Pore Size Control of γ-Alumina Obtained from Polyhydroxoaluminum-Polyethylenglycol Composite Gels

Abstract

The addition of polyethyleneglycol (PEG) to polynuclear hydroxoaluminum (PHA) ion solutions having high [OH/Al] ratios led to transparent composite gels on drying. PHA-PEG composite gels having high content of PEG were transformed into a single phase of γ-alumina upon heating above 850°C, while PHA gels were transformed into mixed phases γ- and χ-alumina. The addition of PEG suppressed the phase transition and shifted the transition temperature to higher temperatures, resulting in a high surface area and monomodal pore size distribution for γ-alumina. The grains of γ-alumina thus obtained exhibited transparency and a sharp and homogeneous pore size distribution around 3.4nm in diameter. The state of incorporated PEG phase may control pore distribution of γ-alumina because the interaction between PHA and PEG, through OH and ether groups, promotes the formation of clustered domains of loosely oriented PHA ions. The domains homogeneously dispersed in the matrix of PEG probably resulted in homogeneous precipitation of γ-alumina having a narrow particle distribution, leading to a sharp monomodal pore size distribution for γ-alumina. The addition of polyvinylalcohol (PVA) to PHA solutions had similar effects to that of PEG.