A comparison of hierarchical Pt@CeO2/Si–Al2O3 and Pd@CeO2/Si–Al2O3

• Pt@CeO2/Si–Al2O3 core–shell catalysts calcined at 773 K and 1073 K were studied.
• TEM image shows agglomeration of Pt@CeO2/Si–Al2O3 core–shell calcined at 1073 K.
• Pt@CeO2/Si–Al2O3 has higher stability under WGS conditions than Pd@CeO2/Si–Al2O3.
• Similar CeO2 reducibility in the Pt@CeO2/Si–Al2O3 compared to Pd@CeO2/Si–Al2O3.
• Weaker interaction between Pt and CeO2 than the Pd and CeO2 in these samples.

A comparison of catalytic and adsorption properties for Pt@CeO2/Si–Al2O3 (1-wt% Pt and 9-wt% CeO2) and Pd@CeO2/Si–Al2O3 (1-wt% Pd and 9-wt% CeO2) core–shell catalysts indicates that the CeO2 shell is stable for Pd but not for Pt. Following calcination at 773 K, Pt@CeO2/Si–Al2O3 exhibits water–gas-shift (WGS) rates in 3% H2O and CO that are similar to rates found on conventional Pt/CeO2, implying that there is good contact between the Pt and CeO2 phases, even at the relatively low CeO2 loading. WGS rates on Pt@CeO2/Si–Al2O3 were also reasonably stable with time and unaffected by pre-reduction of the catalyst. By comparison, WGS rates over Pd@CeO2/Si–Al2O3 declined rapidly due to reduction of CeO2 and were suppressed by pre-reduction of CeO2. After calcination to 1073 K, large metal particles were observed with Pt@CeO2/Si–Al2O3, but not on Pd@CeO2/Si–Al2O3. Coulometric titration measurements on these two materials suggest stronger interactions between CeO2 and Pd and these are likely responsible for the higher stability of the core–shell structure in Pd@CeO2 compared to Pd@CeO2.

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