1. Some data (the book’s table
2. for illustration only):

finely divided Ni — hydrogenation of oils;

• finely divided Fe — Haber–Bosch N₂ + 3H₂ ⇌ 2NH₃ (about 500 °C, 200 atm);
• V₂O₅ — contact process 2SO₂ + O₂ ⇌ 2SO₃, then SO₃ + H₂O → H₂SO₄ (via oleum);
• MnO₂ — decomposition of hydrogen peroxide 2H₂O₂ → 2H₂O + O₂ (the catalyst gives a lower-energy path, so the activation-energy barrier on the energy diagram is lower while the net energy released by the forward reaction is unchanged).
• Reason:
• the 4s and 3d electrons can form temporary bonds between the metal-surface atoms and the reacting molecules.
• This raises the concentration of reactants on the surface, weakens bonds inside the reactant molecules and so lowers the activation energy, increasing the reaction rate.
• Their ability to exist in several oxidation states also helps them form intermediates.
• A catalyst is not consumed, and it does not change the position of equilibrium or the heat of reaction.