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Bulk CrZrO x , supported CrO x /LaZrO x , and CrO x /Al 2 O 3 catalysts were prepared with Cr surface site density varying between 0.04 and 2.3 nm −2 . They were characterized by BET, XRD, temperature-programmed reduction with H 2 , and NH 3 temperature-programmed desorption. Their activity, selectivity, and durability in non-oxidative propane dehydrogenation (PDH) were determined under industrially relevant conditions. The catalysts on the basis of ZrO 2 outperform their Al 2 O 3 -based counterparts in terms of PDH activity. This was explained by the presence of two catalytically active sites, i.e. CrO x and coordinatively unsaturated Zr 4+ (Zr cus ) sites. The former species promote formation of Zr cus under reaction conditions or upon reductive catalyst treatment. Practical relevance of CrZrO x and CrO x /LaZrO x catalysts was checked in a series of 10 PDH/regeneration cycles performed at 550 °C. The catalysts possessing up to 40 times lower chromium content performed superior to an analogue of commercial K-CrO x /Al 2 O 3 with respect to space time yield of propene and the amount of propene formed within one PDH cycle. In terms of durability, bulk promoting of ZrO 2 with Cr was found to be advantageous over simple deposition of CrO x on the surface of LaZrO x . [ABSTRACT FROM AUTHOR]

[Display omitted] • Co/ZrO 2 catalysts with single Co2+ are efficient for C 3 H 8 dehydrogenation to C 3 H 6. • 1Co/ZrO 2 performed durable over multiple dehydrogenation/regeneration cycles. • 1Co/ZrO 2 showed higher activity than a commercial analogue of K-CrO x /Al 2 O 3. • The high activity results from a synergy effect between Co2+ and Zr cus. • Recombination of surface H species is the rate-limiting step in C 3 H 6 formation. Due to the increased production of shale gas containing propane, the share of non-oxidative propane dehydrogenation (PDH) in the large-scale production of propene is expected to continue to grow. There are, however, some ecofriendly and cost shortcomings associated with the currently applied Cr- or Pt-containing catalysts. Against this background, we present here Co/ZrO 2 alternatives and reveal the fundamentals affecting their activity, which can be used for purposeful catalyst design. Co2+ species homogeneously distributed within the lattice of ZrO 2 significantly increase the activity of coordinatively unsaturated Zr4+ for the PDH reaction. The increase is caused by accelerating both the cleavage of CH bonds in propane and the recombination of surface H species, with the latter reaction being the rate-limiting step. The best-performing catalyst outperformed an analogue of commercial K-CrO x /Al 2 O 3 in terms of the rate of propene formation and demonstrated durable performance over a series of 10 PDH/regeneration cycles under industrially relevant conditions. It also outperformed most previously developed Co-containing catalysts in terms of propene productivity. The space–time yield of propene formation achieved at 57 % equilibrium propane conversion at 550 °C was 0.71 kg·h−1·kg cat -1. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Monoclinic or tetragonal ZrO 2 were tested for non-oxidative C 3 H 8 dehydrogenation. • Propene selectivity and formation rate increase with a decrease in crystallite size. • DFT calculations predict same active sites for monoclinic and tetragonal ZrO 2. • Monoclinic ZrO 2 performs superior to tetragonal ZrO 2. • The effect of the phase composition is related to the number of active sites. Abstract A series of bare ZrO 2 materials composed either of monoclinic or tetragonal phase with the size of crystallites varying between 3.7 and 43.4 nm were prepared by precipitation, hydrothermal or thermal calcination methods. The samples were characterized by XRD, BET, CO-TPR, NH 3 -TPD, electrical conductivity measurements and operando UV–vis spectroscopy. Density functional theory calculations provided molecular insights into the kind of active site and individual steps of propane dehydrogenation to propene and hydrogen. Regardless of the phase composition, two Zr cations located at an oxygen vacancy, i.e. coordinatively unsaturated Zr cations (Zr cus sites) having, nevertheless, different chemical environment in tetragonal and monoclinic ZrO 2 , were concluded to be responsible for homolytic breaking of C H bonds in propane. Monoclinic ZrO 2 showed, however, higher rate of propene formation and higher propene selectivity than ZrO 2 stabilized in the tetragonal phase. Both the activity and the selectivity to propene increased with a decrease in the size of crystallites. The effects of phase composition and crystallite size on the PDH performance were related to the ability of ZrO 2 to release lattice oxygen upon reductive catalyst treatment and thus to create Zr cus sites. The knowledge derived can be used for further optimizing PDH performance of ZrO 2 -based catalysts and also extended to other non-reducible metal oxides. [ABSTRACT FROM AUTHOR]