Effects of oxygen coverage on rates and selectivity of propane-CO2 reactions on molybdenum carbide

Mark M. Sullivan, Aditya Bhan

Research output: Contribution to journalArticlepeer-review

25 Scopus citations

Abstract

Mo2C catalyzes propane dehydrogenation and hydrogenolysis at 823 K; carbon selectivity can be tuned to >95% propylene via dehydrogenation in absence of H2, >95% CH4 via hydrogenolysis with H2 co-feed, or >80% CO via reforming pathways with H2 and CO2 co-feed. The changes in selectivity are mediated by an evolution in the coverage of oxidized (O) and carbidic () surface sites which results in an evolution of O[sbnd]O, O[sbnd], and [sbnd] site pairs that catalyze propane dehydrogenation. The fraction of O in relation to was assessed from measured CO2/CO ratios because reverse water gas shift equilibrium exists under H2/CO2 co-feed steady state reaction conditions. Kinetic models based on the two-site dehydrogenation mechanism could be used to quantitatively describe measured rates of propane dehydrogenation at steady state with or without H2 and/or CO2 co-feed and the transient evolution in dehydrogenation rates upon removing H2 or CO2 in the influent stream to note that O[sbnd] site pairs exhibit the highest rate per gram. This model also provides a rationale for O inhibition of H-activated hydrogenolysis pathways and for promotion of oxidative dehydrogenation rates with the introduction of hydrogen into CO2-propane influent streams. This study extends concepts developed for examining the catalytic effects of O coverage on oxidative light alkane conversion from transition metal catalysts to also include carbidic formulations.

Original languageEnglish (US)
Pages (from-to)195-205
Number of pages11
JournalJournal of Catalysis
Volume357
DOIs
StatePublished - Jan 2018

Bibliographical note

Funding Information:
This research was supported by Office of Basic Energy Sciences, the U.S. Department of Energy under award number no. DE- SC0008418 (DOE Early Career Program). Mark M. Sullivan also acknowledges financial support from the University of Minnesota Doctoral Dissertation Fellowship Program . Part of this work was carried out in the College of Science and Engineering Characterization Facility, University of Minnesota, which has received capital equipment funding from the NSF through the MRSEC program, and we thank Javier Garcia Barriocanal for assistance with the X-ray diffraction studies.

Publisher Copyright:
© 2017 Elsevier Inc.

Keywords

  • CO
  • C[sbnd]H bond activation
  • Oxidative dehydrogenation
  • Oxophilic metal carbides
  • Propane

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