How to apply KINETIC rate equation on walls
 

I have a 2-D micro-channel (simplerectangular) with 300 micro-meter width and 3291 micro-meter lenght. The catalyst is loaded on the both walls. At inlet mixture of water & methanol is supplied and due to catalystic wall reaction we get hydrogen and carbon-dioxide at out let. Flow is laminar, diffusion through walls is nigligible.

Now I have a "steam reforming" rate equation with units [mol/(m^2.s)].

How I can apply this kinatic rate equation on walls? I can apply it as a FLUX or as sink/source terms at walls for methanol and hydrogen? (as methanol is consuming and hydrogen is producing)