Engineering spatial locations of Pt in hierarchically porous KL zeolite by atomic layer deposition with enhanced n-heptane aromatization

Abstract

Atomic layer deposition (ALD) is an efficient method to confine the Pt particles in the channels of KL zeolite to improve the durability of catalysts. However, the diffusion of metal precursors is impeded by the size of micropore. Herein, using polyethylene glycol (PEG) as zeolite growth modifier to limit the growth of KL zeolite in [001] direction, a unique KL zeolite with trimodal porosity (native and larger micropores, mesopores) was successfully synthesized. Hierarchically porous structure engineered the spatial location of Pt precursor during ALD process. The obtained micro/mesoporous structure favored the diffusion of the Pt precursor into the pores of KL zeolite, and led to the formation of highly dispersed Pt clusters in micropores, mesopores, and intersection of micro/mesopores of KL zeolite. The resultant Pt/KLP2 catalyst showed the enhanced n-heptane aromatization performances operated at low temperature (420 °C). Systematic characterizations reveal the synergetic effect of spatial environment of hierarchical porous KL zeolite promoted the n-heptane aromatization and molecular diffusion. Namely, micropores enhanced the n-heptane dehydrocyclization, and the mesopores with shortened diffusion length facilitated the mass transport of aromatics and inhibited secondary hydrogenolysis efficiently. The present work broadens the fundamental understanding of the role of zeolite channels for alkane reforming reactions.