The effect of feed contaminants on the conversion of heavy reformate and toluene mixture over a catalyst containing 4 wt% Mo impregnated on a bifunctional hierarchical composite of mordenite and ZSM-5 is reported. Specifically, the effects of contaminants in the feed (water, 1,2,4,5-tetramethylbenzene (1245-TeMB) and indene) and contaminants in hydrogen (H₂S and CO) were investigated through catalytic performance tests in a fixed-bed micro-reactor at 350 °C and 20 bar H₂. The presence of >35 ppm water in the feed caused significant reduction in the dealkylation of methylethylbenzenes (MEBs) due to a decrease in catalyst's acidity. Hence a dried feed (containing 35 ppm water) was used. An increase of 1.2 wt% in the formation of xylenes was observed with the introduction of 10 wt% 1245-TeMB in the feed due to an increase in the methyl/ring ratio. The addition of 1 wt% indene in the feed resulted in a 4 wt% drop in the formation of xylenes due to the preferential adsorption of indene. The tests with 50 ppm H₂S and 50 ppm CO in hydrogen showed a drop of about 2 wt% in the formation of xylenes. However, the weak basicity of CO exhibited a much lower impact than the adsorption of H₂S on the dealkylation. The effects of these contaminants are discussed in the light of changes observed in product composition during the introduction of a contaminant (48 h) and after restoring the baseline conditions (48 h).