Moller, Karin and Bein, Thomas
EXAFS studies on the reduction of palladium(II) in X zeolites.
In: Journal de Physique, Colloque C8, Suppl.12, Vol. 47: pp. 231-236
Palladium tetraammine ion exchange into zeolite, temperature treatments under
different atmospheres, and hydrogen reduction have been studied by EXAFS at
the Pd Κ edge. Complete autoreduction is found to take place between 473 and
623 Κ under vacuum.
Α bidisperse Pd metal phase is formed which agglomerates
at the expense of the small particles upon prolonged heating at 623 Κ. In
contrast, a similar treatment under oxygen suppresses autoreduction , and the
Pd cations remain in zeolite coordination sites. Additional small amounts of
palladium oxide are observed under these conditions. If hydrogen is admitted
to the dehydrated, ionic system at 295 K. the oxygen coordination of the Pd
disappears and evidence is obtained for the formation of Pd(0) dimers that
interact with the framework via a long Pd-0 bond.