Effect of the dealumination procedure on surface properties and catalytic performance of UHP-Y zeolite

The effect of the dealumination procedure on surface properties and catalytic performance of UHP-Y (ultrahydrophobic Y) zeolite was studied. Through manufacturing Route B, hydrothermal treatment increases the crystallinity and secondary pores of chemically treated zeolite instead of reducing them, while through manufacturing Route A, steaming reduces the crystallinity of the starting material. It may be considered that not only further dealumination but also rearrangement of crystal structure of the zeolite occurs during steaming through manufacturing Route B, resulting in the perfect crystal structure. The results of ESCA studies show that A1 concentration in a certain thickness of the zeolite Z, particles remains constant, while an enrichment of A1 on the surface of the zeolite Z(b) is found. A PASCA study indicates that the surface of small cages and micropores in zeolite Z(b) has lower negative charge density than that in zeolite Z(a). Zeolite Z(b) has much lower acid site density than zeolite Z(a), especially the density of strong acid centers. The catalyst based on zeolite Z(b) has lower cracking activity and higher decyclizing activity. Consequently, it has very high activity and selectivity for middle distillates.