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the metals is enhanced with the binding energy of metals
increasing. The selectivity of isomerization increases at first and
then decreases, while the cleavage selectivity shows an opposite
trend, but the magnitude of the change is relatively small.
In the H2-TPR profiles (Fig. S3 in Supporting information),
the reduction temperature for Ni (II) gradually decreases from
596 oC to 481 oC with increasing Cu/Ni ratio, while the reduction
temperature of Cu (II) decreases from 341 oC to 254 oC.
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Additional hydrogen consumptions are observed at 325 C for
NiCu1.19-ZnAl-LDO@Al2O3 and 288 oC for NiCu2.11-ZnAl-
LDO@Al2O3, which suggests the possible formation of NiCu
alloy phase. But the hydrogen consumption at 287 oC almost
diminishes for NiCu3.17-ZnAl-LDO@Al2O3.
The isomerization selectivity on 0.16%Pt/Cu3.91%-ZnAl-
LDO@Al2O3 is 142% higher than on 0.15%Pt/Ni-ZnAl-
LDO@Al2O3. The isomerization reaction rate has been reported
highly dependent on the acidic property of catalysts [4]. But there
is no significant difference in the amount and strength of acidic
sites
between
0.16%Pt/Cu3.91%-ZnAl-LDO@Al2O3
and
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0.15%Pt/Ni-ZnAl-LDO@Al2O3, based on NH3-TPD profiles (Fig.
S4 in Supporting information). So it can be deduced that the Cu
sites promote isomerization selectivity by inhibiting
hydrogenolysis reaction. The synergies of Ni and Cu sites on
alloy phase is mainly responsible for the higher isomerization
selectivity observed with NiCu1.19-ZnAl-LDO@Al2O3 and
NiCu2.11-ZnAl-LDO@Al2O3 than with other catalysts.
In summary, NiCu bimetallic catalyst with uniform NiCu
dispersion has been demonstrated to provide higher activity than
Pt catalyst while with similar selectivity in the reforming reaction
of n-heptane. The synergies between homogeneously dispersed
Ni and Cu sites account for the enhancement of activity and
selectivity.
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mmc1.doc
Acknowledgments
Financial supports from National Nature Science Foundation
of China (NSFC: 91634120, 21521005), the National Key
Research
and
Development
Program
of
China
(2017YFA0206804) and the Fundamental Research Funds for the
Central Universities (XK1802-6) are gratefully acknowledged.
Declaration of Competing Interest
The authors declare no competing financial interest.
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