Structure-activity strategy comparison of (NH4)2CO3 and NH4OH precipitants on MnOx catalyst for low-temperature NO abatement.

• Precipitant style served a vital role on catalyst phase transition and structure features. • Surface acidity induced by precipitants acted as the main motivation for activity. • E-R and L-H paths co-existed on both catalysts while the former contributed more. • Possible structure-activity model of different precipitants on catalyst was proposed. Herein, the structure-activity strategy comparison of two different precipitants on MnO x catalyst for low-temperature NH 3 -SCR was investigated in detail. XRD results confirmed that ammonium carbonate (denoted as AC) could transfer manganese precursor from MnCO 3 to Mn 2 O 3 phase with temperature from 80 to 450 °C, while ammonium hydroxide (denoted as AH) facilitated the phase transition of MnO x from Mn 3 O 4 to the final Mn 5 O 8 phase. Further morphology defined that Mn-AC catalyst possessed a peculiar spherical feature while Mn-AH catalyst presented an accumulation of abundant nano-particles. The activity results suggested that Mn-AC catalyst possessed higher activity compared with Mn-AH catalyst at lower temperature, with over 60% conversion achieved from 100 to 225 °C and the maximum NO conversion reached circa (denoted as ca.) 85% at 175 °C. In addition, Mn-AC catalyst possessed stronger surface acidity and redox properties than Mn-AH catalyst, which served as an important motivation for the difference in activity. More manganese ions with higher valence and surface oxygen favored the superior redox circle of Mn-AC catalyst. Transient reaction revealed that the catalysts followed both Eley–Rideal (E-R) and Langmuir–Hinshelwood (L-H) pathways while the L-H pathway was harder to occur than the former due to the intense NO x transformation over catalysts. On account of these analyses, the possible structure-activity strategy comparison model of (NH 4) 2 CO 3 and NH 4 OH precipitants on MnO x catalyst was proposed. The anions of precipitant played a leading role in the formation of the catalytic phase and surface morphology, in which AC induced active Mn precursor to transfer from MnCO 3 to spherical Mn 2 O 3 while AH developed the initial Mn 3 O 4 to final Mn 5 O 8 phase. The transition behavior of active precursors under different precipitants was the root cause of the internal motivation of catalytic properties. [Display omitted] [ABSTRACT FROM AUTHOR]