Tuning the size and spatial distribution of Pt in bifunctional Pt-zeolite catalysts for direct coupling of ethane and benzene

Abstract

Controlling the dispersion and position of metal active sites in bifunctional metal–acid zeolite catalysts is essential for achieving synergy between the metal and acid sites in tandem catalytic processes, but still challenging nowadays. Herein, we propose an approach to modulate the dispersion and position of Pt particles in ZSM-5 zeolite by employing various types of organic structure-directing agents (OSDAs) in the one-pot synthesis procedure. Systematic characterizations show that the OSDAs mainly influence the encapsulation of the Pt precursor into the ZSM-5 zeolite crystallites during the hydrothermal crystallization process, resulting in discrepancies in the dispersion and spatial distribution of Pt sites in the final Pt-zeolite catalysts. Comparative studies on different Pt-zeolite catalysts show that the formation of subnanometer Pt clusters and the close spatial proximity of Pt and Brønsted acid sites in the zeolite efficiently promote the tandem dehydrogenation-alkylation process and enhance the production rate of ethylbenzene in the direct ethane-benzene coupling reaction. This study offers insights into the design and synthesis of bifunctional metal-zeolite catalysts for tandem catalysis.