Indications for a surface temperature excess in heterogeneous catalysis.
We explored the surface temperature excess DeltaT = 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/gamma-Al(2)O(3) 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.
Zhu
Lianjie
L
Department of Chemical Technology, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands. zhu@nano.ku.dk
Frens
Gert
G