Silica-modified catalyst and use for selective production of para-dialkyl substituted benzenes

A method for preparing a composition comprised of a crystalline zeolite having deposited thereon a coating of silica which extensively covers and resides substantially exclusively on the external surface thereof, which comprises

• contacting a crystalline zeolite with an aqueous emulsion of a silicon-containing compound of a molecular size substantially incapable of entering the pores of the zeolite, said compound having the general formula:
• ##STR2## where R.sub.1 is hydrogen, fluorine, hydroxy, alkyl, aralkyl, alkaryl or fluoro-alkyl, the hydrocarbon substituents containing from 1 to 10 carbon atoms, R.sub.2 is selected from the same group as R.sub.1, other than hydrogen, and other than methyl if R.sub.1 is hydrogen, and n is an integer of at least 10, said contacting at a temperature of from about 10.degree. C. to about 200.degree. C. for a time sufficient to permit from about 0.5 weight percent to about 30 weight percent silica to be deposited on the crystalline zeolite upon heating in an oxygen-containing atmosphere at a temperature of from 300.degree. C. to about 700.degree. C., and
• heating the aqueous emulsion contacted crystalline zeolite in an oxygen-containing atmosphere at a temperature of from about 300.degree. C. to about 700.degree. C. to yield said composition.