CO₂-Induced Gate-Opening Adsorption on a Chabazite/Phillipsite Composite Zeolite Transformed from a Faujasite Zeolite Using Organic Structure-Directing Agent-Free Steam-Assisted Conversion

Organic structure-directing agent-free steam-assisted conversion and Cs + ion exchange were used to transform the faujasite (FAU)-type zeolite to the Cs + -type chabazite/phillipsite (CHA/PHI) composite zeolite. Compared with the pure PHI-type zeolite, the Cs + -type CHA/PHI zeolite showed gate-opening CO 2 adsorption behavior and good thermal stability. In situ powder X-ray diffraction (PXRD) of the CO 2 adsorption was measured to elucidate the mechanism for the gate-opening adsorption on the CHA/PHI zeolite. The Na + -type CHA/PHI zeolite did not show such adsorption behavior, and the PXRD pattern of the Na + -type CHA/PHI zeolite did not change with increasing CO 2 partial pressure, which suggests that this unique adsorption behavior was caused by the PHI framework transition or Cs + ions moving in both the CHA and PHI frameworks. Furthermore, in situ Fourier-transform infrared spectra of CO 2 adsorption and CO 2 breakthrough measurement on the Cs + -type CHA/PHI zeolite suggest that the CHA and PHI frameworks in the CHA/PHI zeolite shared eight-membered-ring windows and that CO 2 molecules could easily diffuse from a CHA cage to a PHI framework. The ideal adsorbed solution theory was used to calculate the CO 2 /N 2 separation selectivity for the Cs + -type CHA/PHI zeolite. At 298 and 318 K, the Cs + -type CHA/PHI composite zeolite showed a high CO 2 /N 2 separation coefficient of >10,000 compared with other zeolites with high CO 2 adsorption capacity. Furthermore, the CO 2 working capacity was calculated for the Cs + -type CHA/PHI zeolite in both the pressure- and temperature-swing processes, and the results showed that the CHA/PHI composite zeolite could selectively separate CO 2 from the CO 2 /N 2 gas mixtures released from power generation plants operating using these processes.