Hydrogen formation during dehydrogenation of C2–C4 alkanes in the presence of oxygen: oxidative or non-oxidative?

The main advantage of oxidative dehydrogenation (ODH) of light alkanes over non-oxidative dehydrogenation (NODH) is the absence of thermodynamic limitations for olefin per-pass yield. It is shown, however, that considerable amounts of molecular hydrogen are formed (in some cases—equivalent to the amounts of produced olefin or even higher) over typical ODH oxide catalysts when C2–C4 alkanes and oxygen are present in the feed gas. The analysis of product yields as functions of reaction parameters (temperature, flow rate, hydrocarbon-to-oxygen ratio) over a series of V- and Sb-containing ODH catalysts has shown that the main kinetic features cannot be described in the framework of a single mechanism. NODH, coking and free-radical oxidation are considered as the most important H2 formation pathways. The ways to optimize the olefin production depending on the predominant mechanism of hydrogen formation over a particular catalyst are discussed.