The Chemical Modification Of The Zsm-12 Zeolite And Its Catalytic Properties

ZSM-12 molecular sieve was prepared by hydrothermal method, and the chemical liquid deposition (CLD) and dealumination have been imposed in the HZSM-12. The structure and acidity for modified HZSM-12 were analyzed and characterized by means of XRD, FT-IR, SEM, N2 adsorption, 27Al NMR, NH3-TPD, Py-IR . The methylation of methylnaphthalene with methanol to synthesis 2,6-DMN as a probe reaction been investigated in a fixed bed reactor. The effects of modification method for HZSM-12 zeolite on their structure, acidity and catalytic properties were investigated .The surface chemical liquid deposition technique for HZSM-12 by MgO and SiO2 was studied. The results show that MgO deposition mainly occurred on the internal surface of HZSM-12, but when the amount deposition more than 0.4% MgO high dispersion on the external surface of HZSM-12 .The interaction of MgO and bridging hydroxyl groups decrease Br?nsted acid sites of HZSM-12 and formed new Lewis acid sites. MgO deposition increase the weak acidic sites ,but significantly decrease the strong acidic sites , leading to the improvement of catalytic stability .After reaction 6h , the conversion decrease 9.1% over modified HZSM-12 compared to 26.1% over untreated HZSM-12. In the contrast, SiO2 deposition mainly on the external surface of HZSM-12. Own to the decrease of the non-selective acidic sites, the probability of side reaction including disproportionation , isomerization of 2,6-DMN decreased and the 2,6-/2,7-DMN increase.Dealumination of HZSM-12 with inorganic acid ,organic acid, steam has studied. The results show that the different dealumination methods have different effects on the pore structure, acidic properties and catalyst preference of modified HZSM-12. Hydrochloric acid eliminates the strong and weak acid sites simultaneously, without destroying the skeleton structure of the zeolite and improving the catalytic activity and stability. 10 mol/L hydrochloric acid treatment induces severe dealumination associated with desilication. In contrast, the citric acid preferred to remove the strongly acid sites and also formed secondary mesopores in the sample, resulting in improved reaction performance. After dealumination the amount of acid sites are markedly reduced, resulting in a lower conversion of naphthalene, but a significantly improved 2,6-/2,7-DMN ratio.