Three separate reactions are listed below. Each reaction is known to be catalyzed, but the dominant catalytic strategy differs among them.
I. Hydrogenation of ethene to ethane using finely divided nickel at 150 °C and 4 atm H₂.
II. Hydration of 2-methylpropene to 2-methyl-2-propanol using aqueous H₃O⁺ at 25 °C.
III. Decomposition of H₂O₂ to H₂O and O₂ mediated by the enzyme catalase at 37 °C.
For each reaction, classify the catalytic strategy and support your choice with chemical reasoning.
(a) For reactions I–III, classify each catalyst as primarily (i) binding/orientation, (ii) covalent (including acid–base), or (iii) surface catalysis. Provide one specific piece of mechanistic evidence or reasoning for each classification.
(b) For one reaction of your choice, explain why the net concentration of the catalyst remains constant throughout the reaction, even though the catalyst is temporarily consumed in an elementary step.