Chemistry Reference
In-Depth Information
d
n
4
r
4
n
g
|
2
Figure 4.5
Impact of oxygen on the selective oxidation of (top left) cinnamyl alcohol,
(bottom left) 1-phenylethanol and (right) 2-octanol.
Adapted from Refs 51, 54 and 57 with permission from Elsevier.
TOFs towards cinnamyl and crotyl alcohol (Figure 4.6).
37,40
In accordance
with the observations of Grunwaldt et al., operando liquid-phase XAS of Pd/C
and Pd/Al
2
O
3
-SBA-15 catalysts during cinnamyl alcohol selox evidenced
in situ reduction of PdO (Figure 4.6); however, by virtue of simultaneously
measuring the rate of alcohol selox, Lee and co-workers were able to prove
that this oxide
.
metal structural transition was accompanied by coincident
deactivation. Together, these findings strongly implicate a (surface) PdO
active phase, consistent with surface science predictions that metallic
palladium favours aldehyde decarbonylation and consequent self-poisoning
by CO and organic residues,
46,64
-
akin to that reported during fatty acid
decarboxylation over Pd/MCF.
65
In order to establish conclusively whether oxide or metal is responsible
for alcohol selox catalysed by dispersed palladium nanoparticles, a multi-
dimensional spectroscopic investigation of vapour-phase crotyl alcohol selox
was undertaken (since XAS is an averaging technique, a complete under-
standing of catalyst operation requires multiple analytical techniques).
66-68
Synchronous, time-resolved diffuse reflectance infrared Fourier transform
spectroscopy (DRIFTS)/mass spectrometry (MS)/XAS measurements of sup-
ported and colloidal palladium were performed in a bespoke environmental
cell
69
to interrogate simultaneously adsorbates on the catalyst surface,
Pd oxidation state and reactivity under transient conditions in the absence of
Search WWH ::
Custom Search