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.

In an effort to develop high-temperature CO 2 adsorbents, we report on the improvement of CO 2 capture performance of our previously developed potassium-promoted CaO double salts (K−Ca) through metal doping with iron and indium. The morphological, chemical, and structural characteristics of K−Ca doped metals were systematically evaluated while their CO 2 capture behavior was investigated at 500−700 °C. Our initial screening tests identified the optimum loading for Fe and In to be 3 wt % with Fe 3 /K−Ca and In 3 /K−Ca displaying CO 2 adsorption capacities of 14.65 and 14.24 mmol/g at 650 °C, respectively, and achieving 90% of their capacities ∼10 min faster than that of bare K−Ca. Moreover, our results revealed that metal doping not only enhances capture capacity but also the kinetics of both CO 2 adsorption and desorption relative to bare K−Ca double salt and that roughly all the adsorbed CO 2 desorbed from both adsorbents. However, the cyclic tests revealed a dramatic loss in CO 2 uptake for both bare and metal-doped materials at 650 °C, whereas at 375 °C, high stability for both doped-metal adsorbents was noted. In situ X-ray diffraction experiments also revealed the reversible nature of crystalline phase alterations during adsorption and desorption, whereas our kinetic analysis showed that the CO 2 uptake rate is controlled by both surface reaction and diffusion. Our findings highlight the necessity of addressing performance-stability trade-off at high temperatures for K-Ca double salts.

The excessive amounts of CO 2 emissions to the atmosphere are a critical issue due to the global warming phenomenon. Development of CO 2 adsorbents at high temperatures is of paramount importance because of their widespread application. In this investigation, sodium-based borate adsorbents have been developed for the CO 2 capture process. Four different sodium precursors (NaOH, NaCl, Na 2 CO 3 , and NaNO 3 ) have been employed as a sodium source, their effects on a boric acid material was investigated, and they were tested for CO 2 capture application under different temperatures (500−700 °C). The proposed adsorbent materials showed promising results in terms of CO 2 capture efficacy. The maximum CO 2 uptake (5.45 mmol/g) and the fastest kinetic (90% of its capture uptake achieved within the first minute) have been obtained from the proposed NB4 (NaNO 3 @H 3 BO 3 ) material at 600 °C and 1 bar. However, NB2 (NaCl@H 3 BO 3 ) and the pristine materials (boric acid) showed no capacity toward CO 2 . Time on stream has also been tested for NB1, NB3, and NB4 after multiple cyclic adsorption−desorption. The materials showed high stability after eight consecutive adsorption−desorption cycles. For further investigation, XRD, FTIR, SEM, and TGA-DSC techniques have been performed for the proposed materials to study their crystalline composition structures, bonding interactions, material degradation, and melting points. The excellent performance of the newly synthesized materials is attributed to the chemical reaction of sodium borate with CO 2 with the aid of the molten phase that facilitates CO 2 diffusion over the proposed materials. The newly proposed materials could open a new avenue for CO 2 capture technology.