The present invention is a mixture comprising by weight 0.01 to 30% of at least one medium or large pore crystalline silicoaluminate, silicoaluminophosphate materials or silicoaluminate mesoporous molecular sieves (co-catalyst) (A) for respectively 99.99 to 70% of at least a MeAPO molecular sieve.Preferably the proportion of (A) is 1 to 15% for respectively 99 to 85% of MeAPO molecular sieves.MeAPO molecular sieves having CHA (SAPO-34) or AEI (SAPO-18) structure or mixture thereof are the most preferable. Si is the most desirable metal in MeAPO.The present invention also relates to catalysts consisting of the above mixture or comprising the above mixture.The present invention also relates to a process (hereunder referred as “XTO process”) for making an olefin product from an oxygen-containing, halogenide-containing or sulphur-containing organic feedstock wherein said oxygen-containing, halogenide-containing or sulphur-containing organic feedstock is contacted with the above catalyst (in the XTO reactor) under conditions effective to convert the oxygen-containing, halogenide-containing or sulphur-containing organic feedstock to olefin products (the XTO reactor effluent).The present invention also relates to a process (hereunder referred as “combined XTO and OCP process”) to make light olefins from an oxygen-containing, halogenide-containing or sulphur-containing organic feedstock comprising:contacting said oxygen-containing, halogenide-containing or sulphur-containing organic feedstock in the XTO reactor with the above catalyst at conditions effective to convert at least a portion of the feedstock to form an XTO reactor effluent comprising light olefins and a heavy hydrocarbon fraction; separating said light olefins from said heavy hydrocarbon fraction; contacting said heavy hydrocarbon fraction in the OCP reactor at conditions effective to convert at least a portion of said heavy hydrocarbon fraction to light olefins.