Study On Synthesis And Catalytic Performances Of Silinaite-based Mesoporous Materials

Silinaite (NaLiSi2O5-2H2O) is a kind of new monophyllosilicate consisting of layers of [SiO4] tetrahedral. The Li+ are held in tetrahedral coordination by the four oxygen ions of four [SiO4] tetrahedral and pull the layers together. Silinaite has a lot of interlayer exchangeable Li+ and Na+ cations. The interlayer exchangeable Li+ and Na+ can be exchanged by inorganic cations and alkylammonium ions. Exchange of the Li+ and Na+ cations by hexadecyltrimethylammoium (CTAB) ions transforms silinaite into the silinaite-based mesoporous materials. These new mesoporous materials are potential useful in petrochemical industry and environmental protection.Silinaite is synthesized by heating dispersions of silica source (water glass) in aqueous solutions of LiOH and NaOH at 125℃ for 4 days. Molar ratios are: LiOH/SiO2=0.5 NaOH/SiO2=0.5 and H2O/SiO2=10. Silinaite was added to an aqueous solutions of CTAB, after the samples were stirred at 70℃ for 3 h, the pH values of the suspensions were adjusted to 8.5 by 2mol/L of hydrochloric acid. The suspensions were stirred at 70℃ for 3 h again, then filtered and calcined to yield the silinaite-based mesoporous materials. Further examination of the reaction conditions revealed effects of thee molar ratios of CTAB/silinaite, value of pH, reaction temperature, reaction time, and caltined temperature. At last, ZnCl2/silinaite-based mesoporous catalysts were prepared using impregnating-vapor method. The liquid phase alkylation of benzene with benzyl chloride to produce diphenyl-methane was carried out over synthetic ZnCl2/silinaite-based mesoporous materials.The silinaite and the mesoporous materials were measured by XRD FT-IR SEM and N2 adsorption-desorption isotherms measurements. The results indicated thatsilinaite can be synthesized using water glass, and silinaite can be transformed into mesoporous materials. It has been found that the suitable synthetic conditions of silinaite-based mesoporous materials are surfactant/silinaite molar ratio of 0.1, pH value of 8.5, reaction time of 3 h, reaction temperature of 70℃, calcined temperature of 450℃. The N2 adsorption-desorption isotherms is type IV curves, according to BDDT classification. The samples have a large BET specific surface area (817.1 m2/g) and a narrow pore size distribution (2.7 nm).Catalytic properties of ZnCh/Silinaite-based mesoporous materials catalysts, in alkylation of benzene with benzyl chloride to produce diphenyl-methane was investigated at last. The results showed that the supported-reagents had the highest activity when it was loading of 4mmoVg ZnCl2 and calcined at 150℃ for 5 h.