Effects of coke formation on the acidity of ZSM-5

The identification of various Ga species in Ga-zeolites plays a crucial role in the development of appropriate catalysts because catalytic performance depends significantly on the state of Ga. This proves to be challenging, however, because of the limited pool of conventional characterization techniques, and the diversity of chemically possible Ga conformations. Here, through investigation on three characteristic Ga-zeolites with distinct states of Ga, we demonstrate that qualitative information on the nature of Ga in these catalysts could be derived by a facile HCl treatment, based on the ability of HCl to preferably eliminate the Ga species that share weaker interaction with the zeolite. Furthermore, the treatment was able to successfully tailor the Ga species in certain Ga-zeolites by selectively retaining the most desirable species for propane activation, leading to a considerable enhancement in propane aromatization performance.