Birdnest-like CuCeZr Mixed Oxides: Synthesis and Excellent Catalysts for Diesel Exhaust Oxidatio

doi:10.15541/jim20160662

Abstract

Abstract:

A series of ternary composite oxides CuCeZrO_x calcined at different temperatures were prepared by a homogeneous precipitation method using urea as the precipitant. X-ray diffraction (XRD), N₂ adsorption-desorption analysis, X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscope (STEM), and temperature-programmed reduction (or desorption, oxidation) (TPR, TPD or TPO) measurements were utilized to investigate the influence of calcination temperatures on the physicochemical property and catalysis performance towards soot catalytic oxidation. The CCZ-350 (calcined at 350℃) sample exhibits the optimized catalysis performance: temperature at the maximum rate of soot oxidation (T₅₀) = 407℃, under test conditions of space velocity = 12000 mL/(g_catalyst·h), c(O₂) = 10vol%, c(NO) = 500×10^-6, and mass ratio of (loosely contacted) catalyst/soot = 10/1. It is believed that theabundant high-reactive adsorbed oxygen species on CCZ-350 surface contribute much to its outstanding catalysis performance. Besides, CCZ-350 with a loose-packing and porous morphology favors its sufficient contact with soot, thus further benefiting the catatlytic activity towards soot combustion. More importantly, CCZ-350 also presents good water vapor and SO₂ resistence performance as well as good capability of eliminating other pollutants in diesel exhaust at low temperatures (150-400℃), such as CO, C₃H₆ and C₃H₈.

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Key words: ternary composite oxides catalyst, CuCeZrOx, soot oxidation, water vapor and SO₂resistence

CLC Number:

TQ174

ZHAO Han, ZHOU Xiao-Xia, PAN Lin-Yu, CHEN Hang-Rong. Birdnest-like CuCeZr Mixed Oxides: Synthesis and Excellent Catalysts for Diesel Exhaust Oxidatio[J]. Journal of Inorganic Materials, 2017, 32(9): 923-930.

Figures/Tables 11

Fig. 1 XRD patterns of the different CCZ-x catalysts(x = 300-1000)

Table 1 Structural properties of different CCZ-x catalysts (x = 300-1000)

Sample	Lattice parameter /nm ^a	S_BET/ (m²·g^-1) ^b	V_BJH/ (cm³·g^-1) ^c	D_p/nm ^c
CCZ-300	5.416	198.0	0.960	33.8
CCZ-350	5.415	186.0	0.900	32.6
CCZ-400	5.420	160.0	0.850	33.6
CCZ-500	5.418	128.0	0.800	32.5
CCZ-600	5.420	110.0	0.700	32.9
CCZ-800	5.415	12.0	0.150	49.0
CCZ-1000	5.389	0.1	0.001	No data

Fig. 2 Temperature-programmed oxidation of soot catalyzed by different CCZ-x catalysts (x = 300-1000): soot conversion curves (a), and the change in characteristic temperatures (T90 and T50) and selectivity to CO2 () with increasing calcination temperature (b)

Fig. 3 Ce 3d (a) , Cu 2p (b), Zr 3d (c), and O 1s (d) XPS patterns of CCZ-x (4: x = 300, 3: x = 350, 2: x = 500, 1: x = 800)

Table 2 XPS surface analyses of different CCZ-x (x = 800, 500, 350, 300)

Sample	Cu: Ce: Zr ^a	O_ads/(O_ads+O_latt)
CCZ-800	0.17: 0.60: 0.23	0.23
CCZ-500	0.15: 0.65: 0.20	0.46
CCZ-350	0.12: 0.67: 0.21	0.64
CCZ-300	0.12: 0.69: 0.19	0.57

Fig. 4 H2-TPR profiles of the selected CCZ-x catalysts (x= 300, 350, 500, and 800) Data in the brackets indicate the integrated area of the H2-TPR curves

Fig. 5 O2-TPD profiles of the selected CCZ-x catalysts (x= 300, 350, 500, and 800) Data in the brackets indicate the integrated area of the O2-TPD curves

Fig. 6 Dark-field (a) and bright-field (b) STEM images and elements mapping (c-e) (corresponding to TEM image in b) of CCZ-350 Scale bars: 100 nm

Fig. 7 Schematic representation of (a) the role of the “nest structure” of CCZ-350 in soot combustion process, and (b) the soot combustion in NOx/O2 over CCZ-350 catalyst

Fig. 8 Water vapor and SO2 resistance properties of catalytic activity towards soot oxidation for CCZ-350

Fig. 9 Catalytic co-oxidation of CO, C3H6 and C3H8 over CCZ-350

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