Investigating NH3-SCR coupled with CO oxidation reaction mechanisms on titanium nanotube-loaded CuMnFe composite metal catalysts

Abstract

NOx and CO are the primary air pollutants emitted from sintering flue gas, and their effective treatment is crucial. However, achieving good N2 selectivity with the CuMnFe composite metal oxide catalyst alone is challenging due to its oxidizing nature. Hence, in this study, titanium dioxide nanotubes were employed as carriers for the catalyst. CuMnFe composite metal oxide catalysts supported on titanium dioxide nanotubes were prepared using the co-precipitation method. The optimized catalysts demonstrated excellent performance, maintaining over 90% conversion of NOx and CO at low temperatures ranging from 120 to 200 ℃. Furthermore, significant improvement in N2 selectivity was achieved using these catalysts. Characterization results revealed several positive effects of incorporating titanium dioxide nanotube carriers into the catalyst. Firstly, it efficiently reduced the mobility of adsorbed oxygen on the catalyst surface, thus decreasing its oxidation capacity. Secondly, the addition of carriers helped balance the acidity on the catalyst surface, leading to an increase in Lewis acid sites. These modifications in the catalyst's surface properties proved advantageous for the selective catalytic reduction reaction. Moreover, the mechanisms of NH3-SCR and CO oxidation over the catalysts were extensively studied using DRIFTS. The results demonstrated that the CO oxidation reaction followed the Mars-van Krevelen mechanism, with a competitive adsorption relationship observed between O2 and CO at the active sites. On the other hand, the NH3-SCR reaction primarily followed the Eley-Rideal mechanism, with minimal occurrence of the Langmuir-Hinshelwood mechanism in the SCR reaction. The presence of NH3 inhibits CO adsorption at the active site, resulting in decreased CO oxidation performance in the NH3-SCR-coupled CO oxidation reaction at low temperatures. Nevertheless, NH3-SCR can enhance NO conversion by utilizing some of the latent heat generated from the exothermic CO oxidation.