CO 2 -Induced Gate-Opening Adsorption on a Chabazite/Phillipsite Composite Zeolite Transformed from a Faujasite Zeolite Using Organic Structure-Directing Agent-Free Steam-Assisted Conversion

• Published in: ACS applied materials & interfaces 2023-08, Vol.15 (32), p.38463-38473
• Main Authors: Higuchi, Yuto, Miyagawa, Sana, Oumi, Yasunori, Inagaki, Satoshi, Tanaka, Shunsuke
• Format: Article
• Language: English
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.3c07313

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 adsorption behavior and good thermal stability. In situ powder X-ray diffraction (PXRD) of the CO 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 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 adsorption and CO 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 molecules could easily diffuse from a CHA cage to a PHI framework. The ideal adsorbed solution theory was used to calculate the CO /N 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 /N separation coefficient of >10,000 compared with other zeolites with high CO adsorption capacity. Furthermore, the CO 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 from the CO /N gas mixtures released from power generation plants operating using these processes.