also show that the physical and catalytic properties of MoO3
will be improved by H2 reduction involving the formation of
HxMoO3 , but not by reduction through MoO2 . As the active
catalysts for the pentane isomerization and the propan-2-ol
dehydration contained the MoOxHy phase, the MoOxHy
phase, which can originate from HxMoO3 is likely to play an
important role in the generation of the acidity.
Conclusions
Reactions of pentane and propan-2-ol were carried out using
H2-reduced MoO3 with noble metals. There was no appreci-
able difference in the pentane isomerization activity and in
the propan-2-ol dehydration activity among Pt, Pd, Rh and
Ir/MoO3 catalysts after reduction at 773 K for 12 h. The iso-
merization and dehydration activities of H2-reduced Ru/
MoO3 were lower than those of the other catalysts. The iso-
merization and the dehydration activities of H2-reduced Pt/
MoO3 varied very little with the amount of Pt. In the case of
H2-reduced Ru/MoO3 , however, the isomerization and dehy-
dration activities were increased and the dehydrogenation
activity was lowered by an increase in the amount of Ru. We
conclude from these results that the isomerization activity of
H2-reduced MoO3 with noble metals can be determined by
the ability to act as an acid catalyst. XRD and TPR studies
showed that the reduction process of Ru/MoO3 was affected
by the amount of Ru. The formation of MoO2 was suppressed
and that of HxMoO3 was promoted by an increase in the
amount of Ru. By contrast, reduction of Pt/MoO3 involved
the formation of a hydrogen molybdenum bronze, HxMoO3 ,
irrespective of the amount of Pt. We suggest from these results
that the active phase for pentane isomerization and propan-
2-ol dehydration can generate from reduction of HxMoO3 .
Fig. 8 TPR spectra of 0.001 mol% Pt/MoO3 (a), 0.1 mol% Ru/
MoO3 (b) and 0.005 mol% Ru/MoO3 (c). Conditions: sample weight,
1 g; gas, 50% H2–Ar; flow rate, 20 ml minÀ1; heating rate, 5 K minÀ1
:
H2 consumption (X), H2O formation (K).
to be attributed to the formation of MoO2 , which can easily be
reduced to Mo metal.
Acknowledgements
This work was supported in part by a Grant-in-Aid for Science
Research (C) from the Japanese Society for the Promotion of
Science.
0.01 mol% Ru/MoO3 had the lowest activities for pentane
isomerization and for propan-2-ol dehydration among the cat-
alysts with 0.01 mol% noble metal after reduction at 773 K for
12 h. The isomerization and the dehydration activities of H2-
reduced Ru/MoO3 was enlarged by an increase in the amount
of Ru loading, whereas those of H2-reduced Pt/MoO3 was
independent of the amount of Pt. Reduction of Pt/MoO3 pro-
ceeded via the HxMoO3 phases, and yielded a MoOxHy phase,
irrespective of the amount of Pt. By contrast, the reduction
process of Ru/MoO3 varied with the amount of Ru. The for-
mation of the MoO2 phase was suppressed and that of
HxMoO3 was enhanced by an increase in the amount of Ru.
No appreciable difference appeared in XRD and TPR results
between 0.01 mol% Pd/MoO3 and 0.01 mol% Pt/MoO3 .
0.01 mol% Rh/MoO3 and 0.01 mol% Ir/MoO3 gave similar
XRD and TPR results to 0.1 mol% Ru/MoO3 . We propose
from these results that the low isomerization and dehydration
activities of H2-reduced 0.005 and 0.01 mol% Ru/MoO3 can
result from its reduction process, which involves the formation
of the MoO2 phase.
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671