Morphological investigations of nanostructured V2O5 over graphene used for the ODHP reaction: from synthesis to physiochemical evaluations

Abstract

Oxidative dehydrogenation of propane (ODHP) in a fixed-bed reactor over synthesized vanadia nanocatalysts was investigated physicochemically. Several vanadium pentoxide (V₂O₅) nanostructures including rod-, belt-, tube-, needle- and flower-like forms were successfully synthesized via reflux and hydrothermal processes utilizing different templates such as monoamines, diamines, aromatic and alcoholic amines. The morphologies of the obtained products were found to be sensitive to the types of templates used. Nanorods obtained were 1.4 μm in length and about 97 nm in width while the VO₂(B) nanotubes were of about 76 nm average diameter and up to 1.2 μm long. The diameters of the V₂O₅ nanotubes varied between 60 and 120 nm with lengths up to 5 μm. In this way, the as-synthesized vanadium nanostructures with amines doped on graphene with a 1 : 1 molar ratio of V : C were prepared both through reflux and hydrothermal methods. The surface morphologies were determined by scanning electron microscopy (SEM). The structure of the prepared samples was then characterized utilizing the XRD, BET/BJH, FTIR, UV-vis and TGA techniques. Amongst the materials investigated, the bulk catalyst of V₂O₅ prepared with dodecylamine and V₂O₅ synthesized by aniline on graphene was shown to be the most active catalyst for the ODHP reaction. The reactor test conditions of 450 °C, feed of C₃H₈/air molar ratio of 0.5 and total feed flow rate of 60 mL min⁻¹ over vanadium on graphene resulted in 53.93% selectivity for propylene at 47.02% propane conversion after 6 h, at the end of the reaction. It was revealed that under these conditions the cracking of propane or propylene along with CO_x formation as a side reaction occurred. Moreover, the effects of different reaction temperatures as well as the propane-to-air ratio on propane conversion and product selectivities on the two optimized catalysts designated as V-DDA and V-A-G were investigated.