Synthesis And Catalytic Performance Of Mesoporous Materials Containing Heteroatoms

A series of M41S mesoporous molecular sievs were firstly discovered by Mobil in 1992.However, pure silica M41S possesses some disadvantages such as small ion-exchange capacity, low catalytic activity, weak surface acidity and poor hydrothermal stability, which limited their application in catalytic reactions. Enhancing its practicability and improving its hydrothermal stability and catalytic activity seemed to be a more interesting task.Zr-MCM-41 mesoporous molecular sieves with different Si/Zr ratios were successfully synthesized by microwave irradiation method and hydrothermal method. The thermal and hydrothermal stabilities of the as synthesized samples were investigated.The results show that the textural properties of the samples syntheszed via novel microvave method are similar to that of the samples by traditional hydrothermal method.By comparing with hydrothermal method, the microwave irradiation method needs short crystallization time.The thermal and hydrothermal stability experimental results show that the samples obtained by two different methods have highly thermal and hydrothermal stabilities, the mesoporous framework still retain even after of the two Zr-MCM-41 mesoporous molecular sieves were calcined at 750℃for 4h or hydrothermal treated at 100℃for 6d.Zr-MCM-48 mesoporous molecular sieves were synthesized hydrothermal by directly adding fluoride ions to the initial gel.The influences of various factors, such as the amount of NaF addition, the Si/Zr molar ratios,crystallization temperature and crystallization time, on the crystalline structure and textural property of Zr-MCM-48 were investigated in detail.The thermal and hydrothermal stabilities results show that Zr-MCM-48 still maintains the Ia3d mesoporous structure after calcination at 800℃for 4h or hydrothermal treatment at 100℃for 24h.The addition of fluoride ions results in short crystallization time and highly hydrothermal stability.Co-MCM-48 and Al-MCM-48 mesoporus molecular sieves were prepared by the above method.The experimental results show that the as synthesized samples possess typical Ia3d cubic mesoporous structure of MCM-48.The thermal and hydrothermal stabilities of Co-MCM-48 mesoporous molecular sieves were also investigated.The results show that the Co-MCM-48 sample still maintains the Ia3d cubic mesoporous framework even after calcination at 800℃for 4h or hydrothermal treatment at 100℃for 12h.The mesoporous structure has completely collapsed after Co-MCM-48 was hydrothermal treated at 100℃for 24h, and the mesoporous ordering becomes poor.SO42-/M-MCM-48 and H-M-MCM-48 (M=Zr, Al) molecular sieve catalyst were prepared by the wet impregnation method with H2SO4 and NH4NO3 solution. Compared with M-MCM-48, the mesoporous ordering of SO42-/M-MCM-48 and H-M-MCM-48 becomes poor, but the cubic structure of MCM-48 still retains.The NH3-TPD profiles suggest the amount of the strong acid and weak acid for SO42-/M-MCM-48 and H-M-MCM-48 are obviously more than these for M-MCM-48.In the alkylation reaction of phenol with tert-butanol, the effects of the different catalysts, reaction temperature and reaction time on the reaction results were examined.The experimental results show that the phenol conversion is higher for the H-Al-MCM-48 than the other catalysts. In addition, the H-Al-MCM-48 and SO42-/Zr-MCM-48 catalyst still maintain higher catalytic activity and hydrothermal stability after alkylation reaction of phenol with tert-butanol for 8h. Compared with H-Zr-MCM-48 and SO42-/Al-MCM-48, we found that the catalytic activities of H-Al-MCM-48 and SO42-/Zr-MCM-48 were enhanced and exhibit higher catalytic activity in the phenol alkylation with tert-butanol under the same conditions.