Inverse CeO2/La2Sn1.7Co0.3O7-δ Catalyst for Methane Catalytic Combustion†

doi:10.7503/cjcu20150117

Abstract

Abstract:

The inverse CeO₂/La₂Sn_1.7Co_0.3O_7-_δ catalyst was prepared by sol-gel and impregnation method calcined at 900 ℃ and investigated in the methane catalytic combustion. The catalytic activity evaluated for methane combustion showed that the methane conversion temperature of T₉₀ was 564 ℃, compared with the pure La₂Sn_1.7Co_0.3O_7-_δ prepared in the same condition and mechanical mixing of La₂Sn_1.7Co_0.3O_7-_δ and CeO₂, T₉₀ decreased by 78 ℃ and 135 ℃, respectively, and the inverse CeO₂/La₂Sn_1.7Co_0.3O_7-_δ catalyst not only had the excellent methane combustion activity, but also had the well thermal stability and reusable performance. The excellent performance of the inverse CeO₂/La₂Sn_1.7Co_0.3O_7-_δ catalyst was represented by the characterizations of XRD, TEM, AFM, TPR, BET, XPS and Mössbauer spectra. XRD characterization showed that the inverse CeO₂/La₂Sn_1.7Co_0.3O_7-_δ catalyst not only had the La₂Sn_1.7Co_0.3O_7-_δ structure, but also had the CeO₂ phase, and the CeO₂ had been well disperse on the La₂Sn_1.7Co_0.3O_7-_δ composite oxide; TPR indicated that the CeO₂/La₂Sn_1.7Co_0.3O_7-_δ had lower reduction temperature compared to La₂Sn_1.7Co_0.3O_7-_δ, XPS and Mössbauer spectra indicated that the Sn⁴⁺ is the main valence state in the inverse catalyst, and the lattice oxygen play an important role in catalytic activity; TEM and BET tests showed that the CeO₂/La₂Sn_1.7Co_0.3O_7-_δ particles had better dispersed and larger surface area than La₂Sn_1.7Co_0.3O_7-_δ. All above explained the reasons of the CeO₂/La₂Sn_1.7Co_0.3O_7-_δ catalyst had excellent catalytic activity toward methane combustion.

Key words: Inverse catalyst, Pyrochlore, Ceric oxide, Methane catalytic combustion

CLC Number:

O643.36

TrendMD:

LI Lingcong, HU Ruisheng, BAI Yaqin, LI Jingjia, TANG Hailian, WANG Junhu, JI Shengfu. Inverse CeO₂/La₂Sn_1.7Co_0.3O_7-_δ Catalyst for Methane Catalytic Combustion^†[J]. Chem. J. Chinese Universities, 2015, 36(7): 1328.

Figures/Tables 11

Fig.1 XRD patterns of the catalystsa. La2Sn1.7Co0.3O7-δ; b. CeO2/La2Sn1.7Co0.3O7-δ; c. CeO2-La2Sn1.7Co0.3O7-δ; d. CeO2.

Table 1 Lattice parameters and average particle size of the La2Sn1.7Co0.3O7-δ

Sample	Catalyst	D/nm	Crystal system	Lattice parameter, a/nm	Unit cell volume/nm³	< $ε 2222$ >^1/2
a	La₂Sn_1.7Co_0.3O_7-_δ	29.6	Cubic	1.07049	1.2267	0.1183
b	CeO₂/La₂Sn_1.7Co_0.3O_7-_δ	14.1	Cubic	1.06867	1.2205	0.1813
c	CeO₂-La₂Sn_1.7Co_0.3O_7-_δ	29.4	Cubic	1.07037	1.2263	0.1210

Table 1 Lattice parameters and average particle size of the La2Sn1.7Co0.3O7-δ

Sample	Catalyst	D/nm	Crystal system	Lattice parameter, a/nm	Unit cell volume/nm³	< $ε 2222$ >^1/2
a	La₂Sn_1.7Co_0.3O_7-_δ	29.6	Cubic	1.07049	1.2267	0.1183
b	CeO₂/La₂Sn_1.7Co_0.3O_7-_δ	14.1	Cubic	1.06867	1.2205	0.1813
c	CeO₂-La₂Sn_1.7Co_0.3O_7-_δ	29.4	Cubic	1.07037	1.2263	0.1210

Fig.2 Catalytic performance of catalysts(A), T90 of catalysts with different calcination temperature of 900, 1000, 1100 and 1200 ℃(B), the cycling runs tests(C) and XRD patterns before(a) and after(b) methane oxidation reaction of inverse CeO2/La2Sn1.7Co0.3O7-δ catalyst calcined at 900 ℃(D)a. La2Sn1.7Co0.3O7-δ; b. CeO2/La2Sn1.7Co0.3O7-δ; c. CeO2-La2Sn1.7Co0.3O7-δ; d. CeO2.

Fig.3 N2 adsorption-desorption isotherms of La2Sn1.7Co0.3O7-δ(a) and CeO2/La2Sn1.7Co0.3O7-δ(b)

Table 2 BET surface area and pore size of the catalysts

Sample	Catalyst	BET surface/(m²·g^-1)	Pore volume/(cm³·g^-1)	Pore size/nm
a	La₂Sn_1.7Co_0.3O_7-_δ	2.4	0.0045	7.55
b	CeO₂/La₂Sn_1.7Co_0.3O_7-_δ	6.1	0.0216	14.25
c	CeO₂-La₂Sn_1.7Co_0.3O_7-_δ	2.5	0.0083	8.04
d	CeO₂	7.5	0.0251	16.98

Fig.4 TEM(A,D), HRTEM(B, E) and AFM(C, F) analyses of La2Sn1.7Co0.3O7-δ(A—C) and CeO2/La2Sn1.7Co0.3O7-δ(D—F)

Fig.5 TPR spectra of La2Sn1.7Co0.3O7-δ(a), CeO2/La2Sn1.7Co0.3O7-δ(b) and CeO2(c)

Fig.6 Mössbauer spectra of La2Sn1.7Co0.3O7-δ(a) and CeO2/La2Sn1.7Co0.3O7-δ(b)

Table 3 Mössbauer parameters of the Sn

Sample	Subspectrum	Spectral area(%)	IS	QS	Oxidation state of Sn
a	Doublet 1	27.4	0.29	4.44	Sn⁴⁺
	Doublet 2	72.6	0.24	1.52	Sn⁴⁺
b	Doublet 1	17.1	0.37	4.72	Sn⁴⁺
	Doublet 2	82.9	0.26	1.55	Sn⁴⁺

Fig.7 XPS spectra of O1s(A), Sn3d(B), La3d(C) for La2Sn1.7Co0.3O7-δ(a) and CeO2/La2Sn1.7Co0.3O7-δ(b)

Table 4 Binding energies of O1s and Sn3d for the catalysts

Catalyst	Binding energy of O₁_s/eV			Binding energy of Sn₃_d/eV
Catalyst	O_lat	O_ads	O_lat/(O_lat+O_ads)	3d_3/2	3d_5/2	ΔE
La₂Sn_1.7Co_0.3O_7-_δ	530.0	532.0	0.64	495.4	487.2	8.2
CeO₂/La₂Sn_1.7Co_0.3O_7-_δ	529.4	532.2	0.72	494.8	486.4	8.4

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Inverse CeO₂/La₂Sn_1.7Co_0.3O_7-_δ Catalyst for Methane Catalytic Combustion^†

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