The adsorption and reaction of propan-2-ol on Ni(1 1 1) has been followed b
y reflection absorption IR spectroscopy and temperature programmed desorpti
on. At 110 K, nondissociative molecular adsorption is observed in the monol
ayer, with randomly oriented multilayers observed at higher exposures. On i
ncreasing substrate temperature to 200 K, scission of the OH bond is observ
ed with formation of a 2-propoxide surface species which is adsorbed with C
, site symmetry and oriented upright with the metal-O-C field close to a 18
0 degrees angle. The alkoxide species is stable to 320 K, above which sciss
ion of the alpha -CH bond occurs, with simultaneous formation and desorptio
n of acetone. This selective dehydrogenation to acetone is the majority rea
ction pathway on the surface and is critically controlled by the high barri
er to alpha -CH bond activation which ensures remarkable stability for the
2-propoxide intermediate. As a result, selective dehydrogenation occurs at
a sufficiently high enough temperature so that acetone desorption competes
very effectively with unselective decomposition to CO, H and CxHy. Acetone
is, therefore, evolved in a reaction-limited process at 340 K, while the mi
nority non-selective decomposition pathway evolves H: and CO in desorption-
limited processes. The ease of bond breaking (O-H > alpha -CH > alpha -CC)
identified for C-1 and C-2 alcohols on Ni(1 1 1) seems also to be valid for
C-3 alcohol chemistry on this surface. (C) 2001 Elsevier Science B.V. All
rights reserved.