Dynamics of structural transformations in the reduction of copper aluminate |
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Authors: | L M Plyasova T M Yur’eva I Yu Molina T A Kriger A M Balagurov L P Davydova V I Zaikovskii G N Kustova V V Malakhov L S Dovlitova |
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Institution: | (1) Boreskov Institute of Catalysis, Siberian Division, Russian Academy of Sciences, 630090 Novosibirsk, Russia;(2) Joint Institute for Nuclear Research, Moscow oblast, 141980 Dubna, Russia |
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Abstract: | The dynamics of structural transformations during copper aluminate reduction in the temperature range used for catalyst activation
was studied by high-temperature X-ray analysis under controlled conditions (hydrogen, 2O–4OO‡C). The techniques of neutron
diffraction analysis, IR spectroscopy, chemical phase analysis, and electron microscopy were also used at particular stages.
In the course of reduction, copper metal is deposited onto the surface of spinel crystals from the bulk. Spinel becomes cation-deficient
with respect to copper. An analysis of powder diffraction patterns demonstrated that copper is reduced and released from tetrahedral
positions of the spinel structure at temperatures below ~300‡C and from octahedral positions only at temperatures above 300‡C.
In this case, a redistribution of aluminum ions was observed simultaneously. It is likely that the electrical neutrality is
attained by the formation of OH groups, the appearance of which in reduced samples was detected by IR spectroscopy and confirmed
by neutron diffraction analysis. At a reduction temperature of 400‡C, the oxygen framework was partially disintegrated. The
structures of reduced copper aluminates and chromites were compared. |
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