Periodic Hybrid DFT Approach (Including Dispersion) to MgCl2‑Supported Ziegler–Natta Catalysts. 2. Model Electron Donor Adsorption on MgCl2 Crystal Surfaces

• Published in: Journal of physical chemistry. C Vol. 117; no. 46; pp. 24345 - 24353
• Main Authors: Capone, Fabio, Rongo, Luca, D’Amore, Maddalena, Budzelaar, Peter H. M, Busico, Vincenzo
• Format: Journal Article
• Language: English
• Published: Columbus, OH American Chemical Society 21-11-2013
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Electron states; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronic transport phenomena in thin films and low-dimensional structures; Exact sciences and technology; Methods of electronic structure calculations; Physics; Solid surfaces and solid-solid interfaces; Structure and morphology; thickness; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thin film structure and morphology; Silanes; Ziegler Natta catalyst; Dispersions; Coverage rate; Crystallographic plane; Supported catalyst; Ammonia; Adsorption; Binding mode; Density functional method; Donor center; Crystal faces; Electron donor
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp406977h

The adsorption of small probe molecules (H2O, NH3 and EtOH) and the small model silane Me2Si(OMe)2 on (104) and (110) surfaces of α-MgCl2 have been studied using periodic DFT calculations including a classical correction (of the type f(R)/R6) for dispersion. The results reveal that donors strongly stabilize both crystal surfaces relative to the bulk solid. Moreover, coordination of two donor molecules to the four-coordinate exposed Mg atom of MgCl2 (110) causes this surface to become preferred over MgCl2 (104) surface with only a single donor per exposed Mg. However, coverage also plays an important role. The model silane preferentially adsorbs in bidentate mode on MgCl2 (110), provided that coverage is 0.5 or lower; at full coverage, there is not enough space for such an arrangement, and only a monodentate binding mode is obtained. Such coverage effects should be even more pronounced for the bulkier silanes used as external donors in real MgCl2-supported Ziegler–Natta systems, as tailored experiments seem to confirm.