摘要
二氧化碳加氢制备烯烃是实现二氧化碳转化的有效途径之一,二氧化碳先后通过逆水煤气反应和费托合成反应生成高附加值产品。铁基催化剂具有很好的逆水煤气以及费托合成活性,然而CO_(2)加氢制备烯烃过程中存在多种副反应,导致烯烃选择性较低。如何提高铁基催化剂性能成为工业化的重要问题。通过定量浸渍法制备一系列不同Na含量的Fe-Zn催化剂,采用稳态反应速率测定、原位X射线光电子能谱(In-situ XPS)、原位X射线衍射(In-situ XRD)以及原位漫反射红外傅里叶变换光谱(In-situ DRIFTS)技术,探究碱金属Na对铁基催化剂结构及CO_(2)加氢直接合成烯烃活性的影响。研究发现:在Fe-Zn催化剂CO还原过程与CO_(2)加氢反应过程中,碱金属Na的引入导致Fe_(3)O_(4)含量降低,Fe_(5)C_(2)含量提高,表明碱金属Na有利于Fe_(5)C_(2)生成,同时XPS结果表明Na与Fe_(5)C_(2)之间存在电子转移,导致Fe_(5)C_(2)电子云密度增大,不利于烯烃二次加氢反应,提高了烯烃与烷烃的比例;此外Na可以调节表面CH_(x)^(*)物种比例,随着Na含量的提高,表面CH^(*)与CH_(2)^(*)之间的比例增大,导致表面CH^(*)物种的相对增加,有利于提高C-C耦合能力;Na的引入可以提高Fe-Zn催化剂催化CO_(2)加氢合成烯烃的性能,在温度593 K和反应压力1.5 MPa时,CO_(2)转化率可达到35%,碳氢化合物中烯烃选择性高达65%,烯烷比大于6,且CO选择性较低为18%。
Formation of olefins directly from CO_(2) hydrogenation is one of the effective and valuable routs for utilization.Formation of high value-added products directly from CO_(2)-H_(2) mixtures may occur via a combination of reverse water-gas-shift(RWGS)reaction and Fisher-Tropsch(FT)synthesis over Fe based catalysts.This route produces by-products,which leads to a complex reaction system and low olefins selectivity.In this stu-dy,a series of Fe-Zn catalysts with Na were synthesized to get a deep insight into the effects of Na on the catalytic hydrogenation of CO_(2) and the structures of Fe-Zn catalyst at working state,by steady-state rate measurements,In-situ X-ray diffraction(In-situ XRD),In-situ X-ray photoelectron spectroscopy(In-situ XPS),In-situ diffuse reflectance infrared Fourier transform spectroscopy(In-situ DRIFTS).Decorating with Na facilitated the formation of Fe_(5)C_(2).Electron transfer occured between Na and Fe_(5)C_(2),resulting in the increase of electron density of Fe sites,which was not conducive to the secondary hydrogenation of olefin and improved the ratio of olefin to alkane.Decorating with Na facilitated C-C coupling by regulating the proportion of surface CH^(*)species.The results showed that the Na exhibited the best catalytic performance for CO_(2) hydrogenation to olefins at 593 K and 1.5 MPa.the selectivity of olefins in hydrocarbons was as high as 65%,the O/P ratio was up to 6,and the CO selectivity was below 18%.
作者
孙超
张振洲
陈宝见
杜春丽
涂维峰
SUN Chao;ZHANG Zhenzhou;CHEN Baojian;DU Chunli;TU Weifeng(School of Chemical Engineering,Zhengzhou University,Zhengzhou 450001,China)
出处
《郑州大学学报（工学版）》
CAS
北大核心
2022年第4期97-103,共7页
Journal of Zhengzhou University（Engineering Science）
基金
国家自然科学基金资助项目(22078307)
河南省高校科技创新团队支持计划(18IRTSTHN)。
关键词
二氧化碳
烯烃
碱金属
铁物种
加氢
carbon dioxide
olefins
alkali metal
iron species
hydrogenation
