CaO‐Based CO₂ Sorbents Effectively Stabilized by Metal Oxides

Abstract

Calcium looping (i.e., CO2 capture by CaO) is a promising second‐generation CO2 capture technology. CaO, derived from naturally occurring limestone, offers an inexpensive solution, but due to the harsh operating conditions of the process, limestone‐derived sorbents undergo a rapid capacity decay induced by the sintering of CaCO3. Here, we report a Pechini method to synthesize cyclically stable, CaO‐based CO2 sorbents with a high CO2 uptake capacity. The sorbents synthesized feature compositional homogeneity in combination with a nanostructured and highly porous morphology. The presence of a single (Al2O3 or Y2O3) or bimetal oxide (Al2O3‐Y2O3) provides cyclic stability, except for MgO which undergoes a significant increase in its particle size with the cycle number. We also demonstrate a direct relationship between the CO2 uptake and the morphology of the synthesized sorbents. After 30 cycles of calcination and carbonation, the best performing sorbent, containing an equimolar mixture of Al2O3 and Y2O3, exhibits a CO2 uptake capacity of 8.7 mmol CO2 g−1 sorbent, which is approximately 360 % higher than that of the reference limestone.

CO2 Uptake and Cyclic Stability of MgO-Based CO2 Sorbents Promoted with Alkali Metal Nitrates and Their Eutectic Mixtures

“…Indeed, deactivation in the range of 30-60% of the initial uptake has been reported 23,33,34 . Previous studies have attributed the decay in the CO2 uptake of MgO largely to sintering, however without providing experimental evidence 23,27,28 , assuming instead an analogy to the behavior of CaO-based sorbents 10,11,37,38 . Only recently, Zhao et al 31 provided evidence that the surface area and pore size of a NaNO3-promoted mesoporous MgO sorbent decreased after carbonation and subsequent regeneration.…”

Optimization of the structural characteristics of CaO and its effective stabilization yield high-capacity CO2 sorbents

“…The effective incorporation of a stabilizer into a porous CaO structure relies on two key aspects: (i) its homogeneous distribution within the CaO matrix on a nanometer or even atomic level, and (ii) the minimization of its quantity to maintain a high fraction of CaO in the material. However, it is also worth noting that several reports have indicated that the presence of a stabilizer per se is not sufficient to realize sorbents featuring both cyclic stability and a high CO 2 uptake capacity 12 , 19 , 25 . Indeed, also the structure of CaO has to meet certain characteristics, such as being composed of small building blocks typically in the form of nanometer-sized particles/grains 11 , 20 , 25 .…”

Adsorption Characteristics of Gas Molecules (H2O, CO2, CO, CH4, and H2) on CaO-Based Catalysts during Biomass Thermal Conversion with in Situ CO2 Capture

“…The in situ CO 2 capture is the core process for the research and development of this technology because it can effectively remove CO 2 , adjust the gas composition, and improve the quality of pyrolysis gas [6][7][8][9][10]. In order to enhance CO 2 adsorption capacity, CaO-based catalysts have been studied in biomass thermochemical conversion with in situ CO 2 capture [1][2][3][11][12][13][14][15][16]. Naeem et al [11] utilized the Pechini method to synthesize Al 2 O 3 -, MgO-, Y 2 O 3 -stabilized, and CaO-based CO 2 sorbents.…”

“…In order to enhance CO 2 adsorption capacity, CaO-based catalysts have been studied in biomass thermochemical conversion with in situ CO 2 capture [1][2][3][11][12][13][14][15][16]. Naeem et al [11] utilized the Pechini method to synthesize Al 2 O 3 -, MgO-, Y 2 O 3 -stabilized, and CaO-based CO 2 sorbents. The experimental results exhibited high CO 2 uptake with improved cyclic stability and superior performance when compared to the performance of limestone-derived benchmark sorbent.…”