Effects in Experimental Catalysis

In the discussions concerning the interpretation of activity data from all of the above methods, it was assumed that the concentration of the gaseous components seen by the catalytic surfaces were identical with those measured or established for the bulk of the gas phase. 

This assumption is not necessarily correct in all experimentation due to the possible competition of the reaction rate on a surface with the 

If the whole assembly be moving in the sense of a flowing gas, this gas flow is superimposed additively, in the vectorial sense, to the random diffusive motion. When the flow is described as laminar, transport of molecules across the flow lines must still rely on diffusion. Even when there is mechanical transport by turbulent motion, diffusion must be relied upon for transport of molecules across the dimensions of the vortex unit. 

The diffusive flux of molecules dn/dt to the surface S in the steady state will be given by the diffusion equation 

while the reaction velocity dn/dt is in general dependent on reactant concentration (formula (4)), diffusion makes the prevailing concentration in turn dependent on the reaction velocity. 

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