Tailoring Defects in Highly Siliceous CHA-Type Zeolite for Enhanced CO ₂ Hydrogenation to Light Olefins

Abstract

The conversion of CO2 to hydrocarbons via the methanol-mediated pathway represents a crucial route for carbon neutrality, yet preferable production of more value-added light olefins remains constrained by the fundamental activity-selectivity trade-off in zeolite catalysts. While previous studies established an acidity regulation mechanism based on balancing acid density with acid strength, the conversion of methanol intermediates is also critically governed by their intracrystalline diffusion, which can be severely hindered by structural defects particularly prevalent in highly siliceous zeolites. This work demonstrates a different approach that synergistically integrates zeolite acidity and defect engineering. A hydrothermal synthesis strategy with a selected inorganic source precisely controls aluminum incorporation into the highly siliceous CHA zeolite framework (Si/Al > 800). Subsequently, a postsynthetic fluorination followed by calcination effectively heals silanol defects. The resulting HS-CHA-F zeolite features a hydrophobic framework that facilitates rapid methanol diffusion while utilizing precisely tuned ultraweak acidity to steer selective C–C coupling. The optimized OXZEO bifunctional catalyst ZnZrOx/HS-CHA-F achieves 38.5% CO2 conversion and 91.3% light olefin selectivity in hydrocarbons at 653 K and 4 MPa, substantially outperforming conventional SSZ-13 and SAPO-34 benchmarks. This study establishes a generalizable method for overcoming long-standing limitations in CO2 hydrogenation through coupled zeolite acidity and defect engineering.