CHEMCATCHEM
FULL PAPERS
erogeneously catalyzed processes to illustrate the applicability
and versatility of synthesized materials and to compare such
activities with similar supported Fe O nanoparticles prepared
2
3
by using other synthetic protocols. Supported Fe O nanoparti-
2
3
cles were reported previously to be highly active and selective
[
25,28]
in oxidations
and Lewis acid-catalyzed processes owing to
[
25,29]
the inherent Lewis acidity of Fe O nanomaterials.
Results
2
3
of the catalytic activity of CFP nanomaterials in the microwave-
assisted selective oxidation of benzyl alcohol are summarized
in Table 2 and compared to previously reported similar Fe/Al-
SBA-15 systems.
CFP iron-containing materials could reach conversions of
45–50% after 5 min of reaction, with high selectivities to ben-
zaldehyde (>75%). Particularly good results were obtained
À1
with CFP2 (Fe/AlZn-SBA, flow rate 2 mLmin ) in terms of con-
version and selectivity to benzaldehyde, which indicated the
reaction was not nanoparticle-size-sensitive. Comparatively,
analogous type of materials synthesized by using the conven-
tional wetness impregnation technique (IMP-Fe/AlZnSBA,
Tables 2 and 3) could reach a maximum conversion of 26%
(98% selectivity to benzaldehyde) under identical reaction con-
ditions. Even Fe-based systems prepared by using advanced
methodologies including microwave-assisted deposition (MW-
Fe/AlZnSBA, Tables 2 and 3) and mechanochemical dry ball-
milling (BM-Fe/AlZnSBA, Tables 2 and 3) provided comparable
activities under identical conditions (conversions of typically
Figure 7. Reuses of CFP0.5 in the microwave-assisted A) oxidation of benzyl
alcohol and B) alkylation of toluene with benzyl chloride (for reaction condi-
tions, see Tables 2 and 3, respectively).
40–45%), illustrating the outstanding catalytic activities of the
CFP nanomaterials.
Fe-containing aluminosilicates were subsequently explored
in the microwave-assisted alkylation of toluene with benzyl
chloride (Table 3). For this particular process, results showed
a remarkable increase in activity for CFP nanomaterials (88–
tion was observed in most cases, in good agreement with pre-
[32,25,28]
vious reports.
Only in the case of the alkylation reaction
(Figure 7B) was significant deactivation observed in the
second and third use that was due partly to the removal of
weakly physisorbed or deposited Fe species (some Fe was ob-
served in solution), owing to the generation of HCl as a byprod-
uct of the reaction of benzyl chloride. Upon regeneration, the
catalytic activity was recovered owing to a combination of the
activity of Fe O nanoparticles and oxychloride species gener-
99% conversion) compared to conventional impregnation, mi-
crowave, and even mechanochemical ball-milling-synthesized
catalysts under otherwise identical reaction conditions. Quanti-
tative conversion of starting material was observed for CFP0.1
and CFP2, which was a significant improvement on the typical
2
3
4
0–65% conversion achieved previously for Fe-containing ma-
ated in the materials, similar to that reported previously for
[33]
terials under identical reaction conditions. Although further in-
vestigations are required to better understand the influence of
analogous Zr-SBA-15 materials.
[30,31]
the electronic structure on catalytic activity in the systems,
Conclusions
the proposed system has potential to provide access to a wide
range of advanced nanomaterials for catalytic applications in
a very simple and straightforward way.
A continuous flow synthesis of supported nanoparticles on
porous materials was reported. Featuring simplicity, efficiency,
better process control, and the possibility of scaling up the
synthesis to the multigram-scale, the synthesized supported
Fe O nanomaterials possessed a remarkable activity and versa-
Stability and reusability of CFP nanomaterials were also in-
vestigated in the key microwave-assisted processes. Iron-con-
taining nanomaterials were deactivated gradually after each
use, with improved catalytic activities only after regeneration
of the materials upon calcination (Figure 7). The most plausible
explanation for the quick deactivation relates to the poisoning
of highly accessible active sites on the external surface of the
support. After calcination and surface cleaning, the materials
showed similar catalytic performances to those of the fresh
catalysts. Selectivities in both reactions were similar after each
reuse, with the exception of an increase in selectivity to ben-
zaldehyde (>90%) after two uses in the selective oxidation of
benzyl alcohol. In all cases, no significant Fe leaching into solu-
2
3
tility in selective oxidation (benzyl alcohol to benzaldehyde)
and acid-catalyzed processes (alkylation of toluene and cetyl
alcohol dehydration). A comparison of these nanomaterials
prepared in continuous flow with previously reported literature
catalysts clearly indicated the comparable, if not superior activ-
ities of the continuous-flow-prepared catalysts compared to
materials prepared by using microwave-assisted or mechano-
chemical techniques, which illustrated the potential of the pro-
posed methodology for the preparation of designer nanocata-
lysts for advanced catalytic processes, including biomass valori-
ꢀ
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 0000, 00, 1 – 9
&
4
&
ÞÞ
These are not the final page numbers!