What are the steps involved in heterogeneous catalysis?

The seven steps are: (1) External diffusion - reactants diffuse from bulk fluid to catalyst surface, (2) Internal diffusion - reactants diffuse through pores to active sites, (3) Adsorption - reactants adsorb on catalyst surface, (4) Surface reaction - reaction occurs on catalyst surface, (5) Desorption - products desorb from surface, (6) Internal diffusion of products out through pores, (7) External diffusion of products into bulk fluid. The slowest step is rate-limiting and determines overall rate.