Preparation, characterization and application of novel surface-modified ZrSnO4 as Sn-based TMOs catalysts for the stearic acid esterification with methanol to biodiesel

Tin zirconium oxide catalysts (Sn-based TMOs) were successfully prepared with three different methods, ultrasonic-assisted hydrothermal, sol-gel, and traditional precipitation method, and applied for biodiesel production. The physicochemical and the catalytic efficiency by the esterification of stearic acid of the as-synthesized catalysts were investigated by different techniques. The production of biodiesel (as methyl stearate) has emerged as a greener and renewable substitute for petro based diesel fuel. The optimization of the esterification conditions for maximum yield of biodiesel was performed by studying different factors as the catalyst preparation method, reaction time, molar ratio of alcohol to stearic acid, reaction temperature, and the catalyst concentration. The preferred catalyst (SnZrh) was optimized as the reaction temperature of 120 °C, 150 M ratio of methanol to stearic acid, 0.2 g catalyst amount and reaction time of 60 min. The SnZrh catalyst exhibited 74% yield of methyl stearate. Also, the kinetic and thermodynamic studies of stearic acid esterification reaction were inspected. The reusability of the optimized tin zirconium oxide catalyst for seventh runs was professionally studied. The computational chemistry study showed that the interaction mechanism between the optimized catalyst and stearic acid was preferable between SnO2 active sites and carbonic group of stearic acid.