(254h) Formation of GaN in Chabazite By Scavenging Framework Gallium

Beyond its significance in optoelectronics and semiconductors, gallium nitride (GaN) has gained attention in the field of catalysis owing to its discovery as a thermal catalyst for non-oxidative aromatization of alkanes. In this presentation, we discuss recent investigations of a new in situ method for generating extra-framework GaN encapsulated within the small pores of a Ga-chabazite (or Ga-CHA) zeolite. This is accomplished by the concerted demetallation of framework Ga in the presence of a nitrogen source (e.g., NH₃ gas) at high temperature. This method involves nitridation through the decomposition of ammonia with concomitant extraction of framework gallium, forming a GaN within the cha cages. This approach avoids post-synthesis impregnation with GaN particles, which is challenging to accomplish with steric effects imposed by small-pore zeolites. GaN formation was validated by multiple techniques that include: (1) a visible shift in the color of extracted powders from white (H-Ga-CHA) to yellow ([GaN]-Ga-CHA), intensifying with increases in Ga content; (2) powder X-ray diffraction (PXRD), which confirmed peak shifts of framework Ga to those of GaN after treatment with ammonia; and (3) X-ray photoelectron spectroscopy (XPS), which shows an increase in extra-framework GaN with higher Ga content. A series of [GaN]-Ga-CHA catalysts were prepared with different Ga content and their performance as catalysts in the ethane dehydrogenation (EDH) reaction was tested. Our findings reveal that the parent sample, H-Ga-CHA, containing predominantly framework Ga, exhibits low activity. Conversely, the in situ generation of [Ga]-Ga-CHA containing extra-framework GaN exhibits higher initial rates of ethylene formation. Collectively, this study is a proof of principle for the method of scavenging metals in zeolites frameworks to generate multifunctional catalysts in situ, thereby circumventing the difficulties associated with encapsulating large active sites in small pores of zeolite catalysts.