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The purpose of this work is to examine critically the correlations between ionization potential or absolute hardness and the catalytic behavior of binary and ternary oxides containing lanthanides (Ln) in alkene oxidation. Five lanthanide oxides (La 2 O 3 , Sm 2 O 3 , Pr 6 O 11 , Tb 4 O 7 , and CeO 2 ) and three praseodymium molybdates (Pr 2 -Mo 3 O 12 , Pr 6 MoO 12 , and Pr 2 MoO 6 ), were used as pure phases or in mixtures with MoO 3 in the partial and total oxidation of isobutene. The catalytic performances of their mixtures with MoO 3 are described in the context of the "remote control mechanism", according to which the lanthanide-based oxides are identified as donors of spillover oxygen. Their donor ability is evaluated through the synergetic effects on methacrolein selectivity and correlated with the physical properties mentioned above. In the case of ternary oxides such as praseodymium molybdates, the concepts of average ionization energy and average absolute hardness are proposed to take into account the fact that the electron density and therefore the reactivity of mobile surface oxygen species are influenced by the presence of both metals in the lattice. The results obtained with the pure Ln-based oxides are in line with the literature concepts of ionization energy and absolute hardness. As far as the mechanical mixtures are concerned, it is shown that the above correlations, when combined with the "remote control" concepts, provide a comprehensive view of the influence of ionization energy or absolute hardness for both single phase and biphasic catalysts exhibiting phase cooperation.

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DLTS results of the third acceptor level of substitutional copper in n-type germanium are presented for the first time. Accurate determination of the signature and the temperature dependence of the electron capture cross section yields an energy level of E, -0.26 eV in agreement with the Hall effect. It is shown that two DLTS bands attributed in the literature to the third copper level should correspond to other defects.

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