Dynamics of structural transformations in the reduction of copper aluminate

The dynamics of structural transformations during copper aluminate reductio n in the temperature range used for catalyst activation was studied by high -temperature X-ray analysis under controlled conditions (hydrogen, 20-400 d egrees C). The techniques of neutron diffraction analysis, IR spectroscopy, chemical phase analysis, and electron microscopy were also used at particu lar stages. In the course of reduction, copper metal is deposited onto the surface of spinel crystals from the bulk. Spinel becomes cation-deficient w ith respect to copper. An analysis of powder diffraction patterns demonstra ted that copper is reduced and released from tetrahedral positions of the s pinel structure at temperatures below similar to 300 degrees C and from oct ahedral positions only at temperatures above 300 degrees 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, t he appearance of which in reduced samples was detected by IR spectroscopy a nd confirmed by neutron diffraction analysis. At a reduction temperature of 400 degrees C, the oxygen framework was partially disintegrated. The struc tures of reduced copper aluminates and chromites were compared.