We explored the surface temperature excess Delta T = T-r - T-m ( real reaction temperature T-r, measured catalyst temperature Tm) on the basis of experimental data, a gradually curved Arrhenius plot for CO oxidation reactions over Pd/gamma-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.(1) The surface temperature excess increases exponentially with the reaction temperature.