Thermal and hydrothermal stability of framework-substituted MCM-41 mesoporous materials

The thermal and hydrothermal stability of framework-substituted MCM-41 with a Si/M molar ratio of 40 (M = Al, Ti) is assessed. Si-MCM-41 with 2.5% substitution of Si by either Al or Ti remains mesoporous when calcined in air at temperatures up to 800°C. The pore structure of Si-MCM-41 and Al-MCM-41 collapses at a calcination temperature of above 800°C, while pore collapse occurs at about 100°C higher for Ti-MCM-41. The addition of La₂O₃ to Al-MCM-41 improves its thermal stability at lower temperatures, but has no effect at higher temperatures. When MCM-41 materials are treated in pure distilled water at 25–100°C for 4 h, Si-MCM-41 suffers a significant loss of BET surface area, while Al-MCM-41 and Ti-MCM-41 are more stable towards such treatment. All the samples investigated are stable in an acidic solution of pH 2, but disintegrate rapidly in a strongly basic medium (pH 12).