IFISUR   23398
INSTITUTO DE FISICA DEL SUR
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Evaluating Pd-Ni layered catalysts for selective hydrogenation of 1,3-butadiene: A theoretical perspective
Autor/es:
GABRIELA F. CABEZA; GUILLERMINA GÓMEZ; PATRICIA G. BELELLI
Lugar:
ontevideo
Reunión:
Workshop; V Workshop on Novel Methods for Electronic Structure Calculations; 2013
Institución organizadora:
ANII-PEDECIBA-CINQUIFIMA
Resumen:
Since its development in the early 1900s, edible oil hydrogenation has remained relatively unchanged. Ni catalysts are still the most commonly used catalysts for vegetable oil hydrogenation. They offer several advantages, including high activity, tailored linoleic and linolenic selectivities, and low cost. In addition, Ni catalysts are easily removed from the processed oil by filtration and processors are experienced in using them. Unfortunately, Ni catalysts also isomerize some of the naturally occurring cis double bonds to the trans configuration. Trans fatty acids have been shown to be harmful to human health and this represents the biggest impetus for developing new and improved oil hydrogenation technologies. Strategies that minimize the formation of trans fatty acids during hydrogenation are required. The use of very small amounts of precious metals to alter Ni?s catalytic ability has also been investigated. For example, small amounts of Pd are reported to decrease the bonding strength of hydrogen to Ni surfaces [1]             The partial hydrogenation of 1,3-butadiene (13BD) as a model of fatty acid, to several C4H8 products, including 1-butene (1B), 2-butene (2B) and butan-1,3-diyl (B13R), on both Pd/Ni3(111) and Pd3/Ni(111) bimetallic surfaces, was theoretically investigated using DFT methods. For that purpose, different intermediates, C4H7 and C4H8 radical species, were evaluated according to the Horiuti-Polanyi mechanism performed in two sequential steps. The whole process was found to be exothermic on Pd/Ni3(111) and endothermic on Pd/Ni3(111). Furthermore, the former surface, where the intermediate adsorptions are more favorable, exhibits lower activation barriers than Pd3/Ni(111). On both surfaces, the B13R formation is associated with high activation barriers through the pathways studied here; for this reason, it is extremely improbable to obtain B13R. Our calculations predict that on the Pd/Ni3(111) catalyst model the products would be mainly the butene isomers, with a little more selectivity towards the 2B, at difference with respect to the pure Pd surface and in agreement with experimental data [2].   references 1.      A.J. Wright, A. Wong, L.L. Diosady, ?Ni catalyst promotion of a Cis-selective Pd catalyst for canola oil hydrogenation?; Food Research International, 36 (2003), p. 1069-1072. 2.      A. Valcárcel, A. Clotet, Josep M. Ricart, Françoise Delbecq, and Philippe Sautet, ?Selectivity Control for the Catalytic 1,3-Butadiene Hydrogenation on Pt(111) and Pd(111) Surfaces: Radical versus Closed-Shell Intermediates?; J. Phys. Chem. B, 109 (2005), p. 14175-14182.