Stable co-production of olefins and aromatics from ethane over Co2+-exchanged HZSM-5 zeolite

• Published in: Catalysis science & technology 2022-06, Vol.12 (11), p.3716-3726
• Main Authors: Hu, Wenjin, Xu, Yuebing, Xin, Jian, Liu, Bing, Jiang, Feng, Liu, Xiaohao
• Format: Article
• Language: English
• Subjects: Alkenes; Catalysts; Catalytic converters; Cleavage; Clusters; Cobalt oxides; Covalent bonds; Ethane; High temperature; Hydrogen bonds; Ion exchange; Paraffins; Pore size; Selectivity; Sintering (powder metallurgy); Zeolites
• ISSN: 2044-4753; 2044-4761
• DOI: 10.1039/d2cy00664b

Catalytic conversion of ethane into olefins and aromatics is an effective approach for the utilization of low-cost light paraffins. In this study, with the ion-exchange method, Co-exchanged HZSM-5 catalysts were prepared in which Co2+ ions were stably anchored at exchangeable sites, i.e., the Brønsted acid sites (–AlF–O(H)–SiF–), to form isolated extra-framework Co(ii) species (–AlF–O–Co(ii)–O–AlF–) in the zeolite. In comparison to the CoOx clusters mainly formed in an impregnated catalyst, the isolated Co(ii) species can withstand the reduction by H2 even at a high temperature, and are only active for C–H bond dissociation but almost inactive for the C–C bond scission, ensuring a high selectivity to the primary ethylene product without serious coke and CH4 formation. Further with appropriate acidity and right pore size of the employed HZSM-5 zeolite, the formed olefins can be partly converted into aromatics with a total selectivity to olefins and aromatics up to 83% under reaction conditions of 600 °C, 0.1 MPa, 3000 mL g−1 h−1 and 90%C2H6/10%N2. Fortunately, at a moderate temperature, the Co(ii) species did not suffer a significant de-anchoring from the zeolite framework to form sintered Co0 clusters, ensuring good catalyst stability.