Molecular Structure and Reactivity of Model Mn/Na2WO4/SiO2 Oxidative Coupling of Methane Catalyst under Operating Conditions

该研究项目致力于将天然气的主要成分甲烷直接催化转化为增值的化学原料。特别是，这项研究为两个甲烷分子如何耦合在一起形成具有两个碳原子的各种分子，即OCM反应的机制提供了基本的见解。 后一种类型的分子是化学工业感兴趣的化学品和燃料。 OCM反应作为大规模、资本密集型甲烷转化路线的更经济的替代方案，特别是对于其甲烷不能经济地运输到集中式化工厂的偏远甲烷储层，目前受到工业界的关注。该项目结合了研究，教学和推广计划，重点是了解最佳性能OCM催化剂的局限性，并探索提高其活性和选择性超过目前水平的方案。 这项研究正在利哈伊谷达芬奇科学中心的年度夏季研讨会上展示，所有年龄段的游客都将接触到正在开发的将甲烷转化为化学物质的新技术。研讨会，课程开发和研究整合到高级化学工程项目设计顶点课程将影响每年约180名不同社会经济背景的初中，高中和本科生。 这项研究是与国际研究人员合作进行的，这将使人们能够使用利哈伊没有的尖端研究设施，提高研究的知名度，并让参与的学生接触到国际领先实验室的研究文化。该项目是建立在这样的假设之上的，即负载Mn/Na 2 WO 4/SiO2催化剂是固定在二氧化硅载体上的孤立的表面WOx物质。研究人员的初步研究首次确定了在OCM过程中催化该反应的未促进和促进的孤立表面WOx位点的存在。该项目的目标是：（1）通过在OCM过程中应用现代原位和操作光谱学，结合动力学研究和密度泛函理论（DFT），建立基本的催化剂结构-活性关系;（2）应用新的基本见解指导在较低温度下运行的先进活性和选择性OCM催化剂的合理设计。各种排列的未促进和Na-，Mn-和Na/Mn-促进的SiO2负载的WOx网站正在合成。二氧化硅载体也用钠金属和纳米连接剂（TiOx、ZrO 2、Al 2 O 3）进行表面改性，这将增加隔离的表面WOx位点的数量并调节其还原性和酸碱特性。促进剂-W的比例正在系统地变化，以探索它们对WOx位点的数量和结构以及OCM活性/选择性的影响。催化剂在制备时和OCM反应条件下用原位和操作光谱（拉曼、UV-vis和NAP-XPS）表征，以确定二氧化硅上WOx位点的分子和电子结构。实验结果正在补充与分子水平的DFT计算，以提供更多的见解，结构-活性关系。相应的动力学研究与同位素CH 4/CD 4和16 O2/18 O2分别解决速率决定步骤和不同的WOx网站的相对参与，后者通过时间分辨拉曼质谱。通过与欧洲合作伙伴的合作，正在利用分子束质谱仪获得有关气相自由基及其与特定催化剂结构的关系的信息。新的见解将导致概念上新的和现实的催化剂模型，将有可能使一步OCM催化过程的发展。成功执行拟议的研究有可能导致从廉价，丰富，但运输甲烷困难和昂贵的C2碳氢化合物的经济可行的生产，从而使美国更接近能源独立，同时也提供了更长的时间来过渡到可持续的化学品。该项目将涉及与Siluria和SABIC两家公司的合作，这将促进新催化剂向化工行业的转移。

This research project addresses the direct catalytic conversion of methane, the primary component of natural gas, to value-added chemical feedstocks. In particular, the research provides fundamental insight into the mechanisms of how two methane molecules couple together to form various molecules with two carbon atoms, the OCM reaction. The latter types of molecules are chemicals and fuels of interest to chemical industries. The OCM reaction is of current industrial interest as a more economical alternative to large-scale, capital-intensive routes for methane conversion, especially for remotely located methane reservoirs whose methane cannot be economically transported to centralized chemical plants. The project combines research, teaching and an outreach plan focused on understanding limitations of the best performing OCM catalyst, and exploring options for improving its activity and selectivity beyond current levels. This research is being showcased in annual summer workshops at the Lehigh Valley Da Vinci Science Center where visitors of all ages will be exposed to the new technologies being developed that convert methane to chemicals. Workshops, curricula development, and research integration into a senior Chemical Engineering Project Design capstone course will impact approximately180 middle-, high-school and undergraduate students of diverse socioeconomic backgrounds per year. The research is being conducted in collaboration with international researchers, which will allow access to cutting edge research facilities not available at Lehigh, enhance visibility of the research, and expose the participating students to the research culture in leading international laboratories.The project is built on the hypothesis that the active site for OCM by supported Mn/Na2WO4/SiO2 catalysts is an isolated surface WOx species anchored to the silica support. The investigators' preliminary studies have identified, for the first time, the presence of unpromoted and promoted isolated surface WOx sites during OCM that catalyze this reaction. The objectives of the project are to (1) establish the fundamental catalyst structure-activity relationships by application of modern in situ and operando spectroscopy during OCM combined with kinetic studies and density functional theory (DFT), and (2) apply the new fundamental insights to guide rational design of advanced active and selective OCM catalysts functioning at lower temperatures. Various permutations of unpromoted and Na-, Mn- and Na/Mn-promoted SiO2-supported WOx sites are being synthesized. The silica support is also being surface-modified with sodium metal and nanolinkers (TiOx, ZrO2, Al2O3) that will increase the number of isolated surface WOx sites and tune their reducibility and acid-base characteristics. The promoters-to-W ratios is being systematically varied to explore their effects on both the number and structure of the WOx sites and OCM activity/selectivity. The catalysts are being characterized as prepared and during OCM reaction conditions with in situ and operando spectroscopy (Raman, UV-vis and NAP-XPS) to determine the molecular and electronic structures of the WOx sites on silica. Experimental findings are being complemented with molecular level DFT calculations to provide additional insights into structure-activity relationships. Corresponding kinetic studies with isotopic CH4/CD4 and 16O2/18O2 are addressing the rate-determining-step and relative participation of different WOx sites, respectively, - the latter via time-resolved Raman-Mass Spectroscopy. Information about gas phase radicals and their relationship to specific catalyst structures is being obtained with Molecular Beam Mass Spectroscopy through collaboration with European partners. The new insights will lead to conceptually new and realistic catalyst models that will have the potential to enable development of one-step OCM catalytic processes. Successful execution of the proposed research has the potential to lead to economically viable production of C2 hydrocarbons from cheap, abundant, yet difficult and costly to transport methane, and thus move the US closer to energy independence while also providing a longer timeframe to transition into sustainable chemicals. The project will involve collaborations with two companies, Siluria and SABIC, that will facilitate transfer of new catalysts to the chemical industry.