Dual-template synthesis of thinner-layered MCM-49 zeolite to boost its alkylation performance

Abstract

MCM-49 zeolite has MWW toplological structure similar to MCM-22 and it possesses connatural more external acid sites, performing more advantages in solid acid catalysis. Herein, a thinner-layered C18-MCM-49 microsphere by using diquaternary ammonium salts (C18–6–6Br2, denoted as C18, or Cn6n series) in mixture sols was achieved. This C18-MCM-49 microsphere possesses a 1–2 µm particle size, for which the crystal sheets decrease to ∼200 nm in size and 5–20 nm in thickness, which originated from that more C18 molecules located in the half cups and supercages pores to achieve the separation of MWW layer thickness in the c direction. The C18-MCM-49 zeolite provides an ultra-large external surface area (212 m2•g−1) and mesopore volume (0.767 cm3•g−1), and compared with traditional MCM-49 (Sext = 133 m2•g−1, Vmes = 0.414 cm3•g−1), external surface area and mesopore volume were increased by 59.4% and 85.3%, respectively. Due to its thinner-layered structure, this C18-MCM-49 microsphere displays more active acid sites on the external surface, leading to an improved ethylbenzene selectivity (94.7%) and benzene conversion (34%) in alkylation reaction. By using synchrotron radiation Small-angle X-ray scattering, we further studied series of synthetic sols during aging period. The results prove the behavior of aluminosilicate species in the mixture plays critical role in thinner-layered MCM-49, specifically, the precursor fractal between 2 and 2.5 is a key factor in synthesizing MCM-49. Collectively, this result offers a convenient and valid way to synthesize other types of zeolites.