Nb2O5 as a radical modulator during oxidative dehydrogenation and as a Lewis acid promoter in CO2 assisted dehydrogenation of octane over confined 2D engineered NiO–Nb2O5–Al2O3

Abstract

Mesoporous 2D NiO–Nb₂O₅–Al₂O₃ nanorods (and, for the first time, template free ordered mesoporous alumina (OMA)) were prepared via glycol-thermal synthesis for the direct transformation of octane to octenes via CO₂ assisted dehydrogenation (CO₂-DH). Nb₂O₅ addition modified the confinement effect and metal support interaction between NiO and alumina. The catalyst with an optimal confinement effect between all metal oxides in the nanorod composite provided 6% steady state n-octane conversion with ∼80% selectivity to C₈ aromatics and olefins. Characterisation data of the fresh and used catalysts, obtained from CO₂-DH as well as reverse water gas shift (RWGS) reactions, was used to identify the possible mechanism over this catalyst. Nb₂O₅ addition to the NiO catalyst facilitates CO₂-DH by promoting RWGS and reverse-Boudouard reactions by forming O* from CO₂ dissociation. Also, application of these materials for the oxidative dehydrogenation of n-octane and propane using air revealed the contribution of a radical mechanism.