NbTi-modified amorphous CeMnOx catalysts for low temperature removal of NO and suppression of N2O formation

Abstract

The abatement of emissions from low-temperature flue gas in non-power industries has emerged as a pressing issue in China, which involves not only the elimination of nitrogen monoxide (NO) but also the prevention of nitrous oxide (N₂O) formation. However, during the denitrification process using ammonia selective catalytic reduction (NH₃-SCR) technology, balancing high NO conversion with low N₂O formation presents a key challenge. Efficiently coupling acidic sites with redox sites has emerged as a promising strategy to address this problem. The selected amorphous CeMn catalyst exhibits high redox capacity. Herein, Nb_xTi_y-CeMn catalysts were prepared using an excess-impregnation method. Nb and Ti are predominantly dispersed on the catalyst's external surface, and Nb_xTi_y-CeMn retain an amorphous nature. With an appropriate Nb content, the surface Nb₂O₅ and the segregated Mn₂O₃ function as Brønsted and Lewis acidic sites, respectively. Such efficient surface coupling of acidic and redox sites maintains high NO conversion of the prepared catalysts while markedly suppressing N₂O formation. Nb_xTi_y-CeMn exhibit excellent low-temperature NH₃-SCR activity, where Nb_10%Ti_15%-CeMn shows T_NO,90% = 120−313 °C and enhanced N₂ selectivity (about 80% at 250 °C). Notably, the acidic, moisture, and sulfur-containing low-temperature flue gas plays a positive role in suppressing N₂O formation. With supplemented acidic and moisture atmosphere, Nb_1%Ti_15%-CeMn achieves desirable low temperature activity (T_NO,90% = 124−407 °C, and N₂ selectivity ≥ 79% at the range of 70−250 °C) than Nb_10%Ti_15%-CeMn. These findings provide valuable insights for designing SCR catalysts with highly redox-active transition metal and rare-earth metal oxides. In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTs) results reveal that the introduction of appropriate Brønsted acid sites maintains the coexistence of Eley-Rideal (E-R) and Langmuir–Hinshelwood (L-H) mechanisms, ensuring the low-temperature activity.