Fabrication of a highly stable Ni–Co bimetallic catalyst for the steam reforming of methane via in situ crystallization of phyllosilicate on porous spherical silica

Abstract

Although Ni nanoparticles are useful as catalytically active species in diverse reactions, their agglomeration restricts their long-term activity. Therefore, improving the thermal stability of Ni nanoparticles on a support is essential for enhancing their activity in processes such as the reforming of hydrocarbons. Herein, we present a synthetic strategy for thermally stable Ni–Co bimetallic nanoparticles supported on porous spherical silica, which is based on the in situ crystallization of a 2 : 1-type phyllosilicate. The synthesis process consisted of the reaction of silica powder with Ni(NO₃)₂ and Co(NO₃)₂ in an aqueous urea solution at 150 °C on the surface of porous silica microspheres, followed by treating the resulting 2 : 1-type phyllosilicate at 800 °C in a H₂ flow to obtain Ni–Co bimetallic nanoparticles and CoSiO₄ supported on micrometer-sized spherical silica. The preservation of the spherical morphology enabled the steam reforming of methane without requiring molding/pelletizing of the powdered microspheres. The as-synthesized Ni–Co bimetallic nanoparticles exhibited higher catalytic activity than those prepared using a conventional impregnation method because the anchoring effect of Co²⁺ in CoSiO₄ prevented nanoparticle agglomeration, thereby improving the catalytic activity. The proposed synthetic strategy using particulate porous silica is feasible for the fabrication of highly functionalized metal nanoparticle-based catalysts resistant to sintering and degradation.