Abstract
Molecular-sized micropores of ZSM-5 zeolite catalysts provide spatial restrictions around catalytic sites that allow for shape-selective catalysis. However, the fact that ZSM-5 has two main pore systems with different geometries is relatively unexploited as a potential source of additional shape selectivity. Here, we use confocal laser-scanning microscopy to show that by changing the polarity of the solvent, the acid-catalyzed furfuryl alcohol oligomerization can be directed to selectively occur within either of two locations in the microporous network. This finding is confirmed for H-ZSM-5 particles with different Si/Al ratios and indicates a general trend for shape-selective catalytic reactions.
Highlights
Molecular-sized micropores of ZSM-5 zeolite catalysts provide spatial restrictions around catalytic sites that allow for shape-selective catalysis
H-ZSM-5 is industrially used in fluid catalytic cracking,[4] the synthesis of ethylbenzene,[5,6] the isomerization of xylenes,[6] and the disproportionation of toluene.[6,7]
With a focus on environmentally sustainable processes, there were numerous and promising studies regarding the activity and shape selectivity of H-ZSM-5 in the catalytic conversion of biomass and its derivatives.[8−11] For example, it was shown that ZSM-5 exhibited the highest aromatic yield and the least amount of coking among 13 zeolites with different pore sizes and shapes when applied in the fast catalytic pyrolysis of glucose.[8]
Summary
Letter orientation of reaction products with respect to the crystalline porous network by using linearly polarized excitation light. In order to confirm our results, we have conducted CLS microscopic imaging of crystals lying on their [100] facet (based on the crystallographic structure of the main body) In this orientation, the straight pores of the main body and sinusoidal pores of the intergrowth are coaligned with the excitation light polarization orientation. This concentration of silanols is in line with earlier reports.[41,42] Controlled addition of water shows the strong interaction with these silanols indicative for a high local polarity From these 1H MAS NMR data in combination with the CLS microscopy observations we conclude that there is a silanol-induced polarity, which is potentially different between the sinusoidal and straight pores with silanols being preferentially present in the sinusoidal pores.
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