Effect of support morphology on the ammonia synthesis activity of Ru/CeO2-based catalysts

Abstract

We investigate the effect of the support morphology on ammonia (NH₃) synthesis activity of Ru/CeO₂-based catalysts using supports derived from various CeO₂ materials under different treatment temperatures with different SiO₂/ZrO₂ additions. These supports are classified by peak pore size into three pore structure types: small (3–4 nm), medium (7–20 nm), and large (50–70 nm). The medium-type supports show the highest specific surface area (SSA), which increases with SiO₂/ZrO₂ addition. The Ru dispersion on each support, regardless of its type and composition, is determined from its SSA. The NH₃-synthesis activity of catalysts at 0.1 MPa and a space velocity (SV) of 36000 h⁻¹ exhibits a volcanic trend with respect to the Ru dispersion. This is explained by the fraction of active B₅-type sites generated. At SVs >72000 h⁻¹, the activity of catalysts with peak pore size <8 nm is less than the above volcanic trend, possibly owing to increased diffusion resistance in the pore.