DOC DAF 106 Three-Layer Catalyst – What Is It?

In the DAF XF 106 truck, the exhaust aftertreatment system that complies with Euro 6 standards consists of several advanced components, the most important of which is the pre-catalyst DOC, also known as the Diesel Oxidation Catalyst. When referring to a three-layer DOC catalyst, it most likely involves technology used in SCR (Selective Catalytic Reduction) and DPF (Diesel Particulate Filter) systems.

Pre-Catalyst DOC – Three-Layer: What Does It Mean?
A three-layer DOC catalyst means that its active coating consists of three layers, each with a different catalytic function. The typical structure is as follows:

1. Oxidation Layer (Pt, Pd)
   Responsible for oxidizing the following:
   • Carbon monoxide (CO) → CO₂
   • Unburned hydrocarbons (HC)
   • Partial conversion of NO to NO₂ (which is important for DPF operation)
2. Layer for Triggering DPF Regeneration
   In the presence of NO₂, passive regeneration of the diesel particulate filter (DPF) is possible.
3. Protective and Anti-Aging Layer
   Protects the catalyst from thermal degradation and contaminants such as ash or sulfur.