Acid properties of MCM-22 and delaminated ITQ-2 studied by IR spectroscopy

摘要

We studied the concentration,acid strength,heterogeneity,accessibility and the distribution of Si-(OH)-Al groups in MCM-22 (of Si/Al=15 and 50) and in their delaminated derivatives obtained from the same precursor.The results of our IR studies suggest that Al atoms first introduced into MCM-22 structure (at high Si/Al) form the hydroxyls both in the supercages and 10-membered channels,whereas Al introduced in the next order (at low Si/Al) forms mostly hydroxyls inside supercages.Hydroxyls in the supercages show higher acid strength than those in 10-membered channels.In MCM-22 zeolites hydroxyls are much more resistant towards dehydroxylation than in others zeolites (ZSM-5).What is more,delamination practically did not change the concentration of Bronsted sites,indicating that the protonic sites were not destroyed during this process.IR studies of CO adsorption showed that delamination did not produce extrazeolitic material.