合成气直接制芳烃嵌入式Co@HZSM-5催化剂的研究

Cobalt-embedded zeolite catalysts for the direct conversion of syngas to aromatics

由于芳烃收率低、催化剂易积碳和反应条件苛刻等问题的存在,合成气直接转化制芳烃技术目前仍然面临很多挑战。采用分步晶化方法合成了嵌入式Co@HZS M-5双功能分子筛催化剂,并通过X射线衍射(XRD)、N 2物理吸附-脱附、扫描电子显微镜(SEM)、氨气程序升温脱附(NH 3-TPD)、氢气程序升温还原(H 2-TPR)以及热重分析(T G-DTA)等手段对催化剂的形貌、晶体结构、酸性、还原性能、积碳行为等理化性质进行了表征,随后在固定床反应器中对Co@HZS M-5催化剂进行了合成气直接催化转化制芳烃的反应性能评价。研究结果表明:嵌入式Co@HZS M-5分子筛催化剂相较于传统负载型Co/HZS M-5分子筛催化剂以及Co/SiO 2催化剂具有更多的酸中心和适宜的酸强度;同时,这种将活性金属纳米颗粒嵌入在分子筛晶体内部的特殊结构在保证活性相结构稳定的同时,还发挥了分子筛的择形限域效应。因此,嵌入式Co@HZS M-5催化剂可有效促进费托合成反应低碳产物的二次芳构化反应,提高芳烃的选择性,同时抑制长链烃类和积碳的生成。

Given the low yields of aromatics,severe coke deposit formation,and harsh reaction conditions required,there are still many challenges to be overcome in the direct conversion of syngas to aromatics.In this study,we have synthesized bifunctional Co@HZS M-5 zeolite catalysts by a two-step crystallization method.The physical and chemical properties of the catalysts,including sample morphology,crystal phase,acidity,reduction performance,and coke deposition,were characterized by XRD,N 2 physical adsorption,SEM,NH 3-TPD,H 2-TPR,and T G-DTA.Their catalytic performance in the direct conversion of syngas to aromatics was evaluated in a fixed bed reactor.The results show that the bifunctional Co@HZS M-5 zeolite catalyst has more acid sites and more suitable acid strength than Co/HZS M-5 and Co/SiO 2 catalysts prepared by traditional impregnation methods.Meanwhile,the novel structure of the Co@HZS M-5 in which the active metal nanoparticles are embedded in the host enhances the stability of the active phase structure,and allows the shape-selective confinement effect of HZS M-5 to be exerted.Therefore,the embedded Co@HZS M-5 catalyst can effectively promote the aromatization reaction of low-carbon products of the Fischer-Tropsch synthesis reaction,and improve the selectivity for aromatics by inhibiting the generation of long-chain hydrocarbons and coke deposition.