Simulation of the adsorption and transport of CO2 on faujasite surfaces

We have investigated the effect of surfaces on the adsorption and transport of CO₂ with faujasite (FAU) using molecular dynamics. We modeled the {111}, {011}, and {100} surfaces of FAU. The {011} and {100} surfaces have incomplete sodalite cages, which adsorb CO₂ more favorably than the most stable {111} surface where the sodalite cages are intact. The surfaces of siliceous, sodium, and potassium FAU were modeled to compare the effect of zeolite composition. The results show that CO₂ diffusion through the surface is intermediate between diffusion in the zeolite and in bulk CO ₂ above the surface. In siliceous FAU the diffusion of bulk CO ₂ is reduced by 42% in the surface region and 61% in the zeolite. CO₂ diffusion is reduced by up to 83% inside aluminosilicate zeolites compared to siliceous. However, the surface adsorption of CO₂ is more affected by the surface structure than the composition, and at the surface there are dense layers of adsorbed CO₂ indicating sites of enhanced adsorption with reduced diffusion across them, particularly associated with the incomplete sodalite cages. Thus, we suggest that spherical particles with these surface sites are likely to be more effective sorbents than {111} faceted particles.