3. Catalytic grain-scale kinetics and transfer

3.1 Chemical kinetics of catalytic reactions

The reactants involved in downflow fixed-bed catalytic reactors are generally a gaseous compound, hydrogen or oxygen, hereafter referred to as A, and a liquid compound, to be hydrogenated or oxidized, referred to as B. The stoichiometric expression used hereafter is presented in Box 9.

Reaction products may be exclusively in liquid form, as hydrogenated or oxidized compounds. In other cases, two products are formed, one of which is gaseous and the other liquid, as in desulfurization and denitrification by hydrogenation where, in addition to the modified hydrocarbon, H ₂ S and NH ₃ are produced respectively.