Compared with other mature industrial fields where multiphase reactors are prevalent, the design of three-phase catalytic reactors for wet air oxidation processes is still in emergence. A series of detailed isothermal unsteady-state two-dimensional models is therefore developed and solved in the context of sub-critical catalytic wet oxidation with a non-deactivating catalyst of organic-containing contaminated wastewaters. A comparative analysis is made for trickle-bed reactors, packed-bubble columns, three-phase fluidized beds and slurry bubble columns. This paper discusses from a multiphase reactor engineering perspective, the design of such contactors by setting an exhaustive modeling framework of catalytic wet oxidation in which the molecular, particle and reactor scales are integrated. The simulation results indicate that when wet oxidation is liquid-reactant limited, packed bubble columns outperform trickle beds regardless of the pressure level, whereas three-phase fluidized beds exhibit a critical particle size maximizing the pollutant conversion. At equal effluent residence times, slurry bubble columns are found less efficient than three-phase fluidized bed reactors.