posted on 2013-02-01, 00:00authored byZhi-Jian Zhao, Lyudmila
V. Moskaleva, Notker Rösch
Using density functional calculations we studied the
conversion
of methylcyclopentane to its various ring-opening products, branched
and unbranched hexanes, that is, 2-methylpentane and 3-methylpentane,
as well as n-hexane. We examined four metal catalysts,
M = Pt, Rh, Ir, and Pd, using slab models of flat M(111) and stepped
M(211) surfaces, to describe terrace-rich large and defect-rich small
M particles, respectively. As C–H bond activation and formation
is rather independent of the particle structure, we focused on C–C
bond scission which is expected to be structure sensitive. The barriers
of C–C bond scission indeed vary from ∼20 kJ mol–1 to ∼140 kJ mol–1 on various
sites of these metal surfaces. In general, lower activation energies
were calculated for Rh and Ir surfaces, in agreement with the higher
experimental activity of these two metals compared to Pt and Pd. From
the calculated C–C bond breaking barriers, we were able to
rationalize the selectivity toward different ring-opening products,
as observed in experiments over the metal catalysts studied.