Cs-Enhanced Vapor-Phase Propylene Epoxidation over Ti-MWW Zeolite with Stabilized Subnanometer Au Clusters

The vapor-phase selective oxidation of propylene to propylene oxide (PO) using molecular hydrogen and oxygen over gold-supported titanosilicate catalysts has attracted scientific interest in recent decades. This catalytic system fundamentally relies on an optimized synergistic interaction between supported Au species and titanium sites in a zeolite framework, enabling in situ hydrogen peroxide synthesis from H₂/O₂mixtures and subsequent olefin epoxidation. Although previous studies have revealed that subnanometer Au clusters positioned near framework Ti centers within zeolite channels demonstrate promising catalytic performance, their practical application faces limitations due to the rapid deactivation caused by Au species migration/aggregation and coking. Consequently, breaking the inherent activity-stability trade-off has emerged as a pivotal challenge. Herein, this work addresses this dilemma by exploiting the structural confinement of MWW-type zeolites coupled with the strategic use of Cs₂CO₃to regulate Au loading. This methodology enabled the successful immobilization and stabilization of ultrasmall Au clusters (0.77 nm) within intracrystalline MWW supercages, positioning adjacent to framework Ti active sites. Besides, the introduced Cs⁺cations effectively neutralized zeolitic acidity to create a hydrophobic microenvironment that facilitated PO desorption/diffusion, suppressing coke-forming side reactions. These synergistic modifications effectively enhanced the PO production rate in tandem catalytic process. The optimized 0.35Au/Ti-MWW(31)-Cs₂CO₃catalyst demonstrated a high performance with an initial PO formation rate of 182 g_POh^–1kg_cat^–1, maintaining 90% activity retention (164 g_POh^–1kg_cat^–1) after 200 h of continuous operation. Compared to conventional Au/TS-1 catalysts prepared by deposition-precipitation, our confinement strategy utilizing the confinement of MWW topology and the function of Cs₂CO₃as a precipitant presents an efficient approach for stabilizing the Au active species in vapor-phase propylene epoxidation catalysis.