Catalytic Characteristic and Application Performance of Catalyzed DPFs Coated with Various Content of Precious Metal in China

摘要

Recent toxicological and epidemiologic studies have shown that diesel emissions have been a significant toxic air contaminant. Catalyzed DPF (CDPF) not only significantly reduces the PM mass emissions (>90%), but also further promotes carrier self-regeneration and oxidize more harmful gaseous pollutants by the catalyst coated on the carrier. However, some ultrafine particles and potentially harmful gaseous pollutants, such as VOCs species, originally emitted in the vapor-phase at high plume temperature, may penetrate through the CDPF filter. Furthermore, the components and content of catalyst coated on the CDPF could influence the physicochemical properties and toxicity intensity of those escaping ultrafine particles and gaseous pollutants. In this work, (1) we investigated the influence of precious metal content as a variable parameter on the physicochemical properties and catalytic activities of the small CDPF samples. Dispersion of the precious metal on the fresh samples presented decreasing tendency, with the precious metal content increasing. While the higher content of precious metal showed inhibitory effect on lattice contraction and sintering. The sample with medium content precious metal can maintain higher Pt ratio in high oxidation state and better oxygen storage capacity. As the precious metal content increasing, the aged samples had stronger degradation resistance performance on CO and NO_2. The sample coated with medium content had better activity and degradation resistance for C_3H_8. (2) Effects of full-scale CDPFs (CDPF-15, CDPF-25 and CDPF-35, the precious metal content were 15, 25 and 35 g/ft~3) on diesel gaseous and particulate components were researched by means of diesel bus chassis dynamometer. For CO and NO_2, CDPF-25 showed higher activity and selectivity, while it presented slightly poor selectivity to THC. CDPF-35 exhibited best activity for THC and lower activity for CO and NO_2 inversely. As for VOCs, the CDPFs exhibited increasing removal efficiency for alkane, oxygenated chemicals and PAHs, 50% ～70%. The precious metal content could influence its selectivity to those VOCs in real diesel emissions. As for OC/EC, there were obvious differences for the OC removal efficiency by various content sample while only slight difference for the EC removal efficiency. On removal efficiency for particle-phase PAHs, the PAHs from diesel vehicle were reduced by 91.1%, 93.1% and 91.1% by CDPF-15, CDPF-25 and CDPF-35, respectively. CDPF-25 showed higher removal efficiency for 4-, 5- and 6-ring PAHs, CDPF-15 showed higher removal efficiency for low-ring PAHs. The CDPFs could obviously reduce the toxicity equivalent of different benzene ring PAHs.