Alkylation in presence of thermally modified crystalline aluminosilicate catalyst

A process for effecting alkylation of an aromatic hydrocarbon charge which comprises contacting said aromatic hydrocarbon charge with an olefinic hydrocarbon alkylating agent under conditions effective for accomplishing said alkylation including a reactor inlet temperature between about 575.degree. F. and about 900.degree. F., a reactor pressure between atmospheric and about 3000 psig, employing a mole ratio of hydrocarbon aromatic charge to olefinic hydrocarbon alkylating agent in the approximate range of 1:1 to 30:1 and a total weight hourly space velocity between about 2 and 2000 in the presence of a catalyst comprising a crystalline aluminosilicate zeolite, having more than 50 percent of the cationic sites thereof occupied by hydrogen ions, said zeolite having a silica to alumina ratio of at least about 12, a constraint index within the approximate range of 1 to 12, said catalyst having been modified by prior thermal treatment at about 1200.degree. F. to about 1800.degree. F. in an inert atmosphere or at about 500.degree. F. to about 1800.degree. F. in steam to reduce the alpha value thereof to less than about 250.