CO 2 ‐Catalyzed Surface Area and Porosity Changes in High‐Surface‐Area CaO Aggregates

The changes in surface area and mesoporosity in aggregates of ∼0.01 μm cross‐section CaO particles when heated in CO 2 at 686°C were determined from N 2 adsorption isotherms. Initially, the surface area decreases rapidly with little change in porosity. When the surface area has decreased below ∼90 m 2 /g, surface area and porosity variations become consistent with expectations for coarsening by grain‐boundary or bulk diffusion. The initial rapid decrease in surface area must result from CO 2 ‐catalyzed surface diffusion, but the data suggest that surface diffusion is not rate‐limiting. The rate‐limiting step may be reaction of CO 2 to form surface CO 3 2‐ ions or decomposition of these ions to O 2‐ ions and CO 2 gas.