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MIL-101 is stable to chromium leaching, behaves as a true heterogeneous catalyst,
can be easily recovered by filtration, and can be reused several times without loss
of catalytic performance.
5.3.2 Post-functionalization for Catalysis
The homogeneously integrated organic functional moieties inside the hybrid
framework permit the potential for post-functionalization to achieve further
physicochemical characteristics, which is mainly based on the organic reactions.
Chemically designed ordered mesoporous titanium phosphonate hybrid materials
have exhibited the capacity to be functionalized by sulfation with chlorosulfonic
acid (ClSO
3
H) to form stable hydrosulfated esters (Fig.
5.15
) [
91
]. The specific
alkyl hydroxyl structure of the coupling molecule HEDP makes its sulfation facile.
Approximately 2.69 and 3.93 mmol g
−
1
of H
+
were assigned to the grafted sul-
fonic groups and the defective P-OH from the hybrid framework, respectively. The
acid strength revealed a Hammett indicator of H
0
<
−
11.35, indicative of a strong
solid acid. It was also proven that the hydrosulfated groups remained at the pore
walls even in hot water (up to 80 °C), which allowed the functionalized sample
to be used as an ion exchanger and acid-base catalyst in room or low temperature
reactions. For example, the sulfated materials could be used in the esterification of
oleic acid and methanol under ambient temperature and pressure, giving a much
higher conversion (87.3 %) than the unfunctionalized materials (4.9 %).
Transition metal-based catalysts are of great significance in sustainable envi-
ronmental and energy chemistry. Inspired by the Langmuir adsorption behavior
of metal ions onto porous phosphonates [
11
,
17
], a step further would transform
the metal ions into active components, which could have potential application in
some catalytic reactions. To achieve a high dispersion of CuO nanoparticles, the
Fig. 5.15
Surface functionalization of monolithically ordered mesoporous titanium phospho-
nates prepared from HEDP using the ClSO
3
H treatment. Reprinted with permission from Ref.
[
91
]. Copyright 2010, Royal Society of Chemistry
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