Bc. Khanra et al., EFFECT OF SURFACE SEGREGATION ON THE CATALYTIC ACTIVITY OF ALLOYS - CO HYDROGENATION ON PD-NI(111) SURFACE, Journal of molecular catalysis. A, Chemical, 129(2-3), 1998, pp. 233-240
A semi-empirical model has been presented for studying the effect of s
urface segregation and local environment on the catalytic activity of
the PdNi(111) surface for CO hydrogenation. Large Pd segregation to th
e surface has been found to affect the activation barrier for dissocia
tion of molecules on the surface. It also affects the activation barri
ers for different reaction steps in the CO hydrogenation process to fo
rm methanol on the Pd-Ni surface. It is argued that for the Pd-Ni syst
em, hydrogenation of the adsorbed HCOs species is the rate-limiting st
ep. It has then been shown that an addition of even 5 at% of Pd in bul
k Ni may increase the activity by as much as four orders of magnitude.
So far as the local environmental effect is concerned, it is found th
at the most active centres for the HCOs hydrogenation step are the cen
tre hollow sites having three-fold symmetry with 3 Pd atoms as nearest
neighbours followed by centre hollow sites with two Pd atoms and one
Ni atom as nearest neighbours. (C) 1998 Elsevier Science B.V.