Rare earth oxides doped NiO/[gamma]-Al sub(2)O sub(3) catalyst for oxidative dehydrogenation of cyclohexane

The effect of rare earth oxides (RE=Ce, La, Gd, and Dy) doping of alumina support in NiO/[gamma]-Al sub(2)O sub(3) system was investigated on its catalytic performance in oxidative dehydrogenation (ODH) of cyclohexane. The physicochemical properties of various samples were followed up through N sub(...

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Bibliographic Details
Published in:Journal of rare earths 2015-05, Vol.33 (6), p.611-618
Main Authors: AbdelDayem, Hany M, Faiz, M, Abdel-Samad, Hesham S, Hassan, Salah A
Format: Article
Language:English
Subjects:
Aluminum oxide
Catalysts
Dehydrogenation
Doping
Nickel
Rare earth metals
Surface chemistry
X-ray photoelectron spectroscopy
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Summary:The effect of rare earth oxides (RE=Ce, La, Gd, and Dy) doping of alumina support in NiO/[gamma]-Al sub(2)O sub(3) system was investigated on its catalytic performance in oxidative dehydrogenation (ODH) of cyclohexane. The physicochemical properties of various samples were followed up through N sub(2) physisorption, temperature programmed reduction (H sub(2)-TPR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and potentiometric acid-base titration techniques. In the parent NiO/[gamma]-Al sub(2)O sub(3) catalyst, Ni species were found to be strongly interacted with alumina surface. Addition of rare earth dopants to [gamma]-Al sub(2)O sub(3) in the catalyst system affected the nickel-alumina interaction and resulted in significant modifications in the catalytic performances in the ODH reaction. The results revealed the beneficial role of both La sub(2)O sub(3) and Gd sub(2)O sub(3) doping in enhancing the ODH catalytic activity and selectivity to cyclohexene. H sub(2)-TPR and XPS results indicated that majority of Ni species in NiO/La sub(2)O sub(3) modified [gamma]-Al sub(2)O sub(3) were more weakly interacted with La sub(2)O sub(3) and alumina whereas both NiO like species and nickel aluminate were present on the surface. Doping with cerium or dysprosium increased the nickel-support interaction and led to a decrease in surface nickel concentration. In case of doping with Ce, surface concentration of cerium oxide was higher than those of the other RE oxides; the doped catalyst reached its steady state activity faster than the other catalysts. The acid-base results suggested that RE metals were interacted most likely with acidic surface hydroxyl groups. The degree of nickel-alumina interaction decreased in the following order: LaAl>GdAl>CeAl>DyAl.
ISSN:1002-0721
DOI:10.1016/S1002-0721(14)60461-0