Unveiling the Catalytic Superiority of Ti-MWW Zeolite for Sustainable Lactide Production from Methyl Lactate

Abstract

The gas-phase route from methyl lactate (ML) to lactide (LD) holds significant promise for sustainable monomer production, offering a valuable platform to explore the structure–activity landscape of heterogeneous catalysts. Here, we investigate a series of Ti-containing zeolite catalysts, including both TiO2-impregnated and Ti-incorporated microporous materials, to elucidate the structural and electronic factors governing LD selectivity and productivity. MWW-type titanosilicates, featuring open frameworks and high external surface areas, consistently outperformed conventional microporous and mesoporous counterparts. Notably, Ti-MWW-del, prepared via delamination of a silanol-rich MWW precursor, achieved the highest lactide productivity, enabled by superior Ti site dispersion and framework-accessible active environments. A combination of complementary spectroscopic analyses (UV–vis, Solid-state NMR, and ToF-SIMS) indicates that the enhanced catalytic performance arises from highly dispersed TiO4 species embedded within defect-rich, hydrogen-bonded environments, which enhance the electrophilic character of Ti centers and improve substrate accessibility. We delineate how framework-incorporated, externally accessible open architecture of TiO4 sites in delaminated MWW govern per-site activity, LD selectivity, and durability under realistic throughputs, against TS-1 and TiO2-impregnated supports. These findings highlight the potential of defect-engineered, framework-substituted zeolites for selective biomass-derived chemical transformations.