Modified Y-type molecular sieve, catalytic cracking catalyst comprising the same, its preparation and application thereof

A modified Y-type molecular sieve, having a calcium content of about 0.3-4 wt % calculated on the basis of calcium oxide, a rare earth content of about 2-7 wt % calculated on the basis of rare earth oxide, and a sodium content of no more than about 0.5 wt % calculated on the basis of sodium oxide, on a dry basis and based on the weight of said modified Y-type molecular sieve;

• wherein the modified Y-type molecular sieve has a total pore volume of about 0.33-0.39 ml/g, a proportion of the pore volume of secondary pores having a pore size of 2-100 nm to the total pore volume of about 10-25%, a lattice constant of about 2.440-2.455 nm, a proportion of non-framework aluminum content to the total aluminum content of no more than about 20%, a lattice collapse temperature of not lower than about 1050° C., and a ratio of B acid to L acid in the total acid content of no less than about 2.30, as determined by pyridine adsorption infrared spectroscopy at 200° C.