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The role of amino acids (G, A, N) in the wet chemistry synthesis and thermal development of gamma alumina with specific morphology

Alumina (Al2O3) is critically important material in variety of applications such as catalysis, due to chemical stability and mechanical durability over the wide temperature range. Furthermore, gamma alumina powders having defect cubic spinel structure with nanocrystalline character can be prepared using only moderate thermal treatment to facilitate catalyst support application. Reaching out to advanced morphological features is becoming increasingly important, as the limits of the nano-seized powders have been reached. Here we bring about wet chemistry synthesis using aluminium nitrate nonahydrate (ANN) precursor combined with different amino acid fuel. The amino acids ; glycine (G), alanine (A) and asparagine (N) have been specifically selected in order to show the role of gradual increase of their: 1) molar weight, 2) enthalpy of combustion, 3) amine groups content and 4) ratio to ANN, on the derived morphologies. Namely, the conditions leading to development of different morphologies from gels to powders were found to be heavily under the influence of fuel/oxygen ratio, i.e. on the smouldering vs flaming mechanism of the combustion. Thereof, the thermal evolution of the alumina precursors was monitored in details. Higher content of nitrates (predominately from amino rich amino acids) strongly promoted auto-combustion behaviour. As- derived alumina precursors have been thermally treated at various temperatures (quenched and soaked), to monitor gamma and alpha alumina crystallisation, with respect to the development of morphology. It was shown that this combustion synthesis allows facile tailoring nanocrystalline gamma alumina with different morphological features. Different textures types have been observed, such as porous wormhole, porous particulate and porous flakes. Detailed structural (XRD, FTIR), microstructural (SEM, EDS, BET N2 A/D, PSD) and thermal (DTA, TGA) characterisations confirm the nanocrystalline character, thermomechanical stability and were not diminished for different porous morphologies in the course of this synthesis.

Amino acids, Combustion synthesis

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