Kinetic Study of the Partial Hydrogenation of 1-Heptyne over Ni and Pd Supported on Alumina

MARïA J. MACCARRONE; GERARDO C. TORRES; CECILIA R. LEDHEROS; CAROLINA BETTI; JUAN M. BADANO; MóNICA E. QUIROGA; JUAN C. YORI

Hydrogenation

INTECH

Lugar: Ryjeka; Año: 2012;

Selective hydrogenation reactions are industrially used for the partial hydrogenation of unsaturated organic compounds in order to form more stable products or intermediate materials for different processes.  Alkenes are much appreciated products used in the food (flavours), pharmaceutical (sedatives, anesthetises, vitamins) and fragrance industries.  They are also used for the production of biologically active compounds, resins, polymers and lubricants, etc.   A kinetic study on the hydrogenation of 1-heptyne in liquid phase was carried out using monometallic catalysts of nickel and palladium supported on ã-alumina.  The catalysts were prepared using incipient wetness technique and were characterized by ICP, XPS, XRD, TPR and hydrogen chemisorption.  The characterization results indicate that after a reduction pretreatment only Ni2+ and Pd0 species remain on the alumina surface.   The Ni/Al2O3 and Pd/Al2O3 catalysts were active and selective for producing 1-heptene in the 293-323 K temperature range.  The results indicate that Pd/Al2O3 is more active and selective to the formation of 1-heptene than Ni/Al2O3.  Moreover, for both catalysts it was determined that the 1-heptyne hydrogenation reaction proceeds via two irreversible reactions in parallel while there is alkyne in the reaction media.   Six different kinetic expressions of LHHW type were proposed to describe the partial hydrogenation reaction.  Differences in catalytic activity between both catalysts are due to different rate controlling mechanisms.  For Ni/Al2O3 catalyst, the reaction rate is described by an expression in which the controlling step is the hydrogen dissociative adsorption, while for Pd/Al2O3 is the surface chemical reaction.     Adsorption enthalpies of 1-heptyne (DHA) over Ni/Al2O3 or Pd/Al2O3 catalysts were estimated: -17.91 and -19.64 KJ mol-1, respectively. On the other hand, the models also allow estimating the activation energy for the hydrogen adsorption over Ni (22.2 KJ mol-1) and the activation energy for the hydrogenation reaction of 1-heptyne to 1-heptene (18.58 KJ mol-1).