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 ZnOx 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. ZnOx on the surface of LaZrOx revealed the highest Zn-related TOF of propene formation. However, the following activity order in terms of space time yield of propene formation (STYC3H6) at 550 degree celsius and about 50% equilibrium propane conversion using a feed with 40 vol% propane was obtained: ZnO//TiZrOx > ZnO//SiZrOx > ZnO//LaZrOx > ZnO//TiO2. The best-performing catalyst showed STYC3H6 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.

Ethylene dimerization is an industrial process that is currently carried out using homogeneous catalysts. Here we present a highly active heterogeneous catalyst containing minute amounts of atomically dispersed Pd. It requires no co-catalyst(s) or activator(s) and significantly outperforms previously reported catalysts tested under similar reaction conditions. The selectivity to C4- and C6-hydrocarbons was about 80 % and 10 % at 42 % ethylene conversion at 200 °C using an industrially relevant feed containing 50 vol % ethylene, respectively. Our kinetic and catalyst characterization experiments complemented by density functional theory calculations provide molecular insights into the local environment of isolated Pd(II)Ox species and their role in achieving high activity in the target reaction. When the developed catalyst was rationally integrated with a Mo-containing olefin metathesis catalyst in the same reactor, the formed butenes reacted with ethylene to propylene with a selectivity of 98 % at about 24 % ethylene conversion.

Carbon dioxide (CO2) hydrogenation to methanol (CH3OH) is one of the most promising approaches to provide this platform chemical and to close carbon cycles. In this minireview, we systematically analyze primary and secondary reactions which can take place in this reaction over Cu‐based catalysts. In addition to repeatedly discussed reverse water gas shift reaction (RWGS) and CH3OH production directly from CO2, we consider decomposition, dehydration, dehydrogenation, and steam reforming of the desired alcohol. These reactions are usually ignored in the studies dealing with CO2 hydrogenation to CH3OH but can worsen the catalyst efficiency. Apart from the corresponding thermodynamic analysis, proposed reaction mechanisms and active sites are described and discussed. The effects of co‐fed water, CH3OH and methyl formate on catalyst performance are critically scrutinized, too. We also provide several criteria for unambiguous comparison of different catalysts in terms of CH3OH selectivity and their activity.

Gold-based catalysts have shown high catalytic activity for reverse water gas shift (RWGS) reactions at low temperatures. Despite extensive studies, the RWGS reaction on Au-based catalysts with very low Au content (< 0.1 wt%) has not yet been investigated. In this study, TiO2 and ZrO2 supported gold catalysts with such low gold loading have been synthesized and tested for RWGS. The catalysts were investigated by a series of in/ex-situ characterization techniques, including ICP-OES, XRD, BET, XPS, STEM, STEM-EELS, TAP, in-situ DRIFTS and in -situ EPR. At 250 oC, the Au/TiO2 catalyst showed almost 10 times higher activity than Au/ZrO2. In-situ DRIFTS results suggest that the formate mechanism is the predominant mechanism over Au/ZrO2, while over Au/TiO2 the reaction proceeds via the formation of hydroxycarbonyl intermediates. A combined study including STEM, STEM-EELS, XPS, and in-situ EPR suggests that the interfacial Au-Ov-Ti3+ sites are responsible for the superior activity of Au/TiO2.

Carbon dioxide (CO2) capture and valorization have great potential for mitigating emissions of this greenhouse gas and accordingly for preserving the environment for future generations. In this regard, hydrogenation of CO2 to methanol is highly attractive because this product is a valuable energy carrier and can also be used for production of various everyday commodities. Although many research papers on this topic have been published in the past decades, there is still a lack of fundamentals relevant to control catalyst performance. Herein, we demonstrate how statistically validated Big-Data analysis of available literature data identified hidden descriptors that can be applied for purposeful catalyst development and for identification of optimal reaction conditions. In view of catalyst development, the kinds of structural promoters or supports for bulk or supported Cu-, In-, or Pd-based catalysts are the most important descriptors for methanol selectivity, with Ce and Zr being the most efficient promoters. The type and the parameters of the preparation methods as well as the kind of active component precursors are also important in this regard. To validate the conclusion about the structural promoter, a series of supported CuZn-containing catalysts were prepared. The best-performing CuZn/CeO2 catalyst outperformed the state-of-the-art CuZn-based catalysts tested at a total pressure of up to 30 bar using a feed with the ratio of H2/CO2 of 3. In addition to the catalyst composition and the preparation method, our analysis suggests that the most often used Cu-based catalysts lose their methanol selectivity due to the decomposition of this product to CO. Our control experiments with the developed CuZn-based catalysts proved that this undesired reaction can be hindered when the catalyst support contains Ce or through increasing H2 partial pressure. This knowledge is important for further catalyst development.

CO2 hydrogenation to methanol (CH3OH) is widely accepted to proceed through two parallel reactions: (i) CH3OH formation and (ii) the reverse water gas shift (RWGS) reaction to CO. The latter reaction causes the loss of CH3OH selectivity. Our spatially resolved analysis of rates of product formation over a classical CuZnAlOx catalyst in a broad range of CO2 conversion degrees (from 0 to 90% of equilibrium conversion) suggests revisiting this concept. In comparison with the RWGS reaction, CH3OH decomposition to CO mainly contributes to the loss of CH3OH selectivity with a rising degree of CO2 conversion. Separate CH3OH decomposition tests in a broad range of experimental conditions proved that this side reaction is accelerated by H2O but negatively affected by H2 and rising total pressure. Moreover, the decomposition should occur on other sites rather than those participating in CH3OH synthesis from CO2 and can be practically suppressed above certain partial pressures of CH3OH and H2O due to site saturation. The sites responsible for the hydrogenation of CO2 to CH3OH, however, are not saturated. Thus, this product can be further produced in downstream catalyst layers. As this concept is valid for several CuZn-based catalysts, we provide fundamentals for the design of selective CH3OH synthesis catalysts and for optimizing reaction conditions. Operating under conditions, where the undesired CH3OH decomposition reaction is hindered, enabled us to achieve 93% CH3OH selectivity at 19% CO2 conversion (55% equilibrium conversion) at 50 bar and 200 degrees C using a feed with the ratio of H2/CO2 of 3.

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 ZnOx species on (S-1), dealuminated beta (deAl beta), and ZrO2. The catalysts were prepared through physically mixing ZnO and the support. Force-field molecular dynamics simulations revealed that the effectiveness factor eta 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 < eta < 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 ZnOx/S-1 catalyst, molecular-level insights into individual reaction pathways were derived from density functional theory calculations. The nature of active ZnOx sites was investigated by X-ray absorption spectroscopy and was established to depend on the kind of support material. Binuclear ZnOx species are formed inside small S-1 pores or on the surface of ZrO2, while three-dimensional multinuclear ZnOx clusters are generated in the beta 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 kgC3H6 kgcat-1 h-1 or 6.3 kgi-C4H8 kgcat -1 h-1 at 550 degrees 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.

Propane dehydrogenation (PDH) to propene is an important alternative to oil-based cracking processes, to produce this industrially important platform chemical 1 , 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 regeneration 9 . 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 ZnO x 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 ZnO x species. For benchmarking purposes, the developed ZnO–silicalite-1 and an analogue of commercial K–CrO x /Al 2 O 3 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.

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

A detailed study was carried out to elucidate the factors affecting the activity and, particularly, selectivity of bare Al2O3 in the non-oxidative propane dehydrogenation (PDH) to propene under industrially relevant conditions.

The effect of Cs-, Ca- and P-containing promoters for binary Cr-Zr-O-x on propene selectivity and catalyst stability with time-on-stream in the non-oxidative propane dehydrogenation was elucidated. Large improvements in this catalytic performance were achieved when combining Cs and P promoters. They were suggested to partially block dehydrogenation sites resulting in the isolation of the latter. As a reason thereof, coke formation through propene oligomerization is inhibited in favor of propene desorption from the catalyst surface. The present catalysts achieved similar to 30% conversion of propane at WHSV (C3H8) of 5.89 h(-1) at 550 degrees C in comparison with 20% over K-CrOx/Al2O3. The selectivity to propene was determined to be similar to 94%.

Environmentally friendly and low-cost catalysts are required for large-scale nonoxidative dehydrogenation of propane to propene (PDH) to replace currently used CrOx- or Pt-based catalysts. This work introduces ZnO-containing ZrO2- or MZrOx -supported (M = Ce, La, Ti or Y) catalysts. The most active materials outperformed the state-of-the-art catalysts with supported CrOx, GaOx, ZnOx, or VOx species as well as bulk ZrO2-based catalysts without ZnO. The space-time yield of propene of 1.25 kg(C3H6).kg(cat)(-1).h(-1) at a propane conversion of about 30% with a propene selectivity of 95% was obtained over Zn(4 wt %)/TiZrOx at 550 degrees 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, CO2-TPD, NH3-TPD, pyridine-FTIR, operando UV-vis spectroscopy, Raman spectroscopy, TPO, and temporal analysis of products. In contrast with previous reports that used bulk ZrO2-based catalysts without ZnO, coordinatively unsaturated Zr cations are not the main active sites in the ZnO-containing catalysts. Supported ZnO, 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 a dopant for ZrO2 and by the crystallinity of ZrO2. Isolated tricoordinated Zn2+ species were concluded to show high activity and on-stream stability. Their intrinsic activity is enhanced when TiO2 and ZrO2 coexist in the support or when ZrO2 is promoted by TiO2. This is probably due to accelerating hydrogen formation in the course of the PDH reaction as concluded from temporal analysis of products with sub-millisecond resolution. The results of temperature-programmed oxidation of spent catalysts as well as ex situ Raman and operando UV-vis studies enabled us to conclude that the high on-stream stability of isolated tricoordinated Zn2+ species in the PDH reaction is related to their low ability to form coke. In general, the tendency for coke formation seems to increase with an increase in the degree of ZnOx agglomeration.

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 CrZrOx species. Two neighboring Zr-cus (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 CrOx, ZrO2, and support and on the size of ZrO2 crystallites in CrZrOx. SiO2 weakly interacting with CrOx was found to be a more preferable support than Al2O3- or TiO2-based supports. CrOx species promotes formation of Zr-cus sites and improves their intrinsic activity for the desired reaction. CrOx 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-CrOx/Al2O3 or state-of-the-art Ru/LaZrOx revealed about 2 times higher space-time yield of propene at 30% propane conversion at 550 degrees C. Moreover, this catalyst was durable over 50 dehydrogenation/regeneration cycles lasting 150 h.

Non-oxidative dehydrogenation of propane is one of the most promising technologies for propene production in terms of environmental impact and sustainability.

Non-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.

A series of SiO2-supported CrZrOx-based catalysts with same Cr content but different degrees of ZrO2 crystallinity were synthesized by a simple impregnation-calcination method. The catalysts were studied for their activity, selectivity and on-stream stability in non-oxidative propane dehydrogenation (PDH) under industrially relevant conditions. They were characterized by complementary techniques such as XRD, BET, NH3-TPD, H-2-TPR, operando UV-vis, EPR, Raman spectroscopy and TPO. The results demonstrate that ZrO2 crystallinity plays an important role in propene formation. Although catalyst activity can be significantly augmented upon increasing the degree of crystallinity of ZrO2, no decrease in the selectivity could be observed at the same degree of propane conversion, i.e. 92 % at about 20 % conversion. The catalysts showed good durability in 10 PDH/oxidative regeneration cycles at 550 degrees C.