Recent progress in Cr-based catalysts for oxidative dehydrogenation of light alkanes by employing CO2 as a soft oxidant

CO2 can be used as a soft oxidant for oxidative dehydrogenation of light alkanes (CO2-ODH), which is beneficial to realize the reuse of CO2 and meet the demand for olefins. The core of this reaction is the catalyst. Cr-based catalysts have attracted much attention for their excellent catalytic performance in CO2-ODH reactions due to their various oxidation states and local electronic structures. In this paper, the synthesis and modification methods of Cr-based catalysts for CO2-ODH are reviewed. The structure–activity relationship and reaction mechanism are also summarized. Moreover, the reasons for the deactivation of Cr-based catalysts are analysed and the main challenges faced by Cr-based catalysts in the CO2-ODH process, as well as the future development trend and prospect, are discussed.

CO2 utilization as a soft oxidant for the synthesis of styrene from ethylbenzene over Co3O4 supported on magnesium aluminate spinel: role of spinel activation temperature

Magnesium aluminate spinel (MgAl2O4) supported Co3O4 catalysts are synthesized and tested for the oxidative dehydrogenation (ODH) of ethylbenzene using CO2 as a soft oxidant. The effect of spinel calcination temperature on the catalytic performance has been systematically investigated. With an increase in the activation temperature from 600 to 900 °C, the active presence of a single-phase MgAl2O4 spinel is observed. A catalyst series consisting of MgAl2O4 spinel with varying Co loadings (10–20 wt%) were prepared and systematically distinguished by ICP, XRD, BET, TPR, NH3-TPD, UV–Vis DRS, FT-IR, XPS, SEM, and TEM. Among the tested cobalt catalysts, 15Co/800MA sample derived by calcination of MgAl2O4 support at 800 °C exhibits the most excellent catalytic performance with the maximum ethylbenzene conversion (≥ 82%). Also, high yields of styrene (≥ 81%) could be consistently achieved on the same active catalyst. Further, the catalyst exhibited almost stable activity during 20 h time-on-stream with a slow decrease in the ethylbenzene conversion from 82 to 59%. However, the selectivity of styrene (98%) stayed almost constant during the reaction. Activation of the MgAl2O4 spinel at 800 °C facilitates a dramatic chemical homogeneity for the alignment of Co3O4 nanoparticles on the surface of the active catalyst. Moreover, the isolated Co3O4 clusters have a strong chemical/electronic interaction with the Mg2+ and Al3+ ions on the support perform a crucial role to achieve the maximum catalytic activity.

Outstanding Performance of Highly-Dispersed Zinc Species on Zeolites for the Continuous and Selective Dehydrogenation of Ethane with CO2 as Soft Oxidant

<div> <div> <div> <p>We report herein the preparation, characterization, and outstanding catalytic performance of a series of heterogeneous catalysts featuring highly-dispersed zinc sites on zeolitic SSZ-13 and ZSM-5 frameworks. The materials were evaluated in the oxidative dehydrogenation of ethane with CO2 as a soft oxidant, a very important reaction for the synthesis of platform chemicals. In particular, we found that Zn2.92/NaS50 exhibits high ethane conversion ability, excellent CO2 transformation ability, and good selectivity. In line with the experimental results, we show that the highly-selective character is due to the characteristic compositional structure of the zeolite support and its topology that can effectively confine CO2. An in-depth molecular analysis via operando studies and DFT calculation showed that the rate-limiting step of reaction with CO2 was the second C-H bond dissociation to give ethene. The addition of CO2 effectively reduced the energy barrier of this step, favoring desorption and limiting byproduct formation. Overall, this work demonstrates the breakthrough potential of novel heterogeneous catalysts made of highly-dispersed zinc species on zeolites in relevant transformations. </p> </div> </div> </div>

Outstanding Performance of Highly-Dispersed Zinc Species on Zeolites for the Continuous and Selective Dehydrogenation of Ethane with CO2 as Soft Oxidant

<div> <div> <div> <p>We report herein the preparation, characterization, and outstanding catalytic performance of a series of heterogeneous catalysts featuring highly-dispersed zinc sites on zeolitic SSZ-13 and ZSM-5 frameworks. The materials were evaluated in the oxidative dehydrogenation of ethane with CO2 as a soft oxidant, a very important reaction for the synthesis of platform chemicals. In particular, we found that Zn2.92/NaS50 exhibits high ethane conversion ability, excellent CO2 transformation ability, and good selectivity. In line with the experimental results, we show that the highly-selective character is due to the characteristic compositional structure of the zeolite support and its topology that can effectively confine CO2. An in-depth molecular analysis via operando studies and DFT calculation showed that the rate-limiting step of reaction with CO2 was the second C-H bond dissociation to give ethene. The addition of CO2 effectively reduced the energy barrier of this step, favoring desorption and limiting byproduct formation. Overall, this work demonstrates the breakthrough potential of novel heterogeneous catalysts made of highly-dispersed zinc species on zeolites in relevant transformations. </p> </div> </div> </div>