Enhancing the Ethylene Yield over Hybrid Adsorbent Catalyst Materials in CO₂-Assisted Oxidative Dehydrogenation of Ethane by Tuning Catalyst Support Properties

Abstract

CO2 emissions remediation has become of paramount importance due to the climate change issue. Combined CO2 capture and utilization has been considered as one of the promising technological solutions not only for mitigating CO2 emissions but also for producing valuable commodities such as chemicals and fuels. Herein, we report on the development of materials for combined capture and utilization of CO2 in the oxidative dehydrogenation of ethane to ethylene. The materials consisted of K–Ca double salt, to impart adsorption functionality, and Cr-incorporated SiO2 and H-ZSM-5, to impart catalyst functionality. The combined capture–reaction tests were performed under semi-isothermal conditions with adsorption at 600 °C and reaction at 700 °C. The results revealed that (K–Ca)50/(Cr10@H-ZSM-5)50 material with 10 wt % Cr and zeolite’s SiO2/Al2O3 ratio of 280 exhibited the highest C2H6 conversion of 45.2% and C2H4 selectivity and yield of 78.3 and 35.4%, respectively. The better catalytic activity of this material relative to SiO2-based material was attributed to its higher Cr6+/Cr3+ ratio, as determined by XPS analysis. Moreover, the stability analysis of the materials after four adsorption–reaction cycles revealed a better stability for (K–Ca)50/(Cr10@H-ZSM-5)50 than for (K–Ca)50/(Cr10%@SiO2)50 which retained 72% of its initial CO2 adsorption capacity, 65% of its initial C2H6 conversion, and 76% of its initial C2H4 yield.

Direct Synthesis of Ethylene and Hydrogen from CO2 and Ethane over a Bifunctional Structured CaO/Cr2O3-V2O5/ZSM-5 Adsorbent/Catalyst Monolith

“…In the ODHE reaction, Cr 6+ /Cr 3+ ratios and peak intensities play a key role in affecting the concentration of acid sites and redox properties, mainly due to the high electronic state of Cr 6+ , thereby affecting the reaction products distribution. 24,32 In Figure 6f,g, both samples displayed O 1s in the range of 529−536 eV but the oxygen peak intensity was higher in Cr 1 -V 3 /ZC and slightly shifted to a higher binding energy compared to that in Cr 4 /ZC, as shown in Table 4, indicating the presence of more oxygen species on the surface of Cr 1 -V 3 / ZC, in agreement with the literature. 50 Therefore, O 1s, in both samples, was deconvoluted to determine the oxygen species.…”

“…18,21,22 As an example of using BFMs for in situ CO 2 capture-utilization in ODHE, we previously synthesized various BFMs consisting of CaO, which works as the adsorption phase for CO 2 capture via high-temperature reaction to CaCO 3 , 23 and Cr/ZSM-5 as the heterogeneous catalytic phase. 15,24 Under optimal adsorption−reaction conditions (e.g., adsorption = 600 °C and reaction = 700 °C), 4 mmol/g CO 2 uptake capacity, 42.5% C 2 H 6 conversion, 38.6% C 2 H 4 yield, and 90.6% C 2 H 4 selectivity were achieved over these BFMs. We later formulated these BFMs into monolithic structures using 3D printing, and investigated their CO 2 adsorption-reaction performance.…”

Strategies for Integrated Capture and Conversion of CO2 from Dilute Flue Gases and the Atmosphere

“…A follow up study found that the catalytic efficiency could be enhanced by increasing the Si/Al ratio across the aluminosilicate zeolite supports [56] . For example, when the Si/Al ratio was increased from 50 to 280, the ethane conversion increased from 25 to 45.2 %, for the same experimental condition.…”

Screening of Adsorbent/Catalyst Composite Monoliths for Carbon Capture-Utilization and Ethylene Production

“…This effect was to be anticipated, given that Cr 2 O 3 is a strong acid and is known to greatly enhance catalytic acidity when doped alongside ZSM-5 . Regarding ODHE performance, this result suggested that Cr-CaO/ZSM-5 would generate the best performance because light oxidation-based dehydrogenation of ethane to ethylene, especially the initial H 2 removal step, is generally driven by catalytic acidity. ,,,, Regarding the other samples, In-CaO/ZSM-5, Ce-CaO/ZSM-5, and CaO-ZSM-5 displayed similar peak intensities for both their weak and strong acid sites, whereas Mo-CaO/ZSM-5 showed a decrease in strong acid site density. This stated, the reduction in strong acid site concentration for Mo-CaO/ZSM-5 from the In-doped, Ce-doped, and undoped samples was not that significant, so a generalization about the expected performances of these catalysts could not be solely drawn from NH 3 -TPD.…”