Simultaneous Modulation of Mesoporosity and Al Siting for Superior Performance Zeolite Catalyst in Ethylene Dehydroaromatization to Aromatics

Abstract

Porosity and Al siting are key levers for optimizing zeolite catalysts, yet they are often addressed independently due to the lack of effective integrated tuning strategies. Herein, we report an integrative methodology for preparing hierarchical zeolite (Z_F) with interconnected mesostructures and tunable Al siting, achieved via regioselective dissolution of Al-rich domains by presetting accessible and inaccessible zones within parent zeolite (Z_P). Remarkably, ∼60% of the framework channels' Al atoms were selectively removed without impairing the channel intersections' Al atoms. Despite a 39% reduction in Brønsted acid sites (BAS), Z_F exhibits a 1.8-fold higher turnover frequency (TOF) than Z_P during ethylene transformation at 973K, attributable to the introduction of mesoporosity. Notably, site-specific ³¹P NMR analysis reveals that BAS located at channel intersections exhibits a TOF of 516 h^-1, which is 13 times higher than that of sites within the channels (40 h^-1). The hierarchical zeolite also demonstrates superior durability and enhanced aromatic selectivity compared to Z_P. These results highlight the synergistic benefits of simultaneously tuning porosity and Al siting, offering a new paradigm for the rational design of high-performance zeolite catalysts and providing deeper insights into the interplay between structure and function in zeolite-based catalysis.

Keywords: Al siting; Crystal engineering; Ethylene dehydroaromatization to aromatics; Porosity; Zeolite.

Figure 1

The prevailing methodologies for upgrading zeolite performance through crystal engineering: a) porosity optimization; b) Al siting modulation; and c) the integrated engineering of zeolite porosity and aluminum siting developed in this work.

Figure 2

TEM images of Z_P a) and Z_F b). The cross‐section SEM images of the parent zeolite sample (Z_P, c) and its NH₄F treated counterpart (Z_F, d), and the Al distribution over the cross‐section of samples Z_P e) and Z_F f). The scale bars for (a–f) in Figure 1 are 1 µm, and for the insets in (c) and (d) are 100 nm.

Figure 3

a) N₂ adsorption‐desorption isotherms, b) XRD patterns, c) IR spectra, and d) ²⁷Al NMR spectra of Z_P and Z_F zeolite catalysts.

Figure 4

³¹P NMR spectra of samples Z_P a) and Z_F b) using TMPO; the peaks were attributed according to the work reported by Bornes et al.^{[ 44 ]} and the deconvolution results are summarized in Table 2. c) The schematic illustrates the simultaneous and selective removal of framework Al from ten‐membered ring channels and the formation of a hierarchical structure in zeolite crystals during NH₄F treatment.

Figure 5

a) Ethylene conversion (solid balls) and coke content (empty circles) over Z_P (black) and Z_F (red) catalysts; b) TOF values of Z_P, Z_F, and the BAS sites in 10‐MR channels and channel intersections, respectively; c) molar yields of butenes (isobutene and but‐1‐ene), methane, propylene, benzene, and toluene as functions of time‐on‐stream at 973K, under atmospheric pressure, with diluted ethylene feed (${\mathrm{P}}_{{\mathrm{C}}_2{\mathrm{H}}_4}$ = 0.005 MPa) over Z_P (black) and Z_F (red) catalysts; d) deactivation rate of the Z_P and Z_F catalysts; e) evolution of residual micro‐ and mesopore volumes as a function of coke content. Reaction conditions: 973 K, atmospheric pressure; feed gas: ethylene/N₂ mixture (ethylene partial pressure: 0.005 MPa); ethylene WHSV: 14 h⁻¹; reaction duration: up to 16 h.