Effect of Copper Doping on Lean NOx Trap Performance of Pt/Ba/CuxMg1-xAl2O4 Catalysts at High Temperatures †

doi:10.7503/cjcu20190226

Abstract

Abstract:

A series of Pt/Ba/Cu_xMg_1-_xAl₂O₄ catalysts with Cu doping was synthesized and used in high-temperature NO_x storage reduction reaction. The results demonstrate that BaCO₃, the NO_x storage component, redisperses in the NO_x storage reduction process. Moreover, the De-NO_x activity of the catalysts at high temperatures was determined by the NO_x storage capacity, rather than the NO oxidation and NO_x reduction ability of the catalysts. The NO_x storage capacity of the catalysts is directly linked to the thermal stability of nitrate species stored on the catalysts. NO_x mainly exists in the form of ionic nitrate species on Pt/Ba/MgAl₂O₄, while NO_x mainly co-exists as ionic nitrate and monodentate nitrate species on the Cu-doped catalysts. We discovered that monodentate nitrate species show higher thermal stability than ionic nitrate species. As a result, the Cu-doped catalysts exhibit the larger NO_x storage capacity and hence the higher De-NO_x activity. At the temperature range from 450 ℃ to 500 ℃, the addition of Cu greatly enhanced the NO_x removal percentage of the catalysts. Among all the catalysts, Pt/Ba/Cu_0.1Mg_0.9Al₂O₄ has the highest De-NO_x activity with NO_x removal percentage about 90% at 450 ℃.

Key words: High temperature, Cu doping amount, Pt/Ba/Cu_xMg_1-_xAl₂O₄, Thermal stability, NO_x storage reduction

TrendMD:

YIN Mengxin,LIU Dongsheng,ZHAO Dongyue,DING Tong,TIAN Ye,LI Xingang. Effect of Copper Doping on Lean NO_x Trap Performance of Pt/Ba/Cu_xMg_1-_xAl₂O₄ Catalysts at High Temperatures ^†[J]. Chem. J. Chinese Universities, 2019, 40(10): 2170.

Figures/Tables 11

Fig.1 XRD patterns of the fresh catalysts a. Pt/Ba/MgAl2O4; b. Pt/Ba/Cu0.1Mg0.9Al2O4; c. Pt/Ba/Cu0.3Mg0.7Al2O4.

Support	S_BET/(m²·g^-1)	Pore volume/(cm³·g^-1)	Pore diameter/nm
MgAl₂O₄	162.2	0.4	10.6
Cu_0.1Mg_0.9Al₂O₄	186.9	0.6	12.1
Cu_0.3Mg_0.7Al₂O₄	227.0	0.6	10.2

Fig.2 TEM images of the fresh catalysts Pt/Ba/MgAl2O4(A) and Pt/Ba/Cu0.1Mg0.9Al2O4(B)

Catalyst	O_ads/O_latt	Molar fraction of Pt(%)
Pt/Ba/MgAl₂O₄	0.14	1.1
Pt/Ba/Cu_0.1Mg_0.9Al₂O₄	0.21	1.3
Pt/Ba/Cu_0.3Mg_0.7Al₂O₄	0.17	1.5

Fig.3 NRP values of the catalysts at 250—500 ℃ a. Pt/Ba/MgAl2O4; b. Pt/Ba/Cu0.1Mg0.9Al2O4; c. Pt/Ba/Cu0.3Mg0.7Al2O4.

Fig.4 NOx concentration curves in alternative lean/rich cyclings at 450 ℃ (A) Pt/Ba/MgAl2O4; (B) Pt/Ba/Cu0.1Mg0.9Al2O4; (C) Pt/Ba/Cu0.3Mg0.7Al2O4.

Catalyst	NO to NO₂ conversion(%)	NO_x reduction efficiency(%)	NSC/(mmol·g^-1)	NRP(%)
Pt/Ba/MgAl₂O₄	48.0	87.0	0.58	72.9
Pt/Ba/Cu_0.1Mg_0.9Al₂O₄	53.6	92.1	0.67	89.7
Pt/Ba/Cu_0.3Mg_0.7Al₂O₄	60.9	88.6	0.65	82.9

Fig.5 NOx storage curves of the catalysts during the lean-phase at 450 ℃ a. Pt/Ba/MgAl2O4; b. Pt/Ba/Cu0.1Mg0.9Al2O4; c. Pt/Ba/Cu0.3Mg0.7Al2O4.

Fig.6 NOx-TPD profiles of the catalysts(A) and enlarged view of the red rectangle area in profile (A)(B) a. Pt/Ba/MgAl2O4; b. Pt/Ba/Cu0.1Mg0.9Al2O4; c. Pt/Ba/Cu0.3Mg0.7Al2O4. The dotted line is the trend of temperature over time.

Fig.7 FTIR spectra of the fresh catalysts(A) and the spent catalysts(B) a. Pt/Ba/MgAl2O4; b. Pt/Ba/Cu0.1Mg0.9Al2O4; c. Pt/Ba/Cu0.3Mg0.7Al2O4.

Fig.8 XRD patterns of the spent catalysts a. Pt/Ba/MgAl2O4; b. Pt/Ba/Cu0.1Mg0.9Al2O4; c. Pt/Ba/Cu0.3Mg0.7Al2O4.

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Effect of Copper Doping on Lean NO_x Trap Performance of Pt/Ba/Cu_xMg_1-_xAl₂O₄ Catalysts at High Temperatures ^†

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