Cu–ZnO nanoparticles encapsulated in ZSM-5 for selective conversion of carbon dioxide into oxygenates

Abstract

Engineering copper nanoparticles to achieve high dispersion and thermal stability with stable catalytic activity is crucial and challenging for the direct hydrogenation of CO₂ to oxygenates via tandem catalysis over hybridized catalysts. Herein, hybridized Cu–ZnO nanoparticles were encapsulated in nano-crystalline ZSM-5 overlayers through a steam-assisted crystallization (SAC) approach by optimizing the Cu/Zn ratios of Cu–ZnO nanoparticles, the Si/Al ratio of ZSM-5, crystalline structures, and the oxidation states of active sites to achieve higher and durable direct conversion of CO₂ into dimethyl ether (DME) and methanol. The spatially confined Cu–ZnO nanoparticles inside ZSM-5 frameworks facilitated suppressed nanoparticle aggregation by preserving major Cu⁺ phases of active copper species, which contributed to excellent catalytic performance with CO₂ conversion rate of up to 20.8% and a methanol/DME selectivity of 81.6% (DME selectivity of 62.2%) with a space-time yield (STY) of 13.9 g_DME (g_Cu⁻¹ h⁻¹). In situ DRIFTS, AES/XPS and XANES analyses further revealed that the spatial confinement effects in protective ZSM-5 zeolite overlayers effectively stabilized homogeneously dispersed Cu–ZnO nanoparticles with dominant distribution of Cu⁺ phases, which played key roles in generating formate and methoxy intermediates that are responsible for the enhanced catalytic activity and catalyst durability.