Development of a DOC+SCR Exhaust Catalyst System for Light Duty Truck (N_2 Category) Meeting NS-V Regulation

摘要

The 4JB1 diesel engine originated from Isuzu has large share in the China light duty truck market. However, the tightened NO_x emission target enforced by NS-V legislation compared with NS-IV regulatory standard is very challenging for this engine platform which originally adopted the DOC+POC catalyst layout. Furthermore, combustion characterization of this type engine leads to high soluble organic fraction (SOF) content in engine out particulates, which requires the catalysts in the exhaust after-treatment system (ATS) to deliver high SOF conversion efficiency in order to meet the regulation limit for particulate matters (PM). In this paper, an innovative exhaust catalyst layout with DOC+V-SCR is introduced. The front DOC is specially formulated with optimized PGM (Platinum Group Metal) loading which ensures effective SOF oxidation while keeping sulfuric acid and sulfate generation minimal. The dual DOC bricks in tandem are sophisticatedly engineered to maximize gas-solid surface interaction with the aim of further enhancing particulate removal efficiency. The downstream Vanadium based SCR is designed with improved low temperature deNO_x performance as well as relatively high thermal stability. The robustness of the proposed catalyst system has been demonstrated on 4JB1 type of engines, over 50% reduction in total PM (TPM) and ca. 80% NO_x conversion could be achieved. Catalyst deterioration has been proved to be minor over 750 hours’ and 100,000 kilometers’ durability tests. This DOC+V-SCR catalyst layout represents a cost-effective solution for NS-V applications fit for China market.