(378b) Metal Exchanged Chabazite Zeolite for Non-Oxidative Dehydrogenation of Ethane

Ethylene is a very important building block in the chemical industry with a worldwide consumption of over 150 million tons per year. The most used approach of ethylene production is steam cracking of ethane and naphtha, a process that needs high temperature (>750 ^oC) and emits large amount of CO₂. An alternative is the non-oxidative catalytic dehydrogenation of alkanes, which is less energy intensive and likely to achieve higher selectivity as well as decrease the cost of product separation.

In this work, various metal ion (Ga, In, Mn) exchanged CHA zeolites with different Si/Al ratios were prepared via the incipient wet impregnation method and tested for non-oxidative ethane dehydrogenation. SSZ-13 is a chabazite (CHA)-type aluminosilicate zeolite with high Si/Al ratio often used to catalyze the methanol-to-olefins (MTO) reaction and the selective catalytic reduction of NO_x. The metal-exchanged CHA samples showed high ethylene selectivity and high stability compared to that of the acid H-CHA. The effect of Si/Al ratio of metal exchanged CHA samples on ethane dehydrogenation rates were also investigated: low and high Si/Al ratio samples showed lower rates and lower ethylene selectivity, respectively. Therefore, these studies highlight that optimal Si/Al ratio of metal exchanged CHA samples is required for high ethylene yield. We also observed that the pre-reduction temperature of metal exchanged CHA influences the measured rates and selectivity of non-oxidative ethane dehydrogenation. Based on in-situ FTIR measurements, we concluded that the formation of active sites varies with pre-reduction temperature of catalysts. Different exchanged metal ions were also compared, among which In-CHA delivered the highest ethylene selectivity and Mn-CHA delivered the lowest. This can be explained by their different electronic structure and active sites.