Surface and bulk carbonate formation in calcium oxide during CO2 capture

Abstract

Calcium looping (CaL), the cyclic carbonation and calcination of limestone, is a prominent carbon capture option considering reduced parasitic energy consumption compared to amine scrubbing. The main issue preventing application is sorbent performance decay during cycling. Therefore hydration and extended carbonation reactivation strategies, as well as synthetic approaches to enhance or sustain reactivity, are of interest. Results of an investigation are presented on the impact of reactivation strategies on carbonate formation through detailed study using in-situ infrared spectroscopy. Surface and bulk carbonate formation regimes were readily distinguished allowing the influence of temporal, hydration and thermodynamic conditions within each regime to be studied. Surface chemistry of CaO during two initial cycles was shown to change. Significantly, it was shown that the CaO surface produced from the calcination of Ca(OH)2 possessed more highly reactive sites compared to the surface produced from CaCO3. The presence of water enhanced bulk carbonate formation at 300 °C and influenced the complexation of surface carbonates during looping. The results are of interest in the CaL community, offering molecular scale explanations for macroscale observations, whilst also informing on the role of humidity in direct air capture and sorption enhanced reaction processes.

Hydrogen Production by Formic Acid Decomposition over Ca Promoted Ni/SiO2 Catalysts: Effect of the Calcium Content

“…These bands are very weak in the spectrum of Ca(3.4)-SiO 2 , but they are more intense at high X values (Ca(19.3)-SiO 2 ). The signal centered at 1645 cm −1 and the shoulder at 1240 cm −1 revealed the presence of asymmetric C-O stretching a C-O-H bending modes, respectively, of bicarbonate species [22,29]. For all the Ca-SiO 2 supported catalysts, the presence of formate and bicarbonate species in the catalysts after the reaction was confirmed by FTIR (Figure 10c) and were consistent with TPSR experiments.…”

“…It is noted that the bands decrease in intensity as the content of Ca wt.% increases [20]. For the Ca promoted sample, with 19.3 wt.% of Ca, the broad band at 1458 cm −1 , associated with the band at 876 cm −1 , is assigned to asymmetric C-O stretch and out-of-plane deformation, respectively, of monodentate carbonate species on the CaO phase [22].…”

Oxygen Activation in Oxidative Coupling of Methane on Calcium Oxide

“…Reducing the temperature from 750 to 740 °C, an increase in the catalyst mass can be observed, which is enhanced by further reducing the temperature to 730 °C. A direct conversion from CaO to CaCO 3 is known to take place at these temperatures, whereas at low temperatures the process is slow and is enhanced by the presence of water, first forming hydroxides, which then react with CO 2 . As XRD analysis shows (Figure B), the mass gain can be attributed to a direct calcite formation; no hydroxide residues were found.…”

CO2 Capture for Dry Reforming of Natural Gas: Performance and Process Modeling of Calcium Carbonate Looping Using Acid Based CaCO3 Sorbent

“…Over the years, many studies have been carried out to improve the sorbent performance in the CCL process. Example of improvements include the use of water as a reactivation agent for the sorbent (Ramkumar and Fan, 2010;Mutch et al, 2017), salt doping (Sun et al, 2012;Erans et al, 2018), thermal pre-treatment (Valverde et al, 2017), and acid pre-treatment (Ridha et al, 2013).…”