3.5.4 Transition Metals - Catalysis


Students should:
  • know that transition metals and their compounds can act as heterogeneous and homogeneous catalysts

Transition metal catalysts

Catalysts are substances that increase the rate of a reaction and that can be recovered unchanged chemically at the end of the reaction.

Transition metals and their salts have proven to be very effective catalysts for many reactions. This is normally attributed to the availability of the 'd' orbitals and the variable oxidation states exhibited by transition metals. Below are a few examples.

Transition metal catalyst Process
Nickel Hydrogenation of alkenes
Iron Haber process for ammonia production
Vanadium(V) oxide Contact process for sulfuric acid production
Molybdenum(VI) oxide Oxidation of methanol to methanal
Platinum/Rhodium Nitric acid production
Palladium Exhaust gas conversion
Titanium compounds Zeigler Natta addition polymerisation
Manganese(IV) oxide Hydrogen peroxide decomposition

Example: The industrial manufacture of methanol

On industrial scale methanol is prepared from a mixture of carbon monoxide and hydrogen. The gaseous mixture is subjected to 200 atmospheres and then passed over heated catalyst mixture of ZnO and Cr2O3 kept at 400º C to 450º C. This reaction results the formation of methanol vapours which are then condensed to liquid state.

CO + 2H2 CH3-OH


Heterogeneous and homogeneous catalysis

The state of the catalyst may be the same as that of the reactants, in which case it is termed homogeneous, or it may be in a different state, heterogeneous.

The latter is the most common form of catalysis, as it is more controllable industrially.