| AVS 58th Annual International Symposium and Exhibition | |
| Surface Science Division | Tuesday Sessions |
| Session SS1-TuM |
| Session: | Chemisorption & Surface Reactions |
| Presenter: | Irinder Chopra, University of Texas at Dallas |
| Authors: | I. Chopra, University of Texas at Dallas S. Chaudhuri, Washington State University J.F. Veyan, University of Texas at Dallas Y.J. Chabal, University of Texas at Dallas |
| Correspondent: | Click to Email |
There has been an ongoing quest to find cheaper hydrogen activation routes based on aluminum. Despite theoretical suggestions1,2 it has been difficult to obtain unambiguous experimental evidence for such catalytic activity towards hydrogen activation.
We demonstrate here that aluminum doped with very small amounts of Ti can activate molecular hydrogen at temperatures as low as 90K. The method is based on the ability to introduce a high flux of molecular hydrogen seeded with a guest molecule to probe the catalytic activity and H2 dissociation. Once dissociated, hydrogen forms a complex with adsorbed CO (CO-H), characterized by a substantially and uniquely blue-shifted CO internal frequency. This complex is metastable, and is removed at a temperature (115K). We find that CO does not adsorb even weakly on H-covered Al, and use this finding to clearly show that, once dissociated, hydrogen diffuses away from the catalytic site onto Al sites (i.e. spills over). We use this new method to determine the dependence of the catalytic activity of aluminum surfaces on Ti coverage. Finally we show that the complex with activated hydrogen leads to further reactions at remarkably low temperatures (115K), such as formation of formyl (HCO), formaldehyde (HCHO) or methanol. These results provide the first direct evidence that Ti-doped Al can perform the quintessential first step of molecular hydrogen activation under nearly barrier-less conditions, thereby challenging the monopoly of noble metals in hydrogen activation.3
References:
[1] Chaudhuri, S. & Muckerman, J. T. First-principles study of Ti-catalyzed hydrogen chemisorption on an Al surface: A critical first step for reversible hydrogen storage in NaAlH4. Journal of Physical Chemistry B 109, 6952-6957 (2005).
[2]Chaudhuri, S., Graetz, J., Ignatov, A., Reilly, J. J. & Muckerman, J. T. Understanding the role of Ti in reversible hydrogen storage as sodium alanate: A combined experimental and density functional theoretical approach. , 11404-11415 (2006). B. Author, Nano. Bio. Info. Sci. 001, 1234 (3001).
[3]Chopra, I. S., Chaudhuri, S., Veyan, J.-F., and Chabal, Y. J., Nature materials ( submitted ) 2011.