Tuning the porosity of sulfur-resistant Pd-Pt/MCM-41 bimetallic catalysts for partial hydrogenation of soybean oil-derived biodiesel

Partial hydrogenation of soybean oil-derived fatty acid methyl esters was studied using MCM-41 mesoporous silica-supported Pd-Pt bimetallic catalysts with tunable porosity under mild reaction conditions (100 C, 0.4 MPa H2, 4 h). This process produced partially hydrogenated fatty acid methyl esters (H-FAME) as a new type of highquality biodiesel fuel enriched in monounsaturated fatty acid methyl esters (mono-FAME), which is a potential source for formulating high blends of biodiesel fuel with petrodiesel. MCM-41 supports with various structural properties and morphologies were synthesized by self-assembly with different amounts of ammonia solution as a mineralizing agent. Bimetallic Pd-Pt nanoparticles with a Pd/Pt atomic ratio of 4 were stepwise impregnated on three MCM-41 supports, resulting in a series of Pd-Pt/MCM-41 bimetallic catalysts with tunable porosity (0.89-1.79 cm3 g-1), average pore size (3.2-8.5 nm), and particle size (0.12-0.62 mu m). The Pd-Pt/MCM-41 catalyst prepared with the least amount of ammonia produced the best partial hydrogenation conversion of polyunsaturated FAME into mono-FAME, ascribed to nano-aggregation resulting in a dual-pore system containing large pores for fast molecular diffusion; a high turnover frequency (1920 h-1), larger k1 rate constant (0.60 gcat- 1h- 1), and smaller k2 rate constant (0.37 gcat- 1h- 1) were obtained. Furthermore, this Pd-Pt/MCM-41 catalyst exhibited excellent sulfur resistance in the synthesis of H-FAME, even though the feedstocks contained approximately 5 ppm of sulfur contaminates. These results demonstrate that the sulfur-resistant Pd-Pt/MCM-41 bimetallic catalysts with stable and dual pore system are beneficial for obtaining higher quality BDF to reduce our reliance on fossil fuels.

Automated summary

The study investigated the partial hydrogenation of soybean oil-derived fatty acid methyl esters using MCM-41 mesoporous silica-supported Pd-Pt bimetallic catalysts, resulting in the production of H-FAME enriched in mono-FAME as a potential source for high blends of biodiesel fuel. Various MCM-41 supports with different structural properties and morphologies were synthesized using different amounts of ammonia solution, leading to a series of Pd-Pt/MCM-41 bimetallic catalysts with tunable porosity.