| Summary: | The modification of the Cu(4)/CeO2, catalyst with 1 wt% of Ag resulted in a significant increase in the NO reduction activity compared to 2 and 3 wt% Ag. The Cu(4)/Ag(1)CeO2 catalyst consisted of isolated Cu2+ species and Ag(n)delta+ clusters, while the Cu(4)/Ag(3)CeO2 catalyst contained mostly octahedral Cu2+ species as indicated by the results from the UV-Vis DRS characterization. Therefore, it is presumed that isolated Cu2+ species on the Cu(4)/Ag(1)CeO2 catalyst and Ag(n)delta+ clusters formed active-sites responsible towards a higher catalytic activity for NO reduction by propylene compared to octahedral Cu2+ species. The competitiveness factor S(SCR-HC) for Cu(4)/Ag(3)CeO2
catalyst was much lower than Cu(4)/Ag(1)CeO2 catalyst in the whole temperature range, indicating that the high loading of Ag enhanced the oxidation of C3H6 by O2. As a result, less amount of C3H6 reacted selectively with NO. In addition, the selectivity of CO for NO +C3H6 + O2 reactions was higher than those for C3H6 + O2 reactions on all the Cu(4)/Ag/CeO2 catalysts indicating the generation of organic intermediates by partial oxidation of hydrocarbon which would lead to the production of significant amount of CO related to NO reduction.
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