Suchergebnisse

[EN] Combining IR spectroscopy of NO adsorption on copper exchanged molecular sieves with the chabazite structure, i.e. Cu-SAPO-34 and Cu-SSZ-13, and theoretical calculations, different types of copper species have been identified. On one hand, [Cu¿OH]+ species can be accurately distinguished, characterized by a ¿NO frequency at 1788¿ 1798 cm¿1 depending on their location in the chabazite structure (6R vs. 8R) and composition (Cu-SAPO-34 vs. Cu-SSZ-13). On the other hand, dimeric copper oxo [Cu¿O¿ Cu]2+ species have been properly identified by means of DFT modelling, that proposes a ¿NO stretching frequency of 1887 cm¿1, which has been confirmed experimentally in the Cu-SAPO-34 sample. Finally the location of isolated Cu2+ ions either in the 6R units or in the 8R positions of the chabazite cavity could be accurately defined according to DFT data, and validated in the experimental IR spectra with IR bands between 1907 and 1950 cm¿1. Regarding to Cu+ species, IR spectroscopy of CO reveals different types of Cu+ species as evidenced by their ability to form mono, di and try carbonyls. The unambiguous differentiation of different types of copper species is of great interest in further identification of active sites for the NH3- SCR reaction. ; This work has been supported by the Spanish Government through "Severo Ochoa Program" (SEV 2012-0267), and MAT2015-71261-R, the European Union through ERC-AdG-2014-671093 (SynCatMatch); and the Generalitat Valenciana through the Prometeo program (PROMETEOII/2013/011). R.M. acknowledges "La Caixa - Severo Ochoa" International PhD Fellowships (call 2015). ; Concepción Heydorn, P.; Boronat Zaragoza, M.; Millan, R.; Moliner Marin, M.; Corma Canós, A. (2017). Identification of Distinct Copper Species in Cu-CHA Samples Using NO as Probe Molecule. A Combined IR Spectroscopic and DFT Study. Topics in Catalysis. 60(19-20):1653-1663. https://doi.org/10.1007/s11244-017-0844-7 ; S ; 1653 ; 1663 ; 60 ; 19-20 ; Wilken N, Wijayanti K, Kamasamudram K, Currier NW, Vedaiyan R, Yezerets A, ...

The dynamic nature of the copper cations acting as active sites for selective catalytic reduction of nitrogen oxides with ammonia is investigated using a combined theoretical and spectroscopic approach. Ab initio molecular dynamics simulations of Cu-CHA catalysts in contact with reactants and intermediates at realistic operating conditions show that only ammonia is able to release Cu+ and Cu2+ cations from their positions coordinated to the zeolite framework, forming mobile Cu+(NH3)2 and Cu2+(NH3)4 complexes that migrate to the center of the cavity. Herein, we give evidence that such mobilization of copper cations modifies the vibrational fingerprint in the 800–1000 cm–1 region of the IR spectra. Bands associated with the lattice asymmetric T-O-T vibrations are perturbed by the presence of coordinated cations, and allow one to experimentally follow the dynamic reorganization of the active sites at operating conditions. ; This work has been supported by the European Union through ERC-AdG-2014-671093 (SynCatMatch), Spanish Government through ''Severo Ochoa" (SEV-2016-0683, MINECO), and MAT2017-82288-C2-1-P (AEI/FEDER, UE). Red Española de Supercomputación (RES) and Servei d'Informàtica de la Universitat de València (SIUV) are acknowledged for computational resources and technical support. R.M. thanks ITQ for his contract. V.V.S. and P.C. acknowledge funding from the European Union's Horizon 2020 research and innovation program (consolidator ERC grant agreement No. 647755 - DYNPOR (2015–2020)). V.V.S. acknowledges the Research Board of the Ghent University (BOF). The computational resources and services used were provided by Ghent University (Stevin Supercomputer Infrastructure), the VSC (Flemish Supercomputer Center), funded by the Research Foundation - Flanders (FWO). ; Peer reviewed