Chemistries mediating deactivation in methanol to hydrocarbons conversion and strategies to mitigate them

甲醇转化为碳氢化合物是将煤和页岩气等碳原料升级为高价值燃料和化学品的最后一步。沸石的形状选择特性为轻质烯烃或汽油类碳氢化合物提供了高选择性，但对催化剂的寿命是有害的，因为大量碳氢化合物在微孔内的积累使它们失去活性。本研究的目的是探索形成这些非活性封闭烃的机制，并开发配方和工艺条件，以提高催化剂的寿命和选择性。这项研究将有助于确保能源和化学工业对国家化石燃料资源的有效利用。沸石孔隙中的烯烃和芳烃中间体会自动催化甲醇转化为碳氢化合物，形成所谓的“碳氢化合物池”，充当碳-碳键形成事件的有机助催化剂。本研究旨在探讨活性烃池中间体转化为非活性多环烃的途径。初步结果表明，甲醇在催化过程中作为氢化物供体，甲醇脱氢衍生物作为烷基化剂影响烃池失活。该项目旨在利用同位素方法结合瞬态和稳态动力学测量，确定甲醇脱氢事件发生的速率和机制。研究人员提出，可以通过以下方式提高催化剂的使用寿命：(1)通过引入空间限制来改善无机催化剂，以减少大块碳氢化合物的形成，或通过添加分解醛的金属氧化物来改善无机催化剂；(2)在气相中引入含甲醇流之前引入有机助催化剂。研究人员希望在质子型MFI和CHA沸石的研究中开发的策略将扩展到其他沸石拓扑结构，并将启发设计用于非均相催化的材料，而不仅仅是甲醇到碳氢化合物的催化。除了为本科生和研究生提供培训机会外，首席研究员还将开展教育和推广项目，在K-12课程中介绍催化的概念。

The conversion of methanol-to-hydrocarbons represents the final step in upgrading carbon feedstocks, such as coal and shale gas, to high-value fuels and chemicals. The shape selective characteristics of zeolites afford high selectivity to light olefins or gasoline-range hydrocarbons, but are deleterious for catalyst lifetime, as the accumulation of bulky hydrocarbons inside micropores renders them inactive. The goals of this research are to explore mechanisms involved in forming these inactive occluded hydrocarbon species, and to develop formulations and process conditions to improve catalyst lifetime and selectivity. The research will help ensure efficient utilization of the Nation's fossil fuel resources by the energy and chemical industries.Methanol-to-hydrocarbons conversion proceeds auto-catalytically with olefins- and aromatics-based intermediates localized inside the zeolite pores, constituting the so-called "hydrocarbon pool," acting as organic co-catalysts for carbon-carbon bond formation events. This research seeks to examine the pathways that mediate the conversion of active hydrocarbon pool intermediates to inactive polycyclic hydrocarbons. It is predicated upon preliminary results that suggest methanol acts as a hydride donor during catalysis and derivatives of methanol dehydrogenation act as alkylation agents effecting hydrocarbon pool deactivation. The project is aimed at determining the rate and mechanism by which methanol dehydrogenation events occur using isotopic methods combined with transient and steady state kinetic measurements. The researchers propose that catalyst lifetime can be improved by (i) modifying the inorganic catalyst by introducing spatial constraints to mitigate formation of bulky hydrocarbons or by addition of metal oxides that decompose aldehydes, and (ii) introducing an organic co-catalyst prior to introduction of methanol containing streams in the vapor phase. The researchers expect that the strategies developed in this research for proton-form MFI and CHA zeolites will extend to other zeolite topologies and will inspire the design of materials for applications in heterogeneous catalysis extending beyond methanol-to-hydrocarbons catalysis. In addition to providing opportunities for undergraduate and graduate student training, the principal investigator will pursue educational and outreach programs that introduce concepts of catalysis across the K-12 curriculum.