A process may include contacting an oxygen-containing, halogenide-containing or sulphur-containing organic feedstock in an XTO reactor with a catalyst composite under conditions effective to convert the oxygen-containing, halogenide-containing or sulphur-containing organic feedstock to olefin products. The catalyst composite may include at least 10 weight percent of a modified molecular sieve. The modified molecular sieve may include at least 0.05 weight percent of an alkaline earth metal or a rare earth metal based on a weight of the modified molecular sieve. The modified molecular sieve may include at least 0.3 weight percent of P based on the weight of the modified molecular sieve.