CO2 Capture by Na2TeO4: Structure of Na2- xH xTeO4 and Kinetic Aspects.

ABSTRACT

ß-Na2TeO4 is able to trap CO2 in a humid atmosphere due to a partial Na+/H+ exchange and the formation of NaHCO3. The RT powder X-ray diffraction pattern of the resulting Na2- xH xTeO4 shows broad and narrow hkl lines preventing the structural study. We show by the DIFFaX program that Na+/H+ exchange is topotactic since the structure, as in the mother form, consists of [TeO4] n2 n- chains of TeO6 octahedra. We also show that the broadening of some hkl lines is due to stacking faults which result from the weakness of H-O···H bonds connecting the [TeO4] n2 n- chains. Upon heating, a progressive structural organization takes place which has been followed by powder X-ray diffraction, Raman, and NMR spectroscopies. Around 300 °C, a well organized structure can be described from powder X-ray diffraction refinements in the monoclinic P21/ n space group while ab initio computations allowed location of the hydrogen atoms with satisfactory H-O bonds. In addition, we present the CO2 sorption/desorption by Na2TeO4 and compare its performance to that of Na2SiO3. Finally, the existence of a Na2- xLi xTeO4 solid solution (0 ≤ x ≤ 0.9) is evidenced, and we show that the presence of lithium in the structure leads to the disappearance of the structural transition observed for ß-Na2TeO4 and to a progressive decrease of the CO2 capture ability.