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 CO2 above the surface. In siliceous FAU the diffusion of bulk CO2 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.