HostâGuest Interactions and Their Catalytic Consequences in

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Host-Guest Interactions and Their Catalytic Consequences in Methanol to Olefins Conversion on Zeolites Studied by 13C–27Al Double-Resonance Solid-State NMR Spectroscopy Chao Wang, Jun Xu, Qiang Wang, Xue Zhou, Guodong Qi, Ningdong Feng, Xiaolong Liu, Xiangju Meng, Feng-Shou Xiao, and Feng Deng ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.7b01738 • Publication Date (Web): 31 Jul 2017 Downloaded from http://pubs.acs.org on July 31, 2017

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Host-Guest Interactions and Their Catalytic Consequences in Methanol to Olefins Conversion on Zeolites Studied by

13

C–27Al

Double-Resonance Solid-State NMR Spectroscopy Chao Wang†, Jun Xu*†, Qiang Wang†, Xue Zhou†, Guodong Qi†, Ningdong Feng†, Xiaolong Liu†, Xiangju Meng‡, Fengshou, Xiao‡, Feng Deng*†

†State

Key Laboratory Magnetic Resonance and Atomic and Molecular Physics,

National Center for Magnetic Resonance in Wuhan, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, P. R. China. ‡

Department of Chemistry, Zhejiang University, Hangzhou 310028, P.R. China.

1

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Abstract The methanol conversion over zeolites with different topology (H-ZSM-5, H-SSZ-13 and H-MOR) was studied using solid-state NMR spectroscopy and GC-MS. The host-guest interactions between active hydrocarbon pool (HP) species and zeolite framework (Brønsted acid/base site) were observed and the supramolecular reaction centers (SMCs) generated by the interactions were unambiguously identified by 13

C-27Al double-resonance NMR. The internuclear spatial interaction/proximity

between the

13

C nuclei (associated with HP species) and the

27

Al nuclei (associated

with Brønsted acid/base site) was analyzed and compared over the three zeolites. The product shape selectivity of zeolites greatly influences the catalytic performance that can be linked to the nature of HP species and the host-guest interactions. The closer spatial proximity and stronger interaction between methylbenzenes (MBs) and Brønsted acid/base sites were observed over H-SSZ-13 and H-MOR zeolites, which facilitates the aromatic-based reaction routes and rationalizes the higher selectivity to ethene on the two catalysts. This leads to rapid deactivation at high temperature due to the coke deposition on the active sites caused by the evolution of active MBs. For H-ZSM-5, the less amounts of retained MBs and their weaker interactions with the active sites at high temperature make the aromatics-based reactions insignificant and leads to the prevalence of alkenes-based and carbocations-involved reactions, which are responsible for the high resistance of H-ZSM-5 to deactivation. In contrast, at lower temperature, the aromatic-based reaction route is favored with the prevailing of MBs-composed SMCs. The distribution of the carbonaceous species in deactivated catalysts was revealed by the host-guest interactions. 2


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Key words: methanol conversion, zeolites, mechanism, host-guest interaction, NMR spectroscopy

1. Introduction The conversion of methanol to olefins (MTO) provides a promising alternative to the current industrial process based on the crude oil since the feedstock methanol can be extensively produced from natural gas, coal, or biomass1-4. Regarding the reaction process occurring on acidic zeolite catalysts, hydrocarbon pool mechanism has been considered as the main reaction route to produce light olefins. The hydrocarbon pool route provides rationale for the formation of olefins via an indirect way, in which methanol/dimethyl ethers are added onto a reaction center followed by splitting off olefins, such as ethene or propene5-7. The hydrocarbon pool (HP) mechanism is complicated by the variety of HP species, which are constituted by alkenes, carbocations and aromatics adsorbed on zeolites2,8-14. The HP species are formed over active sites through methylation, polymerization, cyclization or dehydrogenation of alkenes15. These HP species perform co-reaction with methanol/DME to form products. The topology structure of zeolites has significant influence on the MTO reaction. The conversion, products selectivity, catalyst deactivation as well as the reaction routes can be related to variation of the channel system (shape and dimension) in zeolites16-20. Proper size and shape of zeolites channel provide spatial and chemical environment required for formation and stabilization of specific HP species in the MTO reaction. For example, 3


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the bulky MBs such as pentamethylbenzenes, hexamethylbenzenes as well as the heptmethylbenzenium cations are considered as the active HP species in zeolites with 12-member ring (MR) pores and large cages such as H-beta, H-SAPO-34 and H-SSZ-1321-24. However, over medium porous zeolites such as H-ZSM-5, the bulky MBs such as hexamethylbenzene display poor reactivity. Alternatively, alkenes, MBs (up to pentamethylbenzenes) and C5-cyclic carbocations were identified as the key HP species and a ‘dual-cycle’ model was proposed to explain the formation of olefins11,25. The confinement effect imposed by zeolite channels often leads to host-guest interactions between the zeolite framework host and the HP species guest. Connecting with the selective formation of HP species, the host-guest interactions play key roles in the transformation of HP species and thus the function of HP mechanism. This implies that the product shape selectivity of zeolite may affect the host-guest interaction, leading to variable reactivity of HP species. It has been proposed that the active HP species together with the zeolite framework constitute the supramolecular reaction centers (SMCs)26-28. This concept extends the hydrocarbon pools from the only organic compounds to the integration of inorganic and organic components. The HP routes for the methanol conversion and product selectivity on zeolite can thus be described by SMCs in a more general way. In our previous work29, we investigated the active SMCs on H-ZSM-5 by 13C-27Al double resonance NMR technique, proving that the SMCs was formed by the interaction between hydrocarbon pool species (mainly aromatics and carbenzenium ions) and Brønsted acid/base sites on the zeolite. In addition, the SMCs were found to show high reactivity towards reactants, and the 4


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formation and reactivity of SMCs relied on the interaction between the HP species and zeolite framework16,18,19,30,31. Therefore, insights into the host-guest interactions in zeolites would allow a better understanding of the SMCs formed during methanol conversion and the HP chemistry. In this contribution, the host-guest interactions during the MTO reaction were studied over several zeolites with different channel systems by solid-state NMR in combination with GC-MS with aim to get more insight into the MTO mechanism and HP chemistry. The formation and nature of SMCs in the MTO reaction was explored on H-ZSM-5（MFI, sinusoidal channel: 5.5×5.1 Å2, straight channel: 5.3×5.6 Å2）, H-SSZ-13（CHA cage: 6.7×10.9 Å2, 8-MR window opening: 3.8×3.8 Å2 ）and H-MOR（MOR, 12-MR channel: 6.7×7.0 Å2）zeolites which are featured by different shape selectivity. The SMCs were identified on the three catalysts by the

13

C-27Al

double-resonance solid-state NMR experiments, and the shape selectivity of zeolites induced by different pore size and shape was found to produce great impacts on the host-guest interactions and the reactivity of SMCs. The influence of SMCs on methanol conversion, product selectivity and catalyst deactivation was investigated as well. 2. Experimental section 2.1 Characterization of catalysts Powder X-ray diffraction (XRD) was performed on a PANAlytical X’Pert3 Powder X-ray diffraction diffractometer with Cu Kα (λ=1.5406Å), recording at 40 kV and 40 mA. The powder XRD pattern (Figure S1) confirms the presence of well 5


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crystalline MFI, CHA and MOR phase. The BET surface area and pore volumes were measured using a Micromeritics ASAP 2020M system and list in Table S1. All the samples were degassed under vacuum for 12 h at 150 oC before measurements. Catalytic test and product analysis Catalytic tests were conducted in a fixed bed reactor (i. d. 6 mm) at reaction temperature range between 300 and 400 oC. Before each test, the catalyst powder was pressed into pellets between 60-80 mesh. 0.05 g pellets were activated at 400 oC in flowing helium for 1 h prior to reaction. In the continuous flow reaction, methanol with a weight hourly space velocity (WHSV) of 12 h-1 was reacted over the H-ZSM-5 pellets in a fixed bed reactor. The total gas flow through the reactor was 200 sccm. Then the reaction was thermally quenched by pulsing liquid nitrogen onto the catalyst bed, which was achieved by using high-speed valves controlled by a GC computer (H-MOR (1.91)>H-SSZ-13 (0.96). The higher C3/C2 ratio implies that the alkenes-based route is preferred over the aromatics-based routes. Therefore, we can conclude that the aromatics-based routes are notably enhanced over H-SSZ-13 17


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and H-MOR which produce lower C3/C2 ratios compared to H-ZSM-5. This can be understood by considering the reaction behavior of SMCs over the three zeolites. We have shown that the MBs are in close proximity to the Brønsted acid sites on H-SSZ-13 and H-MOR at higher temperature of 400 oC, but far away from the Brønsted acid sites on H-ZSM-5 (Table 1, 2 and 3). In addition, more MBs are retained on H-SSZ-13 and H-MOR. These MBs-composed SMCs would largely prevent other HP species such as alkenes from contacting with the Brønsted acid sites, leading to the prevalence of aromatics-based reactions over H-SSZ-13 and H-MOR. In comparison, the alkenes or cyclopentenyl cations have high possibility to access to the active sites on H-ZSM-5 due to the less amount of MBs retained and their larger spatial distance from the active sites, which results in the prevalence of alkenes-based and cyclopentenyl cations involved reactions at high temperature. It should be noted that the MBs show close spatial proximity to the active sites on H-ZSM-5 at lower temperature of 300 oC (Table 1), indicating that the aromatics-based reactions are more favored at the lower temperature. Indeed, the C3/C2 ratio declines to 2.7 at 300 o

C (Table S3), much lower than that at 400 oC (6.3). These results prove from the

guest-host interaction point of view the significant effect of SMCs on the product selectivity in the MTO reaction.

3.4 The effect of SMCs on catalyst deactivation We have shown the effect of SMCs on the transformation of reactants to products. On the other hand, it has been indicated that the evolution of HP species in MTO reaction could eventually lead to coke deposits and deactivation of zeolites26,42,43. The 18


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critical influence of zeolite topology on the deactivation behavior have been confirmed44,45. Figure 5 shows the methanol conversion over the three zeolites as a function of time on stream (TOS) at 400 oC. H-ZSM-5 zeolite displays excellent performance resistant to deactivation, reflected by almost 100% conversion for reaction time longer than 24 h. Methanol can be completely converted before TOS=30 min over H-SSZ-13 followed by quick decrease to near zero conversion at TOS=250 min. A much rapid deactivation was observed on H-MOR, which lost activity in 90 min. The facile deactivation of MOR in MTO has been previously reported46. There is a consensus that the deactivation is caused by the carbon deposition which covers the active sites or blocks the zeolite channels making it impossible for reactant and product to diffuse through the pores. The previous work shows that the deactivation species in the MTO reaction could be poly-aromatics and carbocations which leads to the formation of coke and graphite-like compounds47,43. From Figure S4-S6, the GC-MS analysis shows a broad distribution of species ranging from MBs to methylated naphthalenes formed over H-MOR and H-SSZ-13 even at short reaction time of 15 min at 400 oC. Previous studies have shown that the poly-aromatics such as methylated naphthalenes are the major deactivating species on SSZ-13 and MOR zeolites46,48-50. However, the bulky aromatics are almost undetectable over H-ZSM-5 at the same reaction time. It can be deduced that the easy accumulation of the bulky aromatics over H-MOR and H-SSZ-13 leads to the catalyst deactivation. The deactivated H-SSZ-13 and H-MOR zeolites were analyzed by 13C CP NMR. As shown in Figure 6, the obtained

13

C NMR spectra of the two catalysts are 19


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dominated by aromatics, which are most likely the polycyclic species. The signals at 19 ppm come from the associated methyl groups, and 120-140 ppm signals correspond to the phenyl rings. The polymerization degree of the aromatics could be to some extent reflected by the ratio of methyl groups to phenyl rings in the poly-aromatics although it’s not strictly quantitative; the larger value corresponds to lower polymerization and vice versa. The integration of the signal intensity in Figure 6 shows that the ratio of methyl groups to phenyl rings on H-MOR and H-SSZ-13 is 0.18 and 0.24 respectively, much lower than that in the steady-state period (0.67 and 0.59 respectively obtained from Figure 1). In agreement with GC-MS results, this confirms the high abundance of poly-aromatics such as methylate naphthalenes on the two deactivated catalysts. The deactivation of H-ZSM-5, H-SSZ-13 and H-MOR can be attributed to the different behaviors of SMCs over the three zeolites. Compared to H-SSZ-13 and H-MOR, the MBs on H-ZSM-5 show less close spatial proximity to Brønsted acid sites at high temperature. Thus it is not easy for these MBs to transform into bulky compounds. Previous reports showed that the deactivation of H-ZSM-5 at higher temperature is caused by the formation of polycyclic species inside pores which grow to end up as graphitic-like compounds on outer surface of the zeolite51-53. It is plausible that the highly active HP species such as cyclopentenyl cations could be responsible for this kind of coking at long reaction time, since these HP species keep strong interactions with the active sites through the whole reaction. By using Uv-vis spectroscopy, Weckhuysen et al., indicated that formation of carbocations in MTO 20


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reaction over ZSM-5 induces the coke species53. On the contrary, the deactivation of H-SSZ-13 and H-MOR could be largely accounted for by the evolutions of MBs that are located close to the active sites. Due to the strong interactions and high reactivity, they can readily grow into poly-aromatics (coke precursor) around the active sites, blocking access to the active sites of H-SSZ-13 and H-MOR. Note that extend coke specie could be subsequently formed on external surface of zeolites54. The disappearance of the carbocations that are expected to give rise to

13

C signal at 25.8

ppm on H-SSZ-13 and 23.5 ppm on H-MOR indicates the involvement of these species as well in the formation of the carbonaceous species. The

13

C-27Al double-resonance experiments were further conducted on the

deactivated H-MOR and H-SSZ-13 zeolites to probe the spatial proximity between polycyclic species and active sites (Figure 7). Note that the signals for the methyl groups at around 19 ppm are resolved into several signals on two zeolites. This is probably due to the presence of methyl-substituted aromatics with different mobility which is differentiated by the rotational-echo NMR. Compared with the non-deactivated catalysts (Table 2-3), the methyl groups of poly-aromatics show different spatial proximities to the active sites on the deactivated samples. For example, on deactivated H-SSZ-13, the methyl groups at 16.3 ppm and 19.4 ppm (Δ S/S0 is 8.5 % and 20.9 % respectively) are further away from the active sites compared to those on the non-deactivated one ( Δ S/S0 is 26.8% and 27.5 % respectively) (Table 1), while the methyl groups at the 24.0 and 21.5 ppm signals exhibit increased interactions with the active sites reflected by the higherΔS/S0 which 21


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are 37.4 % and 30.3 % compared to 31.0 % and 21.6 % respectively on the non-deactivated H-SSZ-13. The observed difference on the spatial proximity and interaction between the polycyclic species and the active sites shows the distribution of

retained

organic

species.

Different

from

H-ZSM-5

inside

which

hexamethylbenzene as the biggest MB can be formed, the larger size of the CHA cage in H-SSZ-13 (0.67 ×10.9 Å2) could hold large carbon species such as methylate naphthalenes formed from the active HP species like MBs and carbocations. Since the naphthalenes can be hardly present in the 8-MR ring channels with narrow size, the increased interactions between the two methyl groups (24.0 and 21.5 ppm) and active sites evidences the formation and growth of the carbonaceous species in the CHA cage of H-SSZ-13. The weaker interactions reflected on the methyl groups (19.4 and 16.3 ppm) suggest that the orientation of poly-aromatics in the cage makes some of the methyl groups farther from active sites. Another possible explanation is the formation of external coke species. In fact, the formation of larger carbonaceous deposits on the outer surface of SSZ-13 zeolites has been observed49. The methyl groups on the external carbonaceous species should show weak interactions with the active sites insides the CHA cage due to the large spatial distance. Similarly to H-SSZ-13, the different interactions of the carbonaceous species with active sites are observe on deactivated H-MOR zeolite (Figure 7); some methyl groups observed at 15.6 ppm become closer to the active sites (ΔS/S0 is 33.0 % v.s. 19.3%), while other methyl groups reflected by the signal at 19.0 ppm are further away from active sites (ΔS/S0 is 14.6 % v.s. 34.3% ) compared to the non-deactivated 22


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H-MOR (Table 3). The wide signals peak widths and lower signals resolution indicates the presence of heavier carbonaceous deposits. Previous study has shown that in addition to methylate naphthalenes, polycyclic aromatics with 3–4 fused aromatic rings were formed as the coke species on H-MOR46. The stronger interactions between the poly-aromatics and active sites indicates the coverage of the active sites by carbonaceous species due to the closer distance observed, leading to rapid catalyst deactivation. On the other hand, the broad distribution of the ploy-aromatics along the 12-MR channel would be responsible for the observation of the weak interactions with the active sites (longer distance). Since the growth of the extend coke compounds on the external zeolite surface has been suggested by Svelle et 54

al. , the accumulation of these species would lead to blockage of the pores, resulting

in the complete deactivation. The schematic illustration the distribution of the coking species (poly-aromatics) in the CHA cage of H-SSZ-13 and 12-MR channel of H-MOR is shown in Figure 8. The active sites are covered and the channels are blocked in the deactivated zeolites. Although it is at present impossible to distinguish external and internal coke species, these observations allow us to conclude that the deactivation can be linked to the formation of HP species and their interactions with the active sites. The spatial proximity between the carbonaceous species and framework in H-SSZ-13 and H-MOR zeolites provides some information on the distribution of these coke species. 4

Conclusions The host-guest interactions generated in the MTO reaction over H-ZSM-5, 23


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H-SSZ-13 and H-MOR zeolites and the relation with catalytic performance were investigated by 13C-27Al double-resonance solid-state NMR spectroscopy and GC-MS. The SMCs were observed to be constituted by zeolite framework (Brønsted acid/base sites) and retained organic hydrocarbon pool species such as cyclopentenyl cations, MBs

and

benzenium

ions

(pentamethylbenzenium

ions

for

H-ZSM-5,

heptamethylbenzenium ions for H-SSZ-13 and H-MOR). The shape selectivity of the zeolites shows significant impact on the formation and reactivity of SMCs, which notably influence the MTO reaction. The lower methanol conversion of H-MOR zeolite compared to H-ZSM-5 and H-SSZ-13 can be ascribed to the unfavorable configuration of the corresponding SMCs in the zeolite related to the sizes of HP species and channel pore. The observed different product selectivity and deactivation on the three zeolites can be linked to the nature of HP species and the interactions. Over H-ZSM-5, less amount of MBs-composed SMCs are formed at high reaction temperature, leading to higher C3/C2 ratio due to the aromatic-based reaction routes being less important. The weaker spatial interaction between the MBs and the active sites could be responsible for the high resistance of H-ZSM-5 to deactivation and indicates that the coke deposits at higher temperature are most likely formed by the carbocation species. However, the prevalence of MBs-composed SMCs over H-SSZ-13 and H-MOR favors the aromatics-based routes, producing a relatively higher selectivity to ethene than on H-ZSM-5. This also leads to a rapid deactivation of H-SSZ-13 and H-MOR due to the evolution of the active MBs into carbonaceous species particularly at high temperature. The analysis of the interactions of the 24


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carbonaceous species with the deactivated H-SSZ-13 and H-MOR zeolites shows the distributions of the coking compounds such as methylated naphthalenes. The covering of the active sites or blockage of the channels are evidenced. As for the olefin HP species, the amounts of the trapped olefins are too little to be detected by the 13C-27Al double resonance NMR experiment due to their instability and high mobility over zeolite. Therefor we can not exactly describe the interaction between the alkenes and zeolite framework (Brønsted acid sites) as we did on the cyclic HP species. However, considering the high reactivity of the alkenes HP species, it is no doubt that such interactions should occur for their transformations. But the SMCs may be not stable as much as that formed by the cyclic species, which is responsible for its hard observation on NMR. It should be noted that the interactions of olefin HP species with Brønsted acid sites should be present for the transformation of olefins in the MTO reactions. However, the corresponding SMCs would be not stable as much as those formed by the cyclic species and would be not easily observed because of the high mobility and short lifetime of olefin HP species in the zeolite channels. The results presented herein demonstrate that the host-guest interactions that are believed to be important in the heterogeneous catalysis play critical role in the MTO reaction. The detailed information on the host-guest interactions obtained on zeolites is helpful for mechanistic understanding of the hydrocarbon pool chemistry and product shape selectivity in zeolite catalysis.

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ASSOCIATED CONTENT Supporting Information. Additional solid state NMR and GC-MS analysis. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author *Email: [email protected] *Email: [email protected] Notes The authors declare no competing financial interests.

ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Grants 21622311, 21473245 and 21603265, 21210005) and key program for frontier science of the Chinese Academy of Science (QYZDB-SSW-SLH027).

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(16) Bhawe, Y.; Moliner-Marin, M.; Lunn, J. D.; Liu, Y.; Malek, A.; Davis, M. ACS Catal. 2012, 2, 2490-2495. (17) Teketel, S.; Skistad, W.; Benard, S.; Olsbye, U.; Lillerud, K. P.; Beato, P.; Svelle, S. ACS Catal. 2012, 2, 26-37. (18) Wang, Q.; Cui, Z. M.; Cao, C. Y.; Song, W. G. J. Phys. Chem. C 2011, 115, 24987-24992. (19) Lesthaeghe, D.; De Sterck, B.; Van Speybroeck, V.; Marin, G. B.; Waroquier, M. Angew. Chem. Int. Ed. 2007, 46, 1311-1314. (20) Cui, Z. M.; Liu, Q.; Song, W. G.; Wan, L. J. Angew. Chem. Int. Ed. 2006, 45, 6512-6515. (21) Bjørgen, M.; Bonino, F.; Kolboe, S.; Lillerud, K. P.; Zecchina, A.; Bordiga, S. J. Am. Chem. Soc. 2003, 125, 15863-15868. (22) Sassi, A.; Wildman, M. A.; Ahn, H. J.; Prasad, P.; Nicholas, J. B.; Haw, J. F. The Journal of Physical Chemistry B 2002, 106, 2294-2303. (23) Bjørgen, M.; Olsbye, U.; Petersen, D.; Kolboe, S. J. Catal. 2004, 221, 1-10. (24) Xu, S. T.; Zheng, A. M.; Wei, Y. X.; Chen, J. R.; Li, J. Z.; Chu, Y. Y.; Zhang, M. Z.; Wang, Q. Y.; Zhou, Y.; Wang, J. B.; Deng, F.; Liu, Z. M. Angew. Chem. Int. Ed. 2013, 52, 11564-11568. (25) Bjørgen, M.; Svelle, S.; Joensen, F.; Nerlov, J.; Kolboe, S.; Bonino, F.; Palumbo, L.; Bordiga, S.; Olsbye, U. J. Catal. 2007, 249, 195-207. (26) Haw, J.; Marcus, D. Top. Catal. 2005, 34, 41-48. (27) McCann, D. M.; Lesthaeghe, D.; Kletnieks, P. W.; Guenther, D. R.; Hayman, M. J.; Van Speybroeck, V.; Waroquier, M.; Haw, J. F. Angew. Chem. Int. Ed. 2008, 47, 5179-5182. (28) Song, W. G.; Fu, H.; Haw, J. F. J. Am. Chem. Soc. 2001, 123, 4749-4754. (29) Wang, C.; Wang, Q.; Xu, J.; Qi, G. D.; Gao, P.; Wang, W. Y.; Zou, Y. Y.; Feng, N. D.; Liu, X. L.; 28


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Deng, F. Angew. Chem. Int. Ed. 2016, 55, 2507-2511. (30) Teketel, S.; Olsbye, U.; Lillerud, K. P.; Beato, P.; Svelle, S. Microporous Mesoporous Mater. 2010, 136, 33-41. (31) De Wispelaere, K.; Hemelsoet, K.; Waroquier, M.; Van Speybroeck, V. J. Catal. 2013, 305, 76-80. (32) Goguen, P. W.; Xu, T.; Barich, D. H.; Skloss, T. W.; Song, W. G.; Wang, Z.; Nicholas, J. B.; Haw, J. F. J. Am. Chem. Soc. 1998, 120, 2650-2651. (33) Pourpoint, F.; Trébosc, J.; Gauvin, R. M.; Wang, Q.; Lafon, O.; Deng, F.; Amoureux, J.-P. ChemPhysChem 2012, 13, 3605-3615. (34) Li, S. H.; Pourpoint, F.; Trébosc, J.; Zhou, L.; Lafon, O.; Shen, M.; Zheng, A. M.; Wang, Q.; Amoureux, J.-P.; Deng, F. J. Phys. Chem. Lett. 2014, 5, 3068-3072. (35) Chen, L.; Wang, Q.; Hu, B.; Lafon, O.; Trebosc, J.; Deng, F.; Amoureux, J. P. PCCP 2010, 12, 9395-9405. (36) Perras, F. A.; Padmos, J. D.; Johnson, R. L.; Wang, L. L.; Schwartz, T. J.; Kobayashi, T.; Horton, J. H.; Dumesic, J. A.; Shanks, B. H.; Johnson, D. D.; Pruski, M. J. Am. Chem. Soc. 2017, 139, 2702-2709. (37) Svelle, S.; Olsbye, U.; Joensen, F.; Bjørgen, M. J. Phys. Chem. C 2007, 111, 17981-17984. (38) Xu, T.; Barich, D. H.; Goguen, P. W.; Song, W. G.; Wang, Z.; Nicholas, J. B.; Haw, J. F. J. Am. Chem. Soc. 1998, 120, 4025-4026. (39) Wang , C.; Chu , Y. Y.; Zheng, A. M.; Xu, J.; Wang, Q.; Gao, P.; Qi, G. D.; Gong, Y. J.; Deng, F. Chem. Eur. J. 2014, 20, 12432-12443. (40) Wang, C.; Yi, X. F.; Xu, J.; Qi, G. D.; Gao, P.; Wang, W. Y.; Chu, Y. Y.; Wang, Q.; Feng, N. D.; Liu, X. L. Chem. Eur. J. 2015, 21, 12061-12068. (41) Li, J. Z.; Wei, Y. X.; Chen, J. R.; Tian, P.; Su, X.; Xu, S. T.; Qi, Y.; Wang, Q. Y.; Zhou, Y.; He, Y. 29


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L.; Liu, Z. M. J. Am. Chem. Soc. 2012, 134, 836-839. (42) Schulz, H. Catal. Today 2010, 154, 183-194. (43) Bleken, F. L.; Barbera, K.; Bonino, F.; Olsbye, U.; Lillerud, K. P.; Bordiga, S.; Beato, P.; Janssens, T. V. W.; Svelle, S. J. Catal. 2013, 307, 62-73. (44) Rojo-Gama, D.; Etemadi, S.; Kirby, E.; Lillerud, K. P.; Beato, P.; Svelle, S.; Olsbye, U. Faraday Discuss. 2017, 197, 421-446. (45) Martinez-Espin, J. S.; Morten, M.; Janssens, T. V. W.; Svelle, S.; Beato, P.; Olsbye, U. Catal. Sci. Technol. 2017. (46) Ji, W. P.; Sun, J. K.; Seo, M.; Sang, Y. K.; Sugi, Y.; Seo, G. Appl. Catal. A Gen. 2008, 349, 76-85. (47) Müller, S.; Liu, Y.; Vishnuvarthan, M.; Sun, X.; van Veen, A. C.; Haller, G. L.; Sanchez-Sanchez, M.; Lercher, J. A. J. Catal. 2015, 325, 48-59. (48) Bleken, F.; Bjørgen, M.; Palumbo, L.; Bordiga, S.; Svelle, S.; Lillerud, K. P.; Olsbye, U. Top. Catal. 2009, 52, 218-228. (49) Goetze, J.; Meirer, F.; Yarulina, I.; Gascon, J.; Kapteijn, F.; Ruiz-Martínez, J.; Weckhuysen, B. M. ACS Catal. 2017, 4033-4046. (50) Brogaard, R. Y.; Weckhuysen, B. M.; Nørskov, J. K. J. Catal. 2013, 300, 235-241. (51) Guisnet, M.; Magnoux, P. Appl. Catal. A Gen. 2001, 212, 83-96. (52) Milina, M.; Mitchell, S.; Crivelli, P.; Cooke, D.; Pérezramírez, J. Nat. Comm. 2014, 5. (53) Mores, D.; Kornatowski , J.; Olsbye, U.; Weckhuysen, B. M. Chem. Eur. J. 2011, 17, 2874-2884. (54) Rojo-Gama, D.; Signorile, M.; Bonino, F.; Bordiga, S.; Olsbye, U.; Lillerud, K. P.; Beato, P.; Svelle, S. J. Catal. 2017, 351, 33-48.

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Table 1 ∆S/S0 experimental 13C-{27Al} S-RESPDOR fractions (%) for the 13C signals of retained species over H-ZSM-5 at elevated temperatures. Chemical shifts 10.0

17.0

19.3

25.2

45.8

48.1

50.3

58.7

60.0

63.4

300 oC

16.9

26.8

38.0

26.1

55.9

46.5

20.9

56.9

36.2

42.1

350 oC

9.3

15.3

19.3

20.9

45.9

42.4

33.6

58.6

41.4

-

400 oC

2.3

11.9

5.0

19.3

43.4

40.1

35.7

55.8

40.8

-

(ppm)

31


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Table 2 ∆S/S0 experimental 13C-{27Al} S-RESPDOR fractions (%) for the 13C signals of retained species over H-SSZ-13 at elevated temperatures. Chemical shifts (ppm) o

300 C o

350 C o

400 C

8.9

10.5

12.7

16.3

19.4

21.7

24.3

25.8

46.8

50.0

57.8

63.4

17.7

12.8

14.5

16.9

27.3

26.8

24.6

27.5

28.9

14.5

59.4

50.5

16.1

23.9

13.6

15.3

26.1

25.4

23.2

26.8

26.1

24.7

-

-

5.7

-

-

26.8

27.5

31.0

21.6

24.6

25.6

28.2

-

-

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ACS Catalysis

Table 3 ∆S/S0 experimental 13C-{27Al} S-RESPDOR fractions (%) for 13C signals of retained species over H-MOR at elevated temperatures. Chemical shifts (ppm) o

300 C o

350 C o

400 C

9.5

11.8

15.2

18.4

21.2

23.5

50

60

18.5

17.7

16.9

-

25.4

20.1

38.6

40.9

22.4

16.1

18.5

32.9

24.6

23.2

37.6

53.3

-

20.9

19.3

34.3

32.9

20.9

40.2

-

33


ACS Catalysis

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Table 4. Methanol/dimethyl ether conversion (%) and product selectivity (C %) over ZSM-5, SSZ-13 and MOR at 400oC for 5 min. Catalysts

Conv. C3/C2

C1

C2 (C2=)

C3 (C3=)

C4 (C4=)

C5

C6 Aromatics(C7-C9)

ZSM-5

98.64

6.33

0.36

7.73 (7.65)

48.94 (48.16)

21.71 (8.47)

8.98 5.46

6.82

SSZ-13

96.40

0.96

0.83

41.71 (40.62)

39.84 (37.45)

13.10 (9.69)

3.95 0.47

0.09

MOR

82.56

1.91

4.91

23.01 (22.36)

44.02 (24.65)

16.57 (7.29)

4.85 1.91

4.74

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ACS Catalysis

Figure captions Figure 1.

13

C CP/MAS NMR spectra obtained from reaction of

13

CH3OH over

H-ZSM-5 (a), H-SSZ-13 (b) and H-MOR (c) at 300 oC, 350 oC and 400 oC for 15, 10 and 5 min respectively. Asterisks denote spinning sidebands.

Figure 2.

13

C MAS NMR spectra of retained products obtained from reaction of

methanol over H-ZSM-5 at 300oC, 350 oC and 400 oC for 15, 10 and 5 min respectively. The black and red lines represent the spectrum observed with (S) and without (S0) 13C-{27Al} S-RESPDOR dipolar dephasing respectively.

Figure 3.

13

C MAS NMR spectra of the retained products obtained from reaction of

methanol over H-SSZ-13 at300 oC, 350 oC and 400 oC for 15, 10 and 5 min respectively. The black and red lines represents the spectrum observed with (S) and without (S0) 13C-{27Al} S-RESPDOR dipolar dephasing respectively.

Figure 4.

13

C MAS NMR spectra of retained products obtained from reaction of

methanol over H-MOR at 300 oC, 350 oC and 400 oC for 15, 10 and 5 min respectively. The black and red lines represents the spectrum observed with (S) and without (S0) 13C-{27Al} S-RESPDOR dipolar dephasing respectively.

Figure 5. Methanol conversion with time-on-stream (min) over H-ZSM-5, H-SSZ-13 and H-MOR at 400 oC. 35


ACS Catalysis

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Figure 6. 13C CP/MAS NMR spectra of deactivated H-SSZ-13 (a) and H-MOR (b). The zeolites are deactivated by conversion of 13CH3OH (20% 13C) over H-SSZ-13 and H-MOR at 400 oC for 250 min and 100 min respectively. Asterisks denote spinning sidebands.

Figure 7. 13C MAS NMR spectra of deactivated H-SSZ-13 (a) and H-MOR (b) at 400 o

C for 250 min and 100 min respectively. The black and red lines represents the

spectrum observed with (S) and without (S0)

13

C-{27Al} S-RESPDOR dipolar

dephasing respectively. The ∆S/S0 is indicated in bracket.

Figure 8. Schematic of the coking species (poly-aromatics) depositing on the active site (Brønsted acid site) and blocking the zeolite pore in the CHA cage of H-SSZ-13 and 12-MR channel of H-MOR zeolite.

36


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ACS Catalysis

Figure 1.

13

C CP/MAS NMR spectra obtained from reaction of

13

CH3OH over

H-ZSM-5 (a), H-SSZ-13 (b) and H-MOR (c) at 300 oC, 350 oC and 400 oC for 15, 10 and 5 min respectively. Asterisks denote spinning sidebands.

37


ACS Catalysis

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Figure 2．．13C MAS NMR spectra of retained products obtained from reaction of methanol over H-ZSM-5 at 300 oC, 350 oC and 400 oC for 15, 10 and 5 min respectively. The black and red lines represent the spectrum observed with (S) and without (S0) 13C-{27Al} S-RESPDOR dipolar dephasing respectively.

38


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ACS Catalysis

Figure 3．．13C MAS NMR spectra of the retained products obtained from reaction of methanol over H-SSZ-13 at300 oC, 350 oC and 400 oC for 15, 10 and 5 min respectively. The black and red lines represents the spectrum observed with (S) and without (S0) 13C-{27Al} S-RESPDOR dipolar dephasing respectively.

39


ACS Catalysis

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Figure 4．．13C MAS NMR spectra of retained products obtained from reaction of methanol over H-MOR at 300 oC, 350 oC and 400 oC for 15, 10 and 5 min respectively. The black and red lines represents the spectrum observed with (S) and without (S0) 13C-{27Al} S-RESPDOR dipolar dephasing respectively.

40


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ACS Catalysis

Figure 5．．Methanol conversion with time-on-stream (min) over H-ZSM-5, H-SSZ-13 and H-MOR at 400 oC.

41


ACS Catalysis

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Figure 6．．13C CP/MAS NMR spectra of deactivated H-SSZ-13 (a) and H-MOR (b). The zeolites are deactivated by conversion of 13CH3OH (20% 13C) over H-SSZ-13 and H-MOR at 400 oC for 250 min and 100 min respectively. Asterisks denote spinning sidebands.

42


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ACS Catalysis

Figure 7．．13C MAS NMR spectra of deactivated H-SSZ-13 (a) and H-MOR (b) at 400 o

C for 250 min and 100 min respectively. The black and red lines represents the

spectrum observed with (S) and without (S0)

13

C-{27Al} S-RESPDOR dipolar

dephasing respectively. The ∆S/S0 is indicated in bracket.

43


ACS Catalysis

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Figure 8. Schematic of the coke species (poly-aromatics) depositing on the active site (Brønsted acid site) and blocking the zeolite pore in CHA cage of H-SSZ-13 and 12-MR channel of H-MOR zeolite.

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ACS Catalysis

TOC

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