Computational and variable-temperature infrared spectroscopic studies on carbon monoxide adsorption on zeolite Ca-A.
Carbon monoxide adsorption on LTA (Linde type 5A) zeolite Ca-A is studied by using a combination of variable-temperature infrared spectroscopy and computational methods involving periodic density functional calculations and the correlation between stretching frequency and bond length of adsorbed CO species (nu(CO)/r(CO) correlation). Based on the agreement between calculated and experimental results, the main adsorption species can be identified as bridged Ca(2+)...CO...Ca(2+) complexes formed on dual-cation sites constituted by a pair of nearby Ca(2+) cations. Two types of such species can be formed: One of them has the two Ca(2+) ions located on six-membered rings of the zeolite framework and is characterized by a C-O stretching frequency in the range of 2174-2179 cm(-1) and an adsorption enthalpy of -31 to -33 kJ mol(-1), whereas the other bridged CO species is formed between a Ca(2+) ion located on an eight-membered ring and another one on a nearby six-membered ring and is characterized by nu(CO) in the range 2183-2188 cm(-1) and an adsorption enthalpy of -46 to -50 kJ mol(-1). Ca(2+)...CO monocarbonyl complexes are also identified, and at a relatively high CO equilibrium pressure, dicarbonyl species can also be formed.
Pulido
Angeles
A
Center for Biomolecules and Complex Molecular Systems, Institute of Organic Chemistry and Biochemistry, Academy of Science of the Czech Republic, Flemingovo nám 2, 166 10 Praha 6, Czech Republic.
Nachtigall
Petr
P
Rodríguez Delgado
Montserrat
M
Otero Areán
Carlos
C
D000327:Adsorption; D002248:Carbon Monoxide / Q000737:chemistry*; D003198:Computer Simulation; D008956:Models, Chemical; D013055:Spectrophotometry, Infrared; D013696:Temperature; D017641:Zeolites / Q000737:chemistry*
D017641:Zeolites; D002248:Carbon Monoxide