effect of the loading of di- and tri-valent metal cations on the performance of sulfated silica-titania nano-catalyst in the esterification reaction

In this study, a series of sulfated silica-titania catalysts were modified by metal cations (al, co, zr, cr, and zn) to enhance the catalytic activity and stability of sulfated silica-titania in the esterification reaction. the results indicated that the sulfate phases of sulfated silica-titania were mostly changed to tio(so4) by the incorporation of support cations. it affected the acidity content of the samples and the bonding strength between the sulfate group and the support surface. moreover, the mean pore size was drastically increased which had a positive influence on the activity of the sample in the esterification reaction. the results of catalytic activity showed that all the samples had suitable activity at 120°c, whereas the sulfated silica-titania catalyst that was reinforced by al^3+ exhibited less activity reduction by setting the temperature to 90°c. the highest conversion of oleic acid (90.7 ± 2%) was obtained under optimal reaction conditions including the temperature of 90°c, methanol/oleic acid molar ratio of 9:1, 3 wt.% catalyst, and reaction time of 3 h. the sulfated silica-titania modified by al^3+ also exhibited good catalytic stability for six cycles while a high reduction in the activity of sulfated silica-titania catalyst was observed.