Cu-ZnO nanoparticles encapsulated with ZSM-5 for selective conversion of carbon dioxide to oxygenates

Abstract

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