Investigation of MoO_x/Al₂O₃ under cyclic operation for oxidative and non-oxidative dehydrogenation of propane

Matam, Santhosh K., Moffat, Caitlin, Hellier, Pip, Bowker, Michael, Silverwood, Ian P., Catlow, C. Richard A., David Jackson, S., Craswell, James, Wells, Peter P., Parker, Stewart F. and Gibson, Emma K. (2020) Investigation of MoO_x/Al₂O₃ under cyclic operation for oxidative and non-oxidative dehydrogenation of propane. Catalysts, 10 (12), 1-13, [1370]. (doi:10.3390/catal10121370).

Abstract

A MoO_x/Al₂O₃ catalyst was synthesised and tested for oxidative (ODP) and non-oxidative (DP) dehydrogenation of propane in a reaction cycle of ODP followed by DP and a second ODP run. Characterisation results show that the fresh catalyst contains highly dispersed Mo oxide species in the +6 oxidation state with tetrahedral coordination as [Mo^VIO₄]²⁻ moieties. In situ X-ray Absorption Spectroscopy (XAS) shows that [Mo^VIO₄]²⁻ is present during the first ODP run of the reaction cycle and is reduced to Mo^IVO₂ in the following DP run. The reduced species are partly re-oxidised in the subsequent second ODP run of the reaction cycle. The partly re-oxidised species exhibit oxidation and coordination states that are lower than 6 but higher than 4 and are referred to as Mo_xO_y. These species significantly improved propene formation (relatively 27% higher) in the second ODP run at similar propane conversion activity. Accordingly, the initial tetrahedral [Mo^VIO₄]²⁻ present during the first ODP run of the reaction cycle is active for propane conversion; however, it is unselective for propene. The reduced Mo^IVO₂ species are relatively less active and selective for DP. It is suggested that the Mo_xO_y species generated by the reaction cycle are active and selective for ODP. The vibrational spectroscopic data indicate that the retained surface species are amorphous carbon deposits with a higher proportion of aromatic/olefinic like species.

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Contributors

Author: James Craswell

Author: Peter P. Wells

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