Sacrificial Trimethyl Phosphate Modification for Phase Stability of Mesoporous γ-Alumina

This study demonstrates a sacrificial surface modification employing trimethyl phosphate (TMP) to enhance the phase stability of mesoporous γ-alumina (γ-Al₂O₃). TMP was grafted onto the γ-Al₂O₃ surface via a simple wetting and calcination process. Complementary analyses─including X-ray diffraction, spectroscopy, thermal analysis, and porosity measurements─revealed the formation of three types of TMP moieties on γ-Al₂O₃ surfaces and their gradual decomposition, subsequent diffusion into alumina, and eventual transformation into aluminum phosphates at elevated temperatures. During these thermal processes, the γ-to-θ phase transformation of alumina was delayed by approximately 200 °C, and the mesoporous structure was retained up to higher temperatures (∼1100 °C) in TMP-treated samples compared to pristine γ-Al₂O₃. These results indicate that TMP acts not only as a coupling agent but also as a sacrificial modifier on γ-Al₂O₃ surfaces to delay the phase transformation induced by surface diffusion. Therefore, the strategy in this study paves the way for the sacrificial use of phosphorus coupling agents to stabilize metastable phases and to design mesoporous materials.