Single and dual cation sites in zeolites: theoretical calculations and FTIR spectroscopic studies on CO adsorption on K-FER.
Interaction of CO with K-FER zeolite was investigated by a combination of variable-temperature IR spectroscopy and computational study. Calculations were performed using omega(CO)/r(CO) correlation method in combination with a periodic density functional theory model. On the basis of agreement between experimental and calculated results, the following carbonyl complexes were identified: (i) mono- and dicarbonyl C-down complexes on single K(+) sites characterized by IR absorption bands at 2163 and 2161 cm(-1), respectively; (ii) complexes formed by CO bridging two K(+) ions separated by about 7-8 A (dual sites) characterized by a band at 2148 cm(-1); and (iii) isocarbonyl (O-down) complexes characterized by a band at 2116 cm(-1). The bridged carbonyl complexes on dual K(+) sites are about 5 kJ/mol more stable than monodentate (monocarbonyl) CO complexes. The C-O stretching frequency of monocarbonyl species in K-FER depends on K(+) location in the zeolite, and not on K(+) coordination to the framework. A combination of theoretical calculations using a periodic density functional model and experimental results showed formation of two types of monocarbonyls. The most abundant type appears at 2163 cm(-1), and the less abundant one at 2172 cm(-1). These experimentally determined wavenumber values coincide, within +/-2 cm(-1), with those derived from theoretical calculations.
Garrone
E
E
Dipartimento di Scienza dei Materiali ed Ingegneria Chimica, Politecnico di Torino, I-10126 Turin, Italy.
Bulánek
R
R
Frolich
K
K
Otero Aréan
C
C
Rodríguez Delgado
M
M
Palomino
G Turnes
GT
Nachtigallová
D
D
Nachtigall
P
P
D000327:Adsorption; D000465:Algorithms; D001665:Binding Sites; D002244:Carbon / Q000737:chemistry; D002412:Cations / Q000737:chemistry; D008958:Models, Molecular; D010100:Oxygen / Q000737:chemistry; D011188:Potassium / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods*; D013816:Thermodynamics; D017641:Zeolites / Q000032:analysis* / Q000737:chemistry*
D002412:Cations; D017641:Zeolites; D002244:Carbon; D011188:Potassium; D010100:Oxygen