NO reduction by CO over Pd/Ce0.6Zr0.4O2/Al2O3 catalysts: In situ FT-IR Studies of NO and CO adsorption

Adsorption of CO-, NO- and CO/NO-containing mixtures was investigated by in situ IR spectroscopy under flow conditions over Pd/δ-Al 2O3 and Pd/Ce0.6Zr0.4O 2/δ-Al2O3. The attention is focused on the effects of Ce0.6Zr0.4O2 addition to Pd/Al2O3 on the catalytic properties and reaction intermediates. Linearly bonded and bridged CO species adsorbed on palladium were clearly identified on Pd/Al2O3 while CO adsorption is inhibited under reaction conditions in the presence of Ce 0.6Zr0.4O2. Addition of Ce0.6Zr 0.4O2 affects the nature of the Pd sites by stabilizing oxidized dispersed Pd species. Evidence is obtained that the presence of the Ce0.6Zr0.4O2 solid solution modifies the adsorption properties of the supported Pd species and promotes the reduction of NO below 500 K via an alternative mechanism. This presumably involves reactive oxygen species at the Pd-Ce0.6Zr0.4O2 interface generated by the redox Ce4+/Ce3+ couple.