Mc. Ma et al., EVALUATION OF THERMAL-DESORPTION SPECTRA FOR HETEROGENEOUS SURFACES -APPLICATION TO CARBON SURFACE OXIDES, Surface science, 297(3), 1993, pp. 312-326
The existence of a distribution of intrinsically heterogeneous surface
sites gives rise to broad spectra in the temperature-programmed decom
position of surface species. A simple method is developed to allow the
determination of activation-energy distributions of population, PSI(E
), and frequency factor, A(E), for the decomposition of surface comple
xes by using a combination of isothermal and linear TPD experiments. T
he main requirement in applying the method is that of very precise mea
surement of sample temperature during TPD. The decomposition of carbon
surface oxide complexes occurs with an intrinsic distribution of acti
vation energies. For complexes formed from oxygen at 520 K, the decomp
osition activation energies range from 150 kJ mol-1 to 420 kJ mol-1, w
ith a mean of 295 kJ mol-1. The frequency factor for decomposition is
approximately constant, with an average value of 10(14+/-0.4) s-1. The
se values cannot be compared directly with the kinetic parameters for
CO desorption from metals because the decomposition of carbon surface
oxides is irreversible and does not occur via a simple bond scission.
The formation of CO2 from carbon oxide decomposition occurs with kinet
ic parameters distinctly different from those observed for CO formatio
n.