The surface acidity of mesoporous silicoaluminophosphates: A FTIR study

Thermally stable mesoporous ALPO and SAPO (Si/Al = 0.6) were synthesised using aluminum sulphate as aluminum source and without the need of HF as mineralizing agent. The mesophases prepared by this procedure were stable to calcination at 773K and presented a structure of non-parallel mesopores in the calcined form. FT-IR spectroscopy supplemented by the use of CO and NH ₃ as probe molecules was used to monitor the surface acidity of these new mesoporous materials and indicated that Al-OH, P-OH groups for meso-ALPO and additionally SiOH groups for meso-SAPO are found on the surface of these molecular sieves. The acidities of P-OH and Al-OH are stronger than SiOH in mesoporous silicas but still weaker than the zeolitic Brönsted acid sites.