Enhanced Hydrodeoxygenation of m-Cresol over Bimetallic Pt-Mo Catalysts through an Oxophilic Metal-Induced Tautomerization Pathway

Allison Robinson, Glen A. Ferguson, James R. Gallagher, Singfoong Cheah, Gregg T. Beckham, Joshua A. Schaidle, Jesse E. Hensley, J. Will Medlin

Research output: Contribution to journalArticle

66 Scopus citations

Abstract

Supported bimetallic catalysts consisting of a noble metal (e.g., Pt) and an oxophilic metal (e.g., Mo) have received considerable attention for the hydrodeoxygenation of oxygenated aromatic compounds produced from biomass fast pyrolysis. Here, we report that PtMo can catalyze m-cresol deoxygenation via a pathway involving an initial tautomerization step. In contrast, the dominant mechanism on monometallic Pt/Al2O3 was found to be sequential Pt-catalyzed ring hydrogenation followed by dehydration on the support. Bimetallic Pt10Mo1 and Pt1Mo1 catalysts were found to produce the completely hydrogenated and deoxygenated product, methylcyclohexane (MCH), with much higher yields than monometallic Pt catalysts with comparable metal loadings and surface areas. Over an inert carbon support, MCH formation was found to be slow over monometallic Pt catalysts, while deoxygenation was significant for PtMo catalysts even in the absence of an acidic support material. Experimental studies of m-cresol deoxygenation together with density functional theory calculations indicated that Mo sites on the PtMo bimetallic surface dramatically lower the barrier for m-cresol tautomerization and subsequent deoxygenation. The accessibility of this pathway arises from the increased interaction between the oxygen of m-cresol and the Mo sites in the Pt surface. This interaction significantly alters the configuration of the precursor and transition states for tautomerization. A suite of catalyst characterization techniques including X-ray absorption spectroscopy (XAS) and temperature-programmed reduction (TPR) indicate that Mo was present in a reduced state on the bimetallic surface under conditions relevant for reaction. Overall, these results suggest that the use of bifunctional metal catalysts can result in new reaction pathways that are unfavorable on monometallic noble metal catalysts.

Original languageEnglish (US)
Pages (from-to)4356-4368
Number of pages13
JournalACS Catalysis
Volume6
Issue number7
DOIs
StatePublished - Jul 1 2016
Externally publishedYes

Keywords

  • bimetallic
  • biomass
  • catalytic fast pyrolysis
  • hydrodeoxygenation
  • molybdenum
  • oxophilic promoter
  • platinum

ASJC Scopus subject areas

  • Catalysis

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  • Cite this

    Robinson, A., Ferguson, G. A., Gallagher, J. R., Cheah, S., Beckham, G. T., Schaidle, J. A., Hensley, J. E., & Medlin, J. W. (2016). Enhanced Hydrodeoxygenation of m-Cresol over Bimetallic Pt-Mo Catalysts through an Oxophilic Metal-Induced Tautomerization Pathway. ACS Catalysis, 6(7), 4356-4368. https://doi.org/10.1021/acscatal.6b01131