Aluminum Distribution in Ferrierite Zeolites Influences the Performance of Methane Oxidation

Abstract

Transition-metal-free aluminosilicate FER-type zeolite has been demonstrated to effectively catalyze methane to methanol using N₂O as the oxidant with distorted tetra-coordinated aluminum (Al_IV-2) and penta-coordinated aluminum (Al_V) as potential active sites. However, the specific effects of Al distribution on the active Al species have not been thoroughly investigated. Herein, aluminosilicate FER-type zeolites with controllable Al distribution were developed. Al distribution, including the arrangement and location of Al atoms, was characterized using ²⁷Al MQMAS/MAS and ²⁹Si MAS NMR spectra. The arrangement of aluminum, particularly the isolated Al and paired Al in as-synthesized samples, influenced the proximity between oxidative and acidic sites in H-type samples. Al locations involved the specific positioning of bifunctional sites and affected the final product. The increased CH₄ conversion at 250–275 °C of FER zeolite with Al preferential population at T4 sites confirmed the higher activity of Al species from T4 sites. Additionally, a higher proportion of Al atoms in 10-ring channels facilitated the tandem conversion of methane to methanol on oxidative sites, followed by methanol to hydrocarbons on acidic sites at 300–375 °C. This study corroborated and expanded upon our recent research and highlighted the significant impact of Al distribution in FER zeolite on methane oxidation.