MÖSSBAUER SPECTROSCOPIC STUDIES OF Ni CATALYSTS : PARTICLE SIZE DETERMINATION AND EFFECT OF HYDROGEN CHEMISORPTION S. Mørup, B.S. Clausen et H. Topsøe J. Phys. Colloques, 40 C2 (1979) C2-78-C2-80 DOI: 10.1051/jphyscol:1979227