Performance and sulfur poisoning of SiO2, γ-Al2O3, and SiO2-Al2O3-supported bimetallic Pd-Pt catalysts in selective hydrogenation of soybean oil-derived fatty acid methyl esters

Abstract

Selective hydrogenation of soybean oil-derived fatty acid methyl esters (FAMEs) with low oxidative stability over supported Pd catalysts is crucial to the production of monounsaturated counterparts (mono-FAME), whose oxidative stability and cold flow properties are suitable for producing fuels with high blend ratios. However, supported Pd catalysts are easily deactivated by sulfur-containing FAMEs. Herein, the performance and sulfur poisoning of Pd-Pt/SiO2, Pd-Pt/γ-Al2O3, and Pd-Pt/SiO2-Al2O3 bimetallic catalysts containing 3–10 nm Pt-Pd alloy particles and possessing surface acidity of 0.1–2.4 mmol NH3 g−1 were examined. Pd-Pt/SiO2 with large Pd-Pt alloy particles (10 nm) and weak acidity (0.1 mmol NH3 g−1) favored the selective hydrogenation of polyunsaturated-FAME (poly-FAME) to mono-FAME, while Pd-Pt/γ-Al2O3 and Pd-Pt/SiO2-Al2O3 with smaller Pd-Pt alloy particles and stronger acidity favored the formation of saturated-FAME. These Pd-Pt catalysts were poisoned when using FAME containing 3.4–5.3 ppm of sulfur. However, the performance of the Pd-Pt/SiO2 catalyst physically mixed with γ-Al2O3 did not deteriorate when using a feedstock containing 5.3 ppm of sulfur because the acidic γ-Al2O3 support could adsorb sulfur. Thus, the combination of acidic γ-Al2O3 and Pd-Pt/SiO2 catalysts can be efficiently used to produce mono-FAME through the selective hydrogenation of commercial biodiesel fuels containing high poly-FAME concentrations.