Superficial Pd nanoparticles supported on carbonaceous SBA-15 as efficient hydrotreating catalyst for upgrading biodiesel fuel

Abstract

Facile synthesis of superficial Pd nanoparticles supported on carbonaceous SBA-15 (denoted as Pd/@SBA-15) as a new hydrotreating catalyst with enhanced activity and sulfur tolerance was accomplished for the production of partially hydrogenated fatty acid methyl esters (H-FAME), a high-quality biodiesel fuel enriched in monosaturated fatty acid methyl esters (mono-FAME) that can be used in high blends. Characterization, especially high-resolution electron microscopes and temperature-programmed techniques, indicated that the Pd nanoparticles (∼7 nm) formed spontaneously at the superficial area of carbonaceous SBA-15 with a hydrophobic surface and low acidity. In the synthesis of H-FAME using commercial palm oil-derived biodiesel fuel as a feedstock under mild conditions (<100 °C, 1 MPa), this new Pd/@SBA-15 catalyst offered high hydrotreating activity with excellent selectivity toward mono-FAME, especially the cis product, and high sulfur resistance, presumably due to fast diffusion and suitable interactions of the reactant and hydrogenated molecules through superficial Pd nanoparticles on the carbonaceous surfaces as the catalytically active sites. On the other hand, commercial Pd catalysts with Pd nanoparticles randomly impregnated inside the supporting materials showed lower activity in H-FAME synthesis and poorer selectivity toward saturated fatty acid methyl esters as undesirable products and lower sulfur tolerance level per Pd site, demonstrating the superiority of our system.