Knowledge Bank

On adsorbing carbon monoxide on LINDE X- and Y-type zeolites containing a variety of cations, (of transition metals and of other metals), a higher than gas-phase frequency infrared band (about $2200cm-1$) is observed, similar to that reported for nickel $oxide1$, zinc $oxide2$, and $chromia3$. Only zeolites having divalent cations give rise to this band and its actual frequency depends on the nature of cation. A correlation is found between the frequency of the CO band and second ionization potential of the atoms and ionic size of the cations. A possible explanation for the occurrence of this high frequency band is discussed.