CONICET | Buscador de Institutos y Recursos Humanos

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. The production of final organic products of high added value or intermediate compounds for the synthesis of fine chemicals is both of industrial and academic importance [1]. Alkenes are much appreciated products used in the food industry (flavours), the pharmaceutical industry (sedatives, anesthetises, vitamins) and in the perfumes industry (fragrances). They are also used for the production of biologically active compounds [2], resins, polymers and lubricants, etc. The partial hydrogenation of acetylenic compounds using homogeneous or heterogeneous metallic catalysts provides a very viable and economically feasible way for the obtaining of these olefinic compounds. Selective catalysts and optimum operational conditions are necessary in order to avoid the complete hydrogenation of the unsaturated bond. Certain transition metals anchored on different solids have demonstrated to be very active and selective catalysts for this type of reaction. They also have the advantage that they can be operated under milder reaction conditions. It is well documented that palladium is a highly active catalyst for hydrogenation [3]. In this sense, Lindlar catalyst (Pd/CaCO3, 5 wt % of Pd modified with Pb(OAc)2) has been used since 1952 as an excellent commercial catalyst for this type of reactions [4]. The argued reasons for the differences in reactivity of Pd indicate that when the metal is electron deficient it becomes less active because alkynes are more weakly adsorbed [5]. During decades a lot of research has been carried out modifying this type of catalysts in order to increase the activity and selectivity: different supports as alumina, coal, silica [5-7] have been tried while modified palladium [8], or nanoparticles of Pd have also been investigated [9-11]. In a recent work of our group very high activities and selectivities of W monometallic and W-Pd bimetallic catalysts were found during the partial hydrogenation of a long chain terminal alkyne [12]. In this contribution it was reported that important variations in the activity and selectivity were produced when the employed pretreatment conditions were changed. The published reports do not give a clear explanation of the effect of each metal. Providing an economic, active and selective metallic catalyst for the production of alkenes via selective hydrogenation is a very important challenge. Besides the bibliography on the kinetics of the reaction of heavy alkynes is scarce [13-15]. In this sense, the kinetic study of the liquid phase hydrogenation reaction of 1-heptyne using monometallic nickel and palladium catalysts anchored on g-alumina made in the current work had three principal objectives: i) to gain knowledge about the reaction system, ii) to obtain kinetic expressions which enable the design of partial hydrogenation reactors, and iii) to give an explanation of the catalytic effect of different metals. The kinetic modelling was used in this work to shed light on these issues.