Ab Initio Molecular Dynamics Study of the Dehydroxylation Reaction in a Smectite Model

作者：Munoz Santiburcio D; Kosa M; Hernandez Laguna A^*; Sainz Diaz C I; Parrinello M

来源：Journal of Physical Chemistry C, 2012, 116(22): 12203-12211.

DOI：10.1021/jp301366r

We have studied the dehydroxylation reaction in a smectite model, with the purpose of determining the influence of the octahedral layer composition and the possible role of the interlayer cations. Employing ab initio molecular dynamics and with the help of metadynamics for accelerating the reaction, we study the two possible mechanisms for the formation of the first water molecule. In the first mechanism, the migration of the proton across the octahedral vacancy takes place by means of a stable intermediate in which the proton is coordinated with an apical oxygen. The formation of this intermediate is not possible without a local deformation of the tetrahedral sheet, in which a Si-O basal bond is broken so that the Si coordinates with the O that releases the H, stabilizing its residual charge. In turn, the basal oxygen that loses the Si is stabilized by the nearest interlayer Na atoms. This tetrahedral deformation is permanent at this step of the reaction. In the second mechanism the proton migrates to the neighboring OH group in the same octahedral units. This takes place without reaction intermediates and it does not imply any permanent distortion in the structure, though it is observed that the environment of a tetrahedral Si spontaneously fluctuates between a tetrahedral and a ditrigonal bipyramidal arrangement.

• 出版日期2012-6-7