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In the mid-1950s, Union Carbide Corporation of the United States first produced X-type and Y-type molecular sieves, which are crystalline aluminosilicates with uniform pore sizes. Their pore sizes are of the order of magnitude of molecular size and can screen molecules. The molecular sieves made by ion exchange in 1960 enhanced the structural stability. In 1962, the small ball molecular sieve catalyst for oil cracking was put into use in a moving bed, and in 1964, the XZ-15 microsphere molecular sieve was used in a fluidized bed, raising the oil refining industry to a new level. Since the emergence of molecular sieves, Union Petroleum Corporation and Esso Standard Oil Company launched metal-loaded molecular sieve cracking catalysts in 1964. Using the shape selectivity of molecular sieves, following the achievements made in the oil refining industry in the 1960s, many important catalytic processes based on molecular sieve catalysts have been developed in the chemical industry since the 1970s. During this perio
