Initial conclusions

Active aluminas are catalytically active material. They participate in multiple reactions, involving isomerisation, hydrogenation, dehydrogenation, oxidation or polymerisation. These active aluminas are formed by dehydroxylation of precursors. High surface areas and porosities are characteristic of those materials. γ- and θ-Al2O3 are typical examples of

low-temperature activation and high-temperature activation aluminas. Surface properties are dependent on coordinatively unsaturated Al cations and O anions, Surface hydroxylation compensates the high surface energies related to these coordinatively unsaturated ions. Characterisation of γ- and θ-Al2O3 adsorbents used in this work revealed the presence of

physisorbed water and a highly hydroxylated surface. Upon heating, different types of surface hydroxyl groups were observed. Coordination of OH groups with unsaturated ions resulted in the presence of weak acid sites. Pyridine adsorption showed the presence of two types of Lewis acid sites. Those sites were postulated to be responsible for the adsorption of molecules. Brønsted acid sites were not shown in acid site measurements. However, the interactions between pyridine and hydroxyl groups suggested the presence of weak Brønsted sites, in line with previous literature for these aluminas

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Chapter 4: