Surface basicity on bulk modified phosphorus alumina through different synthesis methods

Abstract

Bulk modified phosphorus alumina samples were prepared by gel method (GPA) and hydrolysis of phosphide aluminum (HPA). The γ-Al₂O₃ impregnated by phosphates precursor (IPA) was also compared. The basicity of the samples has been investigated through the CO₂ adsorption/desorption processes by in situDRIFT and temperature programmed desorption experiments. It was found that the surface basicity can be adjusted by different location of phosphates species. For the GPA sample, the phosphates species tends to be located in the grain boundaries as they were not stable enough to overcome the structure rearrangement at high temperatures. In contrast, phosphorus was stably anchored in the crystal lattice of HPA sample. Considering the synthesis process of HPA samples, phosphorus changed its valence state from P⁻³ to P⁺⁵ and migrated from anion to cation sites. The anion vacancies left in the lattice facilitated the formation of unsaturated oxygen ions and results in the enhanced basicity.