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| - First Knowledge on the Formation of Novel Core−Shell Structures in PdCu Catalysts andTheir Influence on the Prevention of Catalyst Deactivation
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| - TiO2 supported PdCu catalysts (PdCu/TiO2) showed a good long-time stability (160 h) with high activity(X = 60%) and selectivity (ca. 95%) in the gas phase acetoxylation of toluene to benzyl acetate. Characterizationof these catalysts was mainly carried out using X-ray photoelectron spectroscopy (XPS) and transmissionelectron microscopy (TEM). These methods provided new insights into the dynamic changes occurring duringtime-on-stream particularly in the catalyst structure and the nature of carbon deposition. Migration of Cufrom deeper layers to the near-surface region during the reaction could be observed. In addition, the Pdparticles also grew significantly during the reaction. Interestingly, formation of novel core−shell structureswith Pd core and CuO shell was observed during time-on-stream. Such core−shell arrangement observed forthe first time in PdCu solids was found to influence the nature of carbon deposits during the catalytic reactionshowing a layer-like carbon structure. This observation made on PdCu/TiO2 is in contrast to the depositsfound on PdSb/TiO2, where carbide-like carbon is generated and caused easy deactivation of the samples.The formation of this layer-like kind of carbon in the present PdCu solid seems to weaken the interactionbetween catalytically active surface species (Pd and/or Cu) and carbon atoms from deposited coke, which inturn leads to a stable catalytic performance.
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