Integration of Vanadium and Zeolite Type SCR Functionality into DPF in Exhaust Aftertreatment Systems - Advantages and Challenges

摘要

Today, the DPF and SCR catalysts are combined sequentially in diesel exhaust systems. However, such sequential system configuration has several drawbacks: 1) large volume; 2) insufficient temperature for the SCR catalyst during cold start when DPF is placed in front of SCR; and 3) unfavorable conditions for passive soot regeneration if SCR is placed upstream of the DPF. The problems can potentially be solved by integrating the SCR catalyst into the particulate filter as one multifunctional unit. The study indicates that SCRonDPF based on Cu-zeolite type as SCR material can achieve the NO_x conversion levels close to flow-through SCR catalysts for LDV (Light Duty Vehicles) using forced regenerations. Forced soot regeneration solves potential sulfur poisoning. For HDV (Heavy Duty Vehicles) applications with full managed passive soot regenerations, integration of V-based SCR formulations on DPF represents an attractive solution due to high sulfur resistance accompanied by low-temperature fuel economy. Laboratory tests and engine bench tests as WHTC (World Harmonized Transient Cycle) and NRTC (Non-road transient cycle) on large samples show that a high NO_x conversion comparable to SCR flow-through catalysts is obtainable on both SCR catalyst types with limited pressure drop, when the NO_2/NO_x ratio is managed by an active DOC. Cu-zeolite has an advantage over V-based SCR-catalyst below 300°C. WHTC results show higher NO_x conversion for both Cu-SCR on DPF and V-SCR on DPF compared to similar flow-through catalysts. For the warmer NRTC test V-SCR in filter shows better NO_x conversion than Cu-zeolite in DPF.