**4. Conclusions**

In **Figure 9**, it can be observed that the Lindlar catalyst allows obtaining high values of 1 heptyne total conversion with high selectivity to 1-heptene, between 82% and 86%. Comparing the results obtained with the prepared high-loaded catalysts (5 wt% of Pd, similar to that of Lindlar), a slightly better yield to 1-heptene is obtained with the Pd(5%)/Al catalyst than that obtained with Lindlar catalyst. Besides, it must be remarked that the prepared catalyst has the advantage of being a pelletized material. On the other hand, the lowest yield to 1-heptene is obtained with Pd(5%)/AC. Differences in total conversion can be associated to electronic effects, as the surface palladium species on the Lindlar catalyst are more electron-deficient than those

In **Figure 10**, the initial 1-heptyne hydrogenation rates (calculated per gram of palladium) and the selectivities to the desired product (1-heptene) at 180 min for all of the synthesized catalysts

**Figure 10.** Comparison of initial 1-heptyne hydrogenation rates (a) and selectivities to 1-heptene at 180 min (b) for the

According to the results obtained and shown in **Figure 10**, the tested catalysts showed the

Pd-Ni/Al > PdN(0.4%)/Al > Pd(0.4%)/Al >> Lindlar > Pd(5%)/Al > Pd(5%)/Al\_373 >

Pd(5%)/Al\_373 ≈ Pd-Ni/Al = Pd(0.4%)/Al ≈ PdN(0.4%)/Al = Pd(5%)/AC > Pd(5%)/Al >> Lindlar From **Figure 10**, it can be concluded that the prepared pelletized catalysts are more active and

Finally, pelletized catalysts have additional advantages against the Lindlar catalyst: the easy and cheap way of recovering the catalytic systems from the remaining solution at the end of

present on Pd(5%)/Al or Pd(5%)/AC.

against Lindlar catalyst results are compared.

30 New Advances in Hydrogenation Processes - Fundamentals and Applications

catalytic systems evaluated in the present chapter.

With the following order of selectivities:

selective than the Lindlar catalyst.

following order of activity:

Pd(5%)/AC

the industrial process.

**3.3. Final considerations**

A series of palladium mono- and bimetallic catalysts were synthetized, characterized and tested during the partial hydrogenation of a terminal alkyne. All the prepared catalysts are active and highly selective for the partial hydrogenation of 1-heptyne under mild reaction conditions. Various factors were studied, and the behaviour of the catalysts on activity and selectivity during the hydrogenation of 1-heptyne was evaluated. The studied factors and the principal conclusions obtained are condensed below:


under slurry conditions; therefore, the reagent solution must be purified after the reaction through an uneconomic method to recover the catalyst.

Finally, considering XPS results, this chapter allows concluding that the presence of electrondeficient species on the catalyst surface of the catalysts with high metal loading is an important factor and influences on the activity and selectivity to the desired product. Nevertheless, the influence of geometrical effects and/or mixed sites in the catalysts as well as metal-metal and metal-support interactions cannot be neglected.
