PNNL

Abstract

The fast NH3-SCR kinetics are studied on Cu/SSZ-13 with different Cu loadings, under reaction conditions (temperature and space velocity) where both steady-state and differential NOx conversions are readily achieved. Cu loading is found to greatly influence low-temperature NOx turnover rates, however not to substantially affect apparent activation energies. The high reaction apparent activation energies (~160 kJ/mol) suggest that the rate-limiting kinetics for fast SCR involve the participation of NH4NO3, an intermediate that is of considerable stability in small pore zeolites. The energetically demanding NH4NO3 + NO reactions make low-temperature fast SCR much slower than standard SCR over Cu-exchanged small pore zeolite catalysts, in drastic contrast to vanadium and medium/large pore based zeolite SCR catalysts. The authors gratefully acknowledge the US Department of Energy (DOE), Energy Efficiency and Renewable Energy, Vehicle Technologies Office for the support of this work. The research described in this paper was performed in the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle.