Performance comparison of heterogeneous Pd-supported catalysts: Pd/ZSM-5, Pd/13X and Pd/Al₂O₃ for hydrogenation of benzene in gasoline

In this research, the selective hydrogenation of benzene in a mixture of benzene and normal heptane (5 vol.% of benzene) over various heterogeneous catalysts was evaluated. For this purpose, a series of catalysts with various supports such as Pd/ZSM-5, Pd/13X and Pd/〖"Al" 〗_"2" "O" _"3" were developed. To prepare Pd supported catalysts, the modification of supports was conducted out by a specified amount of palladium nitrate in the aqueous solution. Experimental catalyst evaluation tests were performed in the catalyst assessment set-up (Cata-test). The characterizations of physicochemical properties of the prepared catalysts were performed by XRD, NH₃-TPD and BET. It was found that the conversion of benzene was promoted at the optimized operating conditions of 200 ℃, 1 MPa, WHSV=25 hr-1 and H2/HC(molar ratio)=1.3. Among these catalysts, Pd/13X exhibited the maximum benzene conversion (90%) and the minimum light-cut production at the optimum conditions. The study on stability of catalysts shows that, the activity decline of Pd/13X catalyst is more than the other catalysts (from %90 to %81) in the specified 20 h time on stream, but so far the activity of this catalyst is highest in comparison with other catalysts at the end of the defined time (20 h).