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 wit h 2.5% substitution of Si by either Al or Ti remains mesoporous when c alcined in air at temperatures up to 800 degrees C. The pore structure of Si-MCM-41 and Al-MCM-41 collapses at a calcination temperature of above 800 degrees C, while pore collapse occurs at about 100 degrees 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 wate r at 25-100 degrees 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 towar ds such treatment. All the samples investigated are stable in an acidi c solution of pH 2, but disintegrate rapidly in a strongly basic mediu m (pH 12). (C) 1997 Elsevier Science B.V.