Fine speciation of active sites in zeolites by a CO probe: Dynamics and IR frequencies

The influence of system dynamics onto infrared spectra calculated and measured for probe molecules weakly interacting with active sites is discussed. OH stretching frequencies for BrOnsted sites in Y zeolite and their shift on CO adsorption (measured by IR spectroscopy at ca. 170 K) are simulated from AIMD trajectory, based on BO DFT calculations. We present here very good agreement between experimental and computed OH frequency red-shift on CO adsorption in dealuminated zeolite Y. It is shown that extracting nonharmonic OH frequencies from ab initio molecular dynamics trajectory provides better estimate of experimental IR results than standard vibrational analyses due to realistic computational model and better correspondence with experimental conditions.