Journal
IUCRJ
Volume 1, Issue -, Pages 382-386Publisher
INT UNION CRYSTALLOGRAPHY
DOI: 10.1107/S2052252514020181
Keywords
CHA zeolites; catalytic activity; location of Cu2+; synchrotron powder X-ray diffraction; Rietveld/maximum entropy method
Funding
- Villum Foundation
- Danish National Research Foundation [DNRF93]
- SINO Danish Center
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Accurate structural models of reaction centres in zeolite catalysts are a prerequisite for mechanistic studies and further improvements to the catalytic performance. The Rietveld/maximum entropy method is applied to synchrotron powder X-ray diffraction data on fully dehydrated CHA-type zeolites with and without loading of catalytically active Cu2+ for the selective catalytic reduction of NOx with NH3. The method identifies the known Cu2+ sites in the six-membered ring and a not previously observed site in the eight-membered ring. The sum of the refined Cu occupancies for these two sites matches the chemical analysis and thus all the Cu is accounted for. It is furthermore shown that approximately 80% of the Cu2+ is located in the new 8-ring site for an industrially relevant CHA zeolite with Si/Al = 15.5 and Cu/Al = 0.45. Density functional theory calculations are used to corroborate the positions and identity of the two Cu sites, leading to the most complete structural description of dehydrated silicoaluminate CHA loaded with catalytically active Cu2+ cations.
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