2014 Spring Symposium
Fabio H. Ribeiro*1, W. Nicholas Delgass1, William F. Schneider2, Jeffrey T. Miller3, Aleksey Yezerets4, Trunojoyo Anggara2, Christopher Paolucci2, Shane A. Bates1, Anuj Verma1, and Atish Parekh1
1School of Chemical Engineering, Purdue University, West Lafayette, Indiana 47907 (USA)
2Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, Indiana
3Argonne National Laboratory, Darien, IL 60439 (USA)
4Cummins Inc., Columbus, IN 47202 (USA)
Abstract – The Cu/SSZ-13 catalyst (CHA framework) is preferred for SCR applications because it shows both SCR performance and hydrothermal stability. In this work, the site requirements of the Standard SCR and NO oxidation reactions have been studied on Cu/SSZ-13. Based on an integrated experimental and modeling approach, the active site for the Standard SCR on Cu/SSZ-13 has been assigned to an isolated Cu ion located near the 6 member rings of SSZ-13, while NO oxidation required local Cu – O – Cu bonds in the 8 member cage of SSZ-13. The formation of local Cu – O – Cu bonds was a result of saturation of the number of favorable Al pairs near the 6 member ring to stabilize isolated Cu ions. The variation of the NO oxidation and the SCR rates of reaction with Cu/Al ratios was thus a catalytic consequence of different Cu ion configurations within SSZ-13. The working state of catalyst under SCR, moreover, was examined by Operando X – Ray Absorption Spectroscopy (XAS). Under reaction conditions, the Standard SCR involved a redox mechanism with both Cu(I) and Cu (II) species present. Further experiments using operando XAS to probe the redox cycle of Cu were carried out by removing the oxidizing half-reaction, which produced mostly the Cu(I) state, and then the reducing half reaction, which produced mostly the Cu(II) state. Thus, any mechanism of Standard SCR has to incorporate a redox cycle. In summary, the standard SCR on Cu-SSZ13 required isolated Cu ions to undergo a redox cycle near the 6 member ring of SSZ13.
Biography – Fabio H. Ribeiro is currently the R. Norris and Eleanor Shreve Professor of Chemical Engineering at the School of Chemical Engineering, Purdue University. He received his Ph.D. degree from Stanford University in 1989, 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 consist of the kinetics of heterogeneous catalytic reactions and catalyst characterization by in situ techniques. He was Chair for AIChE’s Catalysis and Reaction Engineering Division (2010) and is editor for Journal of Catalysis.