Development of NO sorbents tolerant to sulfur oxides

Sulfur-tolerant NO sorbents based on Pt/TiO2 were developed by adding base oxide additives such as MxOy (M = Li, Na, K, Cs, Sr, Ba, La). The base oxide additives were effective in improving the NO sorption capacity of Pt/TiO2 under both SO2-free and SO2-containing atmospheres. Under an SO2-containing atmosphere, the NO sorption capacity during sorption reaction for 6 h was not affected over Pt–Li2O/TiO2 but was significantly deteriorated over the other sorbents. TPD spectra of H2S in H2 after a sorption reaction of 6 h in SO2-containing atmosphere showed that SO2 stored on Pt–Li2O/TiO2 was released at the lowest temperature. In addition to the weak basicity of lithium compared with other additives, Li2TiO3 formed over Pt–Li2O/TiO2 could lead to instability of the sulfates on Pt–Li2O/TiO2, giving rise to the desorption of sulfur-containing species at the lowest temperature. In situ FTIR indicated that the formation of bulk-like sulfate that needs high temperature to decompose was slow over Pt–Li2O/TiO2, which also contributed to the excellent SO2 tolerance of Pt–Li2O/TiO2.