The effect of the Li:Na molar ratio on the structural and sorption properties of mixed zirconates for CO2 capture at high temperature

Abstract

Different Li2ZrO3-Na2ZrO3 based sorbents were synthesized by the wet impregnation of a zirconia nanoparticle suspension with a lithium carbonate solution. The solids were characterized by X-ray diffraction, Raman spectroscopy, Scanning Electron Microscopy and X-ray photoelectron spectroscopy, while sorption properties were studied by thermogravimetric measurements carried out at different CO2 partial pressures. The stability experiments were carried out in a thermal programmed desorption system through 20 consecutive capture/desorption cycles. The Li-Na zirconate based-sorbents developed presented capture capacities between 0.187 and 0.211gCO2gmat-1, which represented 80-90% of their theoretical maximum capacity, and fast reaction kinetics even at low CO2 partial pressure equal to 0.1bar. The sorption properties depended on the Li2ZrO3/Na2ZrO3 ratio, which in turn depended on the Li and Na nominal content. In addition, faster desorption rates were obtained as the Li nominal contents increased. Moreover, the presence of Li in the sorbent could enhance the Na2CO3 decomposition, making these processes more efficient. Finally, the evolution of the solid and gaseous species was monitored by operando Raman spectroscopy.