Pd-Al2O3 Applied to the Hydrogenation of Tryglicerides with Supercritical Propane. Experimental and Theoretical Characterization of Catalysts

Abstract

A set of Pd-Al2O3 catalysts of different metallic particle sizes and modified with 2-chloro-butane was used for triglyceride hydrogenation. The experiments were carried out in single-phase conditions using propane as a supercritical solvent. A generalized criterion was used to determine the absence of mass transfer limitations for both reactants inside the pore structure of the catalyst.FTIR spectra of CO on diverse catalysts showed different absorption bands and significant shifts to higher wavelengths of the CO species corresponding to on-top and bridge configurations. In order to test these results, theoretical studies using the density functional theory (DFT) were carried out for the FTIR of CO adsorption on two Pd ensembles, with or without charge deficiency and with Cl adsorbed on them. The results showed similar displacements of the band frequencies to those obtained experimentally, and demonstrate an enhancement of the CO adsorption energy of the on-top, isolated bridge and three-fold bridge CO species on electron deficient ensembles. Enhancement of the adsorption bond strength could promote the direct hydrogenation of the diunsaturated compound to complete saturated fatty acid chains. The decrease of the specific reaction rate (TOF) and the increase of the saturated fatty acids production, as well as a decrease of the monounsaturated and isomers content observed is in line with a possible modification of the electronic properties of the Pd particles. The influence of some planes of Pd clusters intervening on the direct hydrogenation is discussed.