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We found that CO2 was generated at the highest temperature
in all steps. Meanwhile, the temperature of CO2 desorption
showed in TPD-MS-CH3OH has a similar trend with the
conversion of DME. Thus, we deduce that the transformation
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catalyst. As discussed in 3.2.1, the rate-controlling step of DME
SR over GDZ/g-Al2O3 catalysts is an n-type reaction. Therefore,
we deduce the transformation from HCOO– to CO2 is an n-type
reaction, which can be accelerated by doping donor in the lattice
of n-type semiconductor, and we have accelerated the trans-
formation from HCOO– to CO2 by the doping of ZnO with Ga.
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A series of gallium-doped zinc oxide (GDZ) mixed with g-Al2O3
catalysts for DME SR to produce H2 was prepared. Compared
with the conventional catalyst, GDZ/g-Al2O3 catalysts exhibited
higher carbon dioxide selectivity and better stability. XRD
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similar with the conversion of DME trend and the yield of
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GDZ catalyst has the highest conductivity, and the corre-
sponding Zn9Ga1O/g-Al2O3 catalyst has the highest conversion
of DME (95.4%) and yield of hydrogen (95%). The results of
conductivity indicate that the rate-controlling step of DME SR
over the GDZ catalysts is an n-type reaction. XPS results indi-
cated that doping of gallium introduced a large number of
oxygen vacancies into the catalyst, and the vacancies were
benecial to the reaction. According to the results of XPS, TPD-
MS-CH3OH, in situ FTIR of CH3OH and the proposed mecha-
nism with HCOO– as an intermedium, we speculated that the
formation of carbon dioxide might be the rate-controlling step
for DME SR over GDZ/g-Al2O3 catalysts. We deduce the trans-
formation from HCOO– to CO2 is an n-type reaction. The good
conversion of DME, high selectivity of CO2 and high stability of
GDZ/g-Al2O3 catalysts makes it promising for DME SR both in
research and industry.
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Acknowledgements
This work is nancially supported by National Natural Science
foundation of China (No. 21476159, 21476160), the Natural
Science Foundation of Tianjin (No. 15JCZDJC37400), the 973
program (2014CB932403), and the Program for Introducing
Talents of Discipline to Universities of China (No. B06006).
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52420 | RSC Adv., 2016, 6, 52411–52420
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