AL-27 MAS NMR EVIDENCE FOR THE REVERSIBLE TRANSFORMATION OF THE COORDINATION OF ALUMINUM IN DEALUMINATED MAZZITE

The influence of acetylacetone treatment on the aluminum coordination in zeolite mazzite has been studied by Al-27 MAS n.m.r. and FTi.r. spectroscopy. Three steam-dealuminated samples, one before and two after acid leaching, with nearly identical Si/Al framework ratios, have been examined. In the case of the nonleached sample, a progressive increase of the Al-27 resonance of octahedrally coordinated aluminum was seen with increasing contact time with acetylacetone due to the transformation of n.m.r. invisible species into visible ones by complexation. The addition of acetylacetone on the acid-leached samples produces a decrease in peak intensity of the aluminum atoms located in the four-member rings of the framework and an increase of the intensity of the signal due to the octahedrally coordinated atoms. The reversibility of these intensity changes by washing leads to the assumption that it is caused by an in situ complexation and transformation of the coordination of the aluminum T-atoms by the acetylacetone molecules. I.r. measurements of adsorbed acetylacetone support this proposal.