The preparation and characterization of highly dispersed metal nanoparticles in mesoporous silica SBA-15 are reported. The functionalization with organosilane to generate a monolayer of charged groups on the pore surface facilitates uniform distribution of ionexchanged metal precursors in the channels of SBA-15, which, upon reduction, results in highly dispersed metal nanoparticles supported in SBA-15. Under mild reduction conditions, the surface functionality remains and so allows further metal incorporation cycles to achieve higher metal loading. After reduction in hydrogen flow, disk-shaped Pt nanoparticles in Pt/ SBA-15 and spherical Au nanoparticles in Au/SBA-15 have been characterized in the channels of SBA-15 by PXRD, XAS, and TEM. Secondary Pt incorporation in Au/SBA-15 produces coexisting small Pt nanoparticles with large Au nanoparticles in the host channels. This preparation method is capable of template synthesis of various metal nanostructures with controlled morphology and composition inside the channels of mesoporous materials.
A template synthetic method to prepare densely packed metal nanostructures in functionalized (MCM)‐41 and MCM‐48 is described. The intrachannel surface of host silica has been functionalized to carry positive charges for the accommodation of highly concentrated and negatively charged metal complexes. After reduction, Au and Pt nanowire bundles in MCM‐41 as well as Pd nanowire networks in MCM‐48 are formed. The Pt nanowire bundles in MCM‐41 are observed to grow along a preferred direction and stack along Pt {111} planes relative to the pore wall of the host. Furthermore, bimetallic AuPt alloy nanowire bundles in MCM‐41 have also been prepared and characterized.
Vanadium-containing silicate MCM-41 (V-MCM-41) zeolite and
aluminophosphate AFI (VAPO-5) zeolite
were synthesized and characterized by spectroscopic techniques. In
as-synthesized form, the vanadyl ions
(VIVO)2+ were found to be the major
vanadium species in the form of atomic dispersion on AFI by
EPR
and to exist simultaneously with tetrahedral
(T
d) V5+ in MCM-41 by UV−vis.
29Si MAS NMR investigations
suggested that the vanadium ions might attach to MCM-41 through
interaction with the silanol groups on the
internal wall of hexagonal tubes. The V5+ (in
T
d) ions are incorporated into the lattice of
MCM-41 during
synthesis, while the VO2+ (in T
d)
is the loosely bound V species. The results of Raman spectroscopy
indicated
that the rodlike aggregation of cationic surfactant
(cetyltrimethylammonium bromide, CTAB) was encapsulated
in the intrachannel space of synthetic MCM-41 as in an aqueous
solution. After calcination and hydration,
the V4+ species in as-synthesized V-MCM-41 was totally
oxidized to +5 as shown by UV−vis and EPR
spectroscopies, and they further aggregated as two-dimensional vanadate
chain species that were nonuniformly
deposited on the wall of MCM-41 channels as verified by Raman and HREM
with EDS spectroscopies,
while the V5+ species of synthetic V-MCM-41 remains
stable in a tetrahedral coordination. Comparatively,
two types of VO2+ ions were observed in as-synthesized
VAPO-5 by EPR and they could be oxidized by
calcination treatment. The presence of water vapor facilitates the
oxidation of (VIVO)2+ and the
formation
of V2O5 cluster instead of isolated
(VVO)3+ species.
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