Characterization of highly dispersed Ni/Al2O3 catalysts by EXAFS analysis of higher shells |
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Authors: | Shido Takafumi Lok Martin Prins Roel |
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Affiliation: | (1) Laboratory for Technical Chemistry, Swiss Federal Institute of Technology (ETH), 8092 Zürich, Switzerland;(2) Synetix, Cleveland, TS23 1LB, UK |
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Abstract: | The size and morphology of Ni/Al2O3 catalysts in the oxidic, reduced, and passivated state were determined by EXAFS analysis of the higher shells around the
Ni atoms. In the oxidic state, the Ni cations were present in small NiOx particles with predominant (111) plane. Below 4.5 wt% Ni loading, the NiOx particles consisted of one Ni layer, and of two or three Ni layers above 4.5 wt% Ni. A Ni–Al contribution was observed in
samples with low Ni loading. The layer which is in contact with the Al2O3 surface is affected by the support surface and its structure is highly distorted, while the other layers were not distorted
and have a structure similar to that in bulk NiO. In the reduced state, the number of Ni metal atoms in the reduced Ni particles
was smaller than 100 with a narrow distribution below a loading of 15.6 wt% Ni. Above this loading, the particle size suddenly
increased and the distribution became wider. The distances and Debye–Waller factors were similar to those of bulk nickel which
suggested a weak interaction between the particles and the support. In the passivated state, Ni kernels with 20–40 metal atoms
were covered by a one layer thick NiO skin.
This revised version was published online in June 2006 with corrections to the Cover Date. |
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Keywords: | Ni θ -alumina EXAFS passivated |
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