leaving in their place hydrogen ions and or exchange sites which have actually been decationized by further removal of water hydrogen or u201c decationized u201d y zeolites of this nature are more particularly described in u s pat no 3 130 006 mixed polyvalent metal hydrogen zeolites may be prepared by ion exchanging first with an ammonium salt then partially back exchanging with a polyvalent metal salt and then calcining in some cases as in the case of synthetic mordenite the hydrogen forms can be prepared by direct acid treatment of the alkali metal zeolites the preferred cracking bases are those which are at least about 10 percent and preferably at least 20 percent metal cation deficient based on the initial ion exchange capacity a specifically desirable and stable class of zeolites are those wherein at least about 20 percent of the ion exchange capacity is satisfied by hydrogen ions the active metals employed in the preferred hydrocracking catalysts of the present invention as hydrogenation components are those of group viii i e iron cobalt nickel ruthenium rhodium palladium osmium iridium and platinum in addition to these metals other promoters may also be employed in conjunction therewith including the metals of group vib e g molybdenum and tungsten the amount of hydrogenating metal in the catalyst can vary within wide ranges broadly speaking any amount between about 0 05 percent and 30 percent by weight may be used in the case of the noble metals it is normally preferred to use about.