SDPF (Selective Catalytic Reduction Filter) or SCRF (SCR on Filter) is an integrated after‑treatment device that combines a DPF (Diesel Particulate Filter) with an SCR (Selective Catalytic Reduction) catalyst coating on the same substrate. This configuration simultaneously removes particulate matter (soot) and reduces NO_x emissions.

Structure and operating principle:

• The SCRF is positioned close to the engine outlet (tight‑coupled) to reach urea decomposition temperature and SCR light‑off temperature quickly, avoiding excessive NO_x emissions during cold starts.
• Urea is injected upstream of the SCRF; the generated NH₃ reacts with NO_x over the SCR catalyst layer, while the filter walls trap soot.
• At low temperatures (below 200°C), urea decomposition is incomplete and NO₂ conversion is limited. The tight‑coupled SCRF overcomes this by achieving faster warm‑up.
• A downstream under‑floor SCR catalyst (with higher catalyst loading) provides additional NO_x conversion during normal driving. Some heavy‑duty systems also include a small auxiliary SCR with an ASC (Ammonia Slip Catalyst) to control excess NH₃.
• NO_x sensors upstream of the DOC and downstream of the SCRF are used to control urea dosing and monitor SCRF performance.

This layout (DOC + SCRF close‑coupled + under‑floor SCR) is typical for modern Euro 6 heavy‑duty diesel engines.

Although both are wall‑flow ceramic filters, SDPF (SCRF) and DPF differ significantly in design and function:

The key structural difference is that the SDPF/SCRF has higher porosity to accommodate the SCR washcoat without excessively increasing backpressure.

The following diagram illustrates the NO_x conversion efficiency of a close‑coupled SCRF system compared to an under‑floor SCR system, based on real test data.

Diagram interpretation:

• The cc‑SCRF (solid curve) achieves high NO_x conversion (>80%) already at ~250°C, while the under‑floor SCR (dashed curve) reaches the same level only above 400°C.
• Two urea injection points are shown: one upstream of the cc‑SCRF and a second upstream of the under‑floor SCR (for heavy‑duty applications).
• A small auxiliary SCR is placed downstream to handle residual NH₃.
• NO_x sensors before and after the system enable precise urea dosing and performance monitoring.

This configuration ensures optimal NO_x reduction across the entire operating range, especially during transient conditions.

The coating of platinum (Pt) on the SDPF/SCRF significantly affects performance, especially at low temperatures. Here is a detailed comparison:

In summary, Pt coating greatly improves cold‑start NO_x reduction and passive regeneration, but adds cost and complexity. The choice depends on emission targets and operating conditions.

Our SDPF/SCRF products use a copper‑based zeolite (Cu‑zeolite) as the SCR catalyst material.

Key advantages of Cu‑zeolite SCR:

• Excellent low‑temperature activity: Effective even below 200°C, ideal for cold‑start and low‑load conditions.
• High hydrothermal durability: Withstands temperatures up to 650°C without significant degradation.
• Good resistance to sulfur poisoning compared to iron‑based zeolites.
• Broad operating window: Maintains high NO_x conversion from 200°C to 500°C.
• Lower precious metal content than vanadium‑based systems, reducing cost.

This Cu‑zeolite coating is applied to the cordierite or silicon carbide DPF substrate (depending on the model) to provide both particulate filtration and SCR functionality in a single unit.

Main functions:

• Particulate filtration: Traps soot and ash particles from diesel exhaust, reducing PM emissions by > 90%.
• NO_x reduction: Converts nitrogen oxides (NO and NO₂) into harmless nitrogen (N₂) and water (H₂O) via selective catalytic reduction.
• Passive soot oxidation: Generates NO₂ from NO (with Pt coating) to oxidise trapped soot at lower temperatures, reducing regeneration frequency.

Working principle (step‑by‑step):

1. Exhaust gas enters the SCRF – containing NO, NO₂, soot, and other gaseous pollutants.
2. Urea injection – AdBlue (urea‑water solution) is sprayed upstream; it decomposes into NH₃ and CO₂.
3. NH₃ mixes with exhaust and flows into the SCRF channels.
4. Filtration – The wall‑flow structure forces the gas through the porous walls, trapping soot on the inlet channels.
5. SCR reaction – NH₃ reacts with NO_x over the Cu‑zeolite catalyst layer on the filter walls, producing N₂ and H₂O.
6. Regeneration – Accumulated soot is periodically burned off via passive oxidation (using NO₂) or active regeneration (raising exhaust temperature to ~600°C).
7. Clean gas exits – with significantly reduced particulate and NO_x emissions.

This integrated design saves space, reduces system complexity, and improves overall emission control efficiency compared to separate DPF + SCR units.

Both cordierite and silicon carbide (SiC) are used as DPF/SCRF substrates. Their differences are summarized below:

In general, cordierite is cost‑effective and suitable for standard applications, while SiC offers superior thermal durability and is preferred for heavy‑duty and high‑temperature conditions, especially where frequent regeneration is required.

Our minimum order quantities vary by material type:

• Silicon Carbide (SiC) material: 3 pieces (3pcs)
• Cordierite material: 10 pieces (10pcs)

These MOQs are set to ensure efficient production and coating processes. For larger volumes, we offer competitive pricing and shorter lead times. If you require a specific quantity below these MOQs, please contact our sales team to discuss possibilities.

Our company headquarters is located at:

Building C, Zhongguan Innovation Center, Dongcheng 2nd Road, Pujiang Town, Minhang District, Shanghai, China

We welcome business visits by appointment. Please contact us in advance to arrange a suitable time.

You can reach our team directly via WhatsApp or email. We are happy to assist with any questions about products, sizing, orders, or technical support.

We typically respond within 24 hours (Monday–Saturday). Please include your order number or vehicle details for faster assistance.