X1

X1 -100 -50

-70

-90

-110

-130

-150

-170

(ppm)

ACS Paragon Plus Environment Figure 5. Solid-state of calcined ZSM-12 zeolite prior to and after alkaline treatment (A) 27Al MAS NMR spectra, (B) Solid-state 29Si MAS NMR spectra.

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(A) Transmittance (%)

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

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(B)

1200

1000 800 Wavenumber [cm-1]

600

400

ACSZSM-12 Paragon Pluszeolite, Environment Figure 6. FTIR spectra of calcined (A) MTW zeolite exchanged with ammonium nitrate, (B) MTW zeolite exchanged with ammonium fluoride.

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(A)

(B)

100

100

H-MTW (Y1)

H-MTW (X1) La-MTW (X2)

80

La-MTW (Y2)

80

Ce-MTW (Y3)

Ce-MTW (X3)

B-MTW (X4)

60

Conversion [C-mol%]

Conversion [C-mol%]

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

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40

20

B-MTW (Y4)

60

Thermal decomposition (without catalyst) 4.4%

40

20

Thermal decomposition (without catalyst) 4.4%

0

0 0

1

2

3

Time on stream [h]

4

5

0

1

2

3

4

5

Time on stream [h]

Figure 7. Steam catalytic conversion of n-hexane over (A) MTW zeolite exchanged with ACS Paragon Plus Environment ammonium nitrate, (B) MTW zeolite exchanged with ammonium fluoride.

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100

Page 24 of 29

100

Selectivity [C-mol% ]

+ paraffin)




1 2 BTX 80 80 3 4 Undifined 5 60 60 Paraffin 6 7 C1 40 40 8 C4 (olefin 9 10 C3= 20 20 11 C2= 12 0 0 13 20 80 140 200 260 20 80 140 200 260 14 Time on stream [min] Time on stream [min] 15 16 (B) Product selectivity during n-hexane cracking using La17 (A) Product selectivity during n-hexane cracking using H18 MTW (X2) as a catalyst MTW (X1) as a catalyst 19 20 100 21 100 22 23 80 80 24 25 60 26 60 27 28 40 40 29 30 20 20 31 32 0 33 0 20 80 140 200 260 34 20 80 140 200 260 Time on stream [min] 35 Time on stream [min] 36 Fig. Product selectivity during n-hexane cracking using B37(C) Product selectivity during n-hexane cracking using Ce38 MTW (X4) as a catalyst MTW (X3) as a catalyst 39 ACS Paragon Plus Environment 40 41 42

Figure 8. Selectivity of modified MTW zeolite exchanged with ammonium nitrate in steam catalytic cracking of n-hexane.




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Page 25100 of 29

80 80 1 2 BTX 3 60 60 4 Undifined 5 Paraffin 6 40 40 7 C1 8 20 20 9 C4 (olefin 10 C3= 11 0 0 12 C2= 20 80 140 200 260 20 80 140 200 260 13 Time on stream [min] Time on stream [min] 14 15 (A) Product selectivity during n-hexane cracking using H- (B) Product selectivity during n-hexane cracking using La16 MTW (Y2) as a catalyst MTW (Y1) as a catalyst 17 18 19 100 100 20 21 80 80 22 23 24 60 60 25 26 27 40 40 28 29 20 20 30 31 32 0 0 33 20 80 140 200 260 20 80 140 200 260 34 Time on stream [min] Time on stream [min] 35 36(C) Product selectivity during n-hexane cracking using Ce(D) Product selectivity during n-hexane cracking using B37 MTW (Y3) as a catalyst MTW (Y4) as a catalyst 38 39 ACS Paragon Plus Environment 40 41 42

+ paraffin)

Figure 9. Selectivity of modified MTW zeolite exchanged with ammonium fluoride in steam catalytic cracking of n-hexane.

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Table 1. Acidity derived from NH3-TPD for modified ZSM-12 zeolite.

Sample X1 X2 X3 X4 Y1 Y2 Y3 Y4

Total 0.62 0.66 0.64 0.87 0.39 0.28 0.25 0.43

mmol NH3 g-1 solid Weaka Strongb 0.47 0.143 0.52 0.139 0.49 0.148 0.76 0.111 0.30 0.089 0.24 0.037 0.19 0.031 0.36 0.073

aWeak,

from 372 to 560 K bStrong, from 562 to 800 K


Strong/Weak 0.302 0.270 0.301 0.146 0.295 0.155 0.163 0.206

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Table 2. Change in conversion of modified MTW zeolite with time. (A) Samples exchanged with ammonium nitrate, (B) Samples exchanged with ammonium fluoride. (A) Reaction time [h] X1 X2 X3 X4

0.33 56 52 55 20

Conversion[C-mol%] 1.33 2.33 3.33 50 44 32 45 41 36 49 44 35 17 17 12

4.33 22 28 27 15

0.33 19 18 20 6

Conversion[C-mol%] 1.33 2.33 3.33 14 11 9 12 10 9 15 12 11 6 6 6

4.33 9 7 10 7

(B) Reaction time [h] Y1 Y2 Y3 Y4


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Table 3. Product selectivity over modified MTW zeolite exchanged with ammonium nitrate. (A) at time = 20 min (B) at time = 260 min. (A) C1 C2= + C3= C4 BTX Paraffin undefined

X1 2.8 55.1 17.8 0.3 21.6 2.4

X2 2.9 54.5 18.1 0.4 21.5 2.6

X3 2.9 54.4 18.9 0.4 21.2 2.3

X4 3.9 51.4 21.2 0.1 18.1 5.3

X2 3.4 52.7 20.5 0.2 19.5 3.7

X3 3.4 52.5 21.1 0.2 19.0 4.0

X4 4.0 50.3 21.5 0.2 17.2 6.9

(B) C1 C2= + C3= C4 BTX Paraffin undefined

X1 3.4 51.5 20.9 0.2 19.2 4.9


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Table 4. Amount of coke deposited on catalyst after reaction. (A) MTW zeolite exchanged with ammonium nitrate, (B) MTW zeolite exchanged with ammonium fluoride. (A)

(B) after 4.5 h Coke : wt.%

after 4.5 h Coke : wt.% H-MTW (X1) La-MTW (X2) Ce-MTW (X3) B-MTW (X4)

5.9 4.5 3.7 3.4

H-MTW (Y1) La-MTW (Y2) Ce-MTW (Y3) B-MTW (Y4)


2.9 3.4 3.9 2.8

Steam Catalytic Cracking of n-Hexane over Modified MTW Zeolites

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