title: Location of Cu(2+) in CHA zeolite investigated by X-ray diffraction using the Rietveld/maximum entropy method.
abstract: 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 Cu(2+) for the selective catalytic reduction of NO x with NH3. The method identifies the known Cu(2+) 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 Cu(2+) 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 Cu(2+) cations.
authors.affiliation: Center for Materials Crystallography, Department of Chemistry and iNANO, Aarhus University, Langelandsgade 140, Aarhus C, DK-8000, Denmark.
authors.forename: Casper Welzel
authors.initials: CW
authors.lastname: Andersen
authors.affiliation: Center for Materials Crystallography, Department of Chemistry and iNANO, Aarhus University, Langelandsgade 140, Aarhus C, DK-8000, Denmark.
authors.forename: Martin
authors.initials: M
authors.lastname: Bremholm
authors.affiliation: Haldor Topsoe, Nymøllevej 55, Kgs. Lyngby, DK-2800, Denmark.
authors.forename: Peter Nicolai Ravnborg
authors.initials: PN
authors.lastname: Vennestrøm
authors.affiliation: Center for Materials Crystallography, Department of Chemistry and iNANO, Aarhus University, Langelandsgade 140, Aarhus C, DK-8000, Denmark.
authors.forename: Anders Bank
authors.initials: AB
authors.lastname: Blichfeld
authors.affiliation: Haldor Topsoe, Nymøllevej 55, Kgs. Lyngby, DK-2800, Denmark.
authors.forename: Lars Fahl
authors.initials: LF
authors.lastname: Lundegaard
authors.affiliation: Center for Materials Crystallography, Department of Chemistry and iNANO, Aarhus University, Langelandsgade 140, Aarhus C, DK-8000, Denmark.
authors.forename: Bo Brummerstedt
authors.initials: BB
authors.lastname: Iversen
keywords: CHA zeolites; Rietveld/maximum entropy method; catalytic activity; location of Cu2+; synchrotron powder X-ray diffraction