Effect of O2, CO2 and N2O on Ni–Mo/Al2O3 catalyst oxygen mobility in n-butane activation and conversion to 1, 3-butadiene. Issue 15 (5th July 2017)

• Record Type: Journal Article
• Authors: Dasireddy, Venkata D. B. C.; Huš, Matej; Likozar, Blaž
• Is Part Of: Catalysis science & technology. Volume 7:Issue 15(2017)
• Page Start: 3291
• Page End: 3302
• Publication Date: 2017-07-05
• Subjects: Catalysis -- Periodicals; 541.395
• DOI: 10.1039/c7cy01033h
• Languages: English
• ISSNs: 2044-4753

Abstract

Abstract : A commercial heterogeneous Ni–Mo/Al2 O3 catalyst was tested for the oxidative dehydrogenation (ODH) reaction of n -butane with different oxidant species: O2, CO2 and N2 O. Abstract : A commercial heterogeneous Ni–Mo/Al2 O3 catalyst was tested for the oxidative dehydrogenation (ODH) reaction of n -butane with different oxidant species: O2, CO2 and N2 O. The effect of the lattice oxygen mobility and storage in Ni–Mo/Al2 O3 on catalytic conversion performance was investigated. Experiments indicated that a high O2 -storage/release is beneficial for activity, however at the expense of selectivity. A significant amount of butadiene with no oxygenated compound products was formed upon using carbon dioxide and nitrous oxide, while O2 favoured the formation of cracked hydrocarbon chains and CO x . The highest turnover yield to 1, 3-butadiene was achieved at an oxidant-to-butane molar ratio of 2 : 1 at temperatures of 350 °C and 450 °C. With CO2, significant amounts of hydrogen and carbon monoxide have evolved due to a parallel reforming pathway. Partial nickel/molybdenum oxidation was also observed under CO2 and N2 O atmospheres. TPR revealed the transformation of the high valence oxides into structurally distinct metal sub-oxides. In TPRO, three distinct peaks were visible and ascribed to surface oxygen sites and two framework positions. With N2 O, these peaks shifted towards a lower temperature region, indicating better diffusional accessibility and easier bulk-to-surface migration. XRD revealed the presence of an α-NiMoO4 active phase, which was used in DFT modelling as a (110) plane. Theoretical ab initio calculations elucidated fundamentally different reactive chemical intermediates when using CO2 /N2 O or O2 as the oxidant. The former molecules promote Mo atom oxygen termination, while in an O2 environment, Ni is also oxygenated. Consequently, CO2 and N2 O selectively dehydrogenate C4 H10 through serial hydrogen abstraction: butane → butyl → 1-butene → 1-butene-3-nyl → butadiene. With O2, butane is firstly transformed into butanol and then to butanal, which are prone to subsequent C–C bond cleavage. The latter is mirrored in different mechanisms and rate-determining steps, which are essential for efficient butadiene monomer process productivity and the optimisation thereof.