Chemistry Reference
In-Depth Information
Fig. 14 SEM images of HT carbon coating (a) after sulphonation and (b) after ester-
ification reaction of sample prepared from 0.5M glucose. Image (a) shows clearly that the
HT coating has uniform thickness of about 350 nm. Reproduced from Ref. 148 page 1370
with permission of Elsevier.
using samples containing varying amounts and types of sulphur con-
taining surface groups, produced by liquid phase treatment of the carbon
with sulfuric acid at different temperatures and concentrations, the
authors concluded that thiol and sulfonic acid groups participate actively
in the formation of highly reactive radicals.
153
These results are indicative
of the potential interest in using S-doped carbons for advanced oxidation
reactions.
3 Heteroatom-modified carbon materials as catalyst
support
Novel carbon materials doped with heteroatoms, besides being used as
catalyst, they have been used as metal catalyst support for a number of
applications. Several examples are compiled in Table 4. In this case, the
advantages inherent to metal-free catalyst are not attained. Nevertheless,
there are some additional advantages that heteroatom doping can
introduce for the supported metal catalyst, which can render doped
carbon materials also interesting as catalyst support. The first advantage
involves a geometric effect, because the doping can govern the metal
nanoparticle size and structure. Likewise, doping can increase the dis-
persion of the metal or the stability of particle size. On the other side,
doping induces electronic effects in support and hence on metal nano-
particle, due to the high electronic conductivity of graphitic carbons. This
electronic effect may result in increased activity or enhanced selectivity.
This enhanced activity can eventually lead to reduce the amount of metal
necessary for a certain application, which is very important in the case of
critical metals such as noble metals.
3.1 Catalyst supported on oxygen functionalized carbon
The functionalisation of carbon nanostructures with oxygen groups using
an oxidant such a nitric acid, sulfuric acid or mixtures is an standard
procedure for the preparation of supported catalyst.
154,155
This oxidation
stage is almost mandatory for the preparation of catalyst supported on
CNTs or graphene since they have no anchoring sites to keep a high
metal dispersion and prevent catalyst sintering. The use of oxidized CNT
