Operando Spectroscopy Unveils the Catalytic Role of Different Palladium Oxidation States in CO Oxidation on Pd/CeO₂ Catalysts

Abstract

Aiming at knowledge‐driven design of novel metal–ceria catalysts for automotive exhaust abatement, current efforts mostly pertain to the synthesis and understanding of well‐defined systems. In contrast, technical catalysts are often heterogeneous in their metal speciation. Here, we unveiled rich structural dynamics of a conventional impregnated Pd/CeO2 catalyst during CO oxidation. In situ X‐ray photoelectron spectroscopy and operando X‐ray absorption spectroscopy revealed the presence of metallic and oxidic Pd states during the reaction. Using transient operando infrared spectroscopy, we probed the nature and reactivity of the surface intermediates involved in CO oxidation. We found that while low‐temperature activity is associated with sub‐oxidized and interfacial Pd sites, the reaction at elevated temperatures involves metallic Pd. These results highlight the utility of the multi‐technique operando approach for establishing structure–activity relationships of technical catalysts.

Memory-dictated dynamics of single-atom Pt on CeO2 for CO oxidation

“…The kinetic feature of Pt/CeO 2 is also similar to that of reduced Pt/CeO 2 and Pt AT CeO 2 samples obtained after a reduction in CO at 275 °C (Supplementary Fig. S12 ), as well as the Pt or Pd clusters on CeO 2 11 , 24 . This indicates that Pt 1 might sinter in Pt/CeO 2 under CO oxidation conditions.…”

Size of cerium dioxide support nanocrystals dictates reactivity of highly dispersed palladium catalysts

“…S24). As we noted above, redispersion during CO oxidation at elevated temperature does not occur for larger Pd/PdO NPs on CeO 2 ( 38 ).…”

“…The trend in reaction orders was similar for the PdFSPimp catalysts (table S7). These data suggested that CO oxidation on large PdFSP NPs likely followed the Mars-van Krevelen mechanism, which involves O transfer from the support typical for conventional Pd-CeO 2 catalysts ( 38 ).…”

“…In contrast to the as-prepared state, low-frequency bands (<2100 cm −1 ) were also present and likely indicated the formation of metallic Pd clusters during CO oxidation. Metallic Pd species were less active than Pd single atoms at low temperature but could substantially contribute to overall activity at temperatures >125°C ( 31 , 38 ). On large PdFSP NPs, the fraction of metallic and clustered Pd species was considerably higher than that of atomically dispersed Pd, which explained its limited activity at low temperature.…”

Highly Selective Activation of C–H Bond and Inhibition of C–C Bond Cleavage by Tuning Strong Oxidative Pd Sites

“…Supported Pd-based catalysts are widely used in the oxidation reactions with the preeminent catalytic activity; − however, they are prone to cause the deep oxidation of organic compounds, resulting in the low product selectivity. Take the selective oxidation of alcohols for example, supported Pd-based catalysts exhibit high activity for alcohol oxidation whereas tend to cause deep oxidation to CO 2 at the elevated temperature. , The selectivity and yield of the selective oxidation products could be greatly decreased at high conversion of alcohol at high temperature.…”