Pd/Support Interface-Promoted Pd−Ce_0.7Zr_0.3O₂−Al₂O₃ Automobile Three-Way Catalysts: Studying the Dynamic Oxygen Storage Capacity and CO, C₃H₈, and NO Conversion

Abstract

The effect of the Pd-support interface on the dynamic oxygen storage capacity (DOSC) and three-way catalytic activities were investigated using Pd chromatographically distributed between Ce 0.7 Zr 0.3 O 2 and Al 2 O 3 . CO-He pulse, H 2 -TPR, and XPS show that the Pd-(Ce, Zr) Ox interface promotes a higher degree of oxygen releasing than the Pd-(Al 2 O 3 ) interface while maintaining the oxidized states of Pd. Pd promotion at the Pd-(Ce, Zr) Ox interface depends on the oxygen species of ceria-zirconia, and promotion takes place on surface oxygen and subsurface oxygen species. Dynamic CO-O 2 transient measurement shows that DOSC is greatly promoted by the Pd-(Ce, Zr) Ox interface. The transient results indicate that the Pd-(Ce , Zr) Ox interface accelerates the oxygen spillover and back-spillover between Pd and the support oxide, but this phenomenon is not obvious for the Pd-(Al 2 O 3 ) interface. Higher CO oxidation activity was obtained over a catalyst with a higher degree of Pd-(Ce, Zr) Ox interface in proportion to its DOSC performance. A two-step CO oxidation mechanism at the Pd-(Ce , Zr) Ox interface includes oxygen migration and its reaction with the adsorbed CO. Higher NO reduction and C 3 H 8 oxidation rates were obtained with a catalyst with more Pd-(Al 2 O 3 ) interface, showing negative correlation with the DOSC performance.

Influence of thermal treatment on catalytic performance of Pd/(Ce,Zr)Ox–Al2O3 three-way catalysts

“…Decreased intensity of the hydride peak suggests that less Pd was reduced on initial exposure to H 2 for the catalyst with support calcined at higher temperature, and consequently less hydride was formed. This, along with the increased temperature of PdO reduction, is consistent with a stronger interaction between the metal and the support for the catalyst calcined at higher temperature of its support [37,38]. At the same time, the results further show that the dispersion state of active species changes during calcination of the support due to the sintering and the decreasing of the BET surface area of CZA.…”

Chemoselective Hydrogenation of Cinnamaldehyde over Pd/CeO2–ZrO2 Catalysts

“…Zirconia incorporation also increases the thermal stability of CeO 2 and improves the metal-CeO 2 interactions. CeO 2 -ZrO 2 -supported Pd has been used as three-way catalysts [11][12][13][14][15][16], in natural gas combustion [17], total oxidation of hydrocarbons [18], methanol decomposition [19], vapor phase hydrogenation of phenol [20] and in several other reactions [21]. We report here the chemoselective hydrogenation activity of these novel catalysts.…”

Promotion of CeO2–ZrO2–Al2O3 composite by selective doping with barium and its supported Pd-only three-way catalyst

“…A negative peak at about 60 • C is seen for all samples, which is originated from the decomposition of PdH x . In general, metallic Pd would adsorb hydrogen to form PdH x even at room temperature and quite low hydrogen pressure [52,54]. During the temperature-programmed reduction process, PdH x could easily be decomposed and the generated hydrogen species consequently gives rise to the appearance of the negative peak in the TPR profile.…”