Explain the reaction of nitriles to form amines and alkenes to form alkanes

The reaction of nitriles to form amines involves reduction of nitriles with hydrogen gas (H2) and a metal catalyst (e.g., LiAlH4 or NaBH4), while the reaction of alkenes to form alkanes is through hydrogenation using hydrogen gas (H2) and a metal catalyst (e.g., Pt, Pd, or Ni).