Maintaining catalyst activity for converting a hydrocarbon feed

A process for fluid catalytic cracking, comprising:

• contacting a hydrocarbon feed with a catalyst mixture in a reaction vessel wherein the catalyst mixture comprises 99-75% by weight of a large pore zeolite and 1-25% by weight of a medium or smaller pore zeolite having an initial average particle diameter of at least about 20 microns;
• withdrawing the medium or smaller pore zeolite from the reaction vessel and providing fresh catalyst to the reaction vessel at a rate to replace a catalyst inventory of the medium or smaller pore zeolite over a period of up to about 35 days, wherein the fresh catalyst comprises fresh medium or smaller pore zeolite, fresh large pore zeolite, or both;
• providing feed to a riser in the reaction vessel and obtaining a propylene yield of at least about 12% by weight;
• wherein the medium or smaller pore zeolite has a higher attrition rate than the large pore zeolite;
• and
• wherein the medium or smaller pore zeolite is attrited to a size less than 2 microns.