Molecular Structure-Activity/Selectivity of Ethane Oxidative Dehydrogenation to Ethylene by MoVNbTe Mixed Oxide M1 Phase Catalysts

乙烷（天然气的碳氢化合物成分）是生产乙烯的主要原料化学品，乙烯是许多行业中非常理想的原料，最值得注意的是聚乙烯和其他塑料的制造。 目前，乙烯是通过完善的、但能量密集的蒸汽重整吸热过程生产的。 该项目的重点是一种更节能的催化工艺，称为氧化脱氢（ODH），这是一种放热反应，将需要降低约80%的能耗，减少二氧化碳排放，并降低乙烯生产成本。 然而，要实现这些目标（以及其他目标），就需要改进目前最先进的催化剂。 该项目结合了光谱学、动力学分析和理论方法，将为乙烷ODH提供新的见解，从而为改进催化剂性能或确定性能更好的替代品指明了方向。研究结果将被整合到利哈伊的技术课程，在线宣传视频的制作，对当地学校的宣传活动，并与利哈伊谷达芬奇科学中心合作。无载体MoVNbTe混合氧化物M1相催化剂是已知的乙烷ODH最有效的催化剂，但该催化剂体系的许多方面仍需解决。该项目是建立在假设（由研究人员的先前研究支持），即催化活性位点是表面金属氧化物位点（在拟议的外部无定形覆盖层表面和M1相的内部通道壁上），而不是文献中通常假设的结晶M1相的金属氧化物位点。 初步研究揭示了乙烷ODH过程中M1体相的静态性质和表面相的高度动态性质。在乙烷ODH过程中，几乎完全没有关于M1相催化剂的表面信息，这阻碍了对该催化体系的基本理解的发展。M1相的复杂性质需要在乙烷ODH反应条件下应用多个先进的研究实验来理解该催化剂体系，即1）原位和操作光谱学研究（拉曼、IR、NAP-XPS、HS-LEIS、XANES/EXAFS、E-TEM）以确定晶体和表面金属氧化物位点的分子水平行为，和2）瞬态动力学研究（稳态同位素瞬态动力学分析（SSITKA）和调制激发光谱（MES）），以解决每种阳离子和参与氧源的氧化还原动力学（即，(gas相O2（L-H）对晶格O*（MvK））。 分子水平的DFT计算和微动力学建模将补充实验结果，以提供更多的见解结构活性关系。目的是确定存在于外表面和内孔壁上的表面阳离子的动力学：（i）表面组成，（ii）氧化态，（iii）氧化还原动力学（稳态，用乙烷还原和用O2再氧化），和（iv）催化活性位点（外表面或内孔）的位置。新的见解将导致这一重要的，复杂的催化剂系统，将指导先进的M1相混合氧化物催化剂的合理设计的现实结构活性催化剂模型。这个奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

Ethane (a hydrocarbon component of natural gas) is the chief feedstock chemical for the production of ethylene – a highly desirable feedstock used in numerous industries, most notably the manufacture of polyethylene and other plastics. Currently, ethylene is produced through the well-established, but energy-intensive endothermic process of steam reforming. The project focuses on a more energy-efficient catalytic process known as oxidative dehydrogenation (ODH), an exothermic reaction that would require approximately 80% lower energy consumption, reduce CO2 emissions, and lower ethylene production costs. Achieving those goals (and beyond), however, requires improvements to the current state-of-the-art catalyst. The project combines spectroscopy, kinetic analysis, and theoretical methodologies that will provide new insights about ethane ODH, thus pointing the way towards either improved catalyst performance or identification of better performing alternatives. The research findings will be integrated into technical courses at Lehigh, production of online outreach videos, outreach activities to local schools, and work with the Lehigh Valley DaVinci Science Center.The unsupported MoVNbTe mixed oxide M1 phase catalyst is the most efficient catalyst known for ethane ODH, but many aspects of this catalyst system still need to be resolved. The project is built on the hypothesis (supported by the investigator’s prior research) that the catalytically active sites are the surface metal oxide sites (both on the proposed external amorphous overlayer surface and on the internal channel walls of the M1 phase) and not the metal oxide sites of the crystalline M1 phase commonly assumed in the literature. Preliminary studies reveal the somewhat static nature of the M1 bulk phase and the highly dynamic nature of the surface phase during ethane ODH. The almost complete absence of reported surface information about the M1 phase catalyst during ethane ODH has prevented development of fundamental understanding of this catalytic system. The complex nature of the M1 phase necessitates application of multiple advanced research experiments under ethane ODH reaction conditions to understand this catalyst system, namely 1) in situ and operando spectroscopy studies (Raman, IR, NAP-XPS, HS-LEIS, XANES/EXAFS, E-TEM) to determine the molecular level behavior of the crystalline and surface metal oxide sites, and 2) transient kinetic studies (Steady State Isotopic Transient Kinetic Analysis (SSITKA) and Modulation Excitation Spectroscopy (MES)) to address the redox kinetics of each cation and source of participating oxygen (i.e., (gas phase O2 (L-H) vs. lattice O* (MvK)). Molecular level DFT calculations and Microkinetic Modeling will complement the experimental findings to provide additional insights into structure-activity relationships. The objectives are to determine the dynamics of the surface cations present on the external surface and internal pore walls: (i) surface composition, (ii) oxidation states, (iii) redox kinetics (steady state, reduction with ethane and re-oxidation with O2), and (iv) location of catalytically active site(s) (external surface or internal pores). The new insights will lead to realistic structure-activity catalyst models of this important, complex catalyst system that will guide the rational design of advanced M1-phase mixed oxide catalysts.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.