CAREER: Tailoring the Synergy between Catalyst Design and Reaction Engineering for Direct Conversion of Methane to Aromatics

职业：定制催化剂设计和反应工程之间的协同作用，将甲烷直接转化为芳烃

• 批准号: 2245190
• 负责人: Sheima Khatib
• 金额: $ 59.31万
• 依托单位: Virginia Polytechnic Institute and State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-10-01 至 2025-08-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2245190&HistoricalAwards=false
• 关键词: CAREER; Tailoring; Synergy; between; Catalyst

The vast abundance of methane in natural resources makes it an attractive chemical feedstock for conversion into higher hydrocarbon fuels and bulk chemicals of industrial interest. However much of the natural gas is found in stranded locations and is flared due to high transportation and processing costs. Direct transformation routes of methane into liquid chemicals can reduce processing costs but are currently not economically viable due to unanswered scientific challenges. The proposal targets catalytic methane dehydroaromatization (MDA) for the direct conversion of methane to benzene and hydrogen, both mainstays in the chemicals industry. The proposed study seeks to integrate catalysis and reaction engineering to overcome technological challenges arising during MDA. The research results will be integrated with educational and outreach activities.Two major challenges currently prevent the implementation of MDA at an industrial level: (1) thermodynamic limitations leading to low methane equilibrium conversion; (2) rapid catalyst deactivation. While processes involving removal of the hydrogen product from the reaction medium are successful in shifting the equilibrium to the right and increasing methane conversion to benzene, they also accelerate coking. Thus, catalyst deactivation in MDA is a ubiquitous issue that must be addressed. Molybdenum (Mo) oxide supported on HZSM-5 zeolite is the most commonly studied catalyst for the MDA reaction. It is agreed that during an induction period Mo oxide species transform to Mo carbide species that are responsible for the conversion of methane to aromatics. Adding oxidant co-reactants can help the process thermodynamics, however, only low oxidant concentrations can be used since the active Mo carbide phases will otherwise be oxidatively destroyed. At low oxidant concentrations benzene yields are improved but the oxidant distribution in a packed-bed reactor (PBR) is not even, thus kinetic measurements are not representative of the entire catalyst bed. Distributed-feed membrane reactors (DFMR) can overcome the reactor heterogeneity problem and increase benzene yields, but catalyst coking is not fully prevented. The PI has discovered a method to increase catalyst resistance to coking by preparing Mo carbide phases ex situ in the presence of a second metal X (X= Fe, Co, or Ni), but the nature of the Mo-X interaction remains unknown. The proposed project includes studies of stable Mo-X/HZSM-5 catalysts in a DFMR with an oxidant (oxygen or carbon dioxide) as co-reactant to determine the role of Mo-X-C interactions on the reaction and catalyst deactivation pathways. Model catalysts will be prepared by ensuring that the metals (Mo and X) are located inside the zeolite channels by blocking the anchoring sites on the external surface. The structure, location and evolution of the Mo-X phases will be monitored by in situ and Operando experiments using advanced characterization techniques, including X-ray absorption and high-resolution powder diffraction. DFMR operating conditions will be tuned to ensure even axial distribution of the oxidant and maximum enhancement in benzene yield. Kinetic testing will be performed with the DFMR and compared to a PBR as reference. The combination of the kinetic tests, in situ structural characterization and theoretical calculations will result in the determination of the reaction and deactivation pathways of MDA in the presence of oxidants and will provide the basis for the rational design of catalysts tailored for a DFMR. The PI will develop two new graduate courses focused on an integrated interdisciplinary approach to catalysis and an interdisciplinary Science, Technology, Engineering, Art, Mathematics (STEAM) project with the School of Theatre and Dance at Texas Tech University to use storytelling to increase the awareness of the public on the importance of science and engineering and attract students into STEM careers. The stories will be propagated in various formats including theatre performances at local schools, digital stories and podcasts posted on a YouTube channel.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

甲烷在自然资源中的巨大丰度使其成为用于转化为工业利益的高级烃燃料和大宗化学品的有吸引力的化学原料。然而，大部分天然气被发现在搁浅的地点，并由于高运输和加工成本而被燃烧。将甲烷直接转化为液体化学品可以降低加工成本，但由于尚未解决的科学挑战，目前在经济上不可行。该提案的目标是催化甲烷脱氢芳构化（MDA），用于将甲烷直接转化为苯和氢气，这两种物质都是化学工业的支柱。拟议的研究旨在整合催化和反应工程，以克服MDA过程中出现的技术挑战。研究结果将与教育和推广活动相结合。目前阻碍MDA在工业水平上实施的两个主要挑战：（1）导致甲烷平衡转化率低的热力学限制;（2）催化剂快速失活。虽然涉及从反应介质中除去氢产物的方法成功地使平衡向右移动并增加甲烷转化为苯，但它们也加速焦化。因此，MDA中的催化剂失活是必须解决的普遍存在的问题。载于HZSM-5沸石上的钼（Mo）氧化物是用于MDA反应的最常研究的催化剂。人们一致认为，在诱导期钼氧化物物种转化为碳化钼物种，负责甲烷转化为芳烃。添加氧化剂共反应物可有助于工艺热力学，然而，仅可使用低氧化剂浓度，因为否则活性Mo碳化物相将被氧化破坏。在低氧化剂浓度下，苯产率得到改善，但填充床反应器（PBR）中的氧化剂分布不均匀，因此动力学测量不能代表整个催化剂床。分布进料膜反应器（DFMR）可以克服反应器非均匀性问题，提高苯收率，但不能完全防止催化剂结焦。PI已经发现了一种通过在第二金属X（X= Fe、Co或Ni）存在下非原位制备Mo碳化物相来增加催化剂抗焦化性的方法，但是Mo-X相互作用的性质仍然未知。拟议的项目包括在DFMR中以氧化剂（氧气或二氧化碳）作为共反应物研究稳定的Mo-X/HZSM-5催化剂，以确定Mo-X-C相互作用对反应和催化剂失活途径的作用。模型催化剂将通过确保金属（Mo和X）位于沸石通道内，通过封闭外表面上的锚定位点来制备。Mo-X相的结构、位置和演变将通过现场实验和Operando实验进行监测，这些实验使用先进的表征技术，包括X射线吸收和高分辨率粉末衍射。将调整DFMR操作条件以确保氧化剂的均匀轴向分布和苯产率的最大提高。将使用DFMR进行动力学测试，并与PBR（作为参考）进行比较。动力学测试，原位结构表征和理论计算的组合将导致在氧化剂存在下的MDA的反应和失活途径的确定，并将提供为DFMR量身定制的催化剂的合理设计的基础。PI将开发两门新的研究生课程，重点是催化的综合跨学科方法和跨学科科学，技术，工程，艺术，数学（STEAM）项目，与德克萨斯理工大学戏剧与舞蹈学院合作，利用讲故事来提高公众对科学和工程重要性的认识，并吸引学生进入STEM职业生涯。这些故事将以各种形式传播，包括在当地学校的戏剧表演、数字故事和在YouTube频道上发布的播客。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。