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. spe ctroscopy. 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 increas e of the Al-27 resonance of octahedrally coordinated aluminum was seen with increasing contact time with acetylacetone due to the transforma tion of n.m.r. invisible species into visible ones by complexation. Th e addition of acetylacetone on the acid-leached samples produces a dec rease in peak intensity of the aluminum atoms located in the four-memb er rings of the framework and an increase of the intensity of the sign al due to the octahedrally coordinated atoms. The reversibility of the se intensity changes by washing leads to the assumption that it is cau sed by an in situ complexation and transformation of the coordination of the aluminum T-atoms by the acetylacetone molecules. I.r. measureme nts of adsorbed acetylacetone support this proposal.