Search

The oxidative dehydrogenation of propane with CO2 (CO2-ODP) is a promising technology for the efficient production of propene in tandem with CO2 reduction to CO. However, the rational design of high-performance catalysts for this green process is still challenged by limited understanding of the nature of active sites and the reaction mechanism. In this work, the effects of SnO2 promoter on Pt/CeO2 activity and propene selectivity in CO2-ODP are elucidated through varying the Sn/Pt molar ratio. When the ratio increases, propane conversion gradually decreases, while the propene selectivity increases. These dependences are explained by increasing the electron density of Pt through the promoter. The strength of this effect is determined by the Sn/Pt ratio. Owing to the electronic changes of Pt, CO2-ODP becomes more favorable than the undesired CO2 reforming of propane. Sn-modified Pt—O—Ce bonds are reasonably revealed as the active sites for CO2-ODP occurring through a redox mechanism involving the activation of CO2 over oxygen vacancies at Sn-modified Pt and CeO2 boundaries. These atomic-scale understandings are important guidelines for purposeful development of high-performance Pt-based catalysts for CO2-ODP. [ABSTRACT FROM AUTHOR]

Non-oxidative propane dehydrogenation (PDH) to propene is the basis of various large-scale processes suffering however from high costs or environmental incompatibility of currently applied Pt- or Cr-containing catalysts. Herein, we demonstrate that active and selective catalysts can be obtained from cheap and commercially available Zr- or Ti-based supports and ZnO without producing any liquid or solid waste. Catalytically active species formed in situ under PDH conditions are composed of isolated ZnO x as concluded from X-ray absorption spectroscopic analysis. The kind of support affects the geometry of such species that is probably decisive for catalyst activity. ZnO x on the surface of LaZrO x revealed the highest Zn-related TOF of propene formation. However, the following activity order in terms of space time yield of propene formation (STY C3H6) at 550 °C and about 50% equilibrium propane conversion using a feed with 40 vol% propane was obtained: ZnO//TiZrO x > ZnO//SiZrO x > ZnO//LaZrO x > ZnO//TiO 2. The best-performing catalyst showed STY C3H6 of 2 kg kg cat −1 h−1 and was durable in 8 PDH/regeneration cycles. Temporal analysis of products with submillisecond resolution suggests that H 2 formation should be the rate-determining step in the course of the PDH reaction. [Display omitted] • Catalysts consisting of ZnO and commercially available supports were tested in PDH. • The developed ZnO//TiZrO x catalyst showed high activity, selectivity and durability. • The formation of H 2 was concluded to be the rate-determining step. [ABSTRACT FROM AUTHOR]

Conversion of propane or butanes from natural/shale gas into propene or butenes, which are indispensable for the synthesis of commodity chemicals, is an important environmentally friendly alternative to oil-based cracking processes. Herein, we critically analyse recent developments in the non-oxidative, oxidative, and CO2-mediated dehydrogenation of propane and isobutane to the corresponding olefins over metal oxide catalysts. Particular attention is paid to (i) comparing the developed catalysts in terms of their application potential, (ii) structure–activity–selectivity relationships for tailored catalyst design, and (iii) reaction-engineering aspects for improving product selectivity and overall process efficiency. On this basis, possible directions for further research aimed at the development of inexpensive and environmentally friendly catalysts with industrially relevant performance were identified. In addition, we provide general information regarding catalyst preparation and characterization as well as some recommendations for carrying out non-oxidative and CO2-mediated dehydrogenation reactions to ensure unambiguous comparison of catalysts developed in different studies. [ABSTRACT FROM AUTHOR]

This paper demonstrates the potential of Eu2O3 and Gd2O3 as catalysts for non-oxidative propane dehydrogenation to propene. They reveal a higher activity than the state-of-the-art bare ZrO2-based catalysts due to the higher intrinsic activity of Gdcus or Eucus in comparison with that of Zrcus (cus = coordinatively unsaturated). [ABSTRACT FROM AUTHOR]

Non-oxidative propane dehydrogenation (PDH) was investigated over unconventional catalysts, i.e. binary La 2 O 3 -ZrO 2 and Y 2 O 3 -ZrO 2 materials with or without tiny amounts (0.005 or 0.05 wt.%) of Ru in form of nanoparticles with the size of about 1.1 nm. The results of catalytic tests and catalyst characterization with complementary techniques enabled us to conclude that coordinatively unsaturated zirconium cations (Zr cus ) and neighboring lattice oxygen are catalytically active sites responsible for C 3 H 6 formation. Supported Ru species contribute to a minor extent to PDH but promote generation of Zr cus sites upon catalyst reductive treatment or in situ under PDH conditions. The concentration of Zr cus sites can also be increased through doping of ZrO 2 with La 2 O 3 or Y 2 O 3 with the latter being a more efficient dopant. High activity, selectivity, and durability of our catalysts were verified by comparing their performance under industrially relevant conditions with that of a conventional K-CrO x /Al 2 O 3 reference material in a series of 60 PDH/oxidative regeneration cycles at 550, 600, and 625 °C. [ABSTRACT FROM AUTHOR]

[Display omitted] • Approach for anchoring of Pt atoms on isolated Sn4+ is introduced. • Using this approach PtSn/SiO 2 (hexagonal mesoporous silica) catalysts were prepared. • Pt-Sn/atoms/sub nanoclusters were identified on the surface of catalysts. • The catalysts are active, selective, and stable in C 3 H 8 dehydrogenation to C 3 H 6. • Sn is essential to enhance H 2 desorption from Pt that is the rate-limiting step. Owing to propane availability in shale gas and the growing demand for propene, non-oxidative dehydrogenation of this alkane has attracted much attention. Although, catalysts with supported PtSn species are applied on the large scale, a further increase in their activity without loss in propene selectivity at low Pt content would certainly improve process economy. Herein, we introduce a molecularly defined strategy for controlling catalyst activity through anchoring of Pt atoms on isolated Sn4+ firmly confined in the framework of hexagonal mesoporous silica. In addition to the dispersion of Pt species, the presence of Sn4+ in close contact with Pt is essential for increasing the rate of propane dehydrogenation through enhancing H 2 desorption, which is the rate-limiting step. As the anchored Pt atoms/sub nanoclusters do not sinter under reducing conditions, the developed catalysts show high on-stream stability and propene selectivity of above 99 % under industrially relevant conditions. [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]

Abstract: The role of lattice and adsorbed oxygen species in propane dehydrogenation in a perovskite hollow fiber membrane reactor containing a Pt–Sn dehydrogenation catalyst was elucidated by transient analysis of products with a sub-millisecond time resolution. Propane is mainly dehydrogenated non-oxidatively to propene and hydrogen over the catalyst, while lattice oxygen of the perovskite oxidizes preferentially hydrogen to water. For achieving high propene selectivity at high propane conversions, the formation of gas phase O2 on the shell side of the membrane reactor should be avoided. Otherwise, oxygen species adsorbed over the Pt–Sn catalyst participate in non-selective C3H8/C3H6 transformations to C2H4 and COx. [ABSTRACT FROM AUTHOR]

• ZrO 2 -based catalysts with Rh, Ru, Ir or Pt were tested for C 3 H 8 dehydrogenation. • The metals on LaZrO x and YZrO x positively affect the rate: Rh > Ru > Ir > Pt. • The metals facilitate formation of Zr cus sites and accelerate H 2 formation. • The metals affect propene adsorption and thus undesired side reactions. • C 3 H 6 selectivity over Rh- or Ru-containing catalysts increases with temperature. A series of catalysts on the basis of ZrO 2 , LaZrO x and YZrO x with supported Rh, Ru, Pt or Ir nanoparticles (NPs) were prepared. They were tested in the non-oxidative dehydrogenation of propane (PDH) to elucidate the effects of (i) the kind of supported metal and its loading, (ii) the size (1 nm or 5 nm) of NPs, (iii) metal oxide promoter for ZrO 2 and (iv) reaction temperature on PDH performance. Although the metals did not directly participate in propene formation, they improve catalyst activity through (i) promotion of Zr cus (cus means coordinatively unsaturated) formation and (ii) acceleration of hydrogen formation. The kind of metal was also established to be decisive for propene adsorption. The latter property has a negative effect on catalyst activity and propene selectivity. The most active Rh/YZrO x catalyst with 0.05 wt% Rh revealed about 1.6 times higher propene formation rate than a commercial-like K-CrO x /Al 2 O 3 or the state-of-the-art Ru/YZrO x. [ABSTRACT FROM AUTHOR]

[Display omitted] • Metallic Co0 species in situ formed are suggested to be the main active sites for PDH. • CoO x but not Co0 is responsible for the formation of undesired products. • Transformation of CoO x to Co0 depends on the strength of CoO x -support interactions. • Co/Silicalite-1 showed the C 3 H 6 space time yield of 1.50 kg·h−1·kg cat −1 at 550 °C. Although Co-containing catalysts show attractive performance in the non-oxidative propane dehydrogenation to propylene (PDH), their tailored development is hindered by the ambiguity in the kind of active sites (Co0 or Co2+O x) responsible for selective and unselective pathways. Herein, we demonstrate that supported CoO x species expends its lattice oxygen through oxidation of C 3 H 8 to CO 2 /C 3 H 6 and are accordingly transformed into Co0 species. The latter are decisive for the selective dehydrogenation of propane to propylene with high activity. The ability of CoO x to in situ form Co0 is affected by metal-oxide-support interactions (MOSI). In addition to the kind of support, defective OH groups (OH nests) in ZSM-5-type zeolites seem to be relevant for the MOSI effect. In comparison with previous studies highlighting the importance of the size of CoO x species and their acidity for coke formation, we could not establish any direct correlation. Nevertheless, the presence of CoO x seems to be relevant for this undesired reaction because the formation of coke is hindered when CoO x species are transformed to Co0 species. Catalyst acidic sites are responsible for cracking reactions. Thus, the derived mechanistic insights reveal the nature of active sites both for selective and unselective pathways and provide fundamentals for catalyst development. From an industrial viewpoint, the developed Co/Silicalite-1 (Co/S-1) catalyst with the weakest MOSI and accordingly highest fraction of Co0 showed the space time yield of propylene formation of 1.50 kg·h−1·kg cat −1 at 67 % equilibrium propane conversion and propylene selectivity of 95.3 % and the Co-related TOF value of 0.145 s−1 at 550 °C. These both activity values exceed those of the state-of-the-art Co-containing catalysts. The productivity of Co/S-1 is comparable or even higher than that of industrially relevant Pt- or Cr-containing catalysts. [ABSTRACT FROM AUTHOR]