Site-Specific Carbonylation of Dimethoxymethane over Brønsted Acids in the Opened Sodalite Cages of FAU Zeolite

Methyl methoxyacetate (MMAc) is a valuable platform molecule used in biodegradable polymers, polyester fibers, and fine chemicals. While zeolite-catalyzed carbonylation of dimethoxymethane (DMM) to MMAc is a sustainable route, achieving high selectivity, stability, and efficiency simultaneously remains challenging. Herein we demonstrate that strategically opening sodalite (SOD) cages within FAU-type zeolites creates optimal Brønsted acid microenvironments for DMM carbonylation. An H-FAU-I-F zeolite (Si/Al ≈ 6), prepared via mild NH₄F treatment to open SOD cages, maintained 90% MMAc selectivity and a space-time yield of 0.7 g·g^-1·h^-1 over 500 h of continuous operation─representing unprecedented catalytic activity and stability. Solid-state NMR studies (using ²H-DMM and ¹³CO) revealed preferential enrichment of DMM and CO within the opened SOD cages. In situ ¹H-¹³C CP MAS NMR directly captured the insertion of CO into DMM occurring specifically in SOD nanoreactors. DFT calculations attributed their superior activity to enhanced acid strength and transition-state stabilization. This work establishes a cage-engineering strategy for designing efficient and durable industrial carbonylation catalysts.