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Catalysis and Kinetics
Stable Production of Gasoline-Ranged Hydrocarbons from Dimethyl Ether over Iron-Modified ZSM-22 Zeolite Anas Karrar Jamil, Oki Muraza, Koji Miyake, Mohamed H.M. Ahmed, Zain H. Yamani, Yuichiro Hirota, and Norikazu Nishiyama Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b03008 • Publication Date (Web): 04 Oct 2018 Downloaded from http://pubs.acs.org on October 7, 2018
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Stable Production of Gasoline-Ranged Hydrocarbons from Dimethyl Ether over IronModified ZSM-22 Zeolite Anas K. Jamil1, Oki Muraza1*, Koji Miyake2, Mohamed H.M. Ahmed1, Zain H. Yamani1, Yuichiro Hirota2, Norikazu Nishiyama2 1Center
of Excellence in Nanotechnology and Chemical Engineering Department, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia 2 Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan O.M.: E-mail,
[email protected]. Abstract In this work, we developed metal modified ZSM-22 zeolites for the application of converting DME to Gasoline-Ranged Hydrocarbons. ZSM-22 zeolite samples were modified by microwaveassisted ion-exchange (MAIX) with nitrates of iron, nickel, copper, and cobalt, and calcium. In the meantime, the acidity of ZSM-22 zeolite was noticeably changed based on the type of metal. The H-ZSM-22 zeolite showed a high selectivity to light olefins (72%). The iron modified ZSM-22 zeolite showed a stable catalytic activity (more than 3 h) and a high olefins selectivity (54%). Strong hydrogenation behavior was observed over nickel modified sample, in which DME was converted to ethane. While copper, cobalt, and calcium showed a very low DME conversion combined with high selectivity to aromatics and hexane, which can be attributed to the pore blockage. Interestingly, copper modified sample showed a high initial selectivity to ethylene. Calcium modified catalyst showed the lowest textural properties with very low acidity as observed by NH3-TPD analysis. This study will open plethora of further research and application of ZSM22 zeolite and other medium pore zeolites as catalysts for dimethyl ether to gasoline process (DTG). Keywords: DME; ZSM-22, one-dimensional pore zeolite, iron-based catalysts; DTG; DTH. 1 ACS Paragon Plus Environment
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1. Introduction The need to reduce CO2 emissions produced from transportation and industry sectors is environmentally paramount. Meanwhile, finding a green route to convert raw materials such as biomass, natural gas, or coal into highly demanded chemicals or fuels to face the increasing needs of energy is one of the significant industrial challenges. Methanol which is the main feed for the methanol-to-hydrocarbons (MTH) process is produced from the raw material via syngas. The raw material like biomass need to be firstly converted to syngas and then to methanol. However, due to the thermodynamic limitations and operating conditions, syngas can be more efficiently converted to DME than methanol, which is formed in two-steps process, while DME can be formed directly from syngas in one-step process syngas-to-DME (STD) 1, 2. DME can be the future fuel as high energy content and environmentally friendly fuel for transportation and residential cooking. Conversion of dimethyl ether to more valuable hydrocarbons (DTH) is a process of growing interest in the green chemical industry. The reaction pathway can be simplified as follows: CH3OCH3→Olefins(C2 ― C5)→paraffins + aromatics + cycloparaffins + C6+ olefins. Although ZSM-5 (MFI) zeolite is the most established catalyst in the DTH process 2, many reports suggested ZSM-22 (TON) as a promising candidate for converting methanol to hydrocarbons to produce clean fuel
3-5.
Under suitable conditions, ZSM-22 zeolite can produce a product free of
aromatics and rich in branched C5+ olefins and paraffin, which can be converted by hydrogenation to a high-octane fuel
3-5.
Both ZSM-22 and ZSM-5 are classified as medium pore zeolites.
However, unlike ZSM-5, aromatics formation over ZSM-22 during MTO reaction is suppressed, which is attributed to the space restrictions of pore channel that prevent the hydrocarbon pool mechanism required for aromatic formation 6. ZSM-22 is a medium-pore zeolite with TON framework that contained 5, 6- and 10-rings. ZSM-22 zeolite has one-dimensional pores without 2 ACS Paragon Plus Environment
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internal intersects or buckets. These pores are 10-membered ring openings with an effective pore size of 0.46 × 0.57 nm 7. Deactivation is one of the main problems that hinder the catalytic applications in the MTH and DTH reactions. Many of the recent research are devoted to understanding the deactivation phenomena related to each zeolite framework topology in the commercial catalysts, ZSM-5 (MTG) and SAPO-34 (MTO) 8-10. Modifying zeolites with metals is a versatile strategy to enhance zeolites activity and selectivity in the conversion of dimethyl ether and methanol to hydrocarbons. Modification of ZSM-5 zeolite with alkaline earth metals such as calcium was reported to improve lifetime and propylene selectivity of ZSM-5 zeolite, which was attributed to the creation of acid−base centers modification of ZSM-5 apparent pore size
13.
11, 12
and
Bakare et al.14 reported that modifying high
aluminum ZSM-5 with calcium to enhance light olefins selectivity in the DME conversion due to the weak and medium acid sites created by the presence of Ca species. Modification of ZSM-5 with transition metals like Cu and Ni was reported to tune the selectivity towards aromatics 15. The shift in ZSM-5 selectivity towards aromatics in the MTH reaction was attributed to the alter in zeolite acid sites caused by the metal oxide basic sites. Metal oxides stimulate higher yield of propylene that is then being converted to aromatics 15. Selective production of light olefins could be achieved by altering ZSM-5 acidity with metal species, which is believed to prevent further dehydration and methylation of light olefins to higher olefins and paraffin 16. ZSM-22 zeolite is reported to rapidly lose its catalytic activity due to its constricted and limited number of pore mouths that can be easily blocked by coke species
9, 10.
Eventhough, ZSM-22 and ZSM-5 are
classified as medium pore zeolites, reaction and deactivation mechanisms are different due to difference in the framework structure. To the best of our knowledge, there were only few reports 3 ACS Paragon Plus Environment
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investigated the performance of one-dimensional (1D) pore zeolites in the conversion of dimethyl ether to hydrocarbon 14. Therefore, studying performance of 1D pore zeolite in DTH and the effect of metals ion-exchange on the ZSM-22 zeolite selectivity and stability is worth investigating.
2. Experimental 2.1 Materials and Preparation of ZSM-22 Zeolites K-ZSM-22 zeolite samples with nominal Si/Al ratio of 46 were prepared as described thoroughly in our previous reports 17, 18. The template was removed by calcining K-ZSM-22 zeolite samples under the air flow at 650 oC for 12 h. The calcined form of K-ZSM-22 zeolite was then ionexchanged twice under microwave irradiation (microwave-assisted ion exchange, MAIX) at 85 oC for 10 min with a 20 ml of 2 M NH4NO3 solution for each gram of zeolite sample 17. The ionexchange was performed in a microwave lab station (MicroSYNTH, Milestone, Italy). Firstly, the temperature was raised to 85 °C in 5 min by applying 800 W microwave irradiation. Then temperature kept at 85 °C for 10 min by applying 400 W irradiation power, then cooling to room temperature for another 10 min. After the second ion exchange, solution is centrifuged to separate NH4-ZSM-22 zeolite slurry, which was then dried and calcined under the air flow at 650 oC for 12 h to produce H-ZSM-22 zeolite. Metals nitrates used to modify the H-ZSM-22 zeolite samples were calcium (II) nitrate tetrahydrate (99.997%, Sigma Aldrich), nickel (II) nitrate hexahydrate (99.999%, Sigma Aldrich), copper (II) nitrate trihydrate (99.00 %, Sigma Aldrich), cobalt (II) nitrate hexahydrate (99.999%, Sigma Aldrich) and iron (III) nitrate (99.99%, Sigma Aldrich). For the metal ion exchange procedure, 1 g of H-ZSM-22 zeolite was ion-exchanged twice with 20 ml of 2 M desired metal nitrate solution under microwave irradiation with the same microwave program used to prepare H-ZSM-22 4 ACS Paragon Plus Environment
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sample. The mixture of H-ZSM-22 zeolite and the metal salt solution was heated under microwave irradiation at 85 oC for 10 min. The solid slurry was then centrifuged, dried at 110 oC and then calcined for 12 h at 650 oC. Metal exchanged samples were designated as TAN-M (where M = Ca, Cu, Fe, Co, Ni). The letter 'M' stands for the metal used during the ion exchange procedure.
2.2 Characterization and catalytic evaluation ZSM-22 zeolite samples were characterized to study the effect of metals ion exchange on the crystallinity, chemical compositions, textural properties, and morphology. For crystallinity analysis, The X-ray diffraction patterns were recorded over 2𝜽 range of 5o to 50o with a speed of 3 and step size of 0.03 using XRD diffractometer, MiniFlex (Rigaku). The elemental composition was measured by SPECTRO XEPOS XRF spectrometer. The textural properties were analyzed by using nitrogen adsorption-desorption measurements Micromeritics ASAP 2020 porosimeter. The Temperature-programmed desorption of ammonia (NH3-TPD) analysis was carried out using AutoChem II analyzer from Micrometrics. More details about these characterization techniques are described in our previous works 17, 18. The catalytic activity of the prepared ZSM-22 zeolite samples was evaluated in the conversion of dimethyl ether to hydrocarbons (DTH) reaction. 50 mg of ZSM-22 sample, pelletized and sieved in the range of 500–300 μm, was placed inside quartz tube (i.d. 4 mm) in the fixed-bed reactor. The reaction was carried out under atmospheric conditions at 400 ◦C. The flow rate of DME was ca. 1.3 mmol. h-1 and helium which was used as a carrier gas was ca. 19 mmol. h-1. The contact time (W/F) was ca. 0.039 kg. h. mol-1. The analysis of reaction product was conducted by online gas chromatograph (Shimadzu GC-14B) Equipped with a flame ionization detector (FID) and a capillary column (J&W Scientific GS-Alumina).
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Terms of DME conversion, and product selectivity are defined and calculated according to the following Equations: 𝐷𝑀𝐸 𝑐𝑜𝑛𝑣𝑒𝑟𝑠𝑖𝑜𝑛 [%] = (1 ―
𝑎𝑟𝑒𝑎 𝑜𝑓 𝐷𝑀𝐸 𝑎𝑓𝑡𝑒𝑟 𝑟𝑒𝑎𝑐𝑡𝑖𝑜𝑛 𝑖𝑛𝑖𝑡𝑖𝑎𝑙 𝑎𝑟𝑒𝑎 𝑜𝑓 𝐷𝑀𝐸
) × 100 (1)
𝐴𝑖 𝑛𝑖
𝑃𝑟𝑜𝑑𝑢𝑐𝑡 𝑆𝑒𝑙𝑒𝑐𝑡𝑖𝑣𝑖𝑡𝑦 [%] = ∑
(𝐴 𝑖
𝐴𝑖
× 100
(2)
𝑛𝑖
and 𝑛𝑖 represent areas and carbon numbers of hydrocarbon i.)
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3. Results and Discussions Figure 1 shows the XRD patterns of parent and metal ion-exchanged ZSM-22 samples. The metal ion exchange did not affect the crystalline structure of modified samples. All samples showed XRD patterns related to the TON framework with main peaks at 2𝜽 = ca. 8.4, 20.63, 24.5, 24.92, 26.06 and 35.96o. Extra tiny peaks are observed between 2𝜽 of 37 o and 45o, which are related to the presence of metal oxide within the ZSM-22 zeolite samples. Those peaks were mostly weak indicated that the metal species are not well crystallized. As observed from the first column in Table 1, dealumination is observed in Sample TAN-Fe, while desilication is observed after the ion-exchange with calcium, cobalt, copper and nickel solutions. Figure 1. Powder X-ray diffraction patterns of ZSM-22 ion exchanged with: (a) Ni, (b) H, (c) Ca, (d) Fe, (e) Co, (f) Cu.
The N2 isotherms of ZSM-22 zeolite parent and modified samples showed type IV isotherms. The hysteresis loop occurred over a range of high P/P0 indicate the presence of mesopores (See Figure 2). The total surface area was ca. 151 m2g-1, while the external surface area was 33 m2g-1 the total pore volume and micropore volume were ca. 0.154 and 0.095 cm3 g-1, correspondingly (See Table 1). Figure 2. N2 isotherms of ZSM-22 zeolite parent and samples ion exchanged with Ca, Cu, Ni, Fe and Co.
A decrease in N2 uptake and textural properties were observed for all metal ion-exchanged samples, which is obviously related to the partial blockage of pores by metals species. The larger metal molecules size, the more blockage occurred in the sample. The most significant decrease in
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the total surface area was observed for sample TAN-Ca sample, the total surface area was reduced to only 22 m2g-1 (7 times smaller than parent sample). The micropore volume reduced from 0.095 cm3 g-1 for the parent sample to only 0.062 cm3 g-1 for sample TAN-Ca. Sample TAN-Co showed considerable reduction total surface area to 82 m2g-1. Slight variations observed in external surface (36 m2g-1) area, micropore (0.102 cm3 g-1) and mesopore volumes (0.051 cm3 g-1) of sample TANFe and parent sample. Textural properties of ZSM-22 zeolite parent and samples ion exchanged with Ca, Cu, Ni, Fe and Co are summarized in Table 1 below. Table 1. Textural properties of ZSM-22 zeolite parent and samples ion exchanged with Ca, Cu, Ni, Fe, and Co.
The acidity analysis was performed by NH3-TPD analysis for all samples as shown in Figure 3. The typical spectra of H-ZSM-22 zeolite were observed for parent ZSM-22 sample (TAN-Parent) Two peaks were observed at ca. 485 K and 701 K attributed to the weak and strong acid sites, correspondingly. Sample TAN-Fe showed similar spectra to the parent sample (TAN-Parent) with a slight increase in weak/medium acidity. Sample TAN-Ni showed a similar peak intensity related to weak acidity of parent sample. However, a clear enhancement in the medium acidity, which was located between the peaks related the weak and strong acid sites, was observed. The strong peak in sample TAN-Ni was shifted to the left side to ca. 680, indicating the presence weaker strong acid sites. Worth to mention that sample TAN-Ca showed a very low acidity, which can be related to blockage of active sites by the excess large calcium molecules. Sample TAN-Cu showed an interesting change in the type of the acidity. One large peak at ca. 565 K, was observed in Sample TAN-Cu, which can be related to
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medium acid sites. Sample TAN-Co showed the almost same intensity of weak acidity while the strong and medium acidity is reduced. Figure 3. NH3-TPD analysis of H-ZSM-22 zeolite parent and samples ion exchanged with Ca, Cu, Ni, Fe and Co.
The catalytic activity of the parent and modified H-ZSM-22 zeolites samples were investigated in the catalytic conversion of dimethyl ether (DME) to hydrocarbons as shown in Figures 4 below.
Figure 4. Selectivity and DME conversion over parent H-ZSM-22 and samples ion-exchanged with Ni, Fe, Cu and Co at 400 oC for: (a) 5 min, (b) 60 min. Initially, the parent sample (TAN-parent) showed 100% conversion of DME. Most of DME was converted to light olefins (ca. 71%). The produced light olefins consisted of ca. 34% propylene, ca. 21% butylene and ca.15% ethylene. The selectivity to paraffin (C1-C4) was ca. 17% of, while C5+ hydrocarbons were ca. 11%. A negligible amount of aromatics was observed (ca. 1%), which can be related to the structural restrictions of ZSM-22 pores. ZSM-22 zeolite has a onedimensional medium size pore structure, which there was not space enough for the hydrocarbon pool mechanism to induce aromatics formation
19.
Worth to mention that the parent sample
deactivated entirely after 60 min of reaction. On the other hand, the nickel modified sample (TAN-Ni) showed a stable conversion at ca. 75% even after 60 min. However, most of DME was hydrogenated into ethane (ca. 98%), while traces
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amount of C5+ hydrocarbons (ca. 1%) and aromatics (ca. 1%) were observed. The undesired hydrogenation of DME to ethane can be attributed to of hydrogenation nature of nickel species. Unlike sample TAN-Ni, sample (TAN-Fe) showed ca. 55% selectivity towards light olefins. While the selectivity of C5+ hydrocarbons is noticeably increased to ca. 25.5% as a compared to the parent sample (ca. 11%). Paraffin (C1-C4) selectivity was ca. 16%, while small amounts of aromatics were also observed (3.5%). Interestingly, sample TAN-Fe was more stable than the parent. The initial conversion was ca. 66 %, which reached 52% after 60 min. Even after 180 min of reaction, sample TAN-Fe showed a stable conversation (ca. 48%) and high light olefins selectivity (ca. 54%) as shown in Figure 5. H-ZSM-5 zeolite modified with iron showed extended catalytic life, which was attributed to the increase in the weak acidity of modified ZSM-5 zeolite as reported by Li et al. 20. Sample TAN-Cu showed relatively modest initial conversion ca. 22%, which decreased rapidly to ca. 6% after 60 min. Initially, high selectivity toward ethylene (ca. 41%) was observed over the sample TAN-Cu, while no propylene nor butylene was observed. Considerable amounts of paraffin (mainly methane) (ca. 24%) and C5+ hydrocarbons (ca. 23%) were also produced. As compared to the parent sample, more aromatics (mainly toluene) was observed over TAN-Cu (ca. 12%). After 60 min, a dramatic increase in aromatics (ca. 40%) and C5+ hydrocarbons (ca. 35%) were noticed. In the meantime, methane selectivity remained the same (ca. 24%), while there was no selectivity to light olefins. Ethylene is possibly produced via DME isomerization followed by dehydration of ethanol over Brønsted sites to ethylene21, 22. On the other hand, the increase in aromatics selectivity can be attributed due to pore blockage beside acidity alter by the presence of copper species.
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The low initial conversion was observed on TAN-Co (ca. 7%). However, the conversion increased to ca. 16% after 60 min. The dominant product observed over sample TAN-Co was aromatics (mainly xylene) (ca. 73%), followed by ethylene (ca. 17%) then hexane (ca. 8%). Traces of propylene, butylene, paraffin (C1-C4) were also observed. Interestingly, after 60 min of reaction, the selectivity to hexane increased to (ca. 50%), while the remaining products were aromatics (toluene). Textural properties analysis in Table 1, showed pore blockage of samples TAN-Co and TAN-Cu, which means that the reaction occurred on the surface and that explained the low conversion combined with high selectivity to aromatics. Aromatization (toluene and xylene), alkylation (C6) and ethylene as a clear indication of hydrocarbon pool cycle mechanism over samples TAN-Co and TAN-Cu. Previous reports showed that blockage of zeolite pores favored the aromatization reactions 23, 24 In the meantime, it was also reported that the presence of transition metals such as copper favored aromatic products 15. Sample TAN-Ca showed a very low catalytic activity in the DTH reaction due to the pore blockage of sample TAN-Ca and very low acidity as shown in Table 1 and Figure 3. The summary of conversion and product selectivity after 5 and 60 min are summarized in Table 2 and Table 3 below. Figure 5. Time on a stream of DME conversion reaction at 400 oC over Fe, H-ZSM-22 sample. Table 2. Product selectivity of DTH after 5 min at 400 oC over ZSM-22 zeolite ion-exchanged with Ni, Fe, Cu and Co. Table 3. Product selectivity of DTH after 60 min at 400 oC over ZSM-22 zeolite ion-exchanged with Ni, Fe, Cu and Co.
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Conclusions Among the modified ZSM-22 samples, the Fe-ZSM-22 zeolite showed a higher catalytic stability even after 3 h of reaction. High selectivity to light olefins, especially propylene was also observed over sample TAN-Fe with a selectivity of ca. 55% and ca. 25 %, respectively. Due to the pore blockage of samples treated with Cu, Co and Ca, very low conversions were observed combined with a high selectivity towards aromatics and higher alkane (C6). Calcium modified ZSM-22 zeolite with showed the lowest activity due to the pore blockage and lack of acidity. Worth mention that DME was dehydrogenated to ethane over nickel modified sample TAN-Ni, while considerable amount of DME was dehydrogenated to methane over copper modified sample (TAN-Cu). On the other hand, TAN-Cu showed interesting initial selectivity towards ethylene (ca. 40%). The works on the iron modified ZSM-22 will stimulate further research on designing better catalysts for selective conversion of DME to green gasoline.
Acknowledgments The authors would like to acknowledge the funding provided by King Abdulaziz City for Science and Technology through the Science & Technology Unit in Center of Research Excellence in Nanotechnology at King Fahd University of Petroleum & Minerals (KFUPM) for supporting this work through project No. 13-NAN1702-04 as part of the National Science, Technology and Innovation Plan.
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18. Jamil, A. K.; Muraza, O.; Osuga, R.; Shafei, E. N.; Choi, K.-H.; Yamani, Z. H.; Somali, A.; Yokoi, T., Hydrothermal stability of one-dimensional pore ZSM-22 zeolite in hot water. The Journal of Physical Chemistry C 2016, 120, (40), 22918-22926. 19. Wang, Q.; Cui, Z.-M.; Cao, C.-Y.; Song, W.-G., 0.3 Å Makes the Difference: Dramatic Changes in Methanol-to-Olefin Activities between H-ZSM-12 and H-ZSM-22 Zeolites. The Journal of Physical Chemistry C 2011, 115, (50), 24987-24992. 20. Li, M.; Huang, Y.; Ju, C.; Fang, Y., Release of full catalytic capacity of desilicated ZSM-5 in MTH reaction: Al migration along mesopore introduction and post engineering. Microporous and Mesoporous Materials 2017, 244, 7-14. 21. Batova, T.; Khivrich, E. K.; Shirobokova, G.; Kolesnichenko, N.; Pavlyuk, Y. V.; Bondarenko, G., The effect of steam on the conversion of dimethyl ether to lower olefins and methanol over zeolite catalysts. Petroleum Chemistry 2013, 53, (6), 383-387. 22. Nasser, G.; Kurniawan, T.; Miyake, K.; Galadima, A.; Hirota, Y.; Nishiyama, N.; Muraza, O., Dimethyl ether to olefins over dealuminated mordenite (MOR) zeolites derived from natural minerals. Journal of Natural Gas Science and Engineering 2016, 28, 566-571. 23. Kaeding, W.; Chu, C.; Young, L.; Weinstein, B.; Butter, S., Selective alkylation of toluene with methanol to produce para-xylene. Journal of Catalysis 1981, 67, (1), 159-174. 24. Zhang, J.; Qian, W.; Kong, C.; Wei, F., Increasing para-xylene selectivity in making aromatics from methanol with a surface-modified Zn/P/ZSM-5 catalyst. ACS Catalysis 2015, 5, (5), 2982-2988.
14 ACS Paragon Plus Environment
Page 15 of 23 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
Energy & Fuels
CO2
STD process
H2
DME
Selective DTG process
(from renewable resources )
Green Gasoline
Bio Syngas (H2+CO)
Biogas (CH4+CO2)
CO2 RM
DME: Dimethyl ether DTG: Dimethylether-to-gasoline CO2 RM: Carbon Dioxide Reforming of Methane Syngas: Synthesis gas (Co+H2) One-step process syngas-to-DME (STD)
DME as Future fuel for transportation and Residential cooking
ACS Paragon Plus Environment
Selective conversion of DME to gasoline using Fe-ZSM-22 zeolite @400 oC
Energy & Fuels
(a) H-ZSM-22 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
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(b) Ni, H-ZSM-22 (c) Ca, H-ZSM-22 (d) Fe, H-ZSM-22 (e) Co, H-ZSM-22 (f) Cu, H-ZSM-22
5
10
15
20
25 30 𝟐𝜽[°]
35
40
45
50
ACS Paragon Plus Environmention exchanged with: (a) Ni, (b) H, (c) Ca, Figure 1. Powder X-ray diffraction patterns of H-ZSM-22 (d) Fe, (e) Co, (f) Cu.
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140
H-ZSM-22 Fe,H-ZSM-22 Ni,H-ZSM-22 Ca,H-ZSM-22 Cu,H-ZSM-22 Co,H-ZSM-22
120
Vads [cm3.g-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
Energy & Fuels
100 80 60 40
20 0 0
0.2
0.4
0.6
0.8
1
P/Po [-]
ACS parent Paragon Plusand Environment Figure 2. N2 isotherms of ZSM-22 zeolite samples ion exchanged with Ca, Cu, Ni, Fe and Co.
Energy & Fuels
H Ca Ni Fe
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
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400
Co
Cu
450
500
550
600
650
700
750
800
T [K]
Paragon Plus Environment Figure 3. NH3-TPD analysis of H-ZSM-22ACSzeolite parent and samples ion exchanged with Ca, Cu, Ni, Fe and Co.
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(a) After 5 min
(b) After 60 min
100%
100%
90%
90%
80%
80%
70%
Aromatic C5
