Interaction of pristine hydrotalcite-like layered double hydroxides with CO2: a thermogravimetric study (original) (raw)
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CO 2 Adsorption at Elevated Pressure and Temperature on Mg–Al Layered Double Hydroxide
Industrial & Engineering Chemistry Research, 2014
CO 2 adsorption at elevated pressure was studied in a Mg−Al (Mg/Al = 3) layered double hydroxide (LDH). The double-layered structure was prepared via a coprecipitation method. The sample's structure and microstructure evolutions were characterized using X-ray diffraction, scanning electron microscopy, N 2 adsorption, and thermogravimetric and calorimetric analyses. The CO 2 adsorption experiments were performed between 5 and 4350 kPa at different temperatures (30−350°C). Elevated pressure experiments showed that this material was able to adsorb different quantities of CO 2 depending on the thermal evolution of its structure and microstructure. The highest CO 2 adsorption (5.7 mmol/g) was produced at 300°C before the layered structure had completely collapsed. At these specific conditions the interlayer space was reduced from 7.78 to 4.39 Å. This interlayer change was attributed to the onset of LDH structural collapse. However, at this temperature the adsorption process must be favored over the adsorption−desorption equilibrium, allowing the maximum CO 2 capture.
Energetics of CO2 Adsorption on Mg–Al Layered Double Hydroxides and Related Mixed Metal Oxides
Energetics of CO2 uptake by layered double hydroxides (LDH) of Mg and Al and their corresponding mixed metal oxides (MMO) of two different compositions (Mg/Al = 2:1 and 3:1) were investigated by gas adsorption calorimetry. The initial adsorption enthalpies for all the LDH and MMO are similar and in the range −90 to −120 kJ/mol, indicating strong chemisorption of CO2. However, the differential adsorption enthalpy varies substantially with increasing coverage for different samples. LDH prepared by coprecipitation (both Mg/Al = 2 and 3) and their corresponding MMO exhibit similar CO2 uptake, which are in the working sorption capacity range (0.6–1 mmol/g), but the one prepared by urea hydrolysis shows poor sorption capacity (0.02–0.35 mmol/g). An integral enthalpy of adsorption of −54 kJ/mol was observed for [Mg–Al–CO3] LDH prepared by urea hydrolysis and −59 kJ/mol and −57 kJ/mol for the ones prepared by coprecipitation with composition 3:1 and 2:1, respectively. Attenuated total reflectance spectroscopy measurements of samples after CO2 uptake aid in identifying the mode of binding of adsorbed carbonate, which gives information about strength of basic sites. The presence of monodentate carbonate in all samples suggests that strong basic sites are available in LDH and MMO, in agreement with the large exothermic initial adsorption enthalpies observed, indicating strong chemisorption.
ACS Applied Materials & Interfaces, 2014
The carbon cycle, by which carbon atoms circulate between atmosphere, oceans, lithosphere, and the biosphere of Earth, is a current hot research topic. The carbon cycle occurring in the lithosphere (e.g., sedimentary carbonates) is based on weathering and metamorphic events so that its processes are considered to occur on the geological time scale (i.e., over millions of years). In contrast, we have recently reported that carbonate anions intercalated within a hydrotalcite (Mg 0.75 Al 0.25 (OH) 2 (CO 3) 0.125 •yH 2 O), a class of a layered double hydroxide (LDH), are dynamically exchanging on time scale of hours with atmospheric CO 2 under ambient conditions. (Ishihara et al., J. Am. Chem. Soc. 2013, 135, 18040−18043). The use of 13 C-labeling enabled monitoring by infrared spectroscopy of the dynamic exchange between the initially intercalated 13 C-labeled carbonate anions and carbonate anions derived from atmospheric CO 2. In this article, we report the significant influence of Mg/Al ratio of LDH on the carbonate anion exchange dynamics. Of three LDHs of various Mg/Al ratios of 2, 3, or 4, magnesium-rich LDH (i.e., Mg/Al ratio = 4) underwent extremely rapid exchange of carbonate anions, and most of the initially intercalated carbonate anions were replaced with carbonate anions derived from atmospheric CO 2 within 30 min. Detailed investigations by using infrared spectroscopy, scanning electron microscopy, powder X-ray diffraction, elemental analysis, adsorption, thermogravimetric analysis, and solid-state NMR revealed that magnesium rich LDH has chemical and structural features that promote the exchange of carbonate anions. Our results indicate that the unique interactions between LDH and CO 2 can be optimized simply by varying the chemical composition of LDH, implying that LDH is a promising material for CO 2 storage and/or separation.
Hydrocalumite (½Ca 2 AlðOHÞ 6 2 CO 3 · mH 2 O) was synthesized by precipitation and thermally activated at 300 and 550°C. Its CO 2 chemisorption capacity was evaluated and compared with that of calcium oxide (CaO). Initial thermal analyses showed that CaAl-550 sample has better properties as CO 2 sorbent than CaO, evaluated under similar conditions. It was determined that both materials (CaAl-550 and CaO) have similar kinetic behavior, and the presence of Ca 12 Al 14 O 33 on the CaAl-550 sample did not reduce or interfere with the CO 2 capture. Moreover, when the CO 2 absorption-desorption cyclability was analyzed, the CaAl-550 sample apparently possessed better CO 2 capture efficiency and thermal stability than CaO. In fact, different characterization analyses (nuclear magnetic resonance and scanning electron microscopy) suggest that CO 2 capture efficiency and thermal stability observed on the CaAl-550 sample can be attributed to the aluminum presence, as Ca 12 Al 14 O 33 .
Reconstruction Effects on Surface Properties of Co/Mg/Al Layered Double Hydroxide
Materials Science, 2017
Layered double hydroxides having different cationic (Mg 2+ , Co 2+ , Al 3+) composition were successfully synthesized by the low supersaturation method. The samples were thermally decomposed and reconstructed using water and nitrate media at different temperatures. X-ray powder diffraction analysis, X-ray fluorescence analysis, thermogravimetry and BET/BJH methods were used to investigate the differences between the directly obtained layered materials and those after the reconstruction process.
Chemical Engineering Science, 2002
Several in situ techniques have been used to investigate the thermal evolution of the structure of a Mg-Al-CO3 layered double hydroxide (LDH) under an inert atmosphere. Based on the results of the study, a model is proposed to describe the structural evolution of the Mg-Al-CO3 LDH. According to this model as the temperature is increased, loosely held interlayer water is lost in the temperature range of 70 -190 • C, but the LDH structure still remains intact. The OH − group, likely in a Al-(OH) -Mg conÿguration, begins to disappear at 190 • C, and is completely lost at 280 • C; a gradual transformation of the LDH structure begins in the same range of temperatures. The OH − group, likely in a Mg-(OH) -Mg conÿguration, begins to disappear at 280 • C and is completely lost at 405 • C; a gradual degradation of the LDH structure is observed in the same range. Although some CO 2− 3 loss is observed at lower temperatures, its substantial loss begins at 410
The journal of physical chemistry. A, 2011
The carbonation process of a calcined Mg-Al layered double hydroxide (LDH) was systematically analyzed at low temperatures, varying the relative humidity. Qualitative and quantitative experiments were performed. In a first set of experiments, the relative humidity was varied while maintaining a constant temperature. Characterization of the rehydrated products by thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR) and solid-state NMR revealed that the samples did not recover the LDH structure; instead hydrated MgCO(3) was produced. The results were compared with similar experiments performed on magnesium oxide for comparison purposes. Then, in the second set of experiments, a kinetic analysis was performed. The results showed that the highest CO(2) capture was obtained at 50 °C and 70% of relative humidity, with a CO(2) absorption capacity of 2.13 mmol/g.
CO2 adsorption and desorption properties of calcined layered double hydroxides
Journal of Thermal Analysis and Calorimetry, 2018
In this study, the CO 2 adsorption properties of different metal mixed oxides (MMO) obtained by calcination of different layered double hydroxides (LDH) are addressed. Four types of LDH, with composition M 2þ 1Àx M 3þ x OH ð Þ 2  à xþ Á½A nÀ x=n Á mH 2 O xÀ ; where M 2? =Zn, Cu, Ni, M 3? =Al, x = 0.33, n = 2 and A = CO 3 2-, were studied by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and thermogravimetric analysis coupled with mass spectrometry (TG-MS). Different thermal behaviors upon heating were observed depending on the LDH composition, resulting in the exploitation of different calcination temperatures to convert LDH into mixed metal oxides (MMO). MMO were exposed to ambient air or pure carbon dioxide atmosphere to evaluate CO 2 adsorption properties. Aging in ambient condition leads to adsorption of both CO 2 and water, from ambient moisture, with variable ratios depending on the MMO composition. Furthermore, all the MMO were demonstrated to be able to adsorb CO 2 in pure gas stream, in the absence of moisture. In both ambient and pure CO 2 conditions, the performance of MMO is strongly dependent on the metal composition of MMO. In particular, the presence of Cu in the structure turned out to be beneficial in terms of adsorption capacity, with a maximum mass gain for CuAl MMO of 4 and 15% in pure CO 2 and in atmospheric conditions, respectively.