Highly Active and Coke-Tolerant Hierarchical Mordenite Catalysts Synthesized by Recrystallization for the Isopropylation of Naphthalene

Abstract

In the isopropylation of naphthalene for the production of 2,6-naphthalenedicarboxylate, the monomer of polyethylene naphthalate plastic, a shape-selective mordenite (MOR) zeolite catalyst provides the best selectivity for the desired 2,6-diisopropylnaphthalene. However, the small pore size of the zeolite limits the naphthalene conversion and lowers the stability because of pore-mouth blocking by coke. We discovered that these problems could be mitigated by synthesizing a micro-meso hierarchical pore structure in the MOR zeolite by the recrystallization of MOR with cetyltrimethylammonium bromide as a mesopore-forming surfactant. The recrystallized catalysts allow the facile diffusion of bulky molecules through connected meso- and micropores to and from active catalytic sites located in the small MOR pores. Relative to microporous MOR, the hierarchical MOR catalyst demonstrated a greatly enhanced activity, stability, and coke tolerance, and the intrinsic high shape selectivity of MOR for 2,6-diisopropylnaphthalene was maintained. Mild desilication enlarged the pore volume and formed additional acid sites to increase the activity further.