ZSM-5/MgO质量比对复合催化剂物化性质及合成甲硫醇反应的影响

Effects of the Mass Ratio of ZSM-5/MgO on the Physicochemical Properties and Catalytic Performance in the Synthesis of Methanethiol

采用介孔碱性MgO对微孔酸性ZSM-5分子筛进行复合改性,利用液相沉淀包覆技术制备了ZSM-5/MgO复合催化剂,研究了ZSM-5与MgO质量比对复合催化剂物化性质和合成甲硫醇催化性能的影响。采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、比表面积及孔隙分析仪(BET)和化学吸附分析仪(CO2/NH3-TPD)等手段对不同复合催化剂的晶相组成、微观形貌、孔结构及表面酸碱性进行分析表征。结果表明:ZSM-5/MgO质量比对ZSM-5/MgO复合催化剂的物化性质和催化性能影响较大。过高或过低ZSM-5/MgO质量比制得复合催化剂中MgO结晶度都有所降低,且未形成包覆相结构;ZSM-5/MgO质量比为1/3时制得复合催化剂形成了均匀包覆相结构和微-介孔结构(总比表面积为162m^2/g,总孔体积0.46cm^3/g),同时具有酸碱特性;在反应压力1.0MPa、反应温度370℃、H2S/CH3OH摩尔比2/1、N2流速80mL/min、H2S流速4.9mL/min反应条件下合成甲硫醇,复合催化剂表现出优越的催化性能、稳定性及寿命,CH3OH转化率、CH3SH选择性和CH3SH收率分别达到90.48%、90.04%和81.47%,催化剂寿命达到18h。与单一ZSM-5分子筛相比,复合催化剂寿命延长了7h,CH3SH收率提高了13.97百分点。

ZSM-5/MgO composite catalysts were fabricated by using acidic microporous ZSM-5 molecular sieve and mesoporous alkaline MgO,based on liquid-phase precipitation coating route.The effect of mass ratio of ZSM-5 to MgO on the physicochemical properties and their catalytic performance in the synthesis of methanethiol was investigated.These obtained composite catalysts were extensively characterized by the X-ray diffractometer (XRD),scanning electron microscope (SEM),specific surface area and pore analyzer (BET) and chemisorption analyzer (CO 2/NH 3-TPD) techniques to investigate their crystalline property,morphology,pore structure and surface acidity-basicity,respectively.Results indicate that various mass ratios of ZSM-5 to MgO pose significant impact on the physicochemical properties and their catalytic performance.The crystallinity and content of MgO in composite catalyst is greatly affected by the ZSM-5/MgO mass ratio.As ZSM-5/MgO mass ratio of 1/3,the homogeneously continuous coating phase and hierarchical structure (total specific surface area of 162 m^2/g,the total pore volume of 0.46 cm^3/g) with acidity and basicity are successfully obtained,which exhibits excellent catalytic performances,stability and reaction lifetime,with methanol conversion of 90.48%,methanethiol selectivity of 90.04%,methanethiol yield of 81.47%,and catalyst lifetime of 18 h under the conditions of reaction pressure of 1.0 MPa,reaction temperature of 370 ℃,H 2S/CH 3OH molar ratio of 2/1,nitrogen flow rate of 80 mL/min and hydrogen sulfide flow rate of 4.9 mL/min.Compared with ZSM-5 molecular sieve,the reaction lifetime of the composite catalyst is extended by 7 h and the yield of methanethiol is increased by 13.97 percentage.