Surface hydroxyl groups configurations

Figure 4.3 Different configurations of surface hydroxyl groups produce different, atomically dispersed surface bound metal species.

The model of Knozinger and Ratnasamy [60] is widely accepted as the most comprehensive way to rationalize the reactivity of the Al-OH groups on the alumina surface. This empirical model proposes that y-Al203 has a defective spinel structure, whose (111), (110) and (100) faces are covered by hydroxyl groups. Five configurations for the hydroxyl groups can be present (Scheme 11.3). 

Perform calculations similar to Exercise 4, but for the adsorption of hydroxyl groups, OH, on Pt(lll). What tilt angle does the OH bond form with the surface normal in its preferred adsorption configuration What numerical evidence can you provide that your calculations adequately explored the possible tilt angles ... 

Figures 12a and 12b illustrate the ESR spectra at —180°C and 25°C, respectively, of Nb(7r-allyl)4 after reaction with Manosil VN3 previously dried at 200°C. Figure 12b is complex and shows a mixture of at least two species present in the system. The major peaks are present in the system. The major peaks are also present in the frozen solution spectrum (Figure 10a) indicating that they arise from a rigidly held surface species. This species arises from the reaction of Nb(7r-allyl)4 with two adjacent hydroxyl groups and is therefore the double oxide bridge configuration (Reaction 3). Upon further addition of Nb(7r-allyl)4 to the silica, the pseudo isotropic spectrum (Figure lib) becomes more evident. This suggests that Nb(7r-allyl)4 reacts preferentially with the paired hydroxyl groups, an observation in accord with the literature (63).

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