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

Lehigh University, Bethlehem PA

Investigators

Abstract

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.