Enhanced stability of Ti-containing silica catalysts for biodiesel epoxidation with hydrogen peroxide: Presence of strong metal-support interactions for alleviating permanent deactivation

The deactivation of titanium catalysts supported by well-ordered silica (SBA-15) and amorphous fumed silica synthesized by incipient wetness impregnation (IWI) and wet impregnation (WI) was comparatively investigated during epoxidation of methyl oleate with H2O2 at 50 degrees C. The formation of oxygen vacancies during epoxidation resulted in the loss of active species, leading to permanent catalyst deactivation. The WI-based catalysts exhibited superior stability to that of the IWI-based equivalents. Moreover, the use of SBA-15 as a support enabled higher stability than that of SiO2. The permanent deactivation rates for the 4Ti/SiO2-IWI, 4Ti/SBA-15-IWI, 4Ti/SiO2-WI, and 4Ti/SBA-15-WI catalysts were approximately 44.0%, 32.6%, 8.1%, and 0%, respectively. Various catalyst characterization data revealed that the configuration featuring stable surface Ti was present in the 4Ti/SBA-15WI catalyst with strong metal-support interactions. This was attributed to the strong Ti4+ tetrahedral coordination achieved through Si-O-Ti bonds, the low degree of reducibility of the Ti catalyst, and the high dispersion and small particle size of Ti. Consequently, this modified surface can mitigate permanent catalyst deactivation caused by the surface oxygen vacancies.