Atomic Layer Deposition in Nanoporous Catalyst Materials - Atomically-Precise Methods for Synthesis of Solid Catalysts - page 182

d n 9 r 4 n g | 7

Figure 7.14 High resolution SEM (left) and TEM (right) images of ALD-grown Pt
nanoparticles (size 2-3 nm) on a mesoporous silica support.

(corresponding to 90 m 2 g 1 and 220 m 2 g 1 , respectively) were loaded with
the Ir precursor. Higher saturated loadings were achieved in the zeolite with
the higher mesoporosity. It was also shown that the Ir content was reduced
almost by half when the zeolitic support was treated with Hacac prior to the
Ir(acac) 3 chemisorption step. TEM images revealed the presence of 2-3 nm Ir
particles. The ALD catalysts were tested in the decalin ring opening reaction
and were found to be more active and selective than samples prepared by wet
impregnation of the zeolites using IrCl 3 3H 2 O in water.
King et al. demonstrated the feasibility of ALD for the fabrication of Pt
nanoparticles on the inner surfaces of carbon aerogels. 48 The aerogel sup-
port with a surface area of 480 m 2 g 1 exhibited a macroporous network

formed by interconnected microporous carbon particles. Pt was deposited
using 2, 5 or 10 ALD cycles of the (methylcyclopentadienyl)trimethyl
platinum (MeCpPtMe 3 )/O 2 process at 320 1C. TEM images revealed the
presence of evenly dispersed Pt nanoparticles ( o 5 nm). Remarkably, despite
the lower amount of Pt, the catalyst prepared with 2 ALD cycles was as active
as the 10 cycle catalyst for the oxidation of CO.
Li et al. used the MeCpPtMe 3 /O 2 process to disperse Pt particles on the
interior surface of mesoporous silica gel.*** ,49 The application of 3, 5 and 10
ALD cycles resulted in 1.2, 1.9 and 2.3 nm nanoparticles, respectively. The
three-cycle sample was subjected to a thermal stability test. After 4 h of heat
treatment at 450 1C in air, the particle size was increased from 1.2 to 2 nm,
indicating sintering of the particles. After following heating cycles, however,
no additional sintering was observed. The Pt catalysts showed high activity
for the oxidation of CO.
Pt nanoparticles were also deposited on nonporous, single-crystalline,
cubic-shaped SrTiO 3 (STO) particles with an average edge length of 60 nm
and a surface area of 20 m 2 g 1 . 50 STO particles treated with one
MeCpPtMe 3 /O 2 ALD cycle were evaluated in the oxidation of propane. The

B

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***Silica gel (Aldrich): particle size 30-75 mm, surface area 513 m 2 g 1 , pore volume 0.75 cm 3
g 1 , and average pore size 6 nm.