Preparation and Characterization of Silica-, Alumina-Based Catalysts for Methanol Dehydration
|Course||Physical and chemical|
|Keywords||Methanol dehydration Dimethyl ether Solid-acid catalysts SBA-15|
In this work, we mainly made the following three aspect of work: firstly, a series of silica-, titania-, and tungsten oxide-modified alumina catalysts with different modifier contents were prepared using boehmite as precursor of alumina and used for the reaction of methanol dehydration. Secondly, the kinetic behavior of the silica-modified alumina catalyst with the best activity for the MTD reaction had been investigated. We have gotten the activation energy. Thirdly, we have successfully synthesized the mesoporous material of SBA-15, and prepared alumina-, titania-, and tungsten oxide-modified SBA-15 catalysts and used for the reaction of methanol dehydration. The catalysts were characterized by means of TEM, XRD, BET, FT-IR, TG-DTA, TPD. The effects of the active component, carriers, preparation and reaction conditions were also investigated in the reaction of methanol dehydration.（1） We have prepared silica-, titania-, and tungsten oxide-modifiedγ-Al2O3 catalysts by atomic layer deposition method, and all the catalysts were characterized by many methods. The conversion of methanol and selectivity of DME of the catalyst with the best activity were up to 86.5% and 99.95% at 310°C, respectively. The catalyst displayed a nice stability during the 84 h on stream without a reduction in activity. We also studied the surface acidity and acid strength distribution of the silica-, titania-, and tungsten oxide-modifiedγ-Al2O3 catalysts, and we got the conclusion that silica modifier improves the Br?nsted acidity ofγ-Al2O3 catalyst.（2） The apparent activation energy of the reaction was determined over the catalyst with 7at.% Si/Al ratios. The values of the reaction rate constant k were 1.08×10-5, 2.56×10-5 and 5.48×10-5 in the 170, 190 and 210 oC, respectively. The apparent activation energy was determined to be 72.53 kJ mol-1 in the temperature range of 190–230 oC, basing on Langmuir–Hinshelwood model. （3） We have prepared alumina modified SBA-15 with different alumina loadings by the atomic layer deposition method. The alumina modified SBA-15 catalysts show higher activity than titania- and tungsten oxide-modified SBA-15 catalysts for the reaction of MTD. NMR results confirm that Al has been successfully incorporated into the framework of SBA-15 materials. Both Br（?）nsted and Lewis acid sites co-exist in dehydrated alumina modified SBA-15 surfaces. The catalyst with 7wt.% Al2O3/SiO2 ratios and calcined at 600 oC has the best catalytic activity.