1) Advection (VOCs and precursor species are carried by airflows),
2) Mass transfer of the reactants from the main flow to the exterior surface of the catalyst particle,
3) Molecular diffusion and/or Knudsen diffusion of the reactants from the exterior surface of the catalyst particle into the interior pore structure,
4) Adsorption onto the interior catalyst surface,
5) Photochemical reaction on the catalyst surface,
6) Desorption of the reaction product(s) from the surface of the catalyst, and
7) Mass transfer of the products from the interior catalyst pores to the gross external surface of the catalyst by ordinary molecular diffusion and/or Knudsen diffusion, and finally external
diffusion to the main flow