Department Seminar: Alexander Katz
Understanding How Environment Affects Catalysis on Surfaces
My talk will be devoted to elucidating how environment affects catalytic activity, within the context of (i) ligand effects brought about by coordination of an organic ligand on a metal surface, on a metal atom that is adjacent to a catalytically active metal atom, on a supported cluster catalyst; and (ii) how changing the support from an amorphous to a crystalline silicate can drastically alter catalytic activity of a grafted metal active site acting as a Lewis-acid catalyst, while keeping the inner-sphere coordination environment surrounding this metal center unchanged. In the first area, we rely on a tetrahedral Ir4 carbonyl cluster bound with three calixarene phosphine ligands, which protect the cluster against aggregation, as the simplest model of a multifaceted metal surface. Due to the robustness of the tetrairidium metal core, we can make changes to the ligand sphere in the basal plane, without altering the basic connectivity or any metal-metal bonds within the cluster. When supported on a non-interacting support, such as silica, we can use gas-phase reactions such as ethylene hydrogenation and hydrogen-deuterium exchange, in order to assess the kinetic consequences of ligand environments. Early work in this area was guided using infrared spectroscopic characterization and X-ray absorption spectroscopy, and placed the active site for both reactions alluded to above as the apical site. Building on this, we demonstrate the bonding of oxygen to this supported cluster via Raman spectroscopy, as well as the characterization techniques mentioned above, and investigate the repercussions of this bonding on catalysis. We also examine systematic synthetic replacement (characterized via NMR spectroscopy, ESI MS, and, when possible, single-crystal X-ray diffraction) of other, more electron withdrawing organic ligands for the original phosphines, on the basal plane. Our results demonstrate a pronounced organic ligand-effect for these simple probe reactions, which are central to understanding more complex reactions involving hydrogen transfer. In the second area, my research group has developed a grafted Ti on silica catalyst that is more ~5-fold more active on a per-Ti-site basis than the currently used industrial catalyst for epoxidation catalysis, when using an organic hydroperoxide as oxidant. Using tools of spectroscopy and molecular engineering, we investigate why this is so. Our results point to a unique outer-sphere effect that the silica surface has in this catalysis.
Alexander Katz is a world leader in the molecular design, synthesis, and characterization of active sites for catalysis and adsorption, as controlled by the structure of molecular organic-inorganic interfaces. Alex began his career proving the first example of molecular design and control of solid acid-base bifunctional catalysis, consisting of anchored amines on an oxide support, using spectroscopic probes to determine the structure of the catalyst active site. He invented the composition of matter consisting of grafted calixarenes on oxides. The latter has allowed unprecedented control of environment as enforced by a macrocyclic ligand in Lewis acid catalysts (e.g., open versus closed). He has more recently brought this molecular control of catalysis structure and function to the realm of metal clusters, where he was the first to provide a physical model of S sites – postulated to exist on the basis of kinetic evidence in hydrogen-transfer related reactions for over 75 years – which are catalytic sites on a metal surface that bond hydrogen non-competitively, even in the presence of olefin. More recent accomplishments include molecular design of zeolite delamination without amorphization, and sites for selective adsorption of cations, and sugars for limiting biomass-related separations. He has founded Berkeley Materials Solutions, which is commercializing Ti-containing delaminated-zeolite catalysts, as well separations enabled via selective molecular recognition. Alex was born in Minsk, Belarus and immigrated to the United States at age four with his family. Alex and his parents moved to Minnesota, where he grew up in and attended public schools, and graduated University of Minnesota as a Bachelor of Chemical Engineering, Cum Laude in 1992 and a research M.S. in Chemical Engineering with Prof. Michael D. Ward as advisor. It is at that time that he first became inspired by chemical engineering on the molecular level and controlling properties of functional materials via synthesis. He was awarded a Fannie and John Hertz Foundation Fellowship for doctoral studies in catalyst synthesis and characterization with Prof. Mark Davis at California Institute of Technology in 1994, and later, in 1998, undertook postdoctoral studies in supramolecular chemistry at Institut Le Bel in Strasbourg, France, with Prof. Mir Wais Hosseini, as a NSF International Awards Postdoctoral Fellow. Alex began a multidisciplinary research program as Assistant Professor of Chemical Engineering at UC Berkeley in 2000, and has since been promoted to the rank of Professor. He was a Technion-Fulbright Fellow visiting professor at the Wolfson Department of Chemical Engineering in Haifa, Israel in 2008-2009. The current list of students in academia who have been individually trained and mentored by Alex includes: 1) Justin Notestein (Northwestern); 2) Feng Wang (Dalian Inst of Chem Phys); 3) Isao Ogino (Hokkaido University); 4) Oz Gazit (Technion); 5) Cedric Chung (Academia Sinica); 6) Ron Runnebaum (UC Davis); (7) Michael Nigra (University of Utah). Alex is the recipient of Hellman Family and 3M Young Faculty Awards, and a Young Scientist Prize from IACS (International Association of Catalysis Societies). He has also been recognized with numerous departmental and best engineering professor on campus teaching awards at Berkeley.