Sulfur Poisoning Effects on Modern Lean NO_x Trap Catalysts Components

In the present work, a series of different materials was investigated in order to enhance the understanding of the role of modern lean NO_x trap (LNT) components on the sulfur poisoning and regeneration characteristics. Nine different types of model catalysts were prepared, which mainly consisted of three compounds: (i) Al₂O₃, (ii) Mg/Al₂O₃, and (iii) Mg/Ce/Al₂O₃ mixed with Pt, Pd, and Pt-Pd. A micro flow reactor and a diffuse reflectance infrared Fourier transform spectrometer (DRIFTS) were employed in order to investigate the evolution and stability of the species formed during SO₂ poisoning. The results showed that the addition of palladium and magnesium into the LNT formulation can be beneficial for the catalyst desulfation due mainly to the ability to release the sulfur trapped at relatively low temperatures. This was especially evident for Pd/Mg/Al₂O₃ model catalyst, which demonstrated an efficient LNT desulfation with low H₂ consumption. In contrast, the addition of ceria was found to increase the formation of bulk sulfate species during SO₂ poisoning, which requires higher temperatures for the sulfur removal. The noble metal nature was also observed to play an important role on the SO_x storage and release properties. Monometallic Pd-based catalysts exhibited the formation of surface palladium sulfate species during SO₂ exposure, whereas Pt-Pd bimetallic formulations presented higher stability of the sulfur species formed compared to the corresponding Pt- and Pd-monometallic samples. View Full-Text