Methanol to olefins: activity and stability of nanosized SAPO-34 molecular sieves and control of selectivity by silicon distribution

[EN] Nano-SAPO-34 molecular sieves synthesized in a microwave environment with 20 nm crystal size showed a longer lifetime than SAPO-34 prepared by the conventional hydrothermal method in the reaction of methanol to olefins. It has been found that silicon distribution strongly affects the lifetime and selectivity. Thus, silicon at the border of the silicon islands gives a higher lifetime and lower C2/C3 ratio. This change in activity and selectivity is better explained in terms of different silicon distribution than by preferential diffusion of ethene through the 8MR pores and agrees with transition-state selectivity. The effects of equilibrium of olefins and deactivation by coke were isolated, showing that after full formation of the hydrocarbon pool, selectivity is independent of deactivation by coke. Financial support by the Spanish MINECO (MAT2012-37160, CSD2009-00050-CONSOLIDER/INGENIO 2010), and Generalitat Valenciana by the PROMETEO program is acknowledged. Z. Li acknowledges China Scholarship Council (CSC) for a fellowship. J. Yu thanks the support by the State Basic Research Project of China (Grant no. 2011CB808703) and the National Natural Science Foundation of China. Li, Z.; Martínez Triguero, LJ.; Concepción Heydorn, P.; Yu, J.; Corma Canós, A. (2013). Methanol to olefins: activity and stability of nanosized SAPO-34 molecular sieves and control of selectivity by silicon distribution. Physical Chemistry Chemical Physics. 15(35):14670-14680. https://doi.org/10.1039/c3cp52247d Bjørgen, M., Joensen, F., Spangsberg Holm, M., Olsbye, U., Lillerud, K.-P., & Svelle, S. (2008). Methanol to gasoline over zeolite H-ZSM-5: Improved catalyst performance by treatment with NaOH. Applied Catalysis A: General, 345(1), 43-50. doi:10.1016/j.apcata.2008.04.020 Vennestrøm, P. N. R., Grill, M., Kustova, M., Egeblad, K., Lundegaard, L. F., Joensen, F., … Beato, P. (2011). Hierarchical ZSM-5 prepared by guanidinium base treatment: Understanding microstructural characteristics and impact on MTG and NH3-SCR catalytic reactions. Catalysis Today, 168(1), 71-79. doi:10.1016/j.cattod.2011.03.045 Barbera, K., Bonino, F., Bordiga, S., Janssens, T. V. W., & Beato, P. (2011). Structure–deactivation relationship for ZSM-5 catalysts governed by framework defects. Journal of Catalysis, 280(2), 196-205. doi:10.1016/j.jcat.2011.03.016 Na, K., Choi, M., & Ryoo, R. (2013). Recent advances in the synthesis of hierarchically nanoporous zeolites. Microporous and Mesoporous Materials, 166