Characterization of the NiSO4 site on a NiSO4-ReOx/γ-Al2O3 catalyst for tandem conversion of ethylene to propylene

A series of NiSO4-ReOx/Al2O3 catalysts were synthesized by a co-impregnation method, tested in the conversion of ethylene to propylene at mild conditions, and thoroughly characterized by different spectroscopy techniques. In particular, the attention was focused on the NiSO4 function, which is directly involved in ethylene conversion to 2-butylene, but also drives the catalyst deactivation. Results shows that the sulfate anions increase the surface acidity of alumina, and simultaneously influence the electronic properties of the Ni sites. Indeed, thermal activation of the catalyst promotes the formation of covalent bonds between the sulfate anions and the Ni2+ or Al3+ cations, while keeping constant the + 2 oxidation state of the Ni sites. Studying the initial steps of the ETP reaction reveals the primary acid-catalyzed formation of branched oligomers. Catalyst deactivation could be due to formation and adsorption of long-chain oligomers, or less interaction of sulfate anions with Ni ions.