The effect of metal ion dopants (V³⁺, Cr³⁺, Fe ³⁺, Mn²⁺, Ce³⁺) and their concentration on the morphology and the texture of doped γ-alumina

Transition-metal-doped γ-alumina with various dopant concentrations was prepared by straightforward template-free sol-gel method. The presence of dopant metal ions, generally, enhanced the gel formation and their behavior was dependent on the nature of the metal ion and its concentration. Certain ions, especially Fe³⁺, resulted in rapid formation of a transparent gel upon hydrolysis. The prepared doped γ-alumina powders weakly crystalline at low dopant ion concentrations, 2%, and became completely amorphous at a concentration of 10%. The morphology of the particles was also dependent on the dopant concentration. While dopant concentration of 2% resulted in nano-particles with significant amount of inter-particle mesopores, 10% concentration led to significant aggregation into larger particles. The prepared doped γ-Al₂O₃ as well as the undoped γ-Al₂O₃ showed high surface areas and pore volumes which were largely dependent on the nature of the dopant metal ions and on their concentrations. While composites with low dopant concentration, 2%, exhibited surface areas and pore volumes comparable to those of undoped γ-alumina, a considerable decrease was associated with higher concentrations. The changes in textural properties were referred to the evident enhanced sintering associated with high dopant concentrations.