Elucidation of puzzling questions regarding the CrOx/Al2O3 catalyst I. X-ray absorption spectroscopy aided identification of the nature of the chromium oxide species in the CrOx/Al2O3 dehydrogenation catalyst system

Hoffman, Adam S.; Greaney, Matthew J.; Finzel, Jordan; Rong, Xing; Covelli, Danielle; Fridman, V. Z.; Lugmair, Claus G.; Bare, Simon R.

doi:10.1016/j.apcata.2023.119187

Cited by 2 publications

(2 citation statements)

References 34 publications

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“…Following high-temperature pretreatment in flowing air for 6 h, X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine-structure (EXAFS) spectra of the as-synthesized sample were collected at room temperature in flowing helium (denoted as calcined). As shown in Figure a, the XANES spectrum of the calcined Cr/Si-MFI displays a prominent pre-edge peak at 5993.0 eV due to the dipole-forbidden transition from 1s to 3d orbitals, which is characteristic of noncentrosymmetric tetrahedral Cr(VI) species. ,− A similar pre-edge peak is also observed in the reference spectrum of the Na 2 CrO 4 compound (Figure S9), indicating that chromium supported by Si-MFI was predominantly present as tetrahedral Cr(VI) before ethane dehydrogenation catalysis. Consistent with previous studies, , the corresponding k 2 -weighted Fourier-transformed EXAFS spectrum (Figure c) exhibits a dominant signal centered at 1.06 Å (phase-uncorrected), which is primarily associated with the shorter CrO double bonds.…”

Section: Resultsmentioning

confidence: 59%

Reduction of Cofed Carbon Dioxide Modifies the Local Coordination Environment of Zeolite-Supported, Atomically Dispersed Chromium to Promote Ethane Dehydrogenation

Zhou,

Felvey,

Guo

et al. 2024

J. Am. Chem. Soc.

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The reduction of CO 2 is known to promote increased alkene yields from alkane dehydrogenations when the reactions are cocatalyzed. The mechanism of this promotion is not understood in the context of catalyst active-site environments because CO 2 is amphoteric, and even general aspects of the chemistry, including the significance of competing side reactions, differ significantly across catalysts. Atomically dispersed chromium cations stabilized in highly siliceous MFI zeolite are shown here to enable the study of the role of parallel CO 2 reduction during ethylene-selective ethane dehydrogenation. Based on infrared spectroscopy and X-ray absorption spectroscopy data interpreted through calculations using density functional theory (DFT), the synthesized catalyst contains atomically dispersed Cr cations stabilized by silanol nests in micropores. Reactor studies show that cofeeding CO 2 increases stable ethylene-selective ethane dehydrogenation rates over a wide range of partial pressures. Operando X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine-structure (EXAFS) spectra indicate that during reaction at 650 °C the Cr cations maintain a nominal 2+ charge and a total Cr−O coordination number of approximately 2. However, CO 2 reduction induces a change, correlated with the CO 2 partial pressure, in the population of two distinct Cr−O scattering paths. This indicates that the promotional effect of parallel CO 2 reduction can be attributed to a subtle change in Cr−O bond lengths in the local coordination environment of the active site. These insights are made possible by simultaneously fitting multiple EXAFS spectra recorded in different reaction conditions; this novel procedure is expected to be generally applicable for interpreting operando catalysis EXAFS data.

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Section: Resultsmentioning

confidence: 59%

Reduction of Cofed Carbon Dioxide Modifies the Local Coordination Environment of Zeolite-Supported, Atomically Dispersed Chromium to Promote Ethane Dehydrogenation

Zhou,

Felvey,

Guo

et al. 2024

J. Am. Chem. Soc.

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“…Details regarding the state and electronic nature of catalysts could guide the development of improved catalytic membrane systems. We note that these questions about catalyst structure and the nature of species exist for conventional operation as well; despite the use of CrO x /Al 2 O 3 catalysts for commercial PDH, the state, and evolution of active species remains an area of active research 16 …”

Section: Metal‐based Membrane Reactorsmentioning

confidence: 99%

Expanding the toolbox for development of metal‐based dual‐functional catalytic membranes

Kulkarni,

Roy,

Khuu

et al. 2023

AIChE Journal

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Catalytic membranes offer opportunities to develop modular, process‐intensified units. Dual‐functional materials, which integrate reactive and separation components in a single material, could play an important role in enabling them. Adapting the various characterization tools that are used to analyze the structures of metal‐based catalysts to these integrated structures could provide vital information for their design and implementation. In this perspective, we highlight the ways in which these tools can be used to analyze nonreactive membranes and non‐integrated systems where the catalyst and the membrane operate as two separate units. A methodology developed to analyze these comparatively simpler systems could be subsequently extended to integrated dual‐functional catalytic membranes. Thus, researchers from the catalysis and membranes communities can work together in a way that will not only lead to fundamental advancements in our understanding of catalytic membranes but also enable their transformation into real, scalable process‐intensified units.

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Elucidation of puzzling questions regarding the CrOx/Al2O3 catalyst I. X-ray absorption spectroscopy aided identification of the nature of the chromium oxide species in the CrOx/Al2O3 dehydrogenation catalyst system

Cited by 2 publications

References 34 publications

Reduction of Cofed Carbon Dioxide Modifies the Local Coordination Environment of Zeolite-Supported, Atomically Dispersed Chromium to Promote Ethane Dehydrogenation

Reduction of Cofed Carbon Dioxide Modifies the Local Coordination Environment of Zeolite-Supported, Atomically Dispersed Chromium to Promote Ethane Dehydrogenation

Expanding the toolbox for development of metal‐based dual‐functional catalytic membranes

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