Indications for a Surface Temperature Excess in Heterogeneous Catalysis

We explored the surface temperature excess ΔT = T r − T m (real reaction temperature T r, measured catalyst temperature T m) on the basis of experimental data, a gradually curved Arrhenius plot for CO oxidation reactions over Pd/γ-Al2O3 catalysts. Such a plot could be an indication of the surface temperature excess in the 2-dimensional reaction surfaces of catalysts. The positive or negative surface temperature excess could be developed to be a general explanation for a gradually curved Arrhenius plot of a gas−solid catalytic system. This is a new insight into solving the puzzle on such common phenomena in heterogeneous catalysis. By using the reciprocal of the real reaction temperature T r in the hypothetical 2-D reaction surface, instead of the experimentally determined catalyst temperature T m or the gas temperature T g, the gradually curved Arrhenius plot becomes linear. We investigated the implications of such a difference among T r, T m, and T g. The surface temperature excess could be the effect of coupling between the fluxes of a chemical reaction and heat transport in the 2-D reaction surface. Its order of magnitude is 10 K for the present model system. The surface temperature excess increases exponentially with the reaction temperature.