MCR history
Dalton UK of Metal Catalysts
The following reactions are the bare minimum examples of transition metals acting as catalysts that everyone studying chemistry and general science should know. Catalysts are written over the reaction arrow, sometimes with (cat) after the formula, to distinguish them from reactants and products.
The Haber Process
This is one of the best known reactions involving a transition metal catalyst. It is the formation of ammonia from nitrogen and hydrogen using iron as the catalyst. This is a heterogeneous system.
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Fe |
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N2(g) + 3H2(g) |
---> |
2NH3(g) |
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Contact Process
This reaction is part of the production of sulphuric acid. The reaction between sulphur dioxide and oxygen to form sulphur trioxide is catalysed by vanadium (V) oxide, V2O5. This is a heterogeneous system.
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V2O5 |
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2SO2(g) + O2(g) |
---> |
2SO3(g) |
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Hydrogenation (Reduction)
Raney nickel, which is very finely divided nickel powder, is a catalyst for the addition of hydrogen across C=C and C=C bonds. Finely divided platinum, and finely divided paladium also catalyse this sort of reaction, but are a bit expensive. This is a heterogeneous system.
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Raney Ni |
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2CH2=CH2(g) + H2(g) |
---> |
2CH3-CH3(g) |
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The margarine industy uses the above type of reaction to convert unsaturated vegetable oils into higher metal point saturated fats - i.e. margarine.
Decomposition
Manganese dioxide catalyses the decomposition of hydrogen peroxide. Lots of other things catalyse this reaction too, but MnO2 is one of the best. This is a heterogeneous system.
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MnO2 |
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2H2O2(l) |
---> |
2H2O(l) +O2(g) |
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Advanced Examples of Catalysts
On more advanced courses, you may come across the following examples of transition metals acting as catalysts.
Catalytic Convertors
The pollutants NO and CO are removed from car exhaust fumes by passing the exhaust gases over platinum and rhodium to produce nitrogen and carbon dioxide. This is a heterogeneous system.
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Pt / Rh |
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NO(g) + CO(g) |
---> |
N2(g) +CO2(g) |
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Decomposition
Cobalt (II) catalyses the decompositon of the chlorate(I) anion, in two steps, as it is easily converted to cobalt (III). This is a heterogeneous system.
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4Co(OH)2(s) + 2ClO-(aq) + 2H20 |
---> |
4Co(OH)3(s) + 2Cl-(aq) |
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4Co(OH)3(s) |
---> |
4Co(OH)2(s) + 2H20 + O2(g) |
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Ziegler-Natta Polymerisation
Titanium tetrachloride in the presence of triethylaluminium polymerises ethene, CH2=CH2. This is a heterogeneous system. A similar system using vanadyl halides exists in the co-polymerisation of styrene, butadiene and either dicyclopentadiene or 1,4-hexadiene to form synthetic rubber.
Many other examples of transiton metals and their compounds acting as catalysts can be found in text books. Yes, text books. Do try reading them sometimes as they are very helpful. |
