Professor, Davidson School of Chemical Engineering
Cu/SSZ-13 zeolites are used commercially in mobile applica ons for the selec ve reduc on of NOx with ammonia. Our data suggest that the cataly c cycle is a redox one involving Cu(I) and Cu(II) spe- cies. During prepara on, the Cu(II) species are the most stable and reside preferen ally on six- member rings containing two aluminum sites. The Cu(II) ions rst populate 2Al sites before the oth- er remaining unpaired sites with 1Al are populated, Cu(II)OH. These sites could be counted ex situ through vibra onal and X-ray absorp on spectroscopies (XAS) and chemical tra ons. In spite of an apparent chemical di erence, the two sites had similar standard SCR reac on turnover rates, appar- ent ac va on energies and apparent reac on orders at SCR condi ons, even on zeolite frameworks other than SSZ13. Operando XAS experiments showed similar Cu(I) – Cu(II) frac ons at steady state, demonstra ng their similarity for SCR redox chemistry. Finally, it is shown that two NH3-solvated Cu(I) ions tethered to the zeolite framework migrate to form a dimer that mediated by O2 is oxidized from Cu(I) to Cu(II), react with NO and break apart to close the cataly c cycle. This study also illus- trates the necessity of a collabora on among experts in synthesis, characteriza on, kine cs and the- ory for a chance to understand the cataly c cycle.
Fabio H. Ribeiro is currently the R. Norris and Eleanor Shreve Professor of Chemical Engineering and Director of the National Science Foundation Engineering Research Center on the Innovative and Strategic Transformation of Alkane Resources (CISTAR) at the Davidson School of Chemical Engineering, Purdue University. He received his Ph.D. degree from Stanford University in 1989, worked for Catalytica, Inc. in Mountain View, California, held a post-doctoral fellowship at the University of California – Berkeley, and was on the Worcester Polytechnic Institute faculty before joining Purdue University in August 2003. His research interests are centered on the kinetics of heterogeneous catalytic reactions and catalyst characterization under reaction conditions. He has over 140 publications in scholarly journals. He was Chair for the American Institute of Chemical Engineer’s Catalysis and Reaction Engineering Division (2010) and is editor for Journal of Catalysis. His honors include the NSF CAREER award (1997-2002), the Excellence in Catalysis Award from the Catalysis Society of Metropolitan New York (2005), the Henry J. Albert Award from the International Precious Metals Institute (2012), the Purdue College of Engineering Faculty Award of Excellence on Research (2014) and the Herman Pines Award from The Chicago Catalysis Club (2015).