Quantum chemical and vibrational investigation of sodium exchanged γ-alumina surfaces

Abstract

The sodium cation is well known as an efficient poison of γ-alumina surface acidity. This poisoning effect has been revealed both by characterization methods and catalytic tests. In this work, we propose an accurate model of sodium exchanged γ-alumina surfaces. On realistic models of hydroxylated γ-alumina surfaces, the location of sodium cation is determined by the use of density functional theory (DFT) methods. For the (100) and (110) surfaces of γ-alumina, the sodium cation is found in a solvated state within an inner solvation sphere complex. Its coordination sphere is constituted by O–μ₂, O–μ₃ and HO–μ₁ surface groups. The stretching frequency of these HO–μ₁ groups is shifted, leading to the appearance of a new band predicted and observed at about 3754 cm⁻¹ on the IR spectrum.