Boron in Functional Materials: from clusters and catalytic surfaces to ultra-hard alloys

DIPC Seminars

Prof. Anastassia Alexandrova, Department of Chemistry and Biochemistry, University of California, Los Angeles (U.C.L.A.) and California NanoSystems Institute
Donostia International Physics Center
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Boron in Functional Materials:  from clusters and catalytic surfaces to ultra-hard alloys **Abstract:** This talk aims to convince you that metal-boron bonds are most unusual and versatile that the Periodic Table has to offer. Boron being a metalloid, can be covalent and metallic, cationic, anionic, and neutral, and flux from one face to another, when bound to metals in equilibrium and during vibrational motion. As a result, many exciting properties arise. I will show how boration can promote selectivity of metal surface catalysts for Fischer-Tropsch synthesis,1 and Pt cluster-based catalyst for dehydrogenation.2,3 This was first predicted by theory, on the basis of understanding the chemical bonding in these surfaces and clusters, and then realized experimentally. Metal-boron bonding also explains the hardness of recently discovered ultra-hard borides.4 The materials are highly valuable, because they free of these limitations of the hardest materials known, diamond and cubic boron nitride, such as high price and complications with processing. However, as we will show, the previously proposed mechanism of their hardness was incomplete. The electronic structure insight shows that M-B bonds and their promiscuous nature explain such properties as anisotropic response to stress in WB,5 and the mechanism of mixed valency in the topological Kondo insulator, SmB6, (which has been an enigma since the 60s).6 Finally, our pursuit led us to find a new class of possible 2D materials, which are metallic and in some cases magnetic.7 This is a theory talk, but the parallel experimental effort will be presented too. ** ** **References:** 1\. Nandula, Trinh, Saeys, Alexandrova, **2015** , _Angew Chem, 54,_ 5312\. 2\. Dadras, Jimenez-Izal, Alexandrova, **2015** , _ACS Catal_., _5_ , 5719-5727 ** __** 3\. Ha, Baxer, Anderson, Alexandrova, **2016** , in preparation. 4\. Cumberland, R. W.; Weinberger, M. B.; Gilman, J. J.; Clark, S. M.; Tolbert, S. H.; Kaner, R. B. _J. Am. Chem. Soc._ **2005** , _127_ , 7264-7265. Chung, H.-Y.; Weinberger, M. B.; Levine, J. B.; Kavner, A.; Yang, J.-M.; Tolbert, S. H.; Kaner, R. B. _Science_ , **2007** , _316_ , 436-439. 5\. Robinson, Tolber, Kaner, Alexandrova, **2016** , in preparation. 6\. Robinson, Zhang, McQeen, Bowen, Alexandrova, **2016** , under review in _PNAS_. 7\. Jimenez-Izal, Saeys, Alexandrova, **2016** , _JPC C, 120,_ DOI: 10.1021/acs.jpca.6b07612 __