(651c) Propane Dehydrogenation on MOF-Derived Iron Carbide Catalysts

The dehydrogenation of light alkanes, sourced from cracking of traditional petrochemical feedstocks and from emerging shale gas, represents an attractive route to alkenes (ethene, propene, butenes), which are the building blocks for valuable polymers and chemicals. Catalysts for alkane dehydrogenation must be active, but also selective, because several undesired side reactions, such as hydrogenolysis, isomerization, and coke formation. Recent studies in our group have found that iron/phosphorous catalysts supported on alumina are active for propane dehydrogenation (PDH) and are reasonably selective to propene [1]. In situ X-ray absorption spectroscopy indicated the precatalyst (FePO₄/Fe₂O₃) is initially reduced under H₂and then proceeds through an induction period under propane flow during which iron carbide is formed as the active and selective phase of the catalyst.

Here, we aim to generate the iron-carbide phase directly. Carbon-supported iron carbide from pyrolysis of Fe-containing metal organic frameworks (MOFs; mainly, Fe-BTC) have been reported as active and stable catalysts for Fischer-Tropsch synthesis at 613 K [2–4]; however, the temperature of pyrolysis was found to influence the iron-carbide phase and the size of the nanoparticles formed. The state of these catalysts under the higher temperature reaction conditions needed for PDH (773-873 K) is investigated here. We have found that the reactivity and selectivity of these MOF derived iron-carbide catalysts are dependent on the temperature of pyrolysis and reaction and correlate these results to differences in phase or structure as determined from various characterization techniques. This work demonstrates how using MOFs as precursors may allow the synthesis of unique catalyst structures that can be designed to obtain desired rates and product selectivities of hydrocarbon processes.

[1] S. Tan, B. Hu, W.-G. Kim, S.H. Pang, J.S. Moore, Y. Liu, R.S. Dixit, J.G. Pendergast, D.S. Sholl, S. Nair, C.W. Jones, ACS Catal. 6 (2016).

[2] V.P. Santos, T.A. Wezendonk, J.J.D. Jaén, A.I. Dugulan, M.A. Nasalevich, H.-U. Islam, A. Chojecki, S. Sartipi, X. Sun, A.A. Hakeem, A.C.J. Koeken, M. Ruitenbeek, T. Davidian, G.R. Meima, G. Sankar, F. Kapteijn, M. Makkee, J. Gascon, Nat Commun 6 (2015).

[3] T.A. Wezendonk, V.P. Santos, M.A. Nasalevich, Q.S.E. Warringa, A.I. Dugulan, A. Chojecki, A.C.J. Koeken, M. Ruitenbeek, G. Meima, H.-U. Islam, G. Sankar, M. Makkee, F. Kapteijn, J. Gascon, ACS Catal. 6 (2016).

[4] T.A. Wezendonk, Q.S.E. Warringa, V.P. Santos, A. Chojecki, M. Ruitenbeek, G. Meima, M. Makkee, F. Kapteijn, J. Gascon, Faraday Discuss. (2017).