It is interesting to take a closer look at the electronic
structure of the OFe(OH)3(H2O)2 cluster as a model for the
so-called α-oxygen formed after low-temperature N2O decomposition
on Fe/ZSM-5 [7] and compare it with the corresponding
Al-containing model. The calculated Mulliken
charge and spin density on the adsorbed oxygen atom,−0.43
and 1.07 a.u., respectively, suggest that it is essentially an
O− ion. These values change only slightly (to −0.48 and
0.90 a.u., respectively) when the calculation is repeated with
the total spin equal to 3/2 instead of 5/2. The metal–oxygen
bond energies in the XO clusters also differ between Fe
and the other two metals. The Fe–Oads bond is stronger by
about 35 kJ/mol than Co–Oads and Rh–Oads and by about
180 kJ/mol than Al–Oads.