Ferrara, Italy
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Credendino R.,University of Salerno | Pater J.T.M.,tta Research Center | Correa A.,University of Salerno | Correa A.,Dutch Polymer Institute | And 3 more authors.
Journal of Physical Chemistry C | Year: 2011

In this work, we report on the structure and formation energy of uncovered MgCl2 crystallites of different shapes (hexagonal and square), sizes (up to crystallites composed of 157 MgCl2 units), and edges (crystallites presenting the (104) and (110) edges). Both uncovered crystallites and crystallites covered by dimethyl ether were considered. Our results indicate that the formation energy of uncovered crystallites, irrespective of shape, size, and edges, linearly depends on the density of vacancies (measured as the ratio between the number of Mg vacancies and the number of MgCl 2 units in the crystallite) and that larger crystallites that present (104) edges are favored. In the case of crystallites completely covered by dimethyl ether, our results indicate that the formation energy of crystallites, again irrespective of shape, size, and edges, inversely depends on the dimethyl ether/Mg ratio. As opposed to uncovered crystallites, in the presence of dimethyl ether, smaller crystallites presenting (110) edges are favored. The knowledge acquired with both uncovered and dimethyl ether-covered crystallites was used to achieve insight into the behavior of carbon monoxide-covered crystallites by performing calculations on a limited number of small crystallites. © 2011 American Chemical Society.


Credendino R.,King Abdullah University of Science and Technology | Liguori D.,tta Research Center | Fan Z.,Zhejiang University | Morini G.,tta Research Center | Cavallo L.,King Abdullah University of Science and Technology
ACS Catalysis | Year: 2015

We propose a model for MgCl2-supported Ziegler-Natta catalysts, which is capable to reconcile the discrepancies emerging in the last 20 years, in which attempts have been made to rationalize experimental data by molecular models. We show that step defects on the thermodynamically more stable (104) facet of MgCl2 can lead to sites for strong TiCl4 adsorption. The corresponding Ti-active site is stereoeselective, and its stereoselectivity can be enhanced by coordination of Al-alkyls or Lewis bases in the close proximity. The surface energy of the step defected (104) MgCl2 facet is clearly lower than that of the well accepted (110) facet. © 2015 American Chemical Society.


Credendino R.,King Abdullah University of Science and Technology | Pater J.T.M.,tta Research Center | Liguori D.,tta Research Center | Morini G.,tta Research Center | And 2 more authors.
Journal of Physical Chemistry C | Year: 2012

In this work, we present a systematic DFT analysis of the effect of surface coverage on the coordination properties of alkoxysilanes to the (104) and (110) surfaces of MgCl 2. Furthermore, we investigated several possible migration pathways for alkoxysilane migration on the same surfaces. Our study clearly shows that complete coverage of the Mg vacancies on the surface by coordinating alkoxysilanes is hampered by steric repulsion between vicinally coordinated donor molecules. Our study clearly indicates that alkoxysilane migration between different MgCl 2 monolayers on the (104) and (110) surfaces requires donor dissociation. The same holds for alkoxysilane migration on a single (110) MgCl 2 monolayer. However, in the case of the (104) surface we found a very low energy pathway for alkoxysilane migration along the same monolayer. © 2012 American Chemical Society.


Credendino R.,King Abdullah University of Science and Technology | Liguori D.,tta Research Center | Morini G.,tta Research Center | Cavallo L.,King Abdullah University of Science and Technology
Journal of Physical Chemistry C | Year: 2014

In this work we present a systematic DFT analysis of the effect of surface coverage on the coordination properties of two industrial Lewis bases, dimethyl phthalate and 9,9-bis(methoxymethyl)fluorene, to the (104) and (110) surfaces of MgCl2. Further, we investigated several possible migration pathways for the migration of the Lewis bases on the same MgCl2 monolayer. Our study clearly shows that complete coverage of the Mg vacancies on the surface by coordinating dimethyl phthalate or 9,9-bis(methoxymethyl)fluorene is hampered by steric repulsion between vicinally coordinated donor molecules. Further, our study clearly indicates that both dimethyl phthalate and 9,9-bis(methoxymethyl) fluorene migration on the same MgCl2 monolayer on the (104) and (110) surfaces basically requires donor dissociation. © 2014 American Chemical Society.

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