Catalysis of Organic..

Nikoshvili et al . 183causes the selectivity gain due to electron donation to Pd resulting in the decrease ofLN adsorption strength (19).DHL hydrogenation using Pd-HPS has never been reported. This catalyst willbe discussed in more detail. Optimal conditions of the hydrogenation process werementioned above (see Table 1). During the kinetic study we obtained the kineticcurves (see Figure 5 (a)) and the dependences of DHL content on the reaction time(see Figure 5 (b)). In Figure 5 q is the ratio of substrate to catalyst (q=C 0 /C c , C 0 –substrate [g], C c – catalyst [g]). From the data presented in Figure 5 ((a) and (b)) onecan see that increase of q leads to a decrease of the hydrogenation rate. The rate ofhydrogenation was determined as a ratio of the volume of absorbed hydrogen pertime unit (m 3 H 2 /s) to the total volume of hydrogen absorbed. These data show thatthe increase of the active phase amount leads to the change of the reaction rate(а)(b)Figure 5. Kinetics of hydrogen consumption (a) and dependences of DHL content onthe reaction time (b) (Pd/Zn-HPS)The dependence of activity and selectivity of the DHL hydrogenation on theamount of the active phase (palladium) was investigated. The original catalystcontained 4.88% Pd, but the catalysts with the lower palladium content andbimetallic catalyst HPS-Pd-Zn were synthesized. The results of the investigations arepresented in Table 3.It is seen from Table 3 that the rate of the reaction increases almost three timeswith the decrease of the palladium content to 1%, and remains constant with thefollowing decrease of the active phase amount. When Pd content is high (4.88%),most of active sites remain in the pores and inaccessible to DHL, so the selectivity israther low. The selectivity of the process increases with the reduction of palladiumcontent that is due to the increasing of the catalytic active sites amount.