MAGNESIUM MODIFIED ULTRA-STABLE RARE EARTH Y-TYPE MOLECULAR SIEVE AND PREPARATION METHOD THEREFOR

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The present invention provides a magnesium modified ultra-stable rare earth Y-type molecular sieve and a preparation method therefor. The method comprises : performing rare earth exchange reaction and dispersion pre-exchange reaction by using an NaY molecular sieve as the raw material, then performing ultra-stable roasting, and finally performing magnesium modification. The molecular sieve contains 0.5%-5% of magnesium oxide by weight, 1%-20% of rare earth oxide by weight, and not greater than 1.2% of sodium oxide by weight, and has the degree of crystallinity being 46%-63% and the cell parameter being 2.454-2.471 nm. Compared with the prior art, the rare earth ions of the molecular sieve prepared through the method are positioned at a sodalite cage, characterized in that no rare earth ion is lost in the counter-exchange process; meanwhile, the particle diameter D (v, 0.5) of the molecular sieve prepared through the method is not greater than 3.0 μm, and the particle diameter D (v, 0.9) is not greater than 20 μm. The molecular sieve has high reliability and desired product selectivity. When the molecular sieve is used as the active component of a catalytic cracking catalyst, high heavy oil conversion capability and high yield of the high-value desired product can be achieved.