Evacuation-Induced Desorption of an OSDA from GaPO4-LTA as an Alternative to Calcination: Microporosity and Framework
Tetsuya Kodaira1, Yoshihiro Kamimura1, Akira Endo1
1National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, Ibaraki305-8565, Japan.
Abstract:
Open-framework gallium phosphates (GaPO4) are generally considered unstable, often collapsing during calcination for the removal of organic structure-directing agents (OSDAs). We developed an effective and simple method to remove dipropylamine (DPA), an OSDA, from GaPO4-LTA (a gallium phosphate with the LTA-type framework) by heating it at 623 K in vacuo, thus avoiding combustion. Following this proposed methodology, the LTA-type framework persisted successfully under an inert atmosphere, although it exhibited signs of strain. Porosity after this treatment was characterized by Ar adsorption-desorption measurements. The isotherms showed Type I curves without hysteresis, characteristic of purely microporous materials. The material exhibited a Brunauer-Emmett-Teller specific area of 428 m2/g and a micropore volume of 0.150 cm3/g. These values suggest the presence of approximately 30 wt % nonporous phase within the sample. GaPO4-LTA exhibited weaker attractive interactions with Ar and N2 adsorbates compared to LTA-type aluminosilicates (Ca-form A and Na-form ZK-4). Thermogravimetry-mass spectrometry revealed that DPA desorbs intact, offering a new route for the recovery and reuse of OSDAs.
