Structure–Property Relationship in the Lanthanum Grafted Zeolite and Its Application as an Efficient Acido-Basic Catalyst for C–C/C–O Bond Formation Reactions

Abstract

A versatile, bi-functional, acido-basic catalyst efficient for two industrially important acetalization and aldol condensation reactions is developed through the grafting of lanthanum into the beta zeolite lattice. The grafting is achieved through the controlled dealumination of a zeolite framework by oxalic acid treatment followed by lanthanum impregnation, leading to the substitution of aluminum in the zeolite framework by lanthanum. The first-of-its-kind catalyst composition with rare-earth metal grafted into a zeolite framework confers highly desirable catalyst properties like high lanthanum dispersion, stability, and the close proximity of acid and base sites. The structure–property relationship, nature, and location of the catalytically active center and conceivable cooperative synergism are realized through the various characterization techniques like X-ray diffraction, Fourier transform infrared spectroscopy, 27Al NMR, 29Si NMR, NH3 temperature-programed desorption (TPD), CO2-TPD, UV–vis spectroscopy, and Raman spectroscopy. The studies allowed us to propose the acid–base pair in the Si–O–La–O–Si group along with the adjacent Bronsted acid site is the active center for the reactions.