INS and IR and NMR Spectroscopic Study of C_1-C_4 Alcohols Adsorbed on Alkali Metal-Exchanged Zeolite X

摘要

The adsorption of short-chain (C_1-C_4) n-alcohols on alkali cation-exchanged X zeolites (Si/Al = 1.2) was studied by inelastic neutron scattering and infrared and NMR spectroscopy.Vibrational and NMR spectra of alcohols adsorbed on the zeolites were compared to those of solid alcohols and isolated alcohol molecules to describe the interactions between the sorbate molecule and the zeolite.The experimental results are compared to theoretically calculated INS spectra for one,two,and three alcohol molecule aggregates.For all alkali-metal cation-exchanged X zeolites,only physically adsorbed alcohol molecules were found on the catalyst's surface.The interactions in the channels of alkali cation-exchanged X zeolites of the short-chain C_1- C_4,alcohols were found to be similar and independent of the chain length.The alcohol oxygen atoms interact via their lone electron pairs with the exchanged alkali-metal cation,and hydrogen-bond formation was found between the alcohol OH protons and the negatively charged oxygen atoms of the framework.With increasing hydrocarbon chain length,the energetic contribution of the hydrogen bonds to the heat of adsorption increased.With increasing framework polarity,that is,from the Na~+ to Cs~+ countercation,large negative shifts of the frequency of the OH stretching modes indicate the strengthening of the hydrogen bonds.