Abstract
Due to the complexity of heterogeneous catalysts, identification of active sites and the ways for their experimental design are not inherently straightforward but important for tailored catalyst preparation. The present study reveals the active sites for efficient C–H bond activation in C1–C4 alkanes over ZrO2 free of any metals or metal oxides usually catalysing this reaction. Quantum chemical calculations suggest that two Zr cations located at an oxygen vacancy are responsible for the homolytic C–H bond dissociation. This pathway differs from that reported for other metal oxides used for alkane activation, where metal cation and neighbouring lattice oxygen form the active site. The concentration of anion vacancies in ZrO2 can be controlled through adjusting the crystallite size. Accordingly designed ZrO2 shows industrially relevant activity and durability in non-oxidative propane dehydrogenation and performs superior to state-of-the-art catalysts possessing Pt, CrOx, GaOx or VOx species.
Highlights
Due to the complexity of heterogeneous catalysts, identification of active sites and the ways for their experimental design are not inherently straightforward but important for tailored catalyst preparation
The scientific background for our study was the fact that the relative ratio of coordinatively unsaturated sites on the surface of metal oxides to their regular counterparts depends on the size of crystallites[24]
Powder X-ray diffraction (XRD) analysis proved that they are mainly composed of the monoclinic phase (Supplementary Fig. 1) but differed in the average size of crystallites determined from the (111) and (111) XRD reflexes
Summary
Due to the complexity of heterogeneous catalysts, identification of active sites and the ways for their experimental design are not inherently straightforward but important for tailored catalyst preparation. Quantum chemical calculations suggest that two Zr cations located at an oxygen vacancy are responsible for the homolytic C–H bond dissociation This pathway differs from that reported for other metal oxides used for alkane activation, where metal cation and neighbouring lattice oxygen form the active site. The active site consists of two Zr cations located at an oxygen vacancy, which homolytically break the C–H bond in alkanes The kind of this site differs from that previously suggested by some of us for doped ZrO2-based catalysts[18,19] and by other researchers for different metal oxides used for PDH21–23, where metal cation and neighbouring lattice oxygen were assumed to form the active site. Bare ZrO2 designed especially to maximize the concentration of the active sites shows industrially relevant performance in comparison with commercial-like catalysts containing CrOx or Pt species and other alternative state-ofthe-art catalysts
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