Yamaguchi Masakuni, Ichikawa Tomoyuki, Kojima Yoshitsugu, Miyaoka Hiroki
Natural Science Center for Basic Research and Development, Hiroshima University 1-3-1, Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8530, Japan.
Hydrolabo Inc., 3-10-31 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-0046, Japan.
ACS Omega. 2023 Jun 14;8(25):23051-23055. doi: 10.1021/acsomega.3c02354. eCollection 2023 Jun 27.
Zirconium phosphate-absorbed ammonia gas and the ammonia concentration (pressure) decreased to 2 ppm (ca. 20 Pa). However, it has not been clarified what the equilibrium pressure of zirconium phosphate is during ammonia gas ab/desorption. In this study, the equilibrium pressure of zirconium phosphate during ammonia ab/desorption was measured using cavity ring-down spectroscopy (CRDS). For ammonia-absorbed zirconium phosphate, a two-step equilibrium plateau pressure was observed during the ammonia desorption in gas. The value of the higher equilibrium plateau pressure at the desorption process was about 25 mPa at room temperature. If the standard entropy change (Δ) of the desorption process is assumed to be equal to the standard molar entropy of ammonia gas (192.77 J/mol/K), the standard enthalpy change (Δ) is about -95 kJ/mol. In addition, we observed hysteresis in zirconium phosphate at different equilibrium pressures during ammonia desorption and absorption. Finally, the CRDS system allows the ammonia equilibrium pressure of a material in the presence of water vapor equilibrium pressure, which cannot be measured by the Sievert-type method.
磷酸锆吸附氨气后，氨气浓度（压力）降至2 ppm（约20 Pa）。然而，磷酸锆在氨气吸附/解吸过程中的平衡压力尚未明确。在本研究中，使用光腔衰荡光谱法（CRDS）测量了磷酸锆在氨气吸附/解吸过程中的平衡压力。对于吸附了氨气的磷酸锆，在气体中氨气解吸过程中观察到了两步平衡平台压力。在室温下，解吸过程中较高平衡平台压力的值约为25 mPa。如果假设解吸过程的标准熵变（Δ）等于氨气的标准摩尔熵（192.77 J/mol/K），则标准焓变（Δ）约为 -95 kJ/mol。此外，我们在氨气解吸和吸附过程中观察到了磷酸锆在不同平衡压力下的滞后现象。最后，CRDS系统能够测量在存在水蒸气平衡压力的情况下材料的氨气平衡压力，而这是Sievert型方法无法测量的。
