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

8 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

Keywords

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

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