Propylene hydrogenation and propane dehydrogenation by a single-site Zn2+ on silica catalyst

Neil M. Schweitzer, Bo Hu, Ujjal Das, Hacksung Kim, Jeffrey Greeley, Larry A. Curtiss, Peter C. Stair, Jeffrey T. Miller*, Adam S. Hock

*Corresponding author for this work

Research output: Contribution to journalArticle

116 Scopus citations

Abstract

This study reports the highly selective (more than 95%) dehydrogenation of propane to propylene as well as the reverse hydrogenation reaction by silica-supported single-site Zn(II) catalyst. The catalyst is thermally stable at dehydrogenation temperature (550 °C and above), and catalytic byproducts are small. In situ UV-resonance Raman, XANES, and EXAFS spectra reveal that tetrahedrally coordinated Zn(II) ions are chemisorbed into the strained three-membered siloxane rings on the amorphous silica surface. Under reaction conditions, the Zn(II) ion loses one Zn-O bond, resulting in a coordinatively unsaturated, 3-coordinate active center. The infrared spectrum of adsorbed pyridine indicates that these are Lewis acid sites. Theoretical calculations based on hybrid density functional theory suggest that the catalyst activates H-H and C-H bonds by a nonredox (metal) mechanism consisting of heterolytic cleavage of C-H bonds, in contrast with the homolytic mechanisms such as oxidative addition/reductive elimination pathways. The computed minority catalytic pathway consists of undesired C-C bond cleavage at Zn(II) site, follows a slightly different mechanism, and has a significantly higher activation energy barrier. These mechanisms are consistent with the high olefin selectivity observed for single-site Zn(II) on SiO2.

Original languageEnglish (US)
Pages (from-to)1091-1098
Number of pages8
JournalACS Catalysis
Volume4
Issue number4
DOIs
StatePublished - Apr 4 2014

Keywords

  • Lewis Acid hydrogenation/dehydrogenation catalysis
  • heterogeneous Zn catalysis
  • propane dehydrogenation
  • propylene hydrogenation
  • single-site catalysts

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)

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