VOx-Nb/La-γAl2O3 catalysts for oxidative dehydrogenation of ethane to ethylene

Abstract

The present study deals with oxidative dehydrogenation (ODH) of ethane to ethylene in absence of gas phase oxygen using VOx-Nb/La-γAl2O3 catalysts. In catalyst formulation, La is used to modify γ-Al2O3, stabilizing its bulk phase transformation. Nb is introduced as a promoter of VOx species. The prepared catalysts are characterized using various physicochemical techniques in order to demonstrate reducibility, oxygen carrying capacity, stability, metal–support interaction and acidity of the catalysts. TPR shows that VOx-Nb/La-γAl2O3 is highly active and stable over repeated reduction and oxidation cycles. XRD analysis indicates that VOx appears both as amorphous and crystalline phases. The presence of Nb minimizes the formation of crystalline V2O5 phases, which is undesirable for ODH reaction. The NH3-TPD analysis reveals an intermediate acidity of the VOx-Nb/La-γAl2O3 catalysts. NH3-TPD kinetics analysis shows that the addition of Nb increases the activation energy of ammonia desorption, suggesting increased V–support interaction and minimized V–V interaction. The ODH of ethane activity and stability is evaluated in a CREC fluidized riser simulator. The addition of Nb increased ethylene selectivity (85.7%) at 20.1% conversion comparatively at low reaction temperature (550°C) and short contact time. Thus, Nb enhances VOx isolation and forms a secondary oxide, resulting a superior catalyst activity.