Impacts of Pb and SO₂ Poisoning on CeO₂-WO₃/TiO₂-SiO₂ SCR Catalyst

A CeO₂-WO₃/TiO₂-SiO₂ catalyst was employed to investigate the poisoning mechanisms of Pb and SO₂ during selective catalytic reduction (SCR). The introduction of Pb and SO₂ suppressed the catalytic performance by decreasing the numbers of surface acid and redox sites. Specifically, Pb preferentially bonded with amorphous WO₃ species rather than with CeO₂, decreasing the numbers of both Lewis and Brønsted acid sites but exerting less influence on the reducibility. SO₂ preferentially bonded with CeO₂ as sulfate species rather than with WO₃, leading to a significant decrease in reducibility and the loss of surface active oxygen groups. Although SO₂ provided additional Brønsted acid sites via the interaction of SO₄^2- and CeO₂, it had little positive effect on catalytic activity. A synergistic deactivation effect of Pb and SO₄^2- on CeO₂ was found. Pb covered portions of the weakly bonded catalyst sites poisoned by SO₄^2-, which increased the decomposition temperature of the sulfate species on the catalyst.