Oxidative Dehydrogenation of Propane into Propene over Chromium Oxides

A series of chromium oxides (CrOx) were prepared using the sol–gel method for the oxidative dehydrogenation of propane into propene (ODHP). After calcination at temperatures ranging from 300 °C to 600 °C, the obtained nanopowders were comprehensively characterized. X-ray diffraction (XRD) results showed an increase in crystallite size with annealing temperature, whereas Brunauer–Emmett–Teller (BET) analysis disclosed a decreasing tendency of specific surface area. Scanning electron microscopy (SEM) results disclosed spherical and smooth shapes with an agglomeration of small fine particles. X-ray photoelectron spectroscopy (XPS) deconvolution revealed a decrement in lattice oxygen, OLat/OAds, and Cr6+/Cr3+ with annealing temperature. Raman and ultraviolet–visible light (UV-vis) spectra reported the presence of isolated and polymeric Cr6+ oxides and the increment of the bandgap energy with the increase of the calcination temperature. Cr-300 exhibited the best catalytic activity due to the smallest crystallite grain size and bandgap energy, the highest OLat/OAds, Cr6+/Cr3+, and OLat with the largest surface specific area. Furthermore, after a stability test of 100 h, all catalysts maintained >90% propane conversion, and Cr-300 was the most stable. The DFT calculations revealed that the Cr–O site is the leading active site in the promotion of ODHP. The high stability and performance of Cr-300 catalyst regarding ODHP could pave the way for further industrial applications.

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