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Metal‐free carbon catalysts represent attractive alternatives to platinum and chromium‐containing systems for the on‐purpose production of propylene, a crucial chemical building block, via non‐oxidative propane dehydrogenation. However, the role of heteroatoms in determining reactivity and stability is poorly understood. Here, the study of a platform of polyaniline‐derived and activated carbons, with distinct porous properties, and heteroatom type, content, and speciation, enables establishing improved structure‐performance relationships. In‐depth characterization reveals that, while several oxygen species potentially catalyze the reaction, carbonyl groups are the main functionality governing the activity. Oxygen loss via propane‐driven water evolution is the main deactivation path. Six‐fold enhanced stability evidenced over carbon catalysts derived from KOH‐post‐treated polyanilines demonstrates the importance of controlling the nanostructure for enhancing longevity. [ABSTRACT FROM AUTHOR]

Identification and quantification of redox‐active centers at relevant conditions for catalysis is pivotal to understand reaction mechanisms and requires development of advanced operando methods. Herein, we demonstrate operando EPR spectroscopy as an important technique to quantify the oxidation state of representative CrPO4 and EuOCl catalysts during propane oxychlorination, an attractive route for propylene production. In particular, we show that the space‐time‐yield of C3H6 correlates with the amount of Cr2+ and Eu2+ ions generated over the catalysts during reaction. These results provide a powerful strategy to gather quantitative understanding of selective alkane oxidation, which could potentially be extrapolated to other functionalization approaches and operating conditions. [ABSTRACT FROM AUTHOR]

The selective catalytic reduction of N2O over steam-activated FeZSM-5 zeolite has been investigated at 473-823 K using C1-C3 hydrocarbons (methane, ethane, ethene, ethyne, propane, and propyne). The assessment of the hydrocarbons for nitrous oxide abatement is discussed according to different criteria: (i) de-N2O activity and operation temperature, (ii) hydrocarbon utilization, that is, the selectivity to react with N2O in O2 excess, (iii) emission of CO and CO2. (iv) sensitivity to NO and NH3, and (v) cost Alkanes are generally more effective reducing agents than unsaturated hydrocarbons. In particular, alkynes require higher temperature to activate N2O and are unselective because of their proneness to react with O2. Ethane is an optimal reductant, featuring a high de-N2O activity, high selectivity, and compared to methane, a lower degree of inhibition by NO. [ABSTRACT FROM AUTHOR]

A novel process for the direct ammoxidation of propane over steam-activated Fe-silicalite at 723–823 K is reported. Yields of acrylonitrile (ACN) and acetonitrile (AcCN) below 5% were obtained using N2O or O2 as the oxidant. Co-feeding N2O and O2 boosts the performance of Fe-silicalite compared to the individual oxidants, leading to AcCN yields of 14% and ACN yields of 11% (propane conversions of 40% and products selectivity of 25–30%). The beneficial effect of O2 on the propane ammoxidation with N2O contrasts with other N2O-mediated selective oxidations over iron-containing zeolites (e.g. hydroxylation of benzene and oxidative dehydrogenation of propane), where a small amount of O2 in the feed dramatically reduces the selectivity to the desired product. It is shown that the productivity of ACN and especially AcCN, expressed as mol product h−1 kg, is significantly higher over Fe-silicalite than over active propane ammoxidation catalysts reported in the literature. Our results open new perspectives to improve the performance of alkane ammoxidation catalysts. [ABSTRACT FROM AUTHOR]

A novel process for the direct ammoxidation of propane over steam-activated Fe-silicalite at 723–823 K is reported. Yields of acrylonitrile (ACN) and acetonitrile (AcCN) below 5% were obtained using N2O or O2 as the oxidant. Co-feeding N2O and O2 boosts the performance of Fe-silicalite compared to the individual oxidants, leading to AcCN yields of 14% and ACN yields of 11% (propane conversions of 40% and products selectivity of 25–30%). The beneficial effect of O2 on the propane ammoxidation with N2O contrasts with other N2O-mediated selective oxidations over iron-containing zeolites (e.g. hydroxylation of benzene and oxidative dehydrogenation of propane), where a small amount of O2 in the feed dramatically reduces the selectivity to the desired product. It is shown that the productivity of ACN and especially AcCN, expressed as mol product h−1 kg, is significantly higher over Fe-silicalite than over active propane ammoxidation catalysts reported in the literature. Our results open new perspectives to improve the performance of alkane ammoxidation catalysts. [ABSTRACT FROM AUTHOR]

Abstract: The performance of differently prepared Fe-ZSM-5 zeolites in the N2O-mediated propane oxidative dehydrogenation to propylene has been investigated at 723K using a tapered element oscillating microbalance (TEOM) coupled to on-line GC analysis. Catalysts were prepared by hydrothermal synthesis followed by calcination and steam treatment, liquid-ion exchange, and chemical vapor deposition, and contain molar Fe/Al ratios in the range of 0.26–1. Propylene yields in the range of 22–25% were attained over steam-activated Fe-ZSM-5, much higher over the iron zeolites prepared by post-synthesis methods (9–16%), with propylene selectivities around 40%. The deactivation behaviour due to coking differs among the catalysts investigated. Calcined H-ZSM-5 with impurities of iron (Fe/Al=0.007) leads to an initial yield of propylene of 8%, and is increased to 16% upon steam treatment, obtaining a selectivity to propylene of 90%. The turnover frequency for propylene production is up to three orders of magnitude higher in steamed H-ZSM-5 than in the synthesized iron zeolites. Our results suggest that traces of well-isolated (mononuclear) Fe species released from framework positions by steaming are extremely active in the oxidative dehydrogenation of propane to propylene, while large iron clusters enhance deep oxidation of important reaction intermediates to COx. [Copyright &y& Elsevier]

The effect of the iron distribution in steam-activated FeZSM-5 and Fe-silicalite on their catalytic performance for direct N2O decomposition and for the oxidative dehydrogenation of propane (ODHP) with N2O and O2 was investigated by means of steady-state and transient pulse experiments. Steam-activated FeZSM-5, containing a large fraction of iron as oligonuclear FexOy clusters, is more active and selective in ODHP and direct N2O decomposition than steam-activated Fe-silicalite, where isolated iron species predominate. This suggests that the same type of iron centers is involved in both conversions. The higher activity of steam-activated FeZSM-5 is associated to the higher mobility of atomic oxygen species attached to oligonuclear iron species, which lead to a faster oxygen desorption in direct N2O decomposition as well as to a faster transfer to propane in the ODHP reaction. Steam-activated FeMFI zeolites were found to be highly effective catalysts for ODHP with N2O, with initial propene yields up to 24%. Relatively high yields of propionaldehyde are also obtained, which mainly originates from the selective oxidation of propene. The unique ODHP performance of iron zeolites requires the use of N2O as monooxygen donor. Such species cannot be created by O2. Only a fraction of oxygen species deposited over iron sites of FeMFI upon N2O activation was found to be active towards propane oxidation under transient vacuum conditions. This is explained by a fast transformation of short-living highly reactive atomic oxygen species into less reactive ones. [Copyright &y& Elsevier]

Steam-activated Fe-zeolites (MFI and BEA) are efficient catalysts for the N2O-mediated oxidative dehydrogenation of propane, with initial propylene yields up to 25% at 723 K, but deactivate as a result of coke formation. A tapered element oscillating microbalance (TEOM) coupled to GC analysis has been applied to correlate activity and deactivation by simultaneous measurements of reaction and coking. The presence of extraframework iron species, generated during steam treatment, is essential for producing active catalysts. The nature and distribution of extraframework iron species, the zeolite host, and the catalyst acidity have no significant effect on the initial propene yield, but strongly influence the deactivation behavior. FeZSM-5 shows a remarkable resistance against deactivation, while a very rapid and complete deactivation occurred in FeBEA. The initial propene yield over FeZSM-5 and FeBEA was remarkably higher than over commercial H-ZSM-5 and H-BEA (with 30–40 times lower iron content), although the residual activities after 400 min on stream were very similar. [Copyright &y& Elsevier]

Keywords: propane dehydrogenation; metal-free catalysis; heteroatom-doped carbons; propylene; structure-performance relationships EN propane dehydrogenation metal-free catalysis heteroatom-doped carbons propylene structure-performance relationships 2540 2540 1 06/10/21 20210608 NES 210608 B The Cover Feature b shows a high-speed train, representing non-oxidative propane dehydrogenation, running on a monorail connected to specific atoms (active sites) on a catalyst surface. Propane dehydrogenation, metal-free catalysis, heteroatom-doped carbons, propylene, structure-performance relationships Cover Feature: Impact of Heteroatom Speciation on the Activity and Stability of Carbon-Based Catalysts for Propane Dehydrogenation (ChemCatChem 11/2021). [Extracted from the article]

Innentitelbild: Quantification of Redox Sites during Catalytic Propane Oxychlorination by Operando EPR Spectroscopy (Angew. Keywords: alkane activation; heterogeneous catalysis; operando EPR spectroscopy; propane oxychlorination; reaction mechanism EN alkane activation heterogeneous catalysis operando EPR spectroscopy propane oxychlorination reaction mechanism 3354 3354 1 02/10/21 20210215 NES 210215 B Operando-EPR wird heiß b Im Forschungsartikel auf S. 3640 demonstrieren Guido Zichittella, Yevhen Polyhach, Javier Pérez-Ramírez et al. die Operando-EPR-Spektroskopie als zentrale Technik zur Bestimmung des Oxidationszustands von CrPO SB 4 sb - und EuOCl-Katalysatoren während der katalytischen Hochtemperatur-Oxychlorierung von Propan. Alkane activation, heterogeneous catalysis, operando EPR spectroscopy, propane oxychlorination, reaction mechanism. [Extracted from the article]

Turning myth into reality. Pérez‐Ramírez et al. show in their Communication on page 13670 ff. the outstanding performance of EuOCl for the production of light olefins from ethane and propane by oxychlorination chemistry. The high activity, selectivity, and stability of the system are illustrated by the mythological princess Europa, who was carried from Asia to the Hellenic world by Zeus, who was disguised as a white bull. Both the continent of Europe and the element europium later took her name. [ABSTRACT FROM AUTHOR]

Abstract: The N2O-mediated oxidative dehydrogenation of propane over iron-containing MFI zeolites was studied by in situ diffuse reflectance Fourier transform infrared spectroscopy, complemented by analyses in a tapered element oscillating microbalance coupled with gas chromatography and characterization by X-ray diffraction, transmission electron microscopy, and N2 adsorption. Samples with different iron speciation and acidic properties, induced by the preparation method (ion-exchange and steam activation) and the framework composition (Fe–Al–Si, Fe–Ga–Si, and Fe–Ge–Si) were analyzed. Real-time monitoring of the reaction under operando conditions allowed us to gain insight into the mechanism and kinetics of deactivation and coke formation, as well as zeolite regeneration in air. Deactivation of iron zeolites in the oxidative dehydrogenation of propane is caused by coke deposition on active extra-framework iron species. The mechanism of coke formation and the nature of the deposits were similar over the samples, independent of the catalytic performance and deactivation pattern. Regeneration in air led to the disappearance of coke-related bands and the practically complete recovery of the original porosity, while the zeolite crystallinity remained intact. The initial propylene yield over the fresh and regenerated Fe–Ga–Si zeolites was the same, but the latter sample exhibited faster deactivation. This is attributed to a change of iron constitution in the first reaction–regeneration cycle. The alteration of the local environment of the iron species was indirectly concluded from the appearance of a band associated with Lewis centers in the infrared spectra of the regenerated zeolite. In support of this, TEM studies demonstrated an extensive degree of iron clustering as FeO x nanoparticles in the regenerated catalyst compared with the fresh and coked catalysts. [Copyright &y& Elsevier]

Abstract: Temporary supply of CO during propyne hydrogenation over a copper-based catalyst derived from a Cu–Al hydrotalcite permanently increased the alkene selectivity from 60% to 92% at 100% alkyne conversion (473K). The superior performance of the CO-modified copper catalyst (higher alkene selectivity and resistance against deactivation by fouling) was further confirmed at lower temperature (373K). Our catalytic results suggested that carbon monoxide in the presence of propyne and hydrogen irreversibly restructures the catalyst surface leading to a smaller copper ensemble that minimizes C–C coupling. Consequently, the enhanced alkene production in the CO-modified catalyst was coupled to a decreased oligomer production and very little propane production. The pretreatment mixture, feed CO concentration, and type of alkyne are important aspects to attain a selective copper catalyst. The CO effect in alkyne hydrogenation over copper radically differs from that over palladium or nickel. On the latter two metals, the increased alkene selectivity in the presence of CO is mostly due to a reduction in the over-hydrogenation channel. In addition, the effect is fully reversible, that is, it vanishes on removing CO from the feed. The permanent modification of the copper ensemble by CO might be advantageous for (chemo) selective hydrogenations of high acetylenic substrates. [Copyright &y& Elsevier]