Propene epoxidation over low-cost Au/TS-1 catalyst: modulation of synergetic effect between Ti and Au sites

Abstract

The direct epoxidation of propylene using H2 and O2 has emerged as a promising alternative to conventional industrial processes, offering superior atom economy, environmental compatibility, and process economics. This work demonstrates a facile design strategy to enhance Au-Ti synergy in Au/TS-1 catalysts through precise control of TPAOH/Si ratios during zeolite synthesis. Systematic reduction of TS-1 crystallite dimensions to 220 nm was achieved through TPAOH/Si ratio optimization, simultaneously producing micro-mesoporous hierarchical architectures while preserving crystallinity. The engineered Au/TS-1 catalyst prepared via deposition-precipitation method exhibited exceptional propylene oxide selectivity (>95%) with stable activity, which is attributed to optimized electronic coupling between Au nanoparticles and framework Ti species. Spectroscopic analyses (XPS/UV-vis) revealed strengthened Au-Ti electronic interactions through positive binding energy shifts (Au 4f7/2: +0.4 eV; Ti 2p1/2: +0.9 eV), correlating with enhanced propylene activation. The catalytic efficiency was further governed by synergistic effects between accessible Ti-surrounded Au sites and surface silanol density. In-situ FT-IR kinetic analysis identified two distinct reaction phases: initial rate-limiting propylene chemisorption (0-20 min) followed by steady-state operation (25-55 min), with acetone and acetaldehyde identified as primary byproducts. This mechanistic understanding of structure-activity relationships advances fundamental principles for designing high-performance epoxidation catalysts while accelerating industrial implementation of sustainable propylene oxide production routes.