Catalytic cracking of hydrocarbons

Claim 1

In the process by which a hydrocarbon feed is catalytically cracked in a cracking unit comprising a cracking zone operating in the absence of added hydrogen, a catalyst regeneration zone, and a circulating inventory of solid acidic cracking catalyst which acquires while in the cracking zone a deposit of coke, said coked catalyst while in the regeneration zone being converted to regenerated catalyst with the formation of a flue gas comprising noxious nitrogen oxides, the improvement which comprises: incorporating with each 100 parts by weight of said circulating catalyst inventory about 0.1 to about 45 parts of additive particles comprising a crystalline zeolite in a titania or zirconia matrix, said crystalline zeolite having a silica to alumina ratio of about 20 to about 100 and a pore size greater than 5 angstroms, said additive particles containing copper metal and/or ions equivalent to at least 0.25 mole of CuO for each mole of A1 2 O 3 in said zeolite and a steam-stabilizing amount of one or more rare earth metal compounds, thereby reducing the content of noxious nitrogen oxides in said flue gas.