Development of phases in the sol-gel derived mixed-metal-oxide (Al2O3-TiO2-ZnO) functional sorbent material

Aluminium-Titanium-Zinc mixed-metal-oxide system was investigated in order to elucidate appropriate sorbent material for the High-Temperature Gas-Desulphurisation (HTGD) in the Integrated Gasification Combined Cycle (IGCC). Conceptually, Zn-based constituent phases support sorption functionality, Ti-based constituent phases support chemical stability and Al-based constituent phases support mechanical durability. Samples were prepared using sol-gel synthesis in a broad compositional range from gahnite to Zn-titanate spinel; i.e. gahnite was Ti-doped on the account of Al (0-100%). Complexing agent was used to control the hydrolysis rate. We monitored the thermal and structural evolution in order to observe and clarify different mechanisms of phase formation, as a function of the doping and temperature conditions. The significance of this work lies within insight in the stability ranges of the observed solid-solutions, whereas gahnite spinel and zinc titanate spinels can interchange cations only in limbed amounts, depending on the conditions, as confirmed from the structure refinement. It was observed that these solid-solution phases exhibit quite different stability when thermally treated. More importantly, observed partial phase-separation at low-temperature thermal treatment (which occur on behalf of different hygroscopic properties of the (Al,Ti)-Zn gels) significantly precludes the mechanisms of phase development at high-temperatures. Thereof, intermediate Zn-based phase was found to be responsible for the facilitated early zincite crystallisation. Microstructural and textural changes were correlated according to structural changes. Characterisation results allowed understanding of compositional and treatment conditions necessary for the selection of sorbent best with best functionality.