Zn改性纳米ZSM-5分子筛的物化性能及催化甲醇制汽油反应性能研究

Study on the Physicochemical Properties and Catalytic Performance of Zn Modified Nano-ZSM-5 Zeolite for Methanol to Gasoline

以晶种引导法合成的纳米ZSM-5分子筛为母体,采用液相沉积法制备了系列不同Zn担载量的改性纳米ZSM-5分子筛催化剂,分别采用SEM、N2物理吸附、H2-TPR、NH3-TPD和Py-IR等手段对催化剂进行了表征,并考察了Zn改性前后的ZSM-5分子筛的物化性质及用于甲醇制汽油(MTG)的催化反应性能。结果表明,随着Zn担载量的增大,改性分子筛的孔容和比表面积减小,由Brφnsted酸提供的强酸位的强度减弱、强酸量减少,由Lewis酸提供的弱酸位的酸量减少、中强酸性位的强度增强、酸量增加,由Zn活性物种形成了新的更强的酸性位。ZnO担载量为2.0%(wt)的改性纳米ZSM-5分子筛2.0ZnNZ5是最适宜的MTG反应催化剂,当甲醇转化率为98.2%时汽油的选择性高达64.7%。

A series of modified nano-ZSM-5 zeolite catalysts with different Zn loadings are prepared by liquid deposition method with the nano-ZSM-5 zeolite as matrix which is synthesized by seed crystal-induced method.The catalysts are characterized by means of SEM,N2 physical adsorption,H2-TPR,NH3-TPD and Py-IR technology.The physicochemical properties of the ZSM-5 and Zn modified zeolite and their catalytic performance in the process of methanol to gasoline(MTG)reaction are investigated.The results show that the pore volume and specific surface area of the modified zeolites decreases,the acid strength of the strong acid site provided by Brφnsted acid becomes weak and the density decreases,the acidity of the medium acid site provided by Lewis acid enhances and the density increases,while the density of the weak acid site decreases with the increase of Zn loading.The new stronger acid sites forms from Zn active species.The modified nano-ZSM-5 zeolite with 2.0%(wt)ZnO loading(2.0 ZnNZ5)is a more suitable catalyst for MTG reaction.A selectivity of 64.7%for gasoline achieves when the the methanol conversion is 98.2%.