Impact of Reaction Conditions on Product Distribution in Oxidative Dehydrogenation of Ethane over MoVNbTeO x Catalysts

Oxidative dehydrogenation of ethane over MoVNbTeOx catalysts offers a less carbon-intensive alternative to steam cracking. This work systematically examines the effects of catalyst bed inert dilution, reactor inlet pressure, molar steam-to-ethane feed ratio, coolant temperature, and weight hourly space velocity on ethane conversion and product distribution under both kinetically oriented, pseudo-isothermal conditions and process-relevant, non-isothermal conditions. Comparative tests confirm that trends observed under pseudo-isothermal conditions persist under process-relevant operating conditions, validating their industrial significance. Increasing the reactor inlet pressure promotes acetic acid formation, whereas a higher weight hourly space velocity favors ethylene selectivity by limiting secondary oxidation. An optimal steam-to-ethane ratio prevents catalyst deactivation while maintaining a high catalytic activity. The ethylene yield reaches a maximum at intermediate steam-to-ethane ratios, whereas the acetic acid yield increases continuously throughout the investigated range. Apparent activation energies determined from quasi-isothermal experiments further indicate a stronger temperature dependence of ethylene formation than that of acetic acid formation. Notably, the steam partial pressure in the wet product gas is the key parameter determining the molar product ratio of ethylene to that of acetic acid. It modulates the degree of coverage of the catalyst surface with water and thus shifts the balance between active sites for ethylene or acetic acid production, enabling a robust basis for the process control strategies. Additional experiments comparing ethane and ethylene oxidation highlight the role of ethylene in the formation of trace products methane and acetylene, detected at ethane conversions above 20%. These findings provide a mechanistic basis for tuning catalytic activity and product distribution through targeted adjustment of key process variables under industrially relevant conditions.