(544fr) Structure/Redox/Reactivity Properties of Dispersed Vanadium Species on TiO2 for the Oxidative Dehydrogenation of Propane with CO2

Propylene is unambiguously one of the prominent feedstock in a wide range of applications in chemical industry. Since the recent shale gas revolution¹, there is large demand of propylene which in turn expedites academic and industrial research interest to develop technologies for ‘on-purpose' production. Direct (DH) and oxidative (ODH) dehydrogenation of propane are currently utilized with the former to be the main source of propylene at the industrial level. Due to the energy consumption under DH conditions, the ODH provides a better alternative due to its exothermicity. However the presence of O₂ limits olefin selectivity due to further combustion reactions. Meanwhile, CO₂ proves to be a mild and effective oxidant in the reaction process². Although the choice of CO₂ as oxidant has proven to be beneficial on the overall olefin selectivity, questions regarding the mechanism over supported metal oxides (which are the dominant catalytic materials) remain unsettled.

In this work, we aim at developing a model system based on vanadium supported catalysts in order to reveal structural-activity relationships via in-situ Raman spectroscopy for the ODH of light alkanes using CO₂. In the first step, we investigate the temperature – dependent evolution of dispersed vanadium species on different metal oxide supports with the ultimate goal to unravel the temperature range that different sites exist on the catalyst surface. We show that above 573K, the vanadium species maintain a mono-oxo configuration in monomeric units. At higher loadings, small crystals of V₂O₅ observed which are probably getting redispersed upon air treatment at elevated temperatures. The redox behavior of these materials at different temperature ranges as revealed by coupling Raman spectroscopic measurements with labeled C¹⁸O₂ will be also discussed to pin down the reoxidation mechanisms of V₂O₅/Me_xO_y in ODH. Relevant catalytic performance data will be presented as an attempt to close the structural-activity relationship loop.

Reference:

1. Bruijnincx, P. C.; Weckhuysen, B. M., Angew Chem Int Ed Engl 2013, 52 (46), 11980-7.
2. Zhaorigetu, B.; Kieffer, R.; Hindermann, J. P., Surf. Sci. Catal. 1996, 101, 1049-1058.