Infrared spectroscopic study of alkyl aldehydes adsorbed on cations supported by layer silicate

The self-supported film specimen of Wyoming montmorillonite as a layer silicate exchanged by cations, Li⁺, Na⁺, K⁺, Ca²⁺, Ni²⁺, and Al³⁺ were allowed to contact acetaldehyde, acrolein and crotonaldehyde within the heatable gas cell. Adsorption mechanism of alkyl aldehydes on cations supported by layer silicate was studied by means of infrared spectroscopy and X-ray. The infrared spectra between 4000 and 1200 cm⁻¹ at different pressures of adsorbates indicated bond formation through carbonyl oxygen. The intensity of the stretching OH was analyzed and resonance form of cationic hydroxyl was proposed as an adsorption site. The carbonyl stretching band, which shifted about 130 cm⁻¹ to lower frequencies was observed only for Ni²⁺, Ca²⁺, and Al³⁺ supported by layer silicate and was attributed to >CO···Mⁿ⁺ complex formation. A sharp band, which appeared as a shoulder at 1722 for acetaldehyde and 1690 for acrolein and crotonaldehyde, was responsible for the interaction of carbonyl with surface hydroxyl. The second broad band, which appeared at about 1710-1660, was responsible for hydrogen bonding between carbonyl oxygen and cationic hydroxyl group.