The Role of Water during CO₂ Adsorption by Ca-Based Sorbents at High Temperature

Abstract

Reactions of CaO, MgO, and decarbonated dolomite (CaOMgO) with CO 2 and added water have been studied with the goal of understanding fundamental issues related to these materials' performance as CO 2 sorbents. We used a fixed bed reactor, in situ XRD, and DRIFTS to monitor the extent and kinetics of carbonation, surface reactions, and performance loss during repetitive adsorption−desorption cycles at industrial relevant conditions. From reactor and in situ XRD experiments, we found that water is essential to reach high carbonation levels (solid conversion >40%) of CaO and CaOMgO, which is in contrast to a situation where only a small fraction (<10%) of the capacity is used. Water has a more pronounced effect when applying CaOMgO as sorbent as compared to CaO, both when considering solid conversions and carbonation rates. DRIFTS shows that water together with CO 2 do in fact react at the MgO surface into carbonates species. Furthermore, H 2 CO 3 may be important for exploiting CaO and CaOMgO materials because hydrogen carbonate is observed as a surface species only during reactions with water.

Synthesis of lanthanide series (La, Ce, Pr, Eu & Gd) promoted Ni/γ-Al2O3 catalysts for methanation of CO2 at low temperature under atmospheric pressure

“…Los OM CaCe sin el precursor de CeO2 exhibe cinco bandas de adsorción asociadas directamente a la interacción entre de CO2 y el Ca del OM (ver Figura 19 A), estas se presentan a 1479, 1433 y 1413 cm -1 asignadas a bicarbonatos y 1552 y 1516 cm -1 que corresponden a carbonatos monodentados [125,185,186], con el transcurso del tiempo se aprecia un leve crecimiento en la intensidad de todas las señales indicando que el sólido sin CeO2 sufre una rápida carbonatación y los carbonatos formados son estables después de 1 h de análisis.…”

Synthesis and Evaluation of K-Promoted Co3-xMgxAl-Oxides as Solid CO2 Sorbents in the Sorption-Enhanced Water−Gas Shift (SEWGS) Reaction

“…However, we know from extensive testing that one can indicate the general cyclic capacity of these materials with satisfactory accuracy after a few cycles. By contrast, CaO-based solid sorbents decline in performance almost from the first run, and the long-term residual capacity must be assessed when considering working capacity . Thus, our main selection criterion for assessing the long-term residual capacity was based on cyclic capacity and resistance to deactivation during these three cycles.…”

“…17 Nuclear Magnetic Resonance Spectroscopy. 27 Al MAS NMR spectra were acquired using a Bruker Avance III spectrometer operating at a magnetic field of 11.74 T at SINTEF, Oslo (Norway). The 27 Al resonance frequency at this field is 130.32 MHz.…”

“…27 Al MAS NMR spectra were acquired using a Bruker Avance III spectrometer operating at a magnetic field of 11.74 T at SINTEF, Oslo (Norway). The 27 Al resonance frequency at this field is 130.32 MHz. For the spectra, a 4 mm double resonance probe or a 3.2 mm triple resonance MAS probe was used.…”

“…All NMR experiments were of the single-pulse type, that is, an initial delay (recovery) time followed by a pulse and an acquisition of the electric signal (free induction decay (FID)). For the 27 Al spectra, a total of 10,000 FIDs were recorded using a recovery time of 0.5 s. Before Fourier transformation of the averaged FIDs, zero filling and apodization were applied to improve line shape definitions and signal-to-noise ratios. The apodization was done by multiplying the accumulated FIDs with a decaying exponential window function with a processing line broadening (LB) factor of 150 Hz.…”