Stepwise dealumination of zeolite beta at specific T-sites observed with Al-27 MAS and Al-27 MQ MAS NMR

Using Al-27 MAS and Al-27 MQ MAS NMR, dealumination of zeolite H-Beta has b een observed at specific T-positions in the framework. Al-27 MQ MAS NMR is able to resolve aluminum in the T1 and T2 positions from the other (T3 - T9 ) positions in the framework. A quantitative analysis of the Al-27 MQ MAS N MR spectra shows that aluminum atoms in positions T1 and T3 resist dealumin ation and do not adopt an octahedral oxygen coordination. Moreover, it is s hown that a heat treatment of 450 degreesC of NH4-Beta gives a single type of fairly symmetric framework octahedral aluminum, which can be reconverted to framework tetrahedral aluminum by ammonia treatment. A more severe heat treatment (550 degreesC under steam) causes some of the tetrahedral framew ork aluminum atoms on positions T3-T9 to convert to at least two different types of octahedral aluminum that are connected to the framework. These sit es are proposed to be different consecutive steps in the process of framewo rk dealumination of zeolite Beta.