Graphene Based Mesoporous Manganese-Cerium Oxides Catalysts: Preparation and Low-temperature Catalytic Reduction of NO

doi:10.15541/jim20230229

Abstract

Abstract:

Manganese and cerium oxides are extensively used for selective catalytic reduction (SCR) in denitrification reaction due to their high redox ability and excellent low-temperature SCR activities. However, these catalysts still face problems such as easy aggregation of active components and low specific surface area, which restricts the enhancement of catalytic activity. Here, graphene based SiO₂ nanocomposites (G@SiO₂) with mesoporous structure was used as the template to prepare series of graphene based mesoporous manganese-cerium oxides (G@MnO_x-CeO₂) catalysts by hydrothermal method. The obtained catalysts were investigated for selective catalytic reduction (SCR) of NO at low temperature (100-300 ℃). The results indicate that G@MnO_x-CeO₂catalyst exhibits better SCR activity than graphene based cerium oxides (G@CeO₂). With the mass ratio of Mn and Ce to G@SiO₂of 0.35 and 0.90, respectively, the G@Mn(0.35)Ce(0.9) catalyst shows the best NO removal activity with the maximum conversion of 80% at 220 ℃. It is found that the addition of appropriate amount of MnO_x increases specific surface area and pore volume but decreases crystallinity of the catalyst G@MnO_x-CeO₂. Furthermore, MnO_xand CeO₂are uniformly distributed on the surface of graphene sheets in the form of nanoparticles. In addition, partial replaced Ce atoms is actually doped with Mn atoms into the structure of CeO₂to form MnO_x-CeO₂ solid solution, resulting in higher percentage of Mn³⁺and Mn⁴⁺ with higher valance states and Ce⁴⁺, and higher concentration of surface chemisorbed oxygen on the surface. These results contribute to higher SCR activity of the G@Mn(0.35)Ce(0.9) catalyst. This work provides promising basic data for the practical application of MnO_x-CeO₂based catalysts in low temperature NH₃-SCR.

Key words: graphene, cerium oxide, manganese oxide, NO, selective catalytic reduction

CLC Number:

TQ426

WANG Yanli, QIAN Xinyi, SHEN Chunyin, ZHAN Liang. Graphene Based Mesoporous Manganese-Cerium Oxides Catalysts: Preparation and Low-temperature Catalytic Reduction of NO[J]. Journal of Inorganic Materials, 2024, 39(1): 81-89.

Figures/Tables 14

Fig. 1 Preparation of G@MnOx-CeO2 catalyst

Fig. 2 NO conversions at different reaction temperatures over various catalysts

Fig. 3 NO conversions over G@MnOx-CeO2 catalysts with different metal loadings

Fig. 4 (a) Nitrogen adsorption/desorption isotherm and (b) corresponding pore size distribution curve of G@SiO2 template

Fig. 5 (a) Nitrogen adsorption/desorption isotherms and (b) corresponding pore size distribution curves of G@MnOx-CeO2 catalysts with different metal loadings

Table 1 Pore parameters of various catalysts

Sample	S_BET/ (m²·g^-1)	V_total/ (cm³·g^-1)	Average pore size/nm
G@Ce(0.9)	65.0	0.125	7.67
G@Mn(0.18)Ce(0.45)	241.2	0.230	3.81
G@Mn(0.35)Ce(0.9)	197.5	0.287	5.82
G@Mn(1)Ce(2.7)	126.6	0.199	6.29

Fig. 6 SEM images of G@Mn(0.35)Ce(0.9) catalyst

Fig. 7 (a-d) TEM images, (e-i) TEM image and corresponding C, Mn, Ce, O element mappings for selected area of G@Mn(0.35)Ce(0.9) catalyst

Fig. 8 XRD patterns of different samples

Fig. 9 Raman spectra of G@Ce(0.9) and G@Mn(0.35)Ce(0.9) catalysts

Fig. 10 XPS spectra of G@Mn(0.35)Ce(0.9) catalyst (a) Total survey; (b) C1s; (c) O1s; (d) Mn2p; (e) Ce3d

Table 2 Surface atomic concentrations of G@Mn(0.35)Ce(0.9) catalyst

Sample	Surface atomic concentration/%				Relative atomic ratio/%
Sample	C	O	Mn	Ce	O_β/O	(Mn³⁺+Mn⁴⁺)/Mn
G@Mn(0.35)Ce(0.9)	18.10	65.72	8.26	7.92	45.2	80.1

Fig. S1 Cyclic NO removal activity of G@Mn(0.35)Ce(0.9) catalyst

Fig. S2 SEM images of G@SiO2 mesoporous template

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