Characterization of Zn promoter in ZnO/HZSM-5 catalyst for propane aromatization

The ZnO/HZSM-5 catalyst for propane aromatization was prepared by mechanically mixing ZnO with HZSM-5. XRD and TEM investigations demonstrated that ZnO located on the external surface of the zeolite crystals can migrate from outside to inside of the channels during calcination, and zinc species are highly dispersed. The migration of zinc species was confirmed by a back-exchange experiment in which the zinc-containing samples were treated by a dilute hydrochloric acid solution, and the experimental results showed that the interaction between zinc species and zeolite surface occurred. The catalyst was characterized. by XPS and IR spectroscopy. It can be seen that only small part of ZnO in the ZnO/HZSM-5 catalyst reacts with the protons of HZSM-5 Bronsted acid sites through solid state ion exchange. The conversion of propane to aromatics over the ZnO/HZSM-5 catalyst was evaluated in a fixed-bed continuous flow reactor and the results indicated that the aromatic selectivity can be improved significantly by introducing promoter zinc by mechanically mixing ZnO with HZSM-5.