Catalysts in Thermal Oxidizers

Catalyst Function in Oxidizers 

Certain types of oxidizers like catalytic oxidizers, recuperative catalytic oxidizers and regenerative catalytic oxidizers (RCOs), introduce a catalyst to promote oxidation of pollutants before they reach the combustion chamber at a significantly lower temperature than a recuperative or regenerative thermal oxidizers. The catalyst reacts with the VOCs and hazardous air pollutants (HAPs), weakening their bonds so they can be eliminated more easily. The effect is that VOCs and HAPs reach oxidation at a lower temperature, reducing the amount of fuel needed to heat the combustion chamber.  

LEARN MORE - Components of Industrial Oxidizers

How Do Catalysts Work?  

A catalyst material is embedded or coated onto a substrate, and polluted air is forced via fan over or through the substrate, normally a bead or monolith, which helps mix the air with the catalyst. The catalyst itself is typically a precious metal, with platinum (Pt) or palladium (Pd) being the most common type of catalyst material. These catalysts lower the amount of energy required within the combustion chamber by weakening their chemical bonds through absorption and reaction with the catalyst’s surface.  

The basic reaction pathway for catalysts like platinum or palladium is: 

• Adsorption → chemical breakdown → release of harmless byproducts (CO₂, H₂O). 

Lower Temperature = Fuel Savings 

Catalysts enable full oxidation at temperatures typically 300–600°F lower than non-catalytic oxidizers, which means significant savings on fuel consumption. For example, palladium-based systems often operate in the 600-800°F range, while platinum-based systems typically require 700-900°F for optimal performance. The lower the temperature required for oxidation, the less an oxidizer must rely on fuel to heat the combustion chamber to the needed temperature.  

Platinum 

Platinum binds with the reactant molecules (hydrogen, for example) and hydrocarbons in polluted airstreams, which helps to break the bonds of HAPs and VOCs before they are further broken down in the combustion chamber. This process also activates the atoms so they can react and bond with the oxygen in the combustion chamber to form water. Through this process, platinum maintains a stable metallic surface, allowing it to repeatedly bind and activate atoms within airstreams.  

Palladium 

Palladium has the unique ability to switch between oxidation states at different times during the catalysis cycle. This is needed because it cannot catalyze a coupling reaction unless it’s in its zero-oxidation state.  It first temporarily inserts itself in the bonds of reactant molecules to help pollutants ultimately form a new product (H2O, for instance) once it’s exposed to the high temps of the combustion stage. This insertion weakens the carbon bonds of the molecules while changing the palladium into a plus-two oxidation state. Now the palladium is less stable and slips out of the bonds with the original molecules which are now weakened, and it reforms in its zero-oxidation state, ready to catalyze with the next set of molecules.    

The steps for palladium catalysis include:  

1. Oxidative Addition - a step that oxidizes the palladium by a factor of two 

2. Transmetalation - pollutive substances react with the palladium and has their bonds broken 

3. Reductive Elimination - this is the microscopic inverse of the oxidative addition step, where the palladium returns to its original oxidation state, ready to repeat the cycle.  

Palladium vs. Platinum 

Certain airstreams are better served by platinum instead of palladium and vice versa. In general, platinum is more expensive and can handle more unpredictability within the airstream than palladium. Palladium is effective at lower temperatures, making it more efficient, but it’s also more prone to fouling.  

Effectiveness 

Palladium is more active for hydrocarbons like alkanes, various solvents and aromatic compounds, while platinum tends to offer more versatility across various operating conditions and a wider range of contaminants.  

Temperature 

Platinum needs slightly higher temperatures to achieve as high conversion efficiencies as palladium, but platinum offers more stability through a wider range of temperatures.  

Poisoning Resistance 

Palladium is more sensitive to contaminants like sulfur, halogens, and siloxanes, while platinum offers greater resistance. Generally, the more contaminated the air, the more platinum becomes the better choice. However, both catalysts can experience fouling under extreme conditions, so proper pre-treatment of airstreams is important.  

Durability 

Platinum holds the edge for temperature stability and is able to withstand temperature spikes better than palladium. Palladium will sinter and lose surface area, reducing its effectiveness in high-temp settings.  

Cost 

Platinum generally costs more than palladium, but both metals are subject to market fluctuations. While palladium may offer upfront savings, its higher sensitivity to fouling can lead to more frequent replacement if not properly managed. 

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KKI Offers Catalyst Guidance 

You don’t need a doctorate in organometallic chemistry to choose the best catalyst for your industrial process airstream. The team at Kono Kogs has the experience working with process airstreams across a wide range of industries to be able to suggest the proper catalyst for your industrial oxidizer. We’ll point you to a cost-effective solution that properly neutralizes airstream VOCs and HAPs so your process and your business can run smoother and in compliance with local pollution regulations.  

Contact our team today for help choosing a catalyst in your oxidizer.  

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