Ammoxidation of Ethane to Acetonitrile and Ethylene: Reaction Transient Analysis for the Co/HZSM-5 Catalyst

[Image: see text] Ethane ammoxidation to acetonitrile and ethylene over the Co/HZSM-5 catalysts was revisited based on both transient and steady-state performance evaluation to elucidate the structure/reactivity relationships. We suggested that the exchanged Co(2+) cation encapsulated in the zeolite favors the formation of acetonitrile and ethylene, whereas nanosized cobalt oxide particles without close proximity with the HZSM-5 only favor CO(2) formation. Excess Brønsted acid sites of the zeolites may act as a reservoir for NH(3), which inhibits the CO(2) formation through the NH(3)-mediated oxidative dehydrogenation mechanism. According to the transient kinetic analysis, the time constants τ from the back-transient decay for NH(3) and CO(2) are both 7.7 min, which decreased to 2.7 min for acetonitrile and further decreased to 3–4 s for ethane, ethylene, and O(2). Assuming first-order reaction kinetics, the rate constants for the formation of acetonitrile and CO(2) are 0.37 and 0.13 min(–1), respectively, from their corresponding reactive intermediates.