Catalytic reactions using zeolites

In a process for alkylation or dealkylation of aromatic hydrocarbons in the presence or absence of hydrogen employing a catalyst, the improvement wherein the catalyst employed is one comprising a zeolite designated NU- 87, said zeolite having a composition expressed on an anhydrous basis (in terms of mole ratios of oxide) by the formula

• 100 XO.sub.2 :
• equal to or less than 10 Y.sub.2 O.sub.3 :
• equal to or less than 20 R.sub.2/n O
• wherein R is at least partly hydrogen, X is silicon and/or germanium, Y is one or more of aluminum, iron, gallium, boron, titanium, vanadium, zirconium, molybdenum, arsenic, antimony, chromium and manganese and having an X-ray diffraction pattern including the lines shown in Table 2.