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

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 B-5-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.