Question

Factors responsible for catalytic activity of transition metals.

• A. Large surface area.
• B. Variable oxidation state.
• C. Ability to form complexes.
• D. Presence of empty d - orbitals.

Answer 1

Answer: (B), (C), (D)

Variable oxidation state, Ability to form complexes, Presence of empty d - orbitals.

Answer 2

The catalytic activity of transition metals is primarily attributed to their unique electronic configurations and chemical properties. The key factors are:

• Variable Oxidation States: Transition metals can exhibit multiple oxidation states due to the small energy difference between their (n-1)d and ns orbitals. This allows them to readily undergo redox reactions, acting as electron donors or acceptors in the reaction mechanism, and forming unstable intermediate compounds with reactants. This ability to cycle through different oxidation states is crucial for many catalytic processes.

• Ability to Form Complexes: Transition metals have vacant d-orbitals and a strong tendency to form coordination complexes with reactant molecules (ligands). The formation of these intermediate complexes brings reactants together, orienting them favorably, and activating them by weakening existing bonds. This provides an alternative reaction pathway with a lower activation energy.

• Presence of Empty/Partially Filled d-orbitals: The availability of vacant or partially filled d-orbitals allows transition metals to accept electron pairs from reactant molecules, forming coordinate bonds. This facilitates the adsorption of reactants onto the metal surface (in heterogeneous catalysis) or the formation of intermediate complexes (in homogeneous catalysis). These orbitals also play a role in the variable oxidation states and electron transfer processes.

• Large Surface Area: While a large surface area is crucial for the efficiency of heterogeneous catalysts (by providing more active sites), it is not the intrinsic chemical/electronic property of the transition metal itself that makes it catalytically active. The fundamental catalytic ability stems from the electronic structure, while surface area enhances the reaction rate. Therefore, it's a factor in effective catalysis but not the sole reason for the metal's inherent catalytic property.