https://doi.org/10.1016/j.jmrt.2020.02.061
“The Na form X zeolite was synthesized by hydrothermal method using RHA as the silica source. The chemical composition ratio of initial gel was Na2O:Al2O3:SiO2:H2O = 5.5:1:4:190. Typically, two identical 90 ml aqueous solutions containing 9.48 g of NaOH were prepared and defined as A and B, respectively. Subsequently, 8.63 g of sodium aluminate was added to the solution A, and 12.65 g of silica was added to the solution B. The B solution was then quickly added to solution A with vigorous stirring until the solution was homogeneous. The mixed gel was transferred to a polypropylene bottle and heated to 90 °C for 24 h. The product was finally filtered, washed with deionized water and ethanol, and completely dried in an oven.
The La and Ce form X zeolites were modified by ion-exchange. One gram of NaX was added to a 0.2 M solution of LaCl3·7H2O and CeCl3·7H2O, respectively. It was then stirred at 60 °C for 12 h and repeated three more times using the fresh solution. The products were finally filtered, washed, dried and defined as LaNaX and CeNaX. Similar to the procedure above, NaX was impregnated with a LiCl·H2O solution prior to ion-exchange of La3+ and Ce3+. These two modified products were defined as LaLiX and CeLiX.”