Elizaveta A. Fedorova

The Pt–(O)–Co coordination number in fresh PtCo/S-1 catalysts correlates positively with their durability in propane dehydrogenation. This is because the Pt–Co bimetallic species becomes more stable and less prone to structural degradation.

Understanding the nature of active sites in heterogeneous catalysts and how to create them purposefully opens up the possibility of tailored catalyst design. Here we report mixed-valence subnanometre CoO _x clusters, consisting of a few metallic Co ⁰ atoms on top of Co ²⁺ , bound to a silicalite-1 support through lattice oxygen atoms as active species for non-oxidative propane dehydrogenation (PDH) to propene. Compared with commercial-like PtSn/Al ₂ O ₃ and K-CrO _x /Al ₂ O ₃ catalysts also tested in the present study, as well as other state-of-the-art Pt- or Co-containing PDH catalysts, this system showed high on-stream stability, propene productivity and selectivity at close-to-equilibrium propane conversion. Moreover, it showed durability in a series of PDH/regeneration cycles between 500 and 550 °C. The performance of this catalyst system is industrially attractive in terms of propene production costs, as suggested by our initial techno-economic assessment.

For CO₂ hydrogenation over iron-based catalysts, revealing the promoting effect of manganese and the nature of catalytically active sites remains a challenge that hinders targeted catalyst design. Here we elucidate the manganese-modulated restructuring of such catalysts during preconditioning and CO₂ hydrogenation using in situ X-ray absorption spectroscopy. The reaction-induced decoration of the surface of iron carbide with a MnO-containing layer is essential to hinder methane formation in favour of C₂–C₄ olefins and C₅₊ hydrocarbons. The selectivity changes were rationalized via spatially resolved steady-state and time-resolved (micro)kinetic tests combined with density functional theory calculations. The promoter affects the ability of iron carbide to generate surface species from H₂, CO₂ and C₂H₄, thus controlling the surface C/H ratio, which is decisive for product selectivity. Consequently, the design of efficient multi-component heterogeneous catalysts requires a thorough understanding of the optimal catalyst architecture and, in particular, how to generate and stabilize it under reaction conditions.

The fundamentals of in situ formation of iron carbides are required for the tailored design of Fe‐based catalysts for the efficient conversion of CO₂ to higher hydrocarbons. Herein, time‐resolved in situ X‐ray absorption spectroscopy has been used to elucidate the mechanism of the formation of Fe₅C₂ from ferrous oxalate (FeC₂O₄) at 350 °C using a H₂/CO=3 reaction feed. Regardless of the kind of alkali metal promoter and reaction pressure (1 or 7.5 bar), FeC₂O₄ is first decomposed to FeO followed by the conversion of the latter to Fe₅C₂. Further insights into the above transformations were derived by kinetic analysis using a Johnson–Mehl–Avrami–Erofeev–Kolmogorov model and kinetics‐constrained neural ordinary differential equations method. Both approaches revealed that the formation of FeO at 1 bar follows a nucleation mechanism, while a diffusion mechanism has a higher contribution at 7.5 bar. The latter mechanism is valid for the conversion of FeO to Fe₅C₂ at both pressures. Alkali metal promoters were found to accelerate the rate of Fe₅C₂ formation. This rate decreases with increasing total pressure due to the stabilization of FeO.

Die Ethylen‐Dimerisierung ist ein industrieller Prozess, der derzeit mit homogenen Katalysatoren durchgeführt wird. Hier stellen wir einen hochaktiven heterogenen Katalysator vor, der winzige Mengen von atomar dispergiertem Pd enthält. Er erfordert keine Cokatalysatoren oder Aktivatoren und übertrifft die Leistung früherer Katalysatoren, die unter ähnlichen Reaktionsbedingungen getestet wurden. Die Selektivität für C₄‐ und C₆‐Kohlenwasserstoffe betrug bei 200 °C etwa 80 % bzw. 10 % bei 42 % C₂H₄‐Umsatz unter Verwendung eines industriell relevanten Reaktionsgemisches mit 50 Vol.‐% Ethylen. Unsere Experimente zur Kinetik und Katalysatorcharakterisierung, ergänzt durch Dichtefunktionaltheorie‐Berechnungen, liefern molekulare Einblicke in die lokale Umgebung isolierter Pd(II)O_x‐Spezies und ihre Rolle bei der Erzielung einer hohen Aktivität in der Zielreaktion. Als der entwickelte Katalysator rationell mit einem Mo‐haltigen Olefinmetathesekatalysator im gleichen Reaktor integriert wurde, reagierten die gebildeten Butene mit Ethylen zu Propylen mit einer Selektivität von 98 % bei etwa 24 % C₂H₄‐Umsatz.

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)O_x 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.

A detailed operando DRIFTS study on the CO₂ Fischer‐Tropsch reaction with K‐promoted Fe/YZrO_x catalysts was performed to investigate the influence of this modification on the catalytic performance in the formation of lower olefins as well as higher hydrocarbons and to gain insights into mechanistic aspects. Catalytic testing revealed an enhanced formation of olefins and hydrocarbons by adding potassium to the catalysts, while spectroscopic studies revealed various stable adsorbates and intermediates such as monodentate carbonates, bicarbonates, formates, formyl, and methoxy on the surface of the K‐promoted Fe/YZrO_x catalysts compared to the unpromoted one. Based on gas‐feed switching experiments and statistical analysis of literature IR data regarding Fe‐containing catalysts, it was found that carbonate species interacting with H₂ are transformed to higher hydrocarbons and methane via formate and formyl formation, while bicarbonate species are decomposed accompanied by the formation of CO, which then further reacts to form formate or formyl and finally hydrocarbons.

We established the structural features of Rh single atom and RhO_x clusters in CeO₂, their Red-Ox reversibility and low temperature CO oxidation activity.