Modified molecular sieve as well as preparation method and application thereof

The invention relates to the technical field of molecular sieves, in particular to a preparation method of a modified molecular sieve, the modified molecular sieve prepared by the preparation method and application of the modified molecular sieve. The preparation method comprises the following steps: (1) performing metal ion exchange on a Na-type molecular sieve to obtain metal ion slurry; (2) adding a first precipitant to perform first precipitation on part of metal ions in the metal ion exchange slurry to obtain first precipitation slurry; (3) sequentially carrying out filtering, first ammonium sulfate exchange, first water washing and first roasting on the first precipitation slurry to obtain one-time-exchange and one-time-roasting molecular sieve dry powder; and (4) adding a second precipitant, carrying out second precipitation on part of metal ions in the dry powder of the once-exchanged and once-baked molecular sieve, and sequentially carrying out second ammonium sulfate exchange, second water washing a