AmericanChemicalSociety.com

The main focus of this research is to understand the role of specific surface reactive sites in addition and condensation reactions catalyzed by silicon nitride. We have prepared the reactive sites postulated to play a role in catalysis by exposing a clean Si(100)-2x1 surface to ammonia in ultra-high vacuum and briefly annealing this surface to a predetermined temperature. This approach yields almost exclusively a model surface with -NH₂ functional groups if room temperature is used, =NH covered surface after a brief anneal to approximately 500 K, and nearly exclusively =N- surface sites after a brief heating to 800K. These sites should be effective to a very different extent in catalyzing alkene isomerization, addition reactions and fuel reforming. These highly basic structures have previously been successfully tested for Knoevenagel condensation of benzylazide and malonitrile and for Michael addition of malononitrile to acrylonitrile, test reactions to characterize the catalytic activity of materials. We have successfully and reproducibly prepared the test reactive sites according to the strategy previously published by our group. We have used a combination of multiple surface analytical techniques and Density Functional Theory calculations to determine the mechanism of interaction of a potential candidate for testing surface isomerization process, 2,3-dimethyl-2-butene with Si(100). We discovered that 2,3-dimethyl-2-butene is uniquely unreactive with respect to this surface compared to any other alkenes studied, unexpectedly opening a wide range of applications for this compound. In the meantime, we have successfully prepared a surface with a unique pattern created by co-adsorption of two different molecules with very different reactivities on silicon. This approach in the future will yield a molecular level control over model catalytic reactions. As the research progressed, it became apparent that a novel method of treating complex thermal desorption data is needed and we developed a multiple curve resolution strategy applied to thermal desorption traces. In addition, a set of model self-assembled monolayers with selective termination has been developed to test the reactivity of the functional groups in ambient conditions. 

Besides the specific results mentioned above, several general publications focused on surface reactivity and acknowledged the support of the donors of the American Chemical Society Petroleum Research Fund. Our most recent work suggests that the surface basicity can be analyzed computationally and the reactivity of functional groups attached to a variety of model and practical substrates can be predicted, keeping in mind that the reactivity of the functional group can be affected profoundly by the nature of the substrate. Currently, the reaction of benzylazide with various aminoterminated model surfaces is being investigated, compared to the primary amine-terminated self-assembled monolayers and will be a subject of further research and upcoming publications.

This research has helped training several graduate students. One student has been fully supported by this grant. He has successfully defended his PhD thesis and is currently teaching chemistry in an undergraduate institution. The research also involved two undergraduate students. Both of these students are female. One has proceeded to graduate school and the other is currently enrolled in the undergraduate program at the University of Delaware.