Abstract Two‐phase upflow/downflow and styrene hydrogenation were explored numerically in vertical and inclined packed‐bed bubble reactors using a dynamic three‐dimensional model which integrates the hydrodynamics via macroscopic volume‐averaged continuity and momentum balance equations, energy and mass conservative equations in liquid/gas phases, and simultaneous diffusion and chemical reaction inside Pd/Al 2 O 3 catalyst particles. Packed‐bed bubble reactors non‐verticality divert the liquid phase from its normally expected axial trajectory and generate an excessive axial symmetry distortion because of amplified secondary liquid flow associated with a larger liquid holdup and because of liquid reversal flow (two‐phase upflow). The significant liquid maldistribution over the packed beds (especially in deeper beds) substantially reduces the performance of the styrene hydrogenation process in inclined packed‐bed bubble reactors, more than in inclined trickle‐bed reactors. This drop in hydrogenation performance is more noticeable in downflow packed‐bed bubble reactors, particularly at higher packed bed inclinations, because of the reduction of catalyst wetting efficiency and overall effectiveness factor of the catalyst particles. Increasing the height and diameter of packed bed is recommended to compensate for reduction in hydrogenation performance in inclined packed‐bed bubble reactors. However, the ratio between the reactor height and diameter should be limited to a maximum value to avoid the excessive liquid maldistribution in deeper beds with a significant bypassing in the vicinity of the bottom of the packed bed.