Use of FTIR spectroscopy of pyridine adsorption at incipient moisture conditions in the interpretation of the hydrophobicity, acidity, and activity on HMOR and HY zeolites

Abstract

The fatty acids (FFA) adsorption on structurally different (HMOR and HY) zeolites with different Si/Al ratios, were studied by FTIR pyridine spectroscopy on incipient moisture conditions and other complementary characterization techniques to improve the understanding of the relationship between hydrophobicity, acidity, and activity. In HMOR with a low density of Si-OH–Al groups, a significant fraction of the FFA molecules are adsorbed onto the less polar sites with its carboxyl groups oriented away from the surface. In HY, the higher density of bridging Si-OH–Al groups, favors the adsorption of FFA molecules with their carboxyl group hydrogen-bonded to these groups.

Se estudiaron zeolitas estructuralmente diferentes (HMOR y HY) mediante espectroscopia FTIR-piridina bajo humedad incipiente y técnicas complementarias. Con la salida del aluminio tetraédrico de la red cristalina aumenta la hidrofobicidad y disminuyen la acidez y la actividad. A crecientes relaciones Si/Al, en mordenitas con baja densidad de sitios Si-OH-Al las moléculas de ácidos grasos se adsorben crecientemente sobre sitios menos polares con sus colas orientadas hacia la superficie. En las faujasitas, su mayor densidad de sitios en puente favorece la adsorción de los ácidos grasos, con sus carboxilos orientados hacia los sitios Si-OH-Al, disminuyendo su adsorción a relaciones Si/Al crecientes.