(727b) Mechanistic Understanding of Redox and Acid Doped Mo8V2Nb1 Catalysts for Ethane Oxidative Dehydrogenation

With global production of over 100 million tons, ethylene is the most widely produced organic compound in the world. However, despite its widespread production and usage, ethylene is mainly produced via an inefficient high temperature (~850°C), energy intensive reaction, namely hydrothermal steam cracking of ethane or crude oil. A more attractive alternative to this pathway is the thermo-catalytic oxidative dehydrogenation of ethane, which operates at milder temperatures and is less energy intensive due to the exothermicity of the reaction that occur over a MoVNb based catalyst [1]. However, the activity of the catalyst must be tightly controlled in order to prevent overoxidation to CO or CO₂. To this end, both redox and acid/base elements are typically incorporated into a base MoVNb catalyst to tune its selectivity, however, a thorough understanding, particularly with in situ experiments for the bulk unsupported mixed metal oxide are currently lacking in the field.

Pd, Ti, Te, TiTe, and PdTe doped catalysts were investigated for their differences in catalytic activity, and their ability to stabilize the active sites. At differential conversion, all catalysts behave similarly except for the Pd catalyst, which more strongly favors combustion products due to its lower reduction temperature as seen via temperature programmed reduction. Further, in situ Raman experiments were conducted in which the M-O-V bridging bonds were monitored (where M is either Mo,V, or Nb), which are a proposed active site for the reaction [2]. Based on the shifting of these bands, it was determined that the incorporation of Ti improved oxygen transport in the catalyst as it resisted significant shifting of the catalytically active band to lower Raman shift indicating a possible reduction of one of the metal species. Ultimately, this work spectroscopically elucidates the mechanism in which the addition of redox and acid dopants influence one potential active site of the complex MoVNb mixed metal oxide catalyst and the subsequent impact on catalytic activity.

[1] C. A. Gärtner, A. C. van Veen, and J. A. Lercher, “Oxidative Dehydrogenation of Ethane: Common Principles and Mechanistic Aspects,” ChemCatChem, vol. 5, no. 11, pp. 3196–3217, Nov. 2013.

[2] L. Annamalai, Y. Liu, S. Ezenwa, Y. Dang, S. L. Suib, and P. Deshlahra, “Influence of Tight Confinement on Selective Oxidative Dehydrogenation of Ethane on MoVTeNb Mixed Oxides,” ACS Catal., vol. 8, no. 8, pp. 7051–7067, Aug. 2018.