How Platinum Is Used for Catalysis

Platinum is one of the most effective and widely used catalytic materials in modern technology. From fuel cells and chemical plants to automotive emission control systems, platinum enables reactions to occur faster, more efficiently, and under milder conditions than would otherwise be possible. To understand why platinum is so valuable, it helps to look at how it works at the atomic level, how it is applied in catalytic converters, and where else it plays a critical industrial role.

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How Does A Platinum Catalyst Work?

If you understand electrolysis, it is helpful to think of a fuel cell as electrolysis reversed.

In water electrolysis, you apply a voltage to split water into hydrogen and oxygen. In theory, a minimum voltage is required to make the reaction happen. In practice, however, you may need more than the minimum voltage. This additional voltage is called "overpotential," and it is a measure of the energy losses that occur because the reaction is not ideal on the electrode surface.

Platinum is special because, for hydrogen reactions, its overpotential is very close to zero. This means that hydrogen reactions happen very efficiently on a platinum surface, with very little energy loss. This is why platinum is so valuable in hydrogen fuel cells and electrolyzers.

A slightly more detailed explanation of why platinum is useful has to do with how platinum interacts with molecules on its surface.

Hydrogen gas (H₂), for example, does not react easily in free space at room temperature. But when H₂ molecules come into contact with a platinum surface, something important happens:

• The hydrogen molecule adsorbs (sticks) onto the platinum surface.
• The H–H bond weakens and breaks.
• Two new Pt–H bonds form.
• Each hydrogen atom can then lose an electron more easily, forming protons (H⁺).

The key is balance. Platinum binds hydrogen strongly enough to break the H–H bond, but not so strongly that the hydrogen atoms remain permanently stuck. Metals that bind hydrogen too weakly cannot activate it efficiently. Metals that bind it too strongly hold onto it and slow the reaction. Platinum sits near the "sweet spot" in this balance, which makes it exceptionally effective.

More broadly, platinum belongs to the group of metals known as the Platinum Group Elements (PGEs), which include palladium, rhodium, ruthenium, iridium, and osmium. These metals share several important characteristics:

• High melting points
• Strong resistance to corrosion
• Multiple oxidation states
• High capacity for adsorbing gases

How Platinum Catalyst Is Commonly Used in Catalytic Converters

One of the most prominent and largest applications of platinum catalysts is in the catalytic converters of automobiles.

The catalytic converter was invented in the mid-1970s as a result of air quality regulations that demanded radical cuts in emissions from automobiles. The Clean Air Act in the United States resulted in the widespread use of catalytic converters from 1975 onwards. Such legislation emerged in Europe and other parts of the world in the 1990s.

The catalytic converter is mounted on the exhaust system of the vehicle. Its complexity is not immediately evident from its exterior design.

Within the stainless steel casing is a ceramic monolith in the form of a honeycomb. The honeycomb design enables a vastly increased surface area with little resistance to the flow of exhaust gases.

The ceramic substrate is then coated with a "washcoat" layer. The washcoat adds to the surface area and also aids in the stabilisation of the active metals. The platinum group metals, which include platinum (Pt), palladium (Pd), and rhodium (Rh), are then dispersed as very fine nanoparticles on the layer. The overall loading of PGEs is normally about 0.1% by weight, but since they are dispersed as particles smaller than 10 nanometres in size when new, their surface area is massive.

In petrol engines, "three-way" catalytic converters perform three simultaneous reactions:

• Oxidation of carbon monoxide (CO) to carbon dioxide (CO₂)
• Oxidation of unburned hydrocarbons (UHCs) to CO₂ and water
• Reduction of nitrogen oxides (NOₓ) to nitrogen (N₂)

Platinum and palladium primarily catalyse the oxidation reactions. Rhodium is particularly effective for NOₓ reduction. In simple terms, platinum inside a catalytic converter provides a reactive surface where harmful exhaust gases are converted into less toxic substances before they leave the tailpipe.

Other Uses of Platinum Catalysts

Although catalytic converters are the most familiar application, platinum's catalytic role extends far beyond the automotive industry.

Fuel Cells and Hydrogen Energy

In proton exchange membrane (PEM) fuel cells, platinum is used at both electrodes:

• At the anode, it catalyses hydrogen oxidation (H₂ → 2H⁺ + 2e⁻).
• At the cathode, it catalyses oxygen reduction (O₂ + 4H⁺ + 4e⁻ → 2H₂O).

These reactions generate electricity with water as the only by-product. Platinum's low overpotential for hydrogen reactions is critical for high fuel cell efficiency.

Chemical Manufacturing

Platinum catalysts are widely used in:

• Hydrogenation of organic compounds
• Petroleum reforming to improve petrol octane ratings
• Production of nitric acid (often using platinum-rhodium gauze for ammonia oxidation)

In many of these processes, platinum operates at high temperatures and in corrosive environments where less noble metals would degrade rapidly.

Silicone and Specialty Chemical Production

Platinum catalysts are essential in hydrosilylation reactions used to produce silicones. These materials are widely applied in electronics, medical devices, sealants, and coatings.

Environmental and Industrial Gas Treatment

Platinum is also used in industrial oxidation processes, air purification systems, and waste gas treatment units. Its durability and recyclability make it suitable for long-term, high-throughput industrial operations.

Conclusion

Platinum's catalytic power comes from a rare combination of properties: it adsorbs gases effectively, activates chemical bonds efficiently, and remains stable under extreme thermal and chemical conditions. In catalytic converters, it transforms harmful exhaust gases into safer emissions. In fuel cells, it enables efficient hydrogen energy conversion. In chemical plants, it drives large-scale industrial reactions with precision and durability.

Reference:

[1] Pianowska, Karolina & Kluczka, Joanna & Benke, Grzegorz & Goc, Karolina & Malarz, Joanna & Ochmański, Michał & Leszczyńska-Sejda, Katarzyna. (2023). Solvent Extraction as a Method of Recovery and Separation of Platinum Group Metals. Materials. 16. 4681. 10.3390/ma16134681.