Synthesis, Characterization Of MSE-Type Zeolite And Their Catalytic Performance In Friedel-Crafts Alkylation

MCM-68with MSE topology is a three-dimensional zeolite with12×10×10membered ring (MR) channels. MCM-68was reported as a potential alkylation catalyst for the alkylation of aromatic compounds, isomerization and cracking. In our country, there are few researches about MCM-68zeolite, and its synthesis conditions and catalytic properties need to be further investigated and evaluated. In this paper, the detailed synthesis strategies, its characterizations as well as its catalytic performance of MSE-type zeolite are reported. The main contents are as follows:MCM-68zeolite was prepared by the direct hydrothermal method. The influence of SiO2/Al2O3ratio, KOH/SiO2ratio, SDA amount and H2O/SiO2on the synthesis of MCM-68zeolite has been investigated. The gel-composition window for the successful crystallization of pure MCM-68is very narrow and the Si/Al ratio of the product is limited to10-11. The alkalinity has great effects on the crystallization of MCM-68. These results suggest that the sodium aluminosilicate gel with higher Si/Al ratio and less KOH/SiO2ratio will provide more favorable condition to crystallize MTW; and the less Si/Al ratio and higher KOH/SiO2ratio in the initial gel will provide more favorable condition to crystallize MOR. The highly crystalline MCM-68zeolite could be synthesized with good reproducibility in a narrow range of the initial sodium aluminosilicate gel compositions:1.0SiO2-(0.10-0.14) TEBOP2+(I-)2-(0.375～0.445)KOH-(0.09-0.10)Al(OH)3-(30-33)H2O.The gel-composition window for the successful crystallization of pure MCM-68is very narrow. Alteration of the chemical composition of the product by direct crystallization is therefore difficult to carry out. A series of dealuminated HMCM-68zeolites were prepared by treatment with steaming or hydrochloric/citric acid leaching. Their catalytic properties were studied using the alkylation of phenol with tert-butyl alcohol as a test reaction. The HMCM-68zeolite modified by citric acid for8h (CAZ8) showed the best catalytic performance due to its improved structural and acidic properties, confirmed by methods of XRD, ICP-AES, SEM, N2adsorption and NH3-TPD. Furthermore, it is proposed that citric acid treatment is the most suitable method for dealumination of HMCM-68zeolite in the alkylation of phenol, which results in the zeolites having appropriate acid amount (0.16mmol/g), as well as enlarged surface area (521m2/g) and pore volume (0.518cm3/g) for the desired transformation. The effect of various reaction parameters such as reaction time, reaction temperature and reactant molar ratio were studied over CAZ8and the catalyst could be reused two times without obvious decrease in the conversion and selectivity.In this study, Fe-containing HMCM-68was prepared by a direct hydrothermal method (Fe-HMCM-68) or by impregnation of HMCM-68with different iron precursors (Fe2O3/HMCM-68, FeCl3/HMCM-68) for the first time. Their structure and acid properties were characterized by XRD, N2adsorption, UV-Vis and NH3-TPD. The catalytic performances of the samples were evaluated by using the model reaction of the benzylation of toluene by benzyl chloride. HMCM-68showed relatively low activity for the toluene benzylation reaction, but its benzylation activity increased drastically by the introduction with HMCM-68with Fe2O3or FeCl3. The activity of the catalysts declined in the following order:FeCl3/HMCM-68≈Fe2O3/HMCM-68> Fe-HMCM-68> HMCM-68. The activity of the Fe-containing HMCM-68catalysts for the toluene benzylation is controlled mainly by their redox properties. We can see that the amounts of weak and medium acid sites increased in FeCl3/HMCM-68and Fe2O3/HMCM-68. Therefore, in addition to the redox function, high amounts of weak and medium acid sites in the catalysts appear to be advantageous to the benzylation of toluene. The stability of the catalysts has been studied by running the reaction successively with the same catalyst (FeCl3/HMCM-68). The results showed that the catalyst could be used two times in the toluene benzylation process without a significant change of its catalytic activity and selectivity.In this work, N,N,N’,N’-tetraethylbicyclo[2.2.2]oct-7-ene-2,3:5,6-dipyrrolidinium diiodide and nordstrandite were respectively used as template and aluminum source to synthesize ZSM-12zeolites. The results of XRD, ICP-AES and27Al MAS NMR indicated that the Si/Al ratios of the pure MTW-type zeolites are in the range of8-23, and these values are lower than the Si/Al ratios of any other conventional ZSM-12 zeolites reported in the previous researches. Catalytic properties of the prepared zeolites (HZT-25and HZT-10) were studied in the ter/-butylation of phenol. Higher para selectivity was obtained on the Al-rich ZSM-12zeolites compared with other types of zeolites, which could be attributed to the pore-size effect of the MTW zeolite. For Al-rich ZSM-12with different Si/Al ratios, HZT-25showed the best catalytic activity because of its high hydrophobic character (high Si/Al ratio). For recyclability, HZT-25catalyst was studied with respect to tert-butylation of phenol. The results showed that the catalyst could be used two times in the butylation of phenol without a significant change of its catalytic activity.