A process for maintaining a particle size distribution in an oxygenate to olefin reaction system, wherein the process comprises the steps of: (a) providing a plurality of catalyst particles in a reaction zone, wherein the plurality of catalyst particles has a d 2 of at least 7 microns, a first median particle diameter, and a d 90 of less than 150 microns, and wherein the plurality of catalyst particles comprises primary catalyst particles of molecular sieve catalyst composition comprising molecular sieve selected from the group consisting of SAPO-5, SAPO-8, SAPO-11, SAPO-16, SAPO-17, SAPO-18, SAPO-20, SAPO-31, SAPO-34, SAPO-35, SAPO-36, SAPO-37, SAPO-40, SAPO-41, SAPO-42, SAPO-44, SAPO-47, SAPO-56, AEI/CHA intergrowths, metal containing forms thereof, intergrown forms thereof, and mixtures thereof; (b) contacting the primary catalyst particles with a feedstock comprising an oxygenate in the reaction zone under conditions effective to convert at least a portion of the feedstock to product comprising one or more olefins; (c) directing the product and at least a portion of the plurality of catalyst particles to a disengaging zone; (d) increasing the first median particle diameter to a second median particle diameter by losing a portion of catalyst fines from the disengaging zone, wherein the catalyst fines have a d 90 of no greater than 44 microns; and (e) decreasing the second median particle diameter to a third median particle diameter by adding co-catalyst particles to the reaction system, wherein the co-catalyst particles are less reactive than said primary catalyst particles, said co-catalyst particles comprising a metal selected from the group consisting of: iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium and platinum. (a) providing a plurality of catalyst particles in a reaction zone, wherein the plurality of catalyst particles has a d 2 of at least 7 microns, a first median particle diameter, and a d 90 of less than 150 microns, and wherein the plurality of catalyst particles comprises primary catalyst particles of molecular sieve catalyst composition comprising molecular sieve selected from the group consisting of SAPO-5, SAPO-8, SAPO-11, SAPO-16, SAPO-17, SAPO-18, SAPO-20, SAPO-31, SAPO-34, SAPO-35, SAPO-36, SAPO-37, SAPO-40, SAPO-41, SAPO-42, SAPO-44, SAPO-47, SAPO-56, AEI/CHA intergrowths, metal containing forms thereof, intergrown forms thereof, and mixtures thereof; (b) contacting the primary catalyst particles with a feedstock comprising an oxygenate in the reaction zone under conditions effective to convert at least a portion of the feedstock to product comprising one or more olefins; (c) directing the product and at least a portion of the plurality of catalyst particles to a disengaging zone; (d) increasing the first median particle diameter to a second median particle diameter by losing a portion of catalyst fines from the disengaging zone, wherein the catalyst fines have a d 90 of no greater than 44 microns; and (e) decreasing the second median particle diameter to a third median particle diameter by adding co-catalyst particles to the reaction system, wherein the co-catalyst particles are less reactive than said primary catalyst particles, said co-catalyst particles comprising a metal selected from the group consisting of: iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium and platinum.