,
Hierarchical, multiscale surface reaction mechanism development: CO and H2 oxidation, water-gas shift, and preferential oxidation of CO on Rh
Journal of Catalysis, 234 (1): 48-63 (2005)
Аннотация
A hierarchical multiscale parameter refinement approach was used to
develop microkinetic models for CO and H2 oxidation, and CO-H2 coupling
for water-gas shift (WGS) and preferential oxidation (PROX) of CO
on Rh. The rate parameters were estimated with a combination of quantum
mechanical density functional theory (DFT), the semi empirical unity
bond index-quadratic exponential potential method, and transition-state
theory. To improve the predictive ability, selected pre-factors of
the CO and H2 oxidation reaction mechanisms were optimized against
multiple experimental data sets, such as ignition, molecular beam,
and laser-induced fluorescence. Thermodynamic consistency of rate
parameters was ensured over a wide temperature range by a combination
of statistical mechanics and constraints-based optimization. DFT
calculations were used to estimate cross adsorbate-adsorbate CO-H
interactions. It is shown that the coupling between the two fuels
arising from these interactions is essential for PROX of CO. Important
reaction pathways in the WGS and PROX chemistries are discussed.
For example, it is shown that the oxidation of CO by OH via the carboxyl
intermediate, and not by O, is the dominant path in PROX. Thus, hydrogen
acts as a "catalyst" for CO combustion under certain conditions.
Finally, the mechanisms are validated against additional sets of
redundant experimental data.
