Catalytic enhancement of SAPO-34 for methanol conversion to light

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Kinetics, Catalysis, and Reaction Engineering

Catalytic enhancement of SAPO-34 for methanol conversion to light olefins using in-situ metal incorporation Hassan Ahmed Salih, Oki Muraza, Basim Abussaud, Talal K. Al-Shammari, and Toshiyuki Yokoi Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b04549 • Publication Date (Web): 10 Apr 2018 Downloaded from http://pubs.acs.org on April 10, 2018

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Industrial & Engineering Chemistry Research

Catalytic enhancement of SAPO-34 for methanol conversion to light olefins Using in-situ metal incorporation Hassan A. Salih a, b, Oki Muraza a, b*, Basim Abussaud a, Talal K. Al-Shammari c, Toshiyuki Yokoi d a

Center of Excellence in Nanotechnology and b Chemical Engineering,

King Fahd University of Petroleum & Minerals (KFUPM), Dhahran 31261, Saudi Arabia c

d

SABIC, P.O Box 42503, Riyadh, 42503, Saudi Arabia

Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku Yokohama, Japan Corresponding author email*: [email protected]

Abstract Parent and MeAPSO-34s (Me=Cu, Ca and W) catalysts were synthesized for methanol conversion to more valuable products such as light olefins. The effect of metal presence on the catalytic performance and physicochemical properties were investigated. The comprehensive characterizations, XRD, EDX, FESEM, FTIR, N2-BET, NH3-TPD and DR-UV-Vis have been applied to characterize the metal modified SAPO-34. Even though the crystallinity of MeAPSO34s decreased compared to parent SAPO-34, the diffusion and acidity properties were improved. Good activity and selectivity for olefins production were observed for all synthesized catalysts. Metal incorporation to the framework of SAPO-34 enhanced the catalytic lifetime and propylene yield. The methanol conversion was stable for 1 h over MeAPSO-34 with W/F=6.6 g h/mole at 350 oC, and 1 bar. The deactivation rate was higher for the parent SAPO-34 as compared to MeAPSO-34. CaAPSO-34 favored propylene production, While CuAPSO-34 favored ethylene.

Keywords: MTO; SAPO-34; in-situ incorporation; light olefins.

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1. Introduction Light olefins are considered as one of the most important feedstocks in petrochemical industries 1

. It is essential to develop innovative technologies to meet olefins demand specially propylene

and ethylene. Light olefins are produced mainly by steam cracking and fluid catalytic cracking (FCC). Other potential source of olefins is methanol-to-olefins (MTO) process2. Microporous zeolite catalysts with different morphologies, pore structures, and acidities have been applied in MTO reaction3-6. SAPO-34 exhibited promising catalytic activity in MTO mainly for their thermal stability, medium acidity and small pores that favors olefins and suppress aromatics yield1,

7, 8

. However, SAPO-34 has catalytic stability issue as it deactivates rapidly as space

velocity increased due to its high aluminum content and pore architecture, which prevent aromatics to escape and make them react with other species to form complex aromatic compounds that cause coking9,

10

. Several metal modifications have been used to enhance its

stability by impregnation, ion exchange and in-situ incorporation11, 12. The modification metals that can be in-situ incorporated to the SAPO-34 framework include transition and alkaline metals13, 14. Cobalt, manganese, and nickel have been incorporated to the SAPO-34 framework by Dubois et al to improve conversion, selectivity, and stability. The most stable catalyst was reported for Mn, while CoAPSO-34 had highest light olefins selectivity15. Sedighi et al studied MeAPSO-34 [Fe, Ni, Co, La and Ce] molecular sieves for MTO16. Better catalytic performance was reported for metal modified SAPO-34 as compared to the parent. CeAPSO-34 had the best lifetime (7 h) and highest selectivity to light olefins (35.6%). While iron (Fe) had lowest selectivity and lifetime among modified samples, also coke formation was analyzed to compare the deactivation of MeAPSO-34 samples. Different metals incorporation has been confirmed by characterization techniques to ensure metal presence inside the framework. 2 ACS Paragon Plus Environment

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Kang et al has investigated the effect of [Ni, Co, and Fe] on catalytic performance of SAPO-34 for a range of temperature. It was reported that catalytic stability and conversion were not improved by this modification. In contrast, light olefins selectivity has increased almost 10%, where the highest selectivity of 93% was achieved over CoAPSO-3417. Co, Mn, and Fe were incorporated successfully into the SAPO-34 framework by Wei et al they achieved a good activity of chloromethane conversion towards light olefins18. Salmasi et al reported that both conversion and selectivity have been enhanced by the presence of Ni and Mg. Also, coke formation was reduced due to its lower acidity, which prolonged catalyst lifetime19. Zirconium has been incorporated inside SAPO-34 by Aghaei et al for MTO reaction20. The ZrO2/Al2O3 ratio was varied from 0.01 to 0.15. Zirconium was reported to favor propylene formation over ethylene due to its acidity contribution. Zirconium enhanced catalytic stability and selectivity towards light olefins for ZrO2/Al2O3 ratio up to the 0.05. Further addition of zirconium has led to worse catalytic performance as compared to parent SAPO-34. Another work studied GaAPSO-34 catalyst with different Ga/Al ratios21. The Gallium addition showed no modification either for conversion or olefins selectivity. The ethylene production favored by GaAPSO-34. This work presents a comparative study of different metals added to the SAPO-34 framework via aluminum isomorphous substitution. Copper, calcium and tungsten were never been reported for in-situ incorporation of SAPO-34. So, those elements have been selected to modify the catalytic performance represented in terms of methanol conversion, selectivity towards olefins and coking resistance. The MeAPSO-34 molecular sieves were synthesized by hydrothermal method. XRD, FE-SEM, N2-BET and NH3-TPD techniques were used to characterize catalytic properties such as crystallinity, morphology, textural and acidity properties. The metal presence



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with the SAPO-34 framework backbone was confirmed by EDX, DR UV-VIS, and FTIR characterizations.

2. Experimental 2.1. Materials Aluminum isopropoxide (Merck, 98%), Snowtex colloidal silica (40 wt.%) and orthophosphoric acid (Merck, 85% aq. solution) were used as precursors for Al, Si, and P, respectively. Tetraethylammonium hydroxide (Aldrich, 40% aq. solution) was used as organic structure directing agent (OSDA). Calcium nitrate tetrahydrate, copper nitrate trihydrate, and tungsten carbide were selected as metal precursors. Deionized (DI) water was used as the synthesis medium to dissolve various precursors 2.2. Synthesis SAPO-34 zeolite was prepared by following the procedure in Figure 1 via in situ crystallization of gel solution that was prepared by dissolution of aluminum isopropoxide in deionized water. Then, orthophosphoric acid was added to the solution and aged for 1 h. Snowtex 40 wt.% colloidal silica was added to the solution then metal source was also added to the solution. Finally, TEAOH solution was added as a structure directing agent. Then final gel solution was aged for 3 h under stirring. The molar composition of the synthesis gel was 1 Al2O3 : 1.15 P2O5 : 0.55 SiO2 : 2 TEAOH : 110 H2O : 0.007 MeOx. Aged gel solution was transferred to PTFE holder and was placed in the autoclave. The crystallization process was carried out inside the hydrothermal oven at a temperature of 180 oC for 72 h. After the synthesis period, the autoclave was cooled by rinsing in cold water. The SAPO-34 was separated from the solution by highspeed centrifuge and washed with deionized water to neutralize pH. Wet powder was dried in an oven at 110 0C overnight. The OSDA was removed by calcination in an automatic furnace at 600 0

C with a ramping rate of 10oC/min for 5 h. Finally, all the synthesized catalysts were formed 4 ACS Paragon Plus Environment

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into pellet shape by mechanical pressing and then crushed and sieved to particles with a diameter of 0.5-1 mm.

Please insert Figure 1 here.

2.3. Characterization techniques The crystallinity and phase of the synthesized powder were analyzed by a diffractometer (Miniflex, Rigaku). Cu Kα radiation of 1.5405 A was applied. The analysis was carried out for 2 in the range of 5–40◦ using a scanning speed of 2 degree per min with a scan step of 0.02◦ and each step has 4 s counting time. LYRA 3 Dual Beam (Tescan) fitted with (Oxford Instruments, EDX) energy dispersive X-ray spectrometry was used for scanning electron microscopy (SEM) with an acceleration voltage 30 kV. Nitrogen adsorption was measured by a Micromeritics ASAP 2020 porosimeter equipped with liquefied N2 adsorption at −196 ◦C. Firstly, sample was degassed at 350 ◦C for 12 h. The surface area and pore volume were calculated based on the BET method. The catalyst acidity was evaluated by ammonia temperature programmed desorption (NH3-TPD) using Micromeritics Autochem II 2920 instrument. The Helium was used as a carrier gas for NH3 stream. The heating rate was 5 ◦C min−1 and the data were recorded from 100 to 750 ◦

C. Fourier transform infrared spectroscopy (FTIR, Nicolet NEXUSFTIR-670 spectrometer) was

used to study the surface groups of calcined catalysts. Zeolite and KBr powder (1 wt %) were mixed together well in 1:99 ratio then pressed into a wafer (50 mg) and placed on the holder to be exposed to infrared rays. UV–vis diffuse reflectance spectra of the samples were analyzed and recorded on the Cary 5000 UV-VIS NIR spectrophotometer equipped with PbSmart detector, which enhances its photometric performance to reach high wavelength up to 3300 nm.



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2.4. Experimental setup for catalytic evaluation Catalytic testing was carried out in a stainless-steel tubular fixed bed reactor at atmospheric pressure. First, the pelletized catalyst was packed in the middle of the bed in between two quartz wool pieces. The catalyst was pretreated prior to testing at 500 oC for 1 h under helium gas flow. The feed to methanol-to-olefins (MTO) reactor consisted of 5 mole% of methanol and 95 mole% He, which was used as a carrier gas to facilitate the flow of the reactants and products. The activity synthesized catalysts was examined at 350 o C for energy saving and better evaluation of their activity at harsh conditions. Methanol conversion and product selectivity were evaluated with varying time of stream (TOS). The reaction experiment was run at constant weight hourly space velocity (WHSV) of 4.85 h-1. Reaction products were analyzed by on-line Shimadzu gas chromatography equipped with a capillary column HP-PLOT (30 m × 0.53 mm, 6 µm film thickness) and a flame ionization detector (FID).

3. Results and discussions 3.1. Physicochemical characterizations 3.1.1. XRD analysis The XRD patterns of the synthesized SAPO-34 and MeAPSO-34 catalysts were presented in Figure 2. It is clear that no extra peak belong to impurities and all peaks represent chabazite structure of the synthesized catalysts. This can be considered as an evidence for the presence of metal heteroatoms in gel solution results in good crystallinity product. The parent SAPO-34 exhibited the highest crystallinity of synthesized samples. In contrast, metal modified samples had lower crystallinity due to size reduction and partial distortion of the crystal structure by 6 ACS Paragon Plus Environment

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metal atoms. Also, it is observed that the peaks shifted slightly to left due to metal isomorphous substitution into the SAPO-34 structure and the lattice parameters and interplanar spacing change11, 14, 22. Please insert Figure 2 here.

3.1.2. FESEM analysis FESEM images of synthesized MeAPSO-34 and parent samples shown on Figure 3 revealed cubic morphology which is common for CHA phase of zeolite and specifically SAPO-3423.it was observed that MeAPSO-34 particles have uniform cubic shape compared to SAPO-34 cubes where were associated with extra irregular shape particles and aggregation.as shown on SEM images presented on Figure 4 the CaAPSO-34 and CuAPSO-34 catalysts tend to have rectangular surface unlike square cubic WAPSO-34 and parent catalyst particles. Also, FESEM images showed that MeAPSO-34 samples have a rough surface which supports XRD finding of crystallinity drop. Moreover, the particle size of SAPO-34 samples reduced after metal incorporation due to slower crystallization. Generally, Particle size distribution of samples is medium and Parent SAPO-34 had largest particle size and calcium and copper addition lowered size by 50%.

Please insert Figure 3 here. Please insert Figure 4 here. 3.1.3. Elemental analysis EDX analysis for MeAPSO-34 samples was shown on Table 1. It indicates metals in the gel solution are attached to the framework and/or stuck on particle surface as an amorphous phase. But, The Successful incorporation into SAPO-34 framework was confirmed by XRD and 7 ACS Paragon Plus Environment


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FESEM analysis which revealed that there is no extra amorphous phase. Also, it was observed that metals were detected with different percentages which mean each metal has a different impact on the silicon incorporation.

Table 1. EDX analysis of MeAPSO-34 samples. Catalyst

Si (%)

Al (%)

P (%)

Ca (%)

Cu (%)

W (%)

SAPO-34

4.916

22.09

14.96

-

-

-

CaAPSO-34

6.116

23.48

13.25

0.2663

-

-

CuAPSO-34

5.088

23.75

15.04

-

0.1384

-

WAPSO-34

5.591

23.12

14.06

-

-

0.3419

3.1.4. BET analysis Table 2 presents specific surface area (SSA) of prepared catalysts. The highest surface area was recorded for the parent SAPO-34 sample (488 m2/g). Then, the SSA declines with metal incorporation because of their lower crystallinity, which is consistent with XRD and FESEM results. On the other hand, metal modification enhanced diffusion properties of the SAPO-34 catalyst due to mesopores that were preferentially formed instead of micropores by aluminum isomorphous substitution24. Calcium modified SAPO-34 had highest mesopore volume which indicates its smooth incorporation as compared with other metals (confirmed by EDX). Table 2: BET analysis for synthesized samples. Catalyst

SBET

Smicro

Sext

VTOT

Vmicro

Vmeso

(m2/g)

(m2/g)

(m2/g)

(cm3/g)

(cm3/g)

(cm3/g)

SAPO-34

488

469

19

0.21

0.20

0.01

CaAPSO-34

467

439

28

0.26

0.21

0.05


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CuAPSO-34

443

420

23

0.23

0.20

0.03

WAPSO-34

364

345

19

0.18

0.17

0.01

3.1.5. NH3-TPD analysis Acidity is a crucial parameter that affects the catalytic properties of acid zeolites. The strength and amount of acid sites of the prepared samples were evaluated by The NH3-TPD. TPD profiles of parent and metal modified SAPO-34 are shown in Figure 5. For all samples, there are two peaks centered around 150–300 and 450–600 °C. The weak and strong acidity are related to low and high-temperature desorption peaks respectively. Quantitative evaluation of catalyst acidity is presented in Table 3. A decrease in acidity was achieved by metal incorporation into the SAPO34 framework as shown in Figure 5 and Table 3. CaAPSO-34 catalyst had the lowest number of acid sites as compared to the other samples. This can be attributed to higher silicon incorporation and silica islands formation due to the metal substitution of aluminum25. The Strong acidity increased in the order of WAPSO-34>CaAPSO-34>CuAPSO-34>SAPO-34. It was agreed that the weak acid sites are favored for DME and water formation, while the strong acid sites are important to convert DME to light olefins as expected for MeAPSO-34 catalysts20, 26. Table 3. The NH3-TPD results for calcined catalysts. Sample

SAPO-34

Acidity (NH3 desorption (mmol/g)) Weak

Strong

150-300 oC

450-600 oC

1.88

0.21



CuAPSO-34

1.65

0.41

CaAPSO-34

0.77

0.63

WAPSO-34

0.89

0.81

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3.1.6. FTIR analysis Fourier transform infrared spectroscopy was used to identify surface groups on modified SAPO34. The framework vibrations of synthesized catalysts are identical to CHA phase as shown in below Figure 6. The peak at a wavenumber of 420 cm-1 is attributed to M-O which supports previous characterizations finding of successful metal incorporation27. Also, it was observed that silicon was incorporated as SiO4 form inside the SAPO-34 structure based on bending at 490 cm1 16

. The XRD finding of SAPO-34 phase for all samples was confirmed by a peak at 640 cm-1

which belongs to D-6 ring formation of CHA20. The peaks at a wavenumber of 710, 1110 and 1650 cm-1 wavenumber are attributed to asymmetric and symmetric O-T-O stretches and physical H2O adsorption, respectively. The peak intensity at 1650 cm-1 is stronger with the presence of metals, which is related to the adsorption properties16. The peaks at a wavenumber of 3450 and 3590 cm-1 are attributed to bridging hydroxyl group of Si-OH-Al which have a share of Bronsted acid sites and hydroxyl group associated with the tetrahedral atom (T-OH)20. Intensity of Si-OH-Al peak was increased after metal modification indicating higher Bronsted acidity, which is favorable for MTO reaction.


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Moreover, the peak of T-OH was almost eliminated after modification, which means less extra frameworks of Si-OH, Al-OH and P-OH supporting the good crystallinity of modified samples from SEM and XRD characterizations19. But all these findings of acidity change need to be verified by Pyridine FTIR which is not feasible for SAPO-34 due to its small pores that will not allow pyridine molecules to diffuse. Therefore, NH3-TPD was used to support our claims.


3.1.7. Diffuse reflectance UV-Vis analysis The DR UV-Vis spectra of various synthesized catalysts are shown in Figure 7. The Metal presence in the SAPO-34 framework was investigated by Dr UV-VIS technique. It was observed that no absorption bands for both parent and MeAPSO-34 samples. The broad band was detected in the wavelength of 220-260 nm for both parent and MeAPSO-34 samples. This band is attributed to Al-O charge transfer transitions of Aluminum tetrahedral species in or outside framework20. There are small bands overlapped with this broad band at low and high wavelength attributed to tetrahedral and octahedral metal species, respectively16, 20. Weak bands were observed as shown in Figure 8 at the wavelength of 260-350 nm, which indicated the metal presence in tetrahedral form MeO4, while no octahedral metals specie was detected in the wavelength of 660-730 nm. Also, the broad band location was shifted to the left for modified samples due to the metal incorporation into the framework. Moreover, there was no aluminum extra framework for both parent and MeAPSO-34 samples as there was no weak band observed at 850-950 nm wavelength28, 29. 11 ACS Paragon Plus Environment


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Please insert Figure 7 here Please insert Figure 8 here. 3.2. Catalytic performance of SAPO-34 and MeAPSO-34 Figures 9 and 10 show the catalytic performance where methanol conversion and light olefins yield were plotted for different catalysts with time on stream. The catalytic testing of synthesized samples was carried out at 350 o C, 1 atm with space-time of 6.6 gcat h/mole. All SAPO-34 based catalysts showed high selectivity towards olefins at the initial time, which can be justified by the acidity and unique pore structure of parent and modified samples. The light olefins yield was declined for all catalysts due to deactivation by coke deposition. But, propylene and butene were affected more than ethylene. Also, the methanol conversion was decreased with time on stream due to pore blockage of SAPO-34 catalyst by coke deposition. MeAPSO-34 catalysts exhibited better catalytic stability during reaction as compared to parent catalyst which was attributed to the decrease of weaker acid sites inhibits formation of heavy aromatics. Moreover, the formation of light olefins was enhanced by the metal presence inside the SAPO-34 structure, which created more active sites that favor olefins production. Table 4. Methanol conversion and product selectivity over different catalysts at 350 °C, 1 atm, 5 mole% of MeOH, TOS=120 min and W/F = 6.6 g h/mole. Catalyst

Conversion (%)

C2= (%)

C3= (%)

Paraffin (%)

DME (%)

Parent

82.1

18.0

22.3

11.5

40.8

CaPASO-34

90.7

24.9

33.8

8.0

23.8

CuPASO-34

87.7

26.3

22.7

7.9

28.5

WPASO-34

74.0

19.8

21.1

10.2

37.2


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Please insert Figure 9 here. Please insert Figure 10 here.

The textural properties are considered as an important parameter that affects the catalytic performance. The metal addition changed the textural properties of synthesized catalysts as shown in Table 2. The metal incorporation slightly enhanced diffusion efficiency by creating mesopores that facilitate the diffusion of methanol and olefins molecules. As presented in Table 2, the mesopores percentage of parent, CaAPSO-34 and CuAPSO-34 catalysts were calculated to be around 5, 19 and 13%, respectively. As result of the presence of mesopores, unwanted hydrogen transfer reactions will be minimized, which improved conversion and yield as shown in Figure 9 and Figure 10. Moreover, the MeAPSO-34 catalysts showed better adsorption properties as shown in FTIR spectra (Figure 6), where adsorption peak intensity at a wavelength of 1650 cm-1 was stronger when metal was introduced to the framework. These changes of textural properties were reflected on conversion stability and selectivity of the MeAPSO-34 catalysts. As presented in Table 4, the metal incorporation into SAPO-34 lowered deactivation rate and the major achievement was the increase of olefin yield. The enhancement in morphological, textural and acidity properties of MeAPSO-34 catalyst favored this superior catalytic performance. As shown in Figure 9, poor catalytic stability was observed for pure SAPO-34 catalyst, which was deactivated rapidly. Oppositely, the CuAPSO-34 catalyst had a stable conversion of 95% for more than 60 min of TOS. The reason for this stability is a reduction of weak acid sites that favors cyclization reactions of aromatics and slower formation of the coke.



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Light olefins yield of 80% was achieved by parent catalyst at the beginning of the reaction, but it reduced quickly which was accompanied with DME formation as an indication of deactivation. On the other hand, the modified catalysts maintained higher yield for almost 1 h of time on stream. Methanol conversion to olefins passes through two steps where methanol is dehydrated first to DME followed by further dehydration to olefins. The first reaction that produces DME requires the defect structural OH groups (including Si-OH, Al-OH, and P-OH) which considered as weak acid sites and the second step requires strong acid sites of bridging hydroxyl groups (SiOH-Al)20. Therefore, MeAPSO-34 catalysts had preferential selectivity towards light olefins due to its lower acidity as confirmed by NH3-TPD and FTIR, where the presence of Si-OH-Al groups was increased as shown in Figure 5. This metal incorporation led to the higher conversion rate of DME to olefins. Calcium incorporation to SAPO-34 seems to contribute to higher production of propylene as presented in Table 4, while CuAPSO-34 favors ethylene formation. This favorable catalytic activity towards specific olefin could be justified by the difference in active sites of dealkylation reactions which produce light olefins. The modified SAPO-34 catalysts showed good catalytic activity in terms of methanol conversion and selectivity, while MeAPSO34 catalysts especially CaAPSO-34, had light olefins selectivity of almost 60%. Although the methanol flowrate was higher and not diluted as compared to other reference16, our MeAPSO-34 catalyst had better outcome which proves its effective catalytic performance. On the other hand, WAPSO-34 catalyst showed almost equal selectivity of ethylene and propylene, which indicates the small gap between weak and strong acid sites. Light olefins yield for different catalysts reduced in the order of CaAPSO-34>CuAPSO-34>WAPSO-34>SAPO-34 As shown in Figure 10. These results reveal the superior enhancement of MTO reaction by earth alkaline metals as compared to transition metals in terms of conversion, selectivity, and yield and


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catalyst lifetime. According to above results, the MeAPSO-34 catalyst represents an attractive alternative of a pure SAPO-34 catalyst to convert methanol to olefins.

4. Conclusions SAPO-34 was prepared by hydrothermal method using TEAOH as a template. Parent SAPO-34 exhibited high crystallinity and average particle size of 6 µm. this catalyst had high conversion and selectivity for minutes then this catalytic performance start to decline. Metals had been added to the structure of SAPO-34 to maintain good performance for a period of time. Catalysts with narrower distribution and better diffusion properties were achieved by creating more mesopores. Copper, calcium, and tungsten were selected for modification of SAPO-34 catalyst and they had been added to gel solution during synthesis. Incorporation of metals into framework reduced the strength of the acid sites as confirmed by NH3-TPD. Metal incorporation improved catalyst lifetime and light olefins selectivity. All catalysts supported propylene production over ethylene due to their high acid sites intensity. The light olefins yield was reduced in the order of CaAPSO-34>CuAPSO-34>WAPSO-34>SAPO-34. CaAPSO-34 and CuAPSO-34 showed lowest deactivation rate among the other catalysts. This superior performance of CaAPSO-34 and CuAPSO-34 catalysts is justified by the reduction of acid sites that catalyze hydrogen transfer reactions where the olefins may be consumed. Finally, it can be concluded that the incorporation of rare earth alkaline metals is an attractive option to modify SAPO-34 for MTO reaction because of better acidity adjustment as compared to transition metals.

Acknowledgment The authors acknowledge the financial support and technical assistance from SABIC Company.



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References (1) Galadima, A.; Muraza, O., Recent Developments on Silicoaluminates and Silicoaluminophosphates in the Methanol-to-Propylene Reaction: A Mini Review. Ind Eng Chem Res 2015, 54, 4891-4905. (2) Nishiyama, N.; Kawaguchi, M.; Hirota, Y.; Van Vu, D.; Egashira, Y.; Ueyama, K., Size control of SAPO-34 crystals and their catalyst lifetime in the methanol-to-olefin reaction. Appl Catal, A 2009, 362, 193-199. (3) Jamil, A. K.; Muraza, O.; Yoshioka, M.; Al-Amer, A. M.; Yamani, Z. H.; Yokoi, T., Selective Production of Propylene from Methanol Conversion over Nanosized ZSM-22 Zeolites. Ind Eng Chem Res 2014, 53, 19498-19505. (4) Li, J.; Wei, Y.; Liu, G.; Qi, Y.; Tian, P.; Li, B.; He, Y.; Liu, Z., Comparative study of MTO conversion over SAPO-34, H-ZSM-5 and H-ZSM-22: Correlating catalytic performance and reaction mechanism to zeolite topology. Catal Today 2011, 171, 221-228. (5) Ahmed, M. H. M.; Muraza, O.; Yoshioka, M.; Yokoi, T., Effect of multi-step desilication and dealumination treatments on the performance of hierarchical EU-1 zeolite for converting methanol to olefins. Microporous Mesoporous Mater 2017, 241, 79-88. (6) Bakare, I. A.; Muraza, O.; Yoshioka, M.; Yamani, Z. H.; Yokoi, T., Conversion of methanol to olefins over Al-rich ZSM-5 modified with alkaline earth metal oxides. Catal Sci Technol 2016, 6, 7852-7859. (7) Charghand, M.; Haghighi, M.; Saedy, S.; Aghamohammadi, S., Efficient hydrothermal synthesis of nanostructured SAPO-34 using ultrasound energy: Physicochemical characterization and catalytic performance toward methanol conversion to light olefins. Adv Powder Technol 2014, 25, 1728-1736. (8) Taheri Najafabadi, A.; Fatemi, S.; Sohrabi, M.; Salmasi, M., Kinetic modeling and optimization of the operating condition of MTO process on SAPO-34 catalyst. J Ind Eng Chem 2012, 18, 29-37. (9) Dai, W.; Wu, G.; Li, L.; Guan, N.; Hunger, M., Mechanisms of the Deactivation of SAPO-34 Materials with Different Crystal Sizes Applied as MTO Catalysts. ACS Catal 2013, 3, 588-596. (10) Qi, G.; Xie, Z.; Yang, W.; Zhong, S.; Liu, H.; Zhang, C.; Chen, Q., Behaviors of coke deposition on SAPO-34 catalyst during methanol conversion to light olefins. Fuel Process Technol 2007, 88, 437-441. 16 ACS Paragon Plus Environment

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(11) Aghaei, E.; Haghighi, M., High temperature synthesis of nanostructured Ce-SAPO-34 catalyst used in conversion of methanol to light olefins: effect of temperature on physicochemical properties and catalytic performance. J Porous Mater 2014, 22, 187-200. (12) Gao, F.; Walter, E. D.; Washton, N. M.; Szanyi, J.; Peden, C. H. F., Synthesis and Evaluation of CuSAPO-34 Catalysts for Ammonia Selective Catalytic Reduction. 1. Aqueous Solution Ion Exchange. ACS Catal 2013, 3, 2083-2093. (13) Aghamohammadi, S.; Haghighi, M., Dual-template synthesis of nanostructured CoAPSO-34 used in methanol to olefins: Effect of template combinations on catalytic performance and coke formation. Chem Eng J 2015, 264, 359-375. (14) Zhang, D.; Wei, Y.; Xu, L.; Chang, F.; Liu, Z.; Meng, S.; Su, B.-L.; Liu, Z., MgAPSO-34 molecular sieves with various Mg stoichiometries: Synthesis, characterization and catalytic behavior in the direct transformation of chloromethane into light olefins. Microporous Mesoporous Mater 2008, 116, 684-692. (15) Dubois, D. R.; Obrzut, D. L.; Liu, J.; Thundimadathil, J.; Adekkanattu, P. M.; Guin, J. A.; Punnoose, A.; Seehra, M. S., Conversion of methanol to olefins over cobalt-, manganese- and nickelincorporated SAPO-34 molecular sieves. Fuel Process Technol 2003, 83, 203-218. (16) Sedighi, M.; Ghasemi, M.; Sadeqzadeh, M.; Hadi, M., Thorough study of the effect of metalincorporated SAPO-34 molecular sieves on catalytic performances in MTO process. Powder Technol 2016, 291, 131-139. (17) Kang, M., Methanol conversion on metal-incorporated SAPO-34s (MeAPSO-34s). J Mol Catal, A 2000, 160, 437-444. (18) Wei, Y.; Zhang, D.; Xu, L.; Chang, F.; He, Y.; Meng, S.; Su, B.-l.; Liu, Z., Synthesis, characterization and catalytic performance of metal-incorporated SAPO-34 for chloromethane transformation to light olefins. Catal Today 2008, 131, 262-269. (19) Salmasi, M.; Fatemi, S.; Taheri Najafabadi, A., Improvement of light olefins selectivity and catalyst lifetime in MTO reaction; using Ni and Mg-modified SAPO-34 synthesized by combination of two templates. J Ind Eng Chem 2011, 17, 755-761. (20) Aghaei, E.; Haghighi, M.; Pazhohniya, Z.; Aghamohammadi, S., One-pot hydrothermal synthesis of nanostructured ZrAPSO-34 powder: Effect of Zr-loading on physicochemical properties and catalytic performance in conversion of methanol to ethylene and propylene. Microporous Mesoporous Mater 2016, 226, 331-343. (21) Kang, M.; Lee, C.-T., Synthesis of Ga-incorporated SAPO-34s (GaAPSO-34) and their catalytic performance on methanol conversion. J Mol Catal, A 1999, 150, 213-222. (22) Varzaneh, A. Z.; Towfighi, J.; Mohamadalizadeh, A., Comparative study of naphtha cracking over SAPO-34 and HZSM-5: Effects of cerium and zirconium on the catalytic performance. J Anal Appl Pyrolysis 2014, 107, 165-173. (23) Lee, K. Y.; Chae, H.-J.; Jeong, S.-Y.; Seo, G., Effect of crystallite size of SAPO-34 catalysts on their induction period and deactivation in methanol-to-olefin reactions. Appl Catal, A 2009, 369, 6066. (24) Li, J.; Wei, Y.; Chen, J.; Xu, S.; Tian, P.; Yang, X.; Li, B.; Wang, J.; Liu, Z., Cavity Controls the Selectivity: Insights of Confinement Effects on MTO Reaction. ACS Catal 2014, 5, 661-665. (25) Tan, J.; Liu, Z.; Bao, X.; Liu, X.; Han, X.; He, C.; Zhai, R., Crystallization and Si incorporation mechanisms of SAPO-34. Microporous Mesoporous Mater 2002, 53, 97-108. (26) Dahl, I. M.; Mostad, H.; Akporiaye, D.; Wendelbo, R., Structural and chemical influences on the MTO reaction: a comparison of chabazite and SAPO-34 as MTO catalysts. Microporous Mesoporous Mater 1999, 29, 185-190.



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(27) Rahmani, F.; Haghighi, M., C2H6/CO2 oxidative dehydrogenation (ODH) reaction on nanostructured CrAPSO-34 catalyst: One-pot hydrothermal vs. conventional hydrothermal/impregnation catalyst synthesis. Korean J Chem Eng 2016, 33, 2555-2566. (28) Jiang, Y.; Huang, J.; Reddy Marthala, V. R.; Ooi, Y. S.; Weitkamp, J.; Hunger, M., In situ MAS NMR–UV/Vis investigation of H-SAPO-34 catalysts partially coked in the methanol-to-olefin conversion under continuous-flow conditions and of their regeneration. Microporous Mesoporous Mater 2007, 105, 132-139. (29) Jiang, Y.; Huang, J.; Weitkamp, J.; Hunger, M., In situ MAS NMR and UV/VIS spectroscopic studies of hydrocarbon pool compounds and coke deposits formed in the methanol-to-olefin conversion on H-SAPO-34. In Stud Surf Sci Catal, Xu, R.; Gao, Z.; Chen, J.; Yan, W., Eds. Elsevier: 2007; Vol. 170, pp 1137-1144.


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ACS Paragon Plus Environment

Figure 1. Schematic diagram of MeAPSO-34 catalyst synthesis.


WAPSO-34

CuAPSO-34

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2ϴ [o] ACS Paragon Plus Environment Figure 2. XRD patterns of different SAPO-34-based catalysts.

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(b)

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10 µm Figure 3. SEM images of MePASO-34 catalyst particles, where (a) SAPO-34, (b) CaAPSO-34, (c) CuAPSO-34 and (d) WAPSO-34. ACS Paragon Plus Environment

Industrial & Engineering Chemistry Research 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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(d)

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Figure 4. SEM images of single crystals of MeAPSO-34 catalysts, where (a) SAPO-34, (b) CaAPSO-34, (c) CuAPSO-34 and (d) ACS Paragon Plus Environment WAPSO-34.

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0.25

0.2 Intensity [A.U.]

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T [°C] Figure 5. NH3-TPD profiles for MeAPSO-34 catalysts compared to parent. ACS Paragon Plus Environment

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0.32 0.27 0.22 0.17

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Paragon Plus Environment Figure 8. UV-VIS spectra at lowACSand high wavelength for MeAPSO-34 samples.

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Figure 9. Methanol conversion using different catalysts. ACS Paragon Plus Environment

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Figure 10. Light olefins yield over different catalysts. ACS Paragon Plus Environment

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For Table of Contents Only 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

MeAPSO-34 Mixing and aging

Crystallization

Si , Al , P , OSDA and metal precursors DI water

SAPO-34

Si , Al , P , OSDA DI Water ACS Paragon Plus Environment

Catalytic enhancement of SAPO-34 for methanol conversion to light

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