化学链甲烷氧化偶联：基于“储氧体”的高效催化剂构筑及晶格氧迁移与选择性调控研究

化学链（Chemical Looping，CL）反应可以将甲烷氧化偶联（OCM）的Red-Ox过程分离而成连串步骤，不仅能有效提高选择性，而且是本质安全过程，但高效CL-OCM过程构建的核心关键在于催化剂活性/选择性晶格氧储氧量的突破性提高。本申请拟开展基于“Mn2+↔Mn3+”化学循环与“储氧体（OSM）”化学复合的高效CL-OCM催化剂的裁剪设计及晶格氧迁移机制与氧化选择性调控本质的研究，考察CeO2-基、含Mn尖晶石/钙钛矿-基OSM的化学构成、晶相、晶粒尺寸和含量以及诸如微量Pd掺杂等对“Mn2+↔Mn3+”化学循环活化O2及与Na2WO4协同活化转化CH4性能的影响，借助17O同位素固体NMR等表征技术，研究揭示OSM晶格氧参与“Mn2+↔Mn3+”化学循环的迁移机制和Na2WO4对晶格氧的选择性调控本质，为发展本质安全、选择性好且易于装置大型化的OCM工艺技术提供新思路。

Chemical Looping concept is opening an opportunity for the development of intrinsically safe and highly efficient oxidative coupling of methane (OCM) to ethylene process, because it permits the REDOX of the OCM reaction to proceed separately as a cascade process of the REDUCTION and OXIDATION in two reactors thereby absolutely avoiding to co-feed methane with oxygen (i.e., no explosion risk). However, it is urgently calling for a groundbreaking catalyst that should have abundant active and selective lattice oxygen atoms is particularly desirable but represents a grand challenge. Herein, we propose a strategy for the development of W-Mn-Na/oxygen-storage-material(OSM) catalysts for the chemical looping OCM (CL-OCM), by chemically fusing the “Mn2+↔Mn3+” cycle that catalyzes the methane oxidation by lattice oxygen atoms with the OSM that serves as a lattice oxygen reservoir. Catalyst performance for the CL-OCM process will be investigated systematically, focusing on the tuning effect of chemical composition, crystal phase/size, content, and doping (such as Pd-doping) of the CeO2-based and Mn-containing spinel/perovskite-based OSM on the synergistic catalysis of “Mn2+↔Mn3+” chemical cycle between Na2WO4-modifier for the O2 and CH4 activation/conversion. The 17O solid-state NMR spectroscopy will be employed to explore the synergistic interaction between “Mn2+↔Mn3+” cycle and OSM. By doing so, we anticipate to reveal how the nonselective lattice oxygen atoms of the OSM transfer into the “Mn2+↔Mn3+” cycle and how the Na2WO4 additive works to make the lattice oxygen atoms migrated from bulk of the OSM through the “Mn2+↔Mn3+” cycle become selective for the methane oxidation to ethylene/ethane. We believe that our findings will stimulate the commercial exploitation of such kind of intrinsically safe and highly efficient CL-OCM process.