Tatiana Otroshchenko

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.

Non-oxidative propane dehydrogenation (PDH) to propene is the basis of several technologies developed for meeting the increasing demand for this olefin. Given the high cost of commercial Pt-based catalysts, a promising direction for improving the economics of propene production by PDH is to reduce Pt content without sacrificing high propene productivity and selectivity. We report that the 1Co-0.1Pt@silicalite-1(1Co-0.1Pt@S-1) catalyst, with only 0.1 wt% Pt and 1 wt% Co, outperforms an analog of commercial Pt–Sn/Al2O3 in terms of activity and on-stream stability despite the approximately 5-fold lower Pt loading. Its performance is also remarkable when compared to other state-of-the-art Pt-containing catalysts. The high activity of the 1Co-0.1Pt@S-1 catalyst is attributed to the presence of ultrasmall PtCo intermetallic compounds formed under reaction conditions. The developed catalyst also demonstrated high on-stream stability, with an apparent deactivation rate constant of just 4 × 10−4 h−1 determined over 110 h on stream at approximately 90% of the equilibrium propane conversion at 500 °C using a feed with 90 vol % propane.

Supported chromium catalysts find broad application due to metal's ability to assume a range of oxidation states and structures. However, the behavior of chromium species on reducible metal oxides under reactive conditions remains poorly understood, despite the potential for unique reactivity through metal-support interactions. Recent studies on CeO₂-supported Crⁿ⁺ single atoms for selective NH₃ oxidation to N₂O underscore this potential, attaining high performance through cocatalytic action with CeO₂, but also suffering from deactivation through agglomeration of isolated sites into Cr₂O₃. To address this challenge, we investigate how distinct CeO₂-supported chromium species evolve under varying reactive environments. We show that under oxidative conditions redispersion of Cr₂O₃ occurs, serving as a catalyst regeneration strategy and enabling the recovery of both structure and performance. Combining advanced microscopy, in situ Raman, UV-vis, electron paramagnetic resonance and X-ray absorption spectroscopies, we follow the transformation from crystalline Cr₂O₃ nanoparticles to isolated chromium species. The redispersion is proposed to proceed via particle amorphization and oxidation of Cr³⁺ to mobile Cr⁶⁺, which diffuse over the support and stabilize as chromate species or as Cr⁵⁺ upon reduction by oxygen vacancies. A slower redispersion rate is observed over less reducible ZrO₂ and TiO₂, with minimal changes on γ-Al₂O₃ and Nb₂O₅, highlighting support reducibility as the driver of the process and reflecting the potential for generating Cr⁶⁺ sites from nontoxic Cr₂O₃ by controlling support properties. These results demonstrate how redox-active supports facilitate reversible changes to metal nanostructure, offering a promising strategy for regenerating catalysts and tuning metal speciation through rational support design for various applications.

La _cus sites on defective La ₂ O ₃ catalyze propane dehydrogenation but deactivate due to strong propene adsorption. In situ decoration of La _cus sites with H ₂ forms new sites, weakens adsorption, and improves catalyst stability and selectivity.

Although supported Mo-containing catalysts have been extensively investigated in the metathesis of ethylene with 2-butene to propene, the mechanisms of the formation and transformation of catalytically active Mo-carbenes in the course of the reaction are still not fully understood. The difficulties arise because only a tiny fraction of MoO_x species can form Mo-carbenes in situ, making the detection of the latter by spectroscopic means very unlikely. Herein, purposefully designed steady-state and transient experiments including their kinetic evaluation and density functional theory calculations enabled us to elucidate mechanistic and kinetic details of the above reaction-induced processes in the metathesis reaction over a Mo/P/SiO₂ catalyst at 50 °C. We established that, in parallel with the desired reaction cycle, molybdacyclobutanes also undergo reversible structural transformations which might be one of the reasons for low steady-state catalyst activity. Based on the results obtained, strategies for controlling the concentration of the inactive species and accordingly catalyst activity have been suggested and experimentally validated.

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.