HZSM-5分子筛硅铝比对催化氯甲烷偶联制备低碳烯烃性能的影响

Effectes of silica-alumina molar ratios of HZSM-5 molecular sieves on catalytic performance of chloromethane coupling to lower olefins

采用硅铝比(n(SiO_2)/n(Al_2O_3))分别为25、38、50、80、200和300的HZSM-5分子筛作为催化氯甲烷偶联制备低碳烯烃(MeXTO)的催化剂,系统地考察HZSM-5分子筛的硅铝比、结构与表面性质对催化性能的影响。利用X线衍射仪(XRD)、N_2吸附-脱附、NH_3程序升温脱附(NH_3-TPD)和O_2程序升温氧化(O_2-TPO)对催化剂进行表征。结果表明:随着硅铝比的增加,分子筛表面的中强酸酸量逐渐降低,酸强度也逐渐减弱,氯甲烷的转化率逐渐降低,而低碳烯烃的总选择性逐渐增大,催化剂的稳定性也逐渐增强,其中,硅铝比为80的HZSM-5分子筛因具有较适宜的表面酸强度和酸量,催化性能最优。在反应温度450℃、空速2.45 h^(-1)下,氯甲烷的转化率达到92.9%,低碳烯烃的选择性达78.3%,反应稳定性达28 h。

HZSM-5 molecular sieves with different SiO 2/Al 2O 3 molar ratios of 25,38,50,80,200 and 300 were selected as the catalysts for the catalytic coupling of chloromethane to lower olefins （MeXTO）.The effects of silica-alumina molar ratios,structure,and surface property of HZSM-5 molecular sieves on catalytic performance were studied.The HZSM-5 molecular sieves were characterized by X-ray diffraction（XRD）,nitrogen adsorption-desorption,ammonia temperature programmed desorption（NH 3-TPD） and oxygen temperature programmed oxidation （O 2-TPO） were investigated systematically.Results showed that the increase ratios of SiO 2/Al2O3 could reduce the acid strength and acid amount of HZSM-5 molecular sieves,which resulted in the decrease conversion of chloromethane and increasing selectivity of lower olefins as well as the prolonged life time of the catalysts.Due to its appropriate acid strength and acid amount in the surface,HZSM-5 molecular sieve with a SiO2/Al 2O3 of 80,showed the best catalytic performance.When the reaction temperature was 450 ℃ and the space velocity was 2.45 h -1 ,conversion of chloromethane and selectivity of lower olefins were 92.9% and 78.3%,respectively,and the reaction could be stable for 28 h.