I encountered catalytic hydrogenation recation, where alkene is converted into alkane using Pt/C or Pd/C as catalyst, but I have a question:

Bond dissociation energy of H2 = 436kJ/mol. But when H2 is adsorbed on the metal surface, the bond is broken. How come this simple step can break this strong bond? Where does the 436kJ energy come from / what gives this activation energy?

First the bond is not broken. H2 will be adsorbed on platinum. The same alkene does. There will interaction and hydrogen will bond to alkene. On the surface Pt-H and Pt- C bonds will built and in further reaction new C-H bonds will developed and the meralbond will be broken again.