2010 Spring Symposium
Dustin W. Fickel and Raul F. Lobo
*Center for Catalytic Science and Technology
Department of Chemical Engineering
University of Delaware
Newark, Delaware 19716
Abstract — Nitrogen oxides (NOx) are a major atmospheric pollutant produced through the combustion of fossil fuels in internal combustion engines. Copper-exchanged zeolites are promising as selective catalytic reduction catalysts for the direct conversion of NO into N2 and O2, and recent reports have shown the enhanced performance of Cu-CHA catalysts over other zeolite frameworks in the NO decomposition of exhaust gas streams.
In the present study, Rietveld refinement of variable-temperature XRD synchrotron data obtained for Cu-SSZ-13 and Cu-SSZ-16 is used to investigate the location of copper cations in the zeolite pores and the effect of temperature on these sites and on framework stability. The XRD patterns show that the thermal stability of SSZ-13 is increased significantly when copper is exchanged into the framework compared with the acid form of the zeolite, H-SSZ-13. Cu-SSZ-13 is also more thermally stable than Cu-SSZ-16. From the refined diffraction patterns, the atomic positions of atoms, copper locations and occupancies, and thermal displacement parameters were determined as a function of temperature for both zeolites. Copper is found in the cages coordinated to three oxygen atoms of the six-membered rings. This study also shows the enhanced performance of copper exchanged small-pore zeolites towards the selective catalytic reduction of nitric oxide compared to Cu-ZSM-5 after hydrothermally treating the zeolites.
* Fickel, D.W., Lobo, R.F., Copper Location Study of Cu-SSZ-13 and Cu-SSZ-16 Variable Temperature XRD Rietfeld Refinement, J. Phys. Chem. C, DOI: 10.1021/jp9105025.