Adsorption of nitrogen on rutile (110): Monte Carlo computer simulations

Grand canonical and canonical ensemble Monte Carlo computer simulations of the adsorption of N-2 on the (110) face of rutile at 77 K are reported. A n ovel ab initio adsorbate-adsorbent interaction potential is employed in con junction with the X1 nitrogen-nitrogen potential to investigate the adsorpt ion mechanism. It is demonstrated that at low pressures (1 Ton and below) t he Ti adsorption sites within the depressed rows of oxides on the rutile (1 10) face (denoted by A) are completely occupied by nitrogen molecules in en d-on orientations with slight alternating tilts perpendicular to the row ax is that are produced by repulsive lateral interactions. At higher pressures , adsorption on rows of exposed oxides (denoted by B) commences, typically with a side-an orientation of the N-2 molecules. The calculated isotherm of adsorption exhibits type II: behavior according to the Brunauer-Deming-Dem ing-Teller classification, in agreement with experimental findings. Althoug h the experimental isotherms ase often evaluated using the Brunauer-Emmett- Teller adsorption model, our simulations indicate that the assumptions of t his model are not fulfilled. The implications of these discrepancies and th eir influence on surface area determinations are discussed.