ICOSAHEDRAL AlMnLn (Ln = Ce, Gd, Dy, Ho) ALLOYS - AN EXAFS STUDY AND CATALYTIC BEHAVIOR

Two series of icosahedral Al(100-x-y)Mn(x)Ln(y) alloys, first consisting of AlMnCe with variable Ce (x = 6 and y = 1, 2, 3, 4: Al93Mn6Ce, Al92Mn6Ce2, Al91Mn6Ce3, and Al90Mn6Ce4) or Mn (x = 8, 10; y = 1: Al89Mn10Ce and Al91Mn8Ce) concentration, and the second consisting of constant alloy composition (Al(91)Mn(6)Ln(3)), while varying the Ln nature (Gd, Dy, and Ho) were prepared. The icosahedral structure of the samples was confirmed by X-ray diffraction (XRD). As shown by EXAFS, the sample Al89Mn10Ce, with the lowest Ce/Mn ratio, display an advanced degree of disorder around the Ce atoms in the structure. Catalytic behavior highly depended on the alloys structure, the higher the degree of disorder around the rare-earth element in the structure, the higher catalytic activity. Replacing Ce with Gd, Dy or Ho in AlMnLn alloys does not result in a significant enhancement of the catalytic performances.