Davidson School of Chemical Engineering
The selective catalytic reduction (SCR) of nitrogen oxides (NOx) with ammonia using Cu-exchanged zeolites is a pollution abatement technology used in automotive emissions control. At low temperatures (<523 K), copper cations become solvated by ammonia reactants to form homogeneous-like copper coordination complexes that are bonded ionically to anionic aluminum centers in zeolite lattices. The ionic tethering of active metal sites to the support confers localized mobility, providing a mechanism for the dynamic and reversible interconversion of mononuclear and multinuclear sites, blurring boundaries between heterogeneous and homogeneous catalysis. We will discuss our recent work to study this phenomenon in zeolites of different crystal topology and Al density and arrangement, to determine how these material properties influence Cu ion mobility and NOx SCR kinetics. We use a combined experimental and computational approach focused on operando interrogation of catalysts under widely varying operating conditions, well outside those typical of commercial operation. We show that the effects of Cu ion mobility are preeminent for low-temperature NOx SCR reactivity, leading to dramatic differences in performance among Cu-zeolites of different bulk and atomic structure.
Raj Gounder is the Larry and Virginia Faith Professor of Chemical Engineering at Purdue University. He received his BS in Chemical Engineering with a double major in Chemistry from Wisconsin in 2006, his PhD in Chemical Engineering from UC Berkeley in 2011, and a postdoctoral appointment at Caltech in 2013. His research group studies catalysis for applications in energy production and environmental protection, including automotive pollution abatement and converting carbon feedstocks such as shale gas to fuels and chemicals. His research focuses on elucidating the kinetic and mechanistic details of catalytic reactions, synthesizing zeolites with tailored site and surface properties, and developing methods to characterize and titrate active sites in catalytic materials. His research has been recognized by the NSF and DOE Early Career Awards, the ACS CATL Early Career Award, and the Sloan Research Fellowship in Chemistry. His teaching has been recognized by the Shreve (undergraduate) and Wankat (graduate) Awards for Outstanding Teaching in Chemical Engineering at Purdue, and his mentoring by the Outstanding Mentoring Award of Engineering Graduate Students at Purdue. He is an Associate Editor of Science Advances and Catalysis Reviews, and on the Editorial Advisory Board of ACS Catalysis and Reaction Chemistry & Engineering.