Synergistic acid–base interplays: Zeolite-catalyzed CH3Cl conversion to light olefins boosted by MgO-driven CH3Cl spillover

Abstract

Chloromethane (CH₃Cl), a reactive C₁ molecule, has been underexplored compared to traditional C₁ molecules like CO, CO₂, CH₄, and CH₃OH that have long been at the center of C₁ chemistry. Herein, the catalytic chloromethane–to–olefin (CMTO) reaction was investigated with zeolite-based heterogeneous acid catalysts. H-ZSM-5 zeolites with controlled Si/Al ratios were investigated, revealing that CH₃Cl conversion, catalyst lifetime, and light olefin ($C_{2-4}^{=}$) selectivity depended on zeolite acidity and MgO addition. While MgO alone enabled CH₃Cl activation via Lewis acid–base interactions, its independent catalytic play pales compared to the superior performance of zeolites. However, balancing the zeolite acidity with MgO loading doubled or even tripled CH₃Cl conversion compared to the independent performance of zeolites, achieving nearly 100 % CH₃Cl conversion with 86.5 % $C_{2-4}^{=}$ selectivity without deactivation. In-situ diffuse reflectance infrared Fourier transform spectroscopy showed that both zeolite acid sites and MgO activated CH₃Cl simultaneously, during which MgO induced a CH₃Cl spillover to the zeolite acidic site, resulting in the boosted CH₃Cl conversion. This study establishes a new road to efficient and selective C₁ molecular conversion using CH₃Cl boosted by CH₃Cl spillover, which would be extended to methyl spillover-mediated catalytic conversion to various chemicals.