The Influence of Mesopore Architecture in Hierarchical H-ZSM-5 on n-Butanol Dehydration

Abstract

Zeolites are among the most widely employed catalysts in the (petro-)chemical industry. However, due to their elaborate microporous network, they are prone to diffusion limitations and deactivation. Several modification methods have been proposed to overcome these limitations, each exhibiting their benefits. In this work, two of the most promising strategies were combined, i.e., limiting the length of one of the crystal axes during synthesis to achieve a platelike morphology and introducing mesoporosity, creating a hierarchical platelike H-ZSM-5. The platelike morphology was obtained by adding urea as a growth modifier to the synthesis mixture, and mesopores were introduced in the platelike H-ZSM-5 through etching with a NaOH/TPAOH mixture. As a benchmark, the same etching procedure was applied to a commercial ZSM-5 counterpart. These materials were tested in the n-butanol dehydration, where the platelike morphology exhibited an improved catalytic performance, significantly increasing the activity per acid site and stability, and slightly increasing the selectivity toward the butenes. The generation of mesopores in commercial ZSM-5 also increased the activity per acid site but reduced the catalyst’s stability, likely due to an increased amount of Lewis acid sites upon etching. When applying the same modification method to the platelike H-ZSM-5, much larger mesopores and some macropores were observed. These further increased the stability of the catalyst but barely affected the activity per acid site, presumably due to the already optimized catalytic performance of the platelike H-ZSM-5.