Following the movement of Cu ions in a SSZ-13 zeolite during dehydration, reduction and adsorption: A combined in situ TP-XRD, XANES/DRIFTS study

• Published in: Journal of catalysis Vol. 314; pp. 83 - 93
• Main Authors: Kwak, Ja Hun, Varga, Tamás, Peden, Charles H.F., Gao, Feng, Hanson, Jonathan C., Szanyi, János
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01.05.2014; Elsevier; Elsevier BV
• Subjects: Adsorption; Catalysis; Cation coordination; Cation movement; Chemistry; Cu-SSZ-13; Dehydration; DRIFTS; Exact sciences and technology; General and physical chemistry; Ion-exchange; Ions; NH3 SCR; Surface physical chemistry; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; XANES; XRD; Zeolites: preparations and properties; Cation movement; XANES; DRIFTS; Cation coordination; Cu-SSZ-13; NH3 SCR; XRD; XANES spectrometry; SCR; In situ; Ions; Zeolite; Dehydration; X ray diffraction; Chemical reduction; Infrared spectrometry; Ammonia; Heterogeneous catalysis; Adsorption; NH
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2014.03.003

[Display omitted] •Combination of XRD, XANES and DRIFTS affords monitoring the cation movement in a Cu-SSZ-13 zeolite.•Fully hydrated Cu2+ ions reside in the large cages of zeolite and weakly perturb framework T–O–T vibrations.•Upon dehydration copper ions move into cationic positions and perturb the nearby T–O–T vibrations.•Reduction of Cu2+ ions located in positions other than the six member rings occur in CO.•Formation of mono- and di-carbonyls on Cu+ ions can easily be followed by both XANES and DRIFTS. Cu-SSZ-13 has been shown to possess high activity and superior N2 formation selectivity in the selective catalytic reduction of NOx under oxygen rich conditions. Here, a combination of synchrotron-based (XRD and XANES) and vibrational (DRIFTS) spectroscopy tools has been used to follow the changes in the location and coordination environment of copper ions in a Cu-SSZ-13 zeolite during calcinations, reduction with CO, and adsorption of CO and H2O. XANES spectra collected during these procedures provide critical information not only on the variation in the oxidation state of the copper species in the zeolite structure, but also on the changes in the coordination environment around these ions as they interact with the framework, and with different adsorbates (H2O and CO). Time-resolved XRD data indicate the movement of copper ions and the consequent variation of the unit cell parameters during dehydration. DRIFT spectra provide information about the adsorbed species present in the zeolite, as well as the oxidation states of and coordination environment around the copper ions. A careful analysis of the asymmetric T–O–T vibrations of the CHA framework perturbed by copper ions in different coordination environments proved to be especially informative. The results of this study will aid the identification of the location, coordination and oxidation states of copper ions obtained during in operando catalytic studies.