Abstract
The effect of O 2 and N 2O on alkane reactivity and olefin selectivity in the oxidative dehydrogenation of ethane, propane, n-butane, and iso-butane over highly dispersed VO x species (0.79 V/nm 2) supported on MCM-41 has been systematically investigated. For all the reactions studied, olefin selectivity was significantly improved upon replacing O 2 with N 2O. This is due to suppressing CO x formation in the presence of N 2O. The most significant improving effect of N 2O was observed for iso-butane dehydrogenation: S(iso-butene) was ca. 67% at X(iso-butane) of 25%. Possible origins of the superior performance of N 2O were derived from transient experiments using 18O 2 traces. 18O 16O species were detected in 18O 2 and 18O 2–C 3H 8 transient experiments indicating reversible oxygen chemisorption. In the presence of alkanes, the isotopic heteroexchange of O 2 strongly increased. Based on the distribution of labeled oxygen in CO x and in O 2 as well as on the increased CO x formation in sequential O 2–C 3H 8 experiments, it is suggested that non-lattice oxygen species (possibly of a bi-atomic nature) originating from O 2 are non-selective ones and responsible for CO x formation. These species are not formed from N 2O.
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