MCM-41, MCM-48 and related mesoporous adsorbents: their synthesis and characterisation

MCM-41, MCM-48, MCM-41 analogue materials and disordered silica xerogels were compared with respect to their long range and short range order, their specific surface area, pore structure and pore structural parameters, pore wall thickness and their surface hydroxyl group concentration. Based on X-ray diffraction data it could be seen that the degree of long range order decreased in the order MCM-41>MCM-48>MCM-41 analogues >amorphous silica xerogels. The particle porosity and pore wall thickness increased in the same sequence such that MCM-41 analogues and amorphous silica xerogels were more stable towards water and water vapour. The concentration of the surface hydroxyl groups increased when moving from MCM-41 to amorphous silica xerogels from 3 μmol OH per m2 (MCM-41, MCM-48) to 5–6 μmol OH per m2 (MCM-41 analogue) and 8–9 μmol OH per m2 (amorphous silica xerogel). Rehydroxylation of the materials (after calcination at 823 K) resulted in the loss of periodic structure for MCM-41. In contrast to this, the MCM-41 analogue retained both its periodic structure and the concentration of surface hydroxyl groups, αOH.