Evidence of Surface Properties by Isopropanol Decomposition Reaction and NH <sub>3</sub> ‐TPD over Ni−Fe Spinel Nanoparticles Prepared <i>via</i> Hydrothermal Route
Rafik Benrabaa, Annick Rubbens, Axel Löfberg, Rose‐Noëlle Vannier
Abstract
Abstract In this work, surface properties evaluated by catalytic conversion of isopropanol and by ammonia Temperature Programmed Reduction (NH 3 ‐TPD) over ferrite spinel nanoparticles was investigated. Bulk NiFe 2 O 4 with specific surface area 114 m 2 /g and crystallites size 6 nm was prepared by hydrothermal synthesis using nitrates as precursors. X‐ray diffraction (XRD), Raman spectroscopy, specific surface area by B.E.T, Scanning Electron Microscopy (SEM) and X‐ray energy dispersive microanalysis (EDS), Transmission Electron Microscopy (TEM) and X‐ray Photoelectron Spectroscopy (XPS) techniques were used for their structural and textural characterizations. The reducibility by hydrogen at variable temperatures was investigated by Temperature Programmed reduction (H 2 ‐TPR) and Thermal Gravimetric Analysis‐ Differential Scanning Calorimetry (TGA‐DSC). The total acidity and acid strength distribution was determined by NH 3 ‐TPD. The synthesized oxide showed the presence of mixed phases containing the inverse spinel structure NiFe 2 O 4 as the major phase and iron oxide α‐Fe 2 O 3 as an additional phase. It was shown that the surface of the powder was richer in Ni 2+ species. The surface acidity (Brönsted and Lewis) determined by NH 3 ‐TPD showed that the number of acidic sites increased dramatically with the temperature. The catalytic conversion of isopropanol yields both acidic and redox/basic sites were available. A good correlation between textural, structural, redox and acid‐base properties of catalyst is established.