Molecular switches are widely studied in optical devices, computer science, DNA sensor systems, and chiral synthesis; however, their use in heterogeneous catalytic processes is rarely reported. Herein, we report a Fe-based redox switch for tuning the acidity of a ZSM-5-based catalyst in the methanol-to-aromatics reaction. In this reaction, the yield of the target product, para-xylene (PX), is low because various types of acids on the catalyst activate side reactions. Fe oxides and zeolite generate medium-strength Lewis acids, which activate the aromatization of methanol but suppress the dealkylation of xylene. Gradual reduction of Fe oxides during the reaction simultaneously decreases the conversion of methanol, the yield of aromatics, and the yield of PX. The oxidation state of the Fe species and the associated catalytic performance can be regenerated in the air at 550 °C. The redox switches caused regular fluctuation in the catalytic performance and remained stable throughout 16 regeneration cycles (up to 80 h). The employed strategy enabled a PX yield of up to 60% (carbon base) using a SiO2-coated Zn/P/Fe/ZSM-5 catalyst, which is 3–6 times higher than previously reported values. The result showed a new mode of acidity modulation of the catalyst.
Wang, S. H.; Han, M. Y.; Huang, D. J. Nitric oxide switches on the photoluminescence of molecularly engineered quantum dots. J. Am. Chem. Soc. 2009, 131, 11692–11694.
Dasari, R.; Zamborini, F. P. Hydrogen switches and sensors fabricated by combining electropolymerization and Pd electrodeposition at microgap electrodes. J. Am. Chem. Soc. 2008, 130, 16138–16139.
Fioravanti, G.; Haraszkiewicz, N.; Kay, E. R.; Mendoza, S. M.; Bruno, C.; Marcaccio, M.; Wiering, P. G.; Paolucci, F.; Rudolf, P.; Brouwer, A. M. et al. Three state redox-active molecular shuttle that switches in solution and on a surface. J. Am. Chem. Soc. 2008, 130, 2593–2601.
Wang, Y.; Tan, X.; Zhang, Y. M.; Zhu, S. Y.; Zhang, I.; Yu, B. H.; Wang, K.; Yang, B.; Li, M. J.; Zou, B. et al. Dynamic behavior of molecular switches in crystal under pressure and its reflection on tactile sensing. J. Am. Chem. Soc. 2015, 137, 931–939.
Belhboub, A.; Boucher, F.; Jacquemin, D. Grafting spiropyran molecular switches on TiO2: A first-principles study. J. Phys. Chem. C 2016, 120, 18281–18288.
Niroui, F.; Wang, A. I.; Sletten, E. M.; Song, Y.; Kong, J.; Yablonovitch, E.; Swager, T. M.; Lang, J. H.; Bulovic, V. Tunneling nanoelectromechanical switches based on compressible molecular thin films. ACS Nano 2015, 9, 7886–7894.
Simpson, G. J.; Hogan, S. W. L.; Caffio, M.; Adams, C. J.; Früchtl, H.; van Mourik, T.; Schaub, R. New class of metal bound molecular switches involving H-tautomerism. Nano Lett. 2014, 14, 634–639.
Ohtake, T.; Tanaka, H.; Matsumoto, T.; Kimura, M.; Ohta, A. Redox-driven molecular switches consisting of bis(benzodithiolyl)bithienyl scaffold and mesogenic moieties: Synthesis and complexes with liquid crystalline polymer. J. Org. Chem. 2014, 79, 6590–6602.
Ali, S. A.; Siddiqui, M. A.; Ali, M. A. Parametric study of catalytic reforming process. React. Kinet. Catal. Lett. 2005, 87, 199–206.
Coppens, M. O.; Froment, G. F. Fractal aspects in the catalytic reforming of naphtha. Chem. Eng. Sci. 1996, 51, 2283–2292.
Sotelo-Boyas, R.; Froment, G. F. Fundamental kinetic modeling of catalytic reforming. Ind. Eng. Chem. Res. 2009, 48, 1107–1119.
Adebajo, M. O.; Long, M. A. The contribution of the methanol-to-aromatics reaction to benzene methylation over ZSM-5 catalysts. Catal. Commun. 2003, 4, 71–76.
Zaidi, H. A.; Pant, K. K. Catalytic conversion of methanol to gasoline range hydrocarbons. Catal. Today 2004, 96, 155–160.
Lalik, E.; Liu, X. S.; Klinowski, J. Role of gallium in the catalytic activity of zeolite [Si, Ga]-Zsm-5 for methanol conversion. J. Phys. Chem. 1992, 96, 805–809.
Wang, T.; Tang, X. P.; Huang, X. F.; Qian, W. Z.; Cui, Y.; Hui, X. Y.; Yang, W.; Wei, F. Conversion of methanol to aromatics in fluidized bed reactor. Catal. Today 2014, 233, 8–13.
Zhang, J. G.; Qian, W. Z.; Tang, X. P.; Shen, K.; Wang, T.; Huang, X. F.; Wei, F. Influence of catalyst acidity on dealkylation, isomerization and alkylation in MTA process. Acta Phys. Chim. Sin. 2013, 29, 1281–1288.
Wang, N.; Qian, W. Z.; Wei, F. Fabrication and catalytic properties of three-dimensional ordered zeolite arrays with interconnected micro-meso-macroporous structure. J. Mater. Chem. A 2016, 4, 10834–10841.
Zhou, J.; Teng, J. W.; Ren, L. P.; Wang, Y. D.; Liu, Z. C.; Liu, W.; Yang, W. M.; Xie, Z. K. Full-crystalline hierarchical monolithic ZSM-5 zeolites as superiorly active and long-lived practical catalysts in methanol-to-hydrocarbons reaction. J. Catal. 2016, 340, 166–176.
Ilias, S.; Bhan, A. Mechanism of the catalytic conversion of methanol to hydrocarbons. ACS Catal. 2013, 3, 18–31.
Olsbye, U.; Svelle, S.; Bjorgen, M.; Beato, P.; Janssens, T. V. W.; Joensen, F.; Bordiga, S.; Lillerud, K. P. Conversion of methanol to hydrocarbons: How zeolite cavity and pore size controls product selectivity. Angew. Chem., Int. Ed. 2012, 51, 5810–5831.
Shen, K.; Qian, W.; Wang, N.; Su, C.; Wei, F. Fabrication of c-axis oriented ZSM-5 hollow fibers based on an in situ solid-solid transformation mechanism. J. Am. Chem. Soc. 2013, 135, 15322–15325.
Shen, K.; Qian, W. Z.; Wang, N.; Zhang, J. G.; Wei, F. Direct synthesis of c-axis oriented ZSM-5 nanoneedles from acid-treated kaolin clay. J. Mater. Chem. A 2013, 1, 3272–3275.
Wang, N.; Qian, W. Z.; Shen, K.; Su, C.; Wei, F. Bayberry-like ZnO/MFI zeolite as high performance methanol-to-aromatics catalyst. Chem. Commun. (Camb.) 2016, 52, 2011–2014.
Zhang, J. G.; Qian, W. Z.; Kong, C. Y.; Wei, F. Increasing para-xylene selectivity in making aromatics from methanol with a surface-modified Zn/P/ZSM-5 catalyst. ACS Catal. 2015, 5, 2982–2988.
Ahn, J. H.; Kolvenbach, R.; Al-Khattaf, S. S.; Jentys, A.; Lercher, J. A. Enhancing shape selectivity without loss of activity-novel mesostructured ZSM5 catalysts for methylation of toluene to p-xylene. Chem. Commun. (Camb.) 2013, 49, 10584–10586.
Young, L. B.; Butter, S. A.; Kaeding, W. W. Shape selective reactions with zeolite catalysts: III. Selectivity in xylene isomerization, toluene-methanol alkylation, and toluene disproportionation over ZSM-5 zeolite catalysts. J. Catal. 1982, 76, 418–432.
Mirth, G.; Cejka, J.; Lercher, J. A. Transport and isomerization of xylenes over HZSM-5 zeolites. J. Catal. 1993, 139, 24–33.
Kaeding, W. W.; Chu, C.; Young, L. B.; Weinstein, B.; Butter, S. A. Selective alkylation of toluene with methanol to produce para-xylene. J. Catal. 1981, 67, 159–174.
Kim, J. H.; Namba, S.; Yashima, T. Para-selectivity of zeolites with MFI structure: Difference between disproportionation and alkylation. Appl. Catal. A Gen. 1992, 83, 51–58.
Ivanova, I. I.; Corma, A. Surface species formed and their reactivity during the alkylation of toluene by methanol and dimethyl ether on zeolites as determined by in situ 13C MAS NMR. J. Phys. Chem. B 1997, 101, 547–551.
Zheng, S.; Heydenrych, H. R.; Röger, H. P.; Jentys, A.; Lercher, J. A. On the enhanced selectivity of HZSM-5 modified by chemical liquid deposition. Top. Catal. 2003, 22, 101–106.
Wang, I.; Ay, C. L.; Lee, B. J.; Chen, M. H. Para-selectivity of dialkylbenzenes over modified HZSM-5 by vapour phase deposition of silica. Appl. Catal. 1989, 54, 257–266.
Miyake, K.; Hirota, Y.; Ono, K.; Uchida, Y.; Tanaka, S.; Nishiyama, N. Direct and selective conversion of methanol to para-xylene over Zn ion doped ZSM-5/silicalite-1 core–shell zeolite catalyst. J. Catal. 2016, 342, 63–66.
Lubango, L. M.; Scurrell, M. S. Light alkanes aromatization to BTX over Zn-ZSM-5 catalysts: Enhancements in BTX selectivity by means of a second transition metal ion. Appl. Catal. A Gen. 2002, 235, 265–272.
Perez-Ramı́rez, J.; Kumar, M. S.; Brückner, A. Reduction of N2O with CO over FeMFI zeolites: Influence of the preparation method on the iron species and catalytic behavior. J. Catal. 2004, 223, 13–27.
Ma, A. Z.; Grünert, W. Selective catalytic reduction of NO by ammonia over Fe-ZSM-5 catalysts. Chem. Commun. 1999, 1, 71–72.
Tan, P. L. Active phase, catalytic activity, and induction period of Fe/zeolite material in nonoxidative aromatization of methane. J. Catal. 2016, 338, 21–29.
Weckhuysen, B. M.; Wang, D. J.; Rosynek, M. P.; Lunsford, J. H. Conversion of methane to benzene over transition metal ion ZSM-5 zeolites: II. Catalyst characterization by X-ray photoelectron spectroscopy. J. Catal. 1998, 175, 347–351.
Shwan, S.; Nedyalkova, R.; Jansson, J.; Korsgren, J.; Olsson, L.; Skoglundh, M. Hydrothermal stability of Fe-BEA as an NH3-SCR catalyst. Ind. Eng. Chem. Res. 2012, 51, 12762–12772.
Jozwiak, W. K.; Kaczmarek, E.; Maniecki, T. P.; Ignaczak, W.; Maniukiewicz, W. Reduction behavior of iron oxides in hydrogen and carbon monoxide atmospheres. Appl. Catal. A Gen. 2007, 326, 17–27.
Kang, S. H.; Bae, J. W.; Sai Prasad, P. S.; Jun, K. W. Fischer–Tropsch synthesis using zeolite-supported iron catalysts for the production of light hydrocarbons. Catal. Lett. 2008, 125, 264–270.
Jin, Y. M.; Datye, A. K. Phase transformations in iron Fischer–Tropsch catalysts during temperature-programmed reduction. J. Catal. 2000, 196, 8–17.
Wang, N.; Li, J.; Sun, W. J.; Hou, Y. L.; Zhang, L.; Hu, X. M.; Yang, Y. F.; Chen, X.; Chen, C. M.; Chen, B. H. et al. Rational design of zinc/zeolite catalyst: Selective formation of p-xylene from methanol to aromatics reaction. Angew. Chem., Int. Ed. 2022, 61, e202114786.
This work is finically supported by the National Natural Science Foundation of China (22278236) and the National Key Research and Development Program of China (2020YFB0606401).
The articles published in this open access journal are distributed under the terms of the Creative Commons Attribution 4.0 International License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.