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d
n
9
r
4
n
g
|
7
27
Al MAS NMR spectrum for the Zeotile-4 powder after ALD treatment
with 10 cycles of the TMA/H
2
O process. Red and violet spheres repre-
sent oxygen and aluminium atoms, respectively. (*) Note that the peak
at 30 ppm could also correspond to distorted tetrahedral Al atoms.
106
Adapted from ref. 11.
Figure 7.15
N
2
adsorption measurements provided an additional proof for the de-
position of Al species in the pores of the Zeotile-4 material. Adsorption/
desorption isotherms of N
2
gas at 77 K measured on the parent and ALD
modified Zeotile-4 material are shown in Figure 7.16. Both isotherms are
characterized by a marked hysteresis loop caused by capillary condensation
in mesopores. A decreased N
2
adsorption capacity is observed for the ALD
modified sample. Quantification revealed a decrease in surface area and
mesopore volume due to the deposition of Al
2
O
3
in the mesopores
(Figure 7.16). The micropores were still largely accessible to N
2
after the ALD
treatment, meaning that they were not closed off by the deposition process.
The catalytic performance of the parent and aluminated Zeotile-4 powder
was evaluated in the hydroconversion of n-decane. The powders were im-
pregnated with an aqueous solution of Pt(NH
4
)
3
Cl
2
to obtain a Pt loading of
0.5 wt%. The Pt is responsible for the dehydrogenation and hydrogenation of
alkanes and alkenes, respectively, while the Al sites catalyze two competing
reactions: hydroisomerization (converting linear alkanes into branched
isomers) and hydro-cracking (converting the molecules into shorter frag-
ments). Figure 7.17 shows the n-decane conversion yield against the reaction
temperature. The as-synthesized Zeotile-4 material was inactive at tem-
peratures below 270 1C. After incorporation of Al by ALD, the Zeotile-4
powder became active starting at 220 1C and reached a conversion yield of
nearly 100% at 300 1C.
In conclusion, this case study demonstrated that the ALD process using
TMA and H
2
O is suited for the incorporation of Al species and the
.
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