Selective Palladium-Catalysed Aerobic Oxidation of Alcohols - Transition Metal Catalysis in Aerobic Alcohol Oxidation - page 101

d n 4 r 4 n g | 2

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Figure 4.7 (Left) cartoon of operando DRIFTS/MS/XAS reaction cell and resulting

temperature-dependent behaviour of Pd oxidation state and associated
reactivity towards crotyl alcohol oxidation over a Pd/meso-Al 2 O 3 catalyst.
Only selective oxidation over surface PdO occurs at 80 1C, whereas
crotonaldehyde decarbonylation and combustion dominate over Pd
metal at 250 1C. (Top right) relationship between Pd oxidation derived
in situ and crotyl alcohol conversion. (Bottom right) summary of
reaction-induced redox processes in Pd-catalysed crotyl alcohol selox.
Adapted with permission from Refs 70 and 72. Copyright 2011 and 2012
American Chemical Society.

confirmed that only two-dimensional Pd 5 O 4 and three-dimensional PdO x
surfaces were capable of crotonaldehyde production (Figure 4.8). 73 However,
even under oxygen-rich conditions, on-stream reduction of the Pd 5 O 4
monolayer oxide occurred at 470 1C accompanied by surface poisoning
by hydrocarbon residues. In contrast, PdO x multilayers were capable of
sustained catalytic turnover of crotyl alcohol to crotonaldehyde, conclusively