• The active metal particles are typically reduced during the activation with hydrogen. Such particles could be oxidized during the calcination or other processing of the catalyst, so the catalyst does not work without the activation.

The added catalyst reduces the activation energy of the hydrogenration reaction and hence this chemical absorption process can take place at lower temperatures.

Hope this helps answer your question.

Professor Yehia Khalil, Yale University, USA

Fellow of the University of Oxford, UK

As already mentioned, the main aim - to reduce the active component into the pure metal form, which is required for selective hydrogenation reactions. I would just add that in some cases there is also an additional target - to provide necessary dispersion of metal particles (which may influence the hydrogenationa activity and selectivity).

Thanks to all who attended our discussion! 

That's mean when we synthesize the Pd/C catalyst and we want to use it as a catalyst for the hydrogenation of phenylacetylene, we must before hydrogenation phenylacetylene, Pd/C catalyst purged with hydrogen at a certain time and temperature, this procedure, to get rid of oxidized during the calcination or other processing of the catalyst, or to reduce the active component into the pure metal form, which is required for selective hydrogenation reactions and to provide necessary dispersion of metal particles (which may influence the hydrogenationa activity and selectivity). 

Can be found literature or articles about it?

About this question i found this article

Article Effect of catalyst pretreatment on activity and selectivity ...