A SURFACE STUDY ON MODEL PD(111) CATALYST MODIFIED WITH BORON

A number of studies have been devoted to borided Group VIII metals as selective hydrogenation catalysts. The present results are a first att empt to characterize formation and behaviour of Pd(111)-B modified sur face. The Pd(111) sample was exposed (UHV, 300 K) to diborane, B2H6, a nd subsequently investigated by LEED, AES and TDS. (1) The dissociativ e B2H6 adsorption resulted in hydrogen and boron ad- and absorption; t he B concentration in the Pd(111) surface layer was determined from AE S. (2) The distinct O2-induced surface segregation of B absorbed in Pd (111) (T greater-than-or-equal-to 600 K, 2 x 10(-6) < p(O2) < 1 X 10(- 5) Pa) was observed; a stable B(x)O(y) adspecies was forming. (3) The presence of both kinds of borided Pd surfaces in catalytic systems has been discussed.