Propane dehydrogenation (PDH) to propene is an important alternative to oil-based cracking processes, to produce this industrially important platform chemical1,2. The commercial PDH technologies utilizing Cr-containing (refs. 3,4) or Pt-containing (refs. 5–8) catalysts suffer from the toxicity of Cr(vi) compounds or the need to use ecologically harmful chlorine for catalyst regeneration9. Here, we introduce a method for preparation of environmentally compatible supported catalysts based on commercial ZnO. This metal oxide and a support (zeolite or common metal oxide) are used as a physical mixture or in the form of two layers with ZnO as the upstream layer. Supported ZnOx species are in situ formed through a reaction of support OH groups with Zn atoms generated from ZnO upon reductive treatment above 550 °C. Using different complementary characterization methods, we identify the decisive role of defective OH groups for the formation of active ZnOx species. For benchmarking purposes, the developed ZnO–silicalite-1 and an analogue of commercial K–CrOx/Al2O3 were tested in the same setup under industrially relevant conditions at close propane conversion over about 400 h on propane stream. The developed catalyst reveals about three times higher propene productivity at similar propene selectivity.

Environmentally friendly and low-cost catalysts are required for large-scale non-oxidative dehydrogenation of propane to propene (PDH) to replace currently used CrO x -or Pt-based catalysts. This work introduces ZnO-containing ZrO 2 -or MZrO x -supported (M=Ce, La, Ti or Y) catalysts. The most active materials outperformed the state-of-the-art catalysts with supported CrO x , GaO x , ZnO x or VO x species as well as bulk ZrO 2 -based catalysts without ZnO. The spacetime yield of propene of 1.25 kg C3H6 •kg -1 cat •h -1 at a propane conversion of about 30% with propene selectivity of 95% was obtained over Zn(4 wt%)/TiZrO x at 550°C.For deriving key insights into the structure of active sites, reactivity, selectivity and onstream stability, the catalysts were characterized by XRD, HRTEM, EDX mapping, XPS, X-ray absorption, CO-TPR, CO 2 -TPD, NH 3 -TPD, Pyridine-FTIR, operando UV-Vis spectroscopy, Raman spectroscopy, TPO and temporal analysis of products. In contrast with previous reports used bulk ZrO 2 -based catalysts without ZnO, coordinatively unsaturated Zr cations are not the main active sites in the ZnO-containing catalysts.Supported ZnO x species were concluded to participate in the PDH reaction. The current X-ray absorption analysis proved that their structure is affected by the type of metal oxide used as dopant for ZrO 2 and on crystallinity of ZrO 2 . Isolated tricoordinated Zn 2+ species

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ZnO-based catalysts are promising for nonoxidative propane dehydrogenation (PDH) to propene owing to their low cost and environmental friendliness but experience serious loss of the active component because of the reduction of ZnO to metallic Zn that evaporates. Here, we demonstrate that MgO-modified ZnO x /silicalite-1 materials prepared through one-pot hydrothermal method are active, selective, and durable in the PDH reaction. The undesired loss of Zn could also be successfully suppressed without negative effect on the PDH performance owing to a strong interaction between Mg2+ and ZnO x , as concluded from the results of X-ray photoelectron and Fourier-transform infrared spectroscopic measurements as well as temperature-programmed reduction with CO. X-ray absorption spectroscopy revealed that atomically dispersed Zn2+ sites are responsible for PDH. Using an industrially relevant feed with 40 vol % propane, propene selectivity between 88 and 95% at propane conversion between 15 and 32% was achieved over six PDH/oxidative regeneration cycles lasting for about 20 h on stream at 550 °C without loss in the initial activity, while some deactivation occurred after longer (up to about 60 h) time on stream. The deactivation (caused by Zn loss) constant of Mg-modified ZnO x /silicalite-1 considering the 2nd and 20th cycles is more than 3 times lower than that of its Mg-free counterpart.

SummaryNon-oxidative propane dehydrogenation (PDH) is an attractive reaction from both an industrial and a scientific viewpoint because it allows direct large-scale production of propene and fundamental analysis of C-H activation respectively. The main challenges are related to achieving high activity, selectivity, and on-stream stability of environment-friendly and cost-efficient catalysts without non-noble metals. Here, we describe an approach for the preparation of supported ultrasmall ZnO nanoparticles (2–4 nm, ZnO NPs) for high-temperature applications. The approach consists of encapsulation of NPs into a nitrogen-doped carbon (NC) layer in situ grown from zeolitic imidazolate framework-8 on a Silicalite-1 support. The NC layer was established to control the size of ZnO NPs and to hinder their loss to a large extent at high temperatures. The designed catalysts exhibited high activity, selectivity, and on-stream stability in PDH. Propene selectivity of about 90% at 44.4% propane conversion was achieved at 600°C after nearly 6 h on stream.

Nanosheet ZSM-5 zeolite with highly exposed (010) crystal planes demonstrates high reactivity and good anti-coking stability for the catalytic cracking of n-heptane, which is attributed to the synergy of high external surface area and acid sites, fully accessible channel intersection acid sites, and hierarchical porosity caused by the unique morphology.

In this work, steady-state tests of propane dehydrogenation, density functional theory calculations, operando UV–vis spectroscopy, ex situ and in situ electron paramagnetic resonance spectroscopy, IR spectroscopy, and temperature-programmed techniques were combined to provide fundamentals for tuning activity and onstream stability of low-loaded catalysts with supported CrZrO x species. Two neighboring Zrcus (cus = coordinatively unsaturated) sites were concluded to be mainly responsible for propane dehydrogenation to propene. They are formed upon reductive catalyst treatment, and their concentration depends on the strength of interaction among CrO x , ZrO2, and support and on the size of ZrO2 crystallites in CrZrO x . SiO2 weakly interacting with CrO x was found to be a more preferable support than Al2O3- or TiO2-based supports. CrO x species promotes formation of Zrcus sites and improves their intrinsic activity for the desired reaction. CrO x also contributes to coke formation as concluded from operando UV–vis analysis. Cr20Zr80/SiO2 possessing about 3.9 or 2.5 times lower amounts of chromium or zirconium in comparison with an analogue of industrial K-CrO x /Al2O3 or state-of-the-art Ru/LaZrO x revealed about 2 times higher space-time yield of propene at 30% propane conversion at 550 °C. Moreover, this catalyst was durable over 50 dehydrogenation/regeneration cycles lasting 150 h.

Heterogeneously catalyzed gas−solid-phase reactions generally suffered from diffusion limitations in large-scale processes or in academic studies when zeolites were used as catalysts or supports. Here, we elucidated the effects of diffusion of reactants/products in nonoxidative propane (PDH) and isobutane dehydrogenation (iBDH) reactions on the performance of catalysts possessing differently structured ZnO x species on (S-1), dealuminated beta (deAl beta), and ZrO 2 . The catalysts were prepared through physically mixing ZnO and the support. Force-field molecular dynamics simulations revealed that the effectiveness factor η is larger than 0.99 in the PDH reaction over all catalysts and in the iBDH reaction over the ZnO-deAl beta catalyst, thus suggesting that mass transport limitations do not play any significant role. However, the iBDH reaction over S-1-based catalysts suffers from some diffusion limitations (0.35 < η < 0.9). Such conditions are favorable for cracking reactions responsible for isobutene selectivity loss. To compare intrinsic catalyst activity in the PDH and iBDH reactions over the ZnO x /S-1 catalyst, molecular-level insights into individual reaction pathways were derived from density functional theory calculations. The nature of active ZnO x sites was investigated by X-ray absorption spectroscopy and was established to depend on the kind of support material. Binuclear ZnO x species are formed inside small S-1 pores or on the surface of ZrO 2 , while three-dimensional multinuclear ZnO x clusters are generated in the β zeolite with larger pores. The latter show higher Zn-related activity in the PDH reaction under conditions free of any diffusion constraints. The developed ZnO−deAl beta showed the space−time yield of propene or isobutene formation of 2 kg Cd 3 Hd 6 kg cat −1 h −1 or 6.3 kg i-Cd 4 Hd 8 kg cat −1 h −1 at 550 °C and about 70−80% equilibrium alkane conversion with an olefin selectivity of about 90%. The activity values are higher than those reported for the state-of-the-art non-noble metal oxide catalysts tested at the same or even higher temperatures.