lighter aromatics can be recycled to the transalkylation zone the catalysts of this invention comprise acidic molecular sieve rhenium tin and germanium molecular sieves include but are not limited to zeolite beta zeolite mtw zeolite y both cubic and hexagonal forms zeolite x mordenite zeolite l zeolite ferrierite mfi and erionite zeolite beta is described in u s pat no 3 308 069 according to its structure composition and preferred methods of synthesis y zeolites are broadly defined in u s pat no 3 130 007 which also includes synthesis and structural details mordenite is a naturally occurring siliceous zeolite which can have molecular channels defined by either 8 or 12 member rings donald w breck describes the structure and properties of mordenite in zeolite molecular sieves john wiley and sons 1974 pp 122 124 and 162 163 zeolite l is defined in u s pat no 3 216 789 which also provides information on its unique structure as well as its synthesis details other examples of zeolites that can be used are those having known structure types as classified according to their three letter designation by the structure commission of the international zeolite association u201c atlas of zeolite structure types u201d by meier w m olsen d h and baerlocher ch 1996 of mfi fer eri mtw and fau zeolite x is a specific example of the latter structure type the.