Influence of Metallic Modification on Ethylbenzene Dealkylation over ZSM-5 Zeolites

A series of metal-modified HZSM-5 catalysts were prepared by impregnation and were used for ethylbenzene dealkylation of the mixed C8 aromatics (ethylbenzene, m-xylene and o-xylene). The effects of different supported metals (Pt, Pd, Ni, Mo) on catalytic performance, including reaction conditions, were investigated. The physicochemical properties of catalysts were characterized by means of XRD, BET, TEM and NH3-TPD. Experimental results showed that metallic modification obviously increased the ethylbenzene conversion and reduced the coke deposition, greatly improving the catalyst stability. The distinction of ethylbenzene conversion depended on the interaction between hydrogenation reactivity and acidic cracking of bifunctional metal-modified zeolites. Compared with Pt and Ni, Pd and Mo were easier to disperse into HZSM-5 micropores during loading metals. The acidic density of different metal-modified HZSM-5 declined in the following order: HZSM-5>Pt/HZSM-5>Pd/HZSM-5>Ni/HZSM-5>Mo/HZSM-5. The activity of ethylene hydrogenation decreased with Pt/HZSM-5>Pd/HZSM-5>Ni/HZSM-5>Mo/HZSM-5. In comparison, Pd/HZSM-5 showed the best catalytic performance with both high activity and high selectivity, with less cracking loss of m-xylene and o-xylene. Moreover, the following reaction conditions were found to be preferable for ethylbenzene dealkylation over Pd/HZSM-5: 340 degrees C, 1.5 MPa H-2, WHSV 4 h(-1), H-2/C8 4 mol/mol.