Deactivation Mechanism of Pd Only Three-way Catalysts under Aging Temperature Gradient

doi:10.15541/jim20250396

Abstract

Abstract:

Pd/CZA catalyst composed of third-generation oxygen storage material CeO₂-ZrO₂-Al₂O₃ (CZA) loaded only with Pd represents a practical three-way catalyst (TWC) owing to its exceptional pollutant conversion efficiency and sintering resistance. Although the thermal degradation mechanism of Pd-based TWC has been confirmed to be closely associated with Pd sintering and the weakening of metal-support interaction (MSI), a systematic investigation into its thermal aging behavior under an extreme high-temperature gradient remains necessary. A series of Pd/CZA catalysts aged at 800-1000 ℃ were prepared in this study and their thermal degradation was systematically explored, presenting a pioneering investigation into the evolution pattern of the microchemical state of Pd with aging temperature gradient. The correlation among the microchemical state of Pd, MSI and aging resistance was evaluated through different characterization techniques. The results showed that catalytic activity exhibited a nonlinear decay with increasing aging temperature. Catalytic performance declined sharply in the range of 850-900 ℃, with increases of 26-40 ℃ and 39-67 ℃ for T₅₀ and T₉₀ (the temperatures at which the pollutant conversions are 50% and 90%, respectively) of carbon monoxide (CO), nitric oxide (NO) and hydrocarbons (HCs), while it showed little variation within the range of 900-1000 ℃. The underlying reason for this sharp decline in activity is an abrupt transformation in the microchemical state of Pd. When the aging temperature increases to 900 ℃, the Pd-O-Ce bond is weakened, which compromises the MSI. Consequently, Pd particles become unanchored, undergo rapid sintering and growth, and exhibit diminished capabilities for adsorbing and activating both reactants and oxygen.

Key words: temperature gradient, thermal aging, Pd-O-Ce bond, metal-support interaction, three-way catalyst

CLC Number:

O643

LIU Xuzi, SONG Zhaohua, ZENG Lu, QU Li, JIAO Yi, JIANG Fajun, LI Dacheng, YAN Huicheng, WANG Jianli, CHEN Yaoqiang. Deactivation Mechanism of Pd Only Three-way Catalysts under Aging Temperature Gradient[J]. Journal of Inorganic Materials, 2026, 41(8): 1148-1156.

Figures/Tables 10

Fig. 1 (a-d) Light-off curves of (a) CO, (b) NO, (c) propane (C3H8) and (d) propylene (C3H6); (e) Operation windows of the aged catalysts Simulated exhaust gas consisted of 4500 μL/L CO, 1200 μL/L NO, 120 μL/L C3H8, 220 μL/L C3H6, 3130 μL/L O2, 1500 μL/L H2, 110 mL/L CO2, 100 mL/L H2O, and N2 as the balance gas. Operation window was tested at 400 ℃. Colorful figures are available on website

Table 1 T50 and T90 values of CO, NO and HCs of the aged catalysts

Sample	CO		NO		C₃H₈		C₃H₆
Sample	T₅₀/℃	T₉₀/℃	T₅₀/℃	T₉₀/℃	T₅₀/℃	T₉₀/℃	T₅₀/℃	T₉₀/℃
Pd/CZA-800	233	254	252	263	269	297	241	255
Pd/CZA-850	237	256	254	266	271	295	242	256
Pd/CZA-900	263	295	292	310	311	362	275	295
Pd/CZA-950	272	302	298	313	314	353	280	300
Pd/CZA-1000	265	295	298	310	303	324	278	295

Table 2 Textural properties of catalysts

Sample	S_BET/(m²•g^-1)	Pore volume/ (mL•g^-1)	Average pore size/nm
Pd/CZA-800	61	0.44	23.2
Pd/CZA-850	67	0.42	24.5
Pd/CZA-900	67	0.41	24.7
Pd/CZA-950	69	0.43	24.6
Pd/CZA-1000	70	0.40	29.1

Fig. 2 (a) H2-TPR curves, (b) O2-TPD curves, (c-g) Pd3d XPS spectra and (h) Pd species ratio of the catalysts Colorful figures are available on website

Fig. 3 (a-c) HRTEM images of (a) Pd/CZA-900, (b) Pd/CZA-950 and (c) Pd/CZA-1000; (d) XRD patterns of the catalysts and partial enlarged view of the pink area; (e) Pd dispersion and particle size of the catalysts

Fig. 4 (a) DOSC profiles of CO-O2 alternating pulse, (b) DOSC values and (c) H2-O2 atmosphere alternating TG curves of the catalysts Colorful figures are available on website

Fig. 5 (a) C3H8 and (b) CO2 desorption signals of C3H8-TPD over the catalysts Colorful figures are available on website

Fig. 6 Schematic diagram of structure-activity relationship

Fig. S1 TEM images of (a) Pd/CZA-800, (b) Pd/CZA-850, (c) Pd/CZA-900, (d) Pd/CZA-950 and (e) Pd/CZA-1000

Fig. S2 HRTEM images of (a) Pd/CZA-800, (b) Pd/CZA-850, (c) Pd/CZA-900, (d) Pd/CZA-950 and (e) Pd/CZA-1000

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