Characterization of Nb-Containing MnO_x−CeO₂ Catalyst for Low-Temperature Selective Catalytic Reduction of NO with NH₃

Abstract

The reactivity in the selective catalytic reduction of the individual and binary components of NbO x −MnO x −CeO2 catalysts has been studied with coated cordierite monoliths in the temperature range of 150−450 °C. FTIRS, DRIFTS, TA, XRD, BET, and XAS have been used to elucidate the structural and catalytic properties. The results confirmed the contribution of the manganese oxides, particularly to the low-temperature NO-to-NO2 oxidation reaction. The significant increase of the surface acidity as a result of niobium oxide addition has been established. The data obtained revealed also the strong interaction between the manganese and niobium catalytic active sites. This phenomenon leads to a very good distribution of the oxidizing and acidic sites in the catalyst structure and also diminishes the unselective NH3 oxidation at higher temperatures. However, in order to keep the low-temperature catalytic activity, an excess of manganese relative to the niobium content is needed.

Promotional effect of Nb additive on the activity and hydrothermal stability for the selective catalytic reduction of NO with NH3 over CeZrO catalyst

“…CeNb 3.0 Zr 2 O x catalyst, with Nb/Ce molar ratio of 3.0:1, exhibited the largest amount of NH 4 + bound to Brønsted acid sites and NH 3 linked to Lewis acid sites among the series catalysts, which was quite in accordance with its highest NH 3 -SCR performance. It has been reported that the surface acidity of NbO x -MnO x -CeO 2 was significantly increased as a result of Nb addition [37]. In addition, the Nb OH bond was • C on Nb2O5 and CeNbaZr2Ox series catalysts.…”

“…It was quite clear that the introduction of Nb decreased both the intensity and quantity of bands assigned to nitrate species, which might arise from the fact that the addition of Nb promoted the formation of more acid sites together with fewer alkali sites where the nitrate species adsorbed [33]. It was also reported that the adsorption of nitrate species on MnO x -NbO x -CeO 2 was weaker than that on MnO x -CeO 2 as a result of Nb addition [37].…”

“…It was reported that the NH 3 -SCR reactivity of Nbcontaining MnO x -CeO 2 was dramatically improved as a result of Nb addition, and the characterization results indicated that the strong interaction between Nb and Mn catalytic active sites resulted in a remarkable dispersion of the oxidizing sites together with acidic sites and inhibited the unselective NH 3 oxidation at high temperatures [15]. CeO 2 -Nb 2 O 5 catalyst containing abundant surface absorbed oxygen, which might result from the short-range activation effect of Nb to Ce species, also exhibited excellent SCR performance [16].…”

Manganese–niobium mixed oxide catalyst for the selective catalytic reduction of NOx with NH3 at low temperatures

“…Niobium oxides have been reported to be introduced into V 2 O 5 /TiO 2 catalysts, and the conversion of NO increased 2-4 times at low temperatures [16]. The addition of Nb to MnO x -CeO 2 was found to be very effective in improving the activity and N 2 selectivity due to the significant increase of the surface acidity [17,18]. In this study, a series of Mn-Nb oxide catalysts were prepared by a homogeneous precipitation method and were applied to low temperature NH 3 -SCR of NO x .…”

Study of the surface evolution of nitrogen species on CuO/CeZrO2 catalysts

“…According to many authors, adsorption of ammonia can proceed at the Brønsted or Lewis acid sites, forming NH 4 ? or adsorbed NH 3 [33,34]. When ammonia is adsorbed on the Brønsted acid sites, the bands in the 1480-1395 cm -1 region of absorption can be observed [2,10,34].…”