Transformation of propane into aromatic hydrocarbons over ZSM-5 zeolites

Transformation of propane into aromatic hydrocarbons over H-ZSM-5 and Ga-exchanged ZSM-5 (Ga-ZSM-5) zeolites were studied. Over H-ZSM-5, the mode of activation of propane changes with the conversion level of propane. Thus, propane undergoes cracking into methane and ethylene by its interaction with acidic hydroxyl groups at low conversion levels, while, at higher conversion levels, it undergoes hydride abstraction by its interaction with carbenium ions. Lower olefins thus formed give oligomerized products, which in turn, undergo dehydrogenation to give aromatic hydrocarbons. The loading of Ga3+ of ZSM-5 greatly improves the selectivity to aromatics as well as the total conversion of propane. Thus, a selectivity of 71% was obtained at 500 °C. Ga species are quite effective for the transformation of intermediate products (i.e., lower olefins) into aromatic compounds, while they have no direct role in propane activation.