Ni,Co/SiO2 and Ni/SiO2,Co bimetallic microsphere catalysts indicating high activity and stability in the dry reforming of methane

Abstract

Two separate synthesis procedures were applied to alter the location of Cobalt (Co) in bimetallic silica (SiO2) microsphere catalyst with Nickel (Ni) as the second active metal. Co was either encapsulated with simultaneous Ni addition inside core structure (Ni,Co/SiO2) or impregnated on the shell following initial encapsulation of Ni inside the microsphere (Ni/SiO2&Co). Catalysts were tested in dry reforming of methane (DRM) reaction at 750 °C with a feed mixture of CH4:CO2:N2 = 1:1:1. Reactions were performed in a stainless steel temperature-controlled tube reactor. Results indicated the highest activity values with 4Ni-1Co ratio in catalyst structure and Co impregnated on catalyst structure revealed higher activity for all loadings compared to Ni,Co/SiO2 catalysts. CH4 and CO2 conversions for 3 h of reaction were obtained as 87 and 94%, and H2/CO ratio was determined as 0.84 in the presence of Ni/SiO2&Co catalyst with 4Ni-1Co loading. Coke formation was not detected for the catalyst with 4Ni-1Co loading and the highest coke amount was 2% among all catalysts. Time on stream test in the presence of Ni/SiO2&Co catalyst with 4Ni-1Co loading was conducted for 12 h in identical conditions, and results revealed a stable activity with conversions equal to 3 h of reaction. Coke suppression during DRM reaction was attributed to microsphere structure, Co presence and SiC formation. SiC formation was introduced as a unique situation emanated as a result of the reaction between SiO2 and C.