The Role of Additives in Precious Metal Catalysts
Briefly introduce the role of additives in precious metal catalysts.
The Role of Additives in Precious Metal Catalysts
Although additives do not directly participate in the catalytic reaction, they significantly improve the overall performance of the catalyst by enhancing its dispersibility, thermal stability, and resistance to poisoning.
Main Functions of Additives
Functions | Mechanisms of Action | Typical Additives |
Improved thermal stability | Inhibited precious metal sintering | CeO₂、ZrO₂、La₂O₃ |
Oxygen storage capacity | Buffered oxygen concentration fluctuations | CeO₂、CeO₂-ZrO₂ |
Anti-toxicity | Preferentially adsorbed poisons | La₂O₃、BaO |
Synergistic catalysis | Reduced ignition temperature | MnO₂、Co₃O₄、CuO |
Rare earth oxide additives
Additives | Core Functions | Key Mechanisms |
CeO₂ | Oxygen Storage + Stabilization | Ce³⁺↔Ce⁴⁺ buffers oxygen concentration, stabilizing Pt/Pd particles |
CeO₂-ZrO₂ | Oxygen Storage + Thermal Stabilization | The solid solution has higher oxygen storage capacity and stronger resistance to sintering |
La₂O₃ | Sulfur Poisoning Resistance | Preferentially reacts with SO₂, protecting precious metals |
CeO₂-ZrO₂ solid solution is the most important additive system, with superior oxygen storage capacity and thermal stability compared to pure CeO₂. La₂O₃ is an essential additive for sulfur-containing waste gas applications.
Transition metal oxide additives
Additives | Core Functions | Effects |
MnO₂ | Synergistically oxidizes VOCs | Lowers ignition temperature by 10-20℃, partially replaces precious metals |
Co₃O₄ | Promotes CO oxidation | Significantly lowers CO ignition temperature |
CuO | Promotes the oxidation of oxygen-containing VOCs | Has low ignition temperature for alcohols and esters |
Transition metal oxide promoters can reduce the amount of precious metals used by 10%-30% while maintaining similar catalytic activity.
Typical Dosage and Selection
Additives | Typical Dosage | Applicable Scenarios |
CeO₂-ZrO₂ | 5%-15% | General Purpose (Oxygen Storage + Thermal Stabilization) |
La₂O₃ | 1%-5% | Sulfur-containing waste gas |
MnO₂/Co₃O₄ | 5%-10% | Requires low-temperature ignition |
The total content of additives generally does not exceed 25% of the carrier mass.
Selection Recommendations
Operating Conditions | Recommended Additives |
General VOCs Treatment | CeO₂-ZrO₂ |
Sulfur-containing Waste Gas | CeO₂-ZrO₂ + La₂O₃ |
High Low-Temperature Start-up Requirements | MnO₂或Co₃O₄ |
High-Temperature Operation (>450℃) | CeO₂-ZrO₂ + La₂O₃ |
Summary
The roles of additives can be summarized as follows: CeO₂-ZrO₂ is the most versatile for oxygen storage and heat stabilization; La₂O₃ is essential for sulfur resistance; and MnO₂/Co₃O₄ provides synergistic effects at low temperatures. Additives can reduce the amount of precious metals used by 10%-30%, but excessive additives may cover active sites. The rational addition of additives is an effective means of balancing the performance and cost of precious metal catalysts.