Enhanced Mass Transport of One-Dimensional Zeolite MTT by Secondary Growth

One-dimensional zeolites have distinct pore topologies for shape-selective catalysis, yet their performance in conventional reactions is frequently compromised by severe diffusion limitations. Creating opportunities to employ one-dimensional (1D) zeolites in catalytic applications requires advanced synthesis methods to design materials with ultrasmall diffusion path lengths. In this study, we show that the postsynthesis modification of ZSM-23 (MTT) using a protocol analogous to the generation of finned zeolites dramatically improves its mass transport properties. This is accomplished by a facile secondary growth process that introduces surface roughness on the exterior surfaces of MTT crystals and creates greater access to interior pores through the putative removal of intrinsic defects. High-resolution electron microscopy images show that roughened interfaces are step bunches of unfinished layers with ultrasmall dimensions that present a series of short 1D channels. Comparison of these materials against conventional and nanosized ZSM-23 catalysts using methanol to hydrocarbons as a benchmark reaction reveals dramatic enhancement in cumulative turnovers and a propene/ethene ratio that is much higher than conventional ZSM-5 (MFI) zeolites. The improved mass transport of MTT catalysts after secondary growth also markedly extends their lifetime at much shorter reactant contact times without any observed changes in the mechanism of coking. Collectively, these findings highlight an efficient route to generate high-performance 1D zeolites as potential catalysts for commercial applications.