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

Abstract

The sodium cation is well known as an efficient poison of gamma-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 gamma-alumina surfaces. On realistic models of hydroxylated gamma-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 gamma-alumina, the sodium cation is found in a solvated state within an inner solvation sphere complex. Its coordination sphere is constituted by O-mu(2), O-mu(3) and HO-mu(1) surface groups. The stretching frequency of these HO-mu(1) groups is shifted, leading to the appearance of a new band predicted and observed at about 3754 cm(-1) on the IR spectrum.

Na-β-Al2O3 stabilized Fe2O3 oxygen carriers for chemical looping water splitting: correlating structure with redox stability

“…These Na K-edge XANES features of Na-γ-Al 2 O 3 are assigned to Na ions dispersed on the surface of γ-Al 2 O 3 (in a solvated state). 55 Thus, using Na K-edge XANES we can distinguish between two different Na environments: (i) a Na-β-Al 2 O 3 like environment, i.e. Na that is located between layers of γ-Al 2 O 3 layers (ordered) and (ii) a Na-γ-Al 2 O 3 like environment in which Na is located on the surface of γ-Al 2 O 3 (surface Na + ).…”

Insights into the Geometry, Stability and Vibrational Properties of OH Groups on γ-Al2O3, TiO2-Anatase and MgO from DFT Calculations

“…c-Al 2 O 3 , [18,19] TiO 2 -anatase [20,21] and MgO [22] have recently been studied at the same level of theory (Density Functional Theory, periodic boundary conditions and PW91 functional). The models proposed have been extensively compared to experiments (TPD, [22,23] IR, [19,[24][25][26][27] 1 H NMR, [28] photoluminescence [29,30]) and used to describe the interaction of the support with active phases (metals, [12,13,31,32] sulfides, [32][33][34] organometallic complexes [35]). …”

Na-β-Al2O3 stabilized Fe2O3 oxygen carriers for chemical looping water splitting: correlating structure with redox stability

“…the reference material prepared by wet impregnation of a solution of NaNO3 onto γ-Al2O3) shows features different to Naβ-Al2O3 and are labelled I (1075 eV) and J (1080 eV) (Figure S3). These Na K-edge XANES features of Na-γ-Al2O3 are assigned to Na ions dispersed on the surface of γ-Al2O3 (in a solvated state) 51 . Thus, using Na K-edge XANES we can distinguish between two different Na environments: (i) a Na-β-Al2O3 like environment, i.e.…”