Ag-modified CuO-Fe2O3 composite catalysts for low-temperature NH3-SCO

Abstract

A series of CuFe and Ag-modified CuFe composite catalysts were prepared for low-temperature selective catalytic oxidation of ammonia (NH₃-SCO). Significant synergistic effects existed between Cu and Fe oxides in the CuFe(7:12) catalyst for catalyzing NH₃ oxidation. Loading 6 wt.% Ag over CuFe(7:12) further enhanced NH₃ conversion and N₂ selectivity. At 200 °C, NH₃ conversion and N₂ selectivity reached 97.1 % and 79.3 %, respectively, over 6Ag/CuFe(7:12). Besides the exceptional catalytic effects of Ag species, the increased surface area, formation of CuFe₂O₄, improved reducibility of Cu and Fe oxides, and increased acid sites due to the composite of Cu and Fe and modification with Ag contributed to the superior performance of the 6Ag/CuFe(7:12) catalyst in NH₃-SCO. In-situ DRIFTS results showed that NH₃ oxidation might follow the internal selective catalytic reduction mechanism: NH₃ was dehydrogenated and oxidized to NO_x and nitrate species, and the formed NO_x and nitrate species were reduced by the remaining NH₃, −NH₂ and −NH species to N₂ and H₂O. Loading Ag over CuFe(7:12) suppressed the formation of NO and NO₂ but promoted that of N₂O during NH₃ oxidation, which could be attributed to the enhanced formation and decomposition of NH₄NO₃ in the presence of Ag.