Effects of the Topological Structure of Different Cu-Zeolites on the Relationship between Soot and NO_x Removal on NH₃-SCRF

Experimental studies were carried out to explore the effect of zeolite topology on NOx purification and soot oxidation in ammonia selective catalytic reduction coated diesel particulate filter (SCRF) catalysts. The catalytic activity of Cu-exchanged zeolites Cu/SSZ-13 (CHA topology), Cu/ZSM-5 (MFI), and Cu/BEA(BEA) was evaluated in the NH3-SCRF. Experiments with XRD and ICP-SFMS demonstrated that the three types of samples retained their typical structural peaks after Cu modification, and the similar ratios of Cu/Al and Si/Al ensure that the primary cause of different catalytic performances was caused by different framework structures. As determined by laboratory experiments with synthetic gas, Cu/SSZ-13 exhibited an extended activity window and a higher deNO(x) efficiency at NO2/NOx below 0.5. In addition, Cu/ZSM-5 consistently exhibited superior CO2 selectivity in soot-loading experiments, regardless of the NO2 concentration. When loaded with soot, Cu/BEA exhibited exceptional deNO(x) performance at NO2/NOx = 0.5. NH3 was observed to have a negative effect on soot oxidation by NO2, while the consumption of NO2 by soot oxidation contributed to the NO2-SCR reaction being aided. Influenced by different zeolite structural features, the degree of diffusion of copper in the zeolite as well as the replacement sites are different, thus forming different ratios of copper species. For instance, the presence of Z2Cu sites, which can adsorb more NH3 molecules than ZCuOH sites as indicated by the in situ DRIFTS results, and the presence of Cu+ with stronger redox properties compared to Cu2+, can be influenced by these structural characteristics. Additionally, soot particles have the ability to act as adsorption sites for the NH3-SCR reaction.