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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. [ABSTRACT FROM AUTHOR]

The metathesis of ethylene with 2‐butenes to propene is an established large‐scale process. However, the fundamentals behind in situ transformation of supported WOx, MoOx, or ReOx species into catalytically active metal‐carbenes and the intrinsic activity of the latter as well as the role of metathesis‐inactive cocatalysts are still unsolved. This is detrimental for catalyst development and process optimization. In this study, we provide the required essentials derived from steady‐state isotopic transient kinetic analysis. For the first time, the steady‐state concentration, the lifetime, and the intrinsic reactivity of metal carbenes were determined. The obtained results can be directly used for the design and the preparation of metathesis‐active catalysts and cocatalysts, thereby opening up possibilities for optimizing propene productivity. [ABSTRACT FROM AUTHOR]

We investigated the effect of supports based on ZrO2, TiO2, Al2O3, and SiO2 on the rate of propene formation in the metathesis of ethylene with 2-butene at 50 °C over Mo-containing catalysts possessing highly dispersed MoOx. Large improvements in this rate were achieved when using supports composed of mixed oxides (ZrO2–SiO2, ZrO2–PO4, TiO2–SiO2; Al2O3–SiO2) rather than of individual oxides (ZrO2, TiO2, Al2O3, SiO2). Although previous literature studies dealing with the metathesis reaction over Al2O3- or SiO2-suppported catalysts at higher temperatures suggest the importance of redox or acidic properties of supported MoOx species for catalyst activity, we were not able to establish any general direct correlation in this regard. Contrarily, the rate of propene formation can be significantly enhanced when promoting supports with an oxide promoter. We suggest that the created support lattice defects may facilitate the transformation of MoOx to Mo carbenes under reaction conditions or improve the intrinsic activity of the latter. [ABSTRACT FROM AUTHOR]

Frontispiece: Performance Descriptors for Catalysts Based on Molybdenum, Tungsten, or Rhenium Oxides for Metathesis of Ethylene with 2-Butenes to Propene Keywords: 2-Butene; Ethylene; Metathesis; Propene; SSITKA EN 2-Butene Ethylene Metathesis Propene SSITKA 1 1 1 09/27/23 20231002 NES 231002 B Heterogeneous Catalysis b . In their Communication (e202308872), Tatiana Otroshchenko, Evgenii V. Kondratenko et al. report performance descriptors for catalysts based on molybdenum, tungsten, or rhenium oxides for ethylene metathesis with 2-butenes to propene. [Extracted from the article]