The structural and morphological changes of the metal phases which occ
ur during regeneration in hydrogen and air/hydrogen cycles have been s
tudied for Ni-USY catalysts which had been deactivated during the hydr
ogenation of benzene. Independent of nickel loading in the zeolite, re
generation in hydrogen alone was not sufficient to restore the initial
:activity. Regeneration in air/hydrogen cycles was more successful for
catalysts with higher Ni loadings, but structural transformations of
the metal particles occurred during the oxidative regeneration process
. Temperature programmed reduction (TPR), photoelectron spectroscopy (
XPS) and FTIR of adsorbed CO have been used to identify these modifica
tions.