Theoretical Study of the Reaction between HF Molecules and Hydroxyl Layers of Mg(OH)₂

Abstract

The reaction of HF molecules with brucite, Mg(OH)(2), leading to the formation of Mg(OH)(2-x)F(x), was theoretically studied by ab initio density functional theory (DFT) with periodic boundary conditions. We proposed as mechanism for this reaction four elementary steps: adsorption of the HF molecule, OH(-) liberation from brucite as a water molecule, desorption of the newly formed H(2)O, and rearrangement of the F(-) anion into a hydroxyl position. For the Mg(OH)(2-x)F(x) formation, with x = 1/9, the final product, outcome from an initially adsorbed HF molecule, we computed the Helmholtz free energy variation DeltaF = -23 kcal/mol. The calculated frequency for the most intense infrared band, a Mg-F stretching mode, was 342 cm(-1). Two transition states, corresponding to the hydroxyl reacting with a proton forming a water molecule and migration of a fluoride anion into a hydroxyl vacancy, were computed. The calculated reaction barriers indicate that the reaction between Mg(OH)(2) layers and HF molecules is slow and irreversible.

How to find an optimum cluster size through topological site properties: MoSxmodel clusters

“…Under such circumstances, the only alternative is to use periodic boundary conditions-see a recent successful application of this approach for a reaction mechanism in a previous work. 26 There are some recent topological investigations that have some resemblance with this work. Krebs et al 27 studied the adsorption modes of toluene and 2-methylthiophene on a Co(Ni)MoS 2 catalyst and used the topological analysis electron localization function to rationalize the process.…”

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“…In this work ab initio calculations were done to provide a clear and more detailed picture of the arrangements of TA in the interlayer region and the interaction between the anion and the hydroxyl layers as the charge layer increases. This work is grounded in previous theoretical works based on DFT of layered materials produced recently (Costa et al, 2008), (Costa et al, 2010), (Costa et al, 2011), (Costa et al, 2012a), (Costa et al, 2012b), (Vaiss et al, 2009), (Vaiss & I., B. J., Leitão, A. A., 2011), (Vaiss et al, 2013).…”

Theoretical study of the anion exchange properties and the thermal decomposition of Zn5(OH)8(NO3)22H2O and Zn5(OH)8(NO3)22NH3

“…The vibrational data were also used to calculate both the contribution of the lattice thermal vibration to the total energy and the zero point energy (ZPE) as shown in our previous work, Eqs. (1) and (2) (Vaiss et al, 2009;Costa et al, 2010;Vaiss et al, 2011;Tavares et al, 2014). The ions and H 2 O and NH 3 molecules in gas state were treated according to the formalism described in our previous works, Eqs.…”

“…The ions and H 2 O and NH 3 molecules in gas state were treated according to the formalism described in our previous works, Eqs. (3) and (4) (Vaiss et al, 2009;Costa et al, 2010;Vaiss et al, 2011;Tavares et al, 2014).…”

“…It was observed that the water molecule stabilizes the compound, but its removal does not lead to any modification of the layer structure (Tavares et al, 2014). We have used the same methodology to study the structures and properties of other layered compounds, such as the Brucite-like compounds and layered double hydroxides (Costa et al, 2008;Vaiss et al, 2009;Costa et al, 2010Costa et al, , 2011Vaiss et al, 2011;Costa et al, 2012a,b;Vaiss et al, 2013). The works with hydrotalcite-like compounds have shown that there are notorious structural changes in the dehydration process of layered double hydroxides containing Cl − and CO 3 2− counteranions (Costa et al, 2011).…”