The 3-D, large-pore zeolite beta (BEA) is effective in trapping large hydrocarbons (HCs). We conducted temperature-programmed desorption (TPD) experiments of a BEA-containing monolithic catalyst prestored with various mixtures of propylene, hexane, and toluene. The addition of propylene to a hexane + toluene mixture results in an unusual interaction during TPD. A rather small concentration of propylene increases the desorption temperature of the hexane from a weakly held into a stronger bound component. A variation in the propylene concentration leads to the nonmonotonic dependence of a high temperature hexane desorption peak. The data suggest that the blockage of hexane desorption by propylene depends on the uptake time. The findings complicate the analysis and design of HC traps used in applications such as vehicle aftertreatment systems.