Catalytic performance of a wide range of rare-earth titanate pyrochlore (RE2Ti2O7, RE = Sm, Gd, Dy, and Yb) microstructures in the epoxidation of cyclooctene: An electro-structural investigation

A series of rare-earth titanate oxides RE2Ti2O7 (RE = Sm, Gd, Dy and Yb) were synthesized using a solid state method. The pyrochlore structures of these compounds were confirmed by the Rietveld method from X-ray diffraction data (XRD). XRD results showed that RE2Ti2O7 structures had cubic crystal system with the Fd(3)m space group. Morphology and mean particle sizes of the samples were obtained by the scanning electron microscope (SEM). Chemical characterizations of the samples were confirmed by energy dispersive x-ray spectroscopy (EDX). The specific surface areas were calculated using BET analyses. Fourier transform infrared spectra of the obtained compounds in (400-4000 cm(-1)) range were also studied. The obtained RE2Ti2O7 pyrochlore materials were used as catalysts for epoxidation of cyclooctene as a model alkene with tert-butyl hydroperoxide. Various parameters including catalyst type and amount, solvent type and amount, oxidant/substrate ratio, and time have been optimized and high catalytic activity and epoxide selectivity have been found. Gd2Ti2O7 showed the best activity and epoxide selectivity.