caa a22 4500 606173811 CHVBK 20210128100735.0 cr unu---uuuuu 210128e20150501xx s 000 0 eng 10.1007/s11244-015-0387-8 doi (NATIONALLICENCE)springer-10.1007/s11244-015-0387-8 The Dynamic Nature of Brønsted Acid Sites in Cu-Zeolites During NOx Selective Catalytic Reduction: Quantification by Gas-Phase Ammonia Titration [Elektronische Daten] [John Di Iorio, Shane Bates, Anuj Verma, W. Delgass, Fabio Ribeiro, Jeffrey Miller, Rajamani Gounder] Brønsted acid sites on Cu-exchanged zeolites can be titrated selectively using gaseous ammonia when NH3 saturation steps are followed by protocols that remove Lewis acid-bound and physisorbed NH3, such as purging in flowing wet helium at 433K. NH3 titrates all H+ sites on small-pore chabazite zeolites (SSZ-13) and leads to the complete disappearance of infrared stretches for Brønsted acidic OH groups after saturation (433K), in contrast with larger n-propylamine titrants that access only a small fraction (<0.25) of H+ sites on SSZ-13 under conditions sufficient to titrate all H+ sites on medium-pore ZSM-5 zeolites (323K, 2h). NH3 titration of the residual H+ sites present in Cu-exchanged SSZ-13 samples (Si/Al=4.5, Cu/Al=0-0.20) after oxidative treatments detects two fewer H+ sites per exchanged Cu2+ ion, as expected to maintain framework charge neutrality. NH3 titrants detect only one fewer H+ site (per Cu) after Cu-SSZ-13 samples undergo a reductive treatment in flowing NO and NH3 (473K), however, indicating that each Cu2+ cation reduces to form a Cu+ and H+ site pair. In the context of low temperature (473K) selective catalytic reduction (SCR) on high aluminum Cu-SSZ-13, we discuss the different mechanistic roles of residual H+ sites that remain after Cu2+ exchange, whose primary function appears to be NH3 storage, and of proximal H+ sites that are generated in situ upon Cu2+ reduction, whose role is to stabilize reactive NH4 + intermediates involved in the standard SCR oxidation half-cycle. We highlight how gaseous NH3 titrants can selectively count H+ sites on small-pore, Cu-exchanged zeolites and, in doing so, enable probing the dynamic nature of active sites and catalytic surfaces during SCR redox cycles. Springer Science+Business Media New York, 2015 Ammonia nationallicence Brønsted acid site nationallicence Copper-exchanged zeolites nationallicence n -Propylamine nationallicence Selective catalytic reduction nationallicence Titration nationallicence Di Iorio John School of Chemical Engineering, Purdue University, 480 Stadium Mall Drive, 47907, West Lafayette, IN, USA aut Bates Shane School of Chemical Engineering, Purdue University, 480 Stadium Mall Drive, 47907, West Lafayette, IN, USA aut Verma Anuj School of Chemical Engineering, Purdue University, 480 Stadium Mall Drive, 47907, West Lafayette, IN, USA aut Delgass W. School of Chemical Engineering, Purdue University, 480 Stadium Mall Drive, 47907, West Lafayette, IN, USA aut Ribeiro Fabio School of Chemical Engineering, Purdue University, 480 Stadium Mall Drive, 47907, West Lafayette, IN, USA aut Miller Jeffrey School of Chemical Engineering, Purdue University, 480 Stadium Mall Drive, 47907, West Lafayette, IN, USA aut Gounder Rajamani School of Chemical Engineering, Purdue University, 480 Stadium Mall Drive, 47907, West Lafayette, IN, USA aut Topics in Catalysis Springer US; http://www.springer-ny.com 58/7-9(2015-05-01), 424-434 1022-5528 58:7-9<424 2015 58 11244 https://doi.org/10.1007/s11244-015-0387-8 text/html Onlinezugriff via DOI BK010053 XK010053 XK010000 Metadata rights reserved Springer special CC-BY-NC licence nationallicence 1 research-article jats NATIONALLICENCE NATIONALLICENCE NL-springer NATIONALLICENCE 856 40 https://doi.org/10.1007/s11244-015-0387-8 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Di Iorio John School of Chemical Engineering, Purdue University, 480 Stadium Mall Drive, 47907, West Lafayette, IN, USA aut NATIONALLICENCE 700 1- Bates Shane School of Chemical Engineering, Purdue University, 480 Stadium Mall Drive, 47907, West Lafayette, IN, USA aut NATIONALLICENCE 700 1- Verma Anuj School of Chemical Engineering, Purdue University, 480 Stadium Mall Drive, 47907, West Lafayette, IN, USA aut NATIONALLICENCE 700 1- Delgass W. School of Chemical Engineering, Purdue University, 480 Stadium Mall Drive, 47907, West Lafayette, IN, USA aut NATIONALLICENCE 700 1- Ribeiro Fabio School of Chemical Engineering, Purdue University, 480 Stadium Mall Drive, 47907, West Lafayette, IN, USA aut NATIONALLICENCE 700 1- Miller Jeffrey School of Chemical Engineering, Purdue University, 480 Stadium Mall Drive, 47907, West Lafayette, IN, USA aut NATIONALLICENCE 700 1- Gounder Rajamani School of Chemical Engineering, Purdue University, 480 Stadium Mall Drive, 47907, West Lafayette, IN, USA aut NATIONALLICENCE 773 0- Topics in Catalysis Springer US; http://www.springer-ny.com 58/7-9(2015-05-01), 424-434 1022-5528 58:7-9<424 2015 58 11244