Catalytically Stable Monodispersed Multi-Core Ni-Co Nanoparticles Encapsulated with SiO ₂ Shells for Dry Reforming of Ch ₄ with CO ₂

Enhanced thermal and catalytic stability of monodispersed Ni-Co bimetal nanoparticles with its even size distribution of ~6 nm encapsulated by SiO2 shell (NC@Si) having multicore-shell structures were verified for a harsh dry reforming of methane with CO2 (DRM). The extents of coke formations and aggregations of Ni-Co nanoparticles were dramatically suppressed with positive contributions of oxophilic Co species as well as by their spatial confinement effects. The optimal N8C2@Si with a Ni/Co molar ratio of ~4 revealed a relatively higher CH4 and CO2 conversion of 74.1 and 83.7% at T = 800℃ without any significant deactivation. The original morphologies of the monodispersed Ni-Co nanoparticles were well preserved even after a long-run DRM reaction for 120 h with an insignificant coke formation and active metal aggregation. The superior catalytic activity and stability of the N8C2@Si were attributed to the highly-dispersed oxophilic metallic cobalt oxides in the monodispersed stable Ni-Co nanoparticles, which enhanced CO2 adsorption capacity as well as increased thermal stability of the spatially confined Ni-Co nanoparticles with the help of mesoporous SiO2 shell at its optimal aging time less than 4 h. The novel multicore-shell structures of the N8C2@Si can effectively suppress the filamentous coke formations as well as minimize the Ni-Co multicore aggregations by stronger metal-SiO2 Interactions in the mesoporous SiO2 matrices.