Effects of synthetic conditions on the Pd particle sizes of Pd/SBA-15 catalysts and their performance for the partial hydrogenation of biodiesel fuels

Mesoporous silica (SBA-15)-supported Pd catalysts (Pd/SBA-15) with Pd particles of various sizes (4–17 nm) were obtained under different calcination conditions. These purpose-made Pd/SBA-15 catalysts are applied in the partial hydrogenation of soybean-oil-derived biodiesel fuel, rich in polyunsaturated fatty acid methyl esters (poly-FAME), to produce partially hydrogenated fatty acid methyl esters (H-FAME), rich in monounsaturated fatty acid methyl esters (mono-FAME), under mild conditions (80 °C, 0.5 MPa H 2 ). The Pd particle size was strongly correlated with hydrogenation rate and selectivity, thereby influencing the composition and fuel properties of H-FAME. The Pd/SBA-15 catalyst with a Pd particle size of approximately 4 nm obtained by calcination at 300 °C in O 2 showed the highest initial hydrogenation rate and mono-FAME selectivity. The resulting H-FAME product was rich in mono-FAME and thus exhibited high oxidative stability and cold-flow properties compliant with high-blend biofuel standards. In contrast, the analog catalysts with Pd particle sizes ranging from 8 to 17 nm obtained by calcination at 300 °C in air and nitrogen and at 500 °C featured lower hydrogenation rates and afforded larger amounts of undesired saturated fatty acid methyl esters. These findings shed light on the effect of the Pd particle size on the hydrogenation of biodiesel and can be readily applied to the hydrogenation of other biofuels.