Formation of acetonitrile and ethylene from activation of ethane over cobalt-exchanged aluminosilicates: Active sites and reaction pathways

Cobalt-exchanged ZSM-5 catalyzes the ammoxidation of ethane (2 CH + 3 O + 2 NH → 2 CHCN + 6 HO), yet the active form of cobalt, the role of the Brønsted acidic zeolite, and the reaction pathways remain elusive. Comparisons of rates and selectivities of reactions at distinctive cobalt sites (Co at Al pair sites (CoZ), CoO, cobalt phyllosilicate, and cobalt aluminate) suggest sites that form from CoZ provide the greatest rates and selectivities for CHCN and CH formation. Significantly, we revealed a large fraction of CHCN appears to form directly through a trimolecular reaction at cobalt ions without desorption of intermediates. In parallel, a more conventional sequential pathway dehydrogenates CH, aminates CH, and oxidatively dehydrogenates CHNH to produce CHCN. Combined rate measurements with temperature programmed reactions and infrared spectra demonstrate that O-derived intermediates at cobalt ions initiate both reaction sequences by abstracting H-atom from CH.