Effect of SiO2 pore size on partial hydrogenation of rapeseed oil-derived FAMEs
Palladium (Pd) supported on different SiO2 pore sizes: Q3, Q10, Q30, and Q50 with pore diameters of 3, 5, 30, and 50 nm, respectively, were studied for the partial hydrogenation of rapeseed oil-derived fatty acid methyl esters (FAMEs). The supports and catalysts were characterized by BET, NH3-adsorption, and CO-chemisorption technique. Highest turn over frequency (TOF) was found for Pd/Q30, while Pd/Q3 exhibited the lowest TOF. The reaction rate constants for each hydrogenation step, consequently from C18:3 to C18:2, C18:1, and C18:0, i.e., k1, k2, and k3, respectively, were determined by POLYMATH Professional 6.2 and could explain the effect of SiO2 pore size on pore diffusion of FAMEs reactant and contact probability between reactant molecules and active sites. Moreover, pore size of the SiO2 support also affected on selectivity toward trans-monounsaturated FAME. The Pd/Q3 catalyst presented the lowest trans-monounsaturated FAME selectivity due to its smallest pore size and acidic properties. In addition, it was found that 0.5 h of hydrogenation time using Pd/Q10, Pd/Q30, and Pd/Q50 could improve the oxidative stability to >10 h.
Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (88 K)Download as PowerPoint slideHighlights► Oxidative stability of fatty acid methyl esters was improved by partial hydrogenation. ► Hydrogenation activity over Pd/SiO2 catalysts strongly depends on pore sizes of SiO2. ► Hydrogenation activity was maximized around the SiO2 pore size of 45 nm. ► Cis–trans selectivity depends on contact probability between reactant and catalyst.
Journal: Applied Catalysis A: General - Volumes 441–442, 28 October 2012, Pages 72–78