The autothermal behavior of platinum catalyzed hydrogen oxidation: Experiments and modeling

The autothermal behavior of H-2/O-2 mixtures over a platinum foil catalyst is investigated experimentally and theoretically. Experiments were conducte d at atmospheric conditions, at levels of nitrogen dilution ranging between 80% and 92% by volume. The stagnation flow geometry was modeled using simp lified multicomponent transport and detailed reaction mechanisms, both in t he gas phase and on the catalyst surface. A maximum autothermal temperature was found at the unexpected, nonstoichismetric, H-2/O-2 volume ratio of ap proximately unity. Experimental and model results for the effect of dilutio n on autothermal temperatures and the flammability limits are presented and discussed. Sensitivity analyses indicate that the upper flammability limit depends on the relative adsorption rates of H-2 and O-2 onto the platinum surface, and the desorption of adsorbed H*, while the location of the maxim um in autothermal temperature depends on the transport of H-2 and O-2. It i s shown that repulsive H*-H* interactions on the surface may be essential f or accurate prediction of the upper flammability limit. (C) 1999 by The Com bustion Institute.