Catalysts, so-called FCCT (catalysts for fluid catalytic cracking (FCC) with "in situ metal traps"), were developed to achieve high dispersion of passivators. These FCCTs were extensively tested and demonstrated experimentally. The catalyst, steamed to achieve equilibrium conditions, was artificially impregnated with a tin compound (0-3750 ppm) and with nickel and vanadium naphthenates. Experimental runs were performed ina microcatalytic fixed bed reactor using different carrier gas flows (120-150 std mL/min) and different temperatures (510-550 degrees C). The unsteady state pulse technique, gas oil pulses reacting with FCC catalyst, was used to study the effects of metal traps in a FCC catalyst contaminated with 3000 ppm of Ni and 4500 ppm of V. The four-lump model featuring gas oil, gasoline, light gases, and coke was used to evaluate the kinetic constants. The equations developed for the four-lump model were also used to evaluate the adsorption constants for gas oil, gasoline, and light gases.;These parameters are of special importance for the simulation of industrial scale FCC risers. Experimental results demonstrated that gas oil conversion recovered significantly with FCCTs. It was also proven that the effects of the addition of the in situ metal traps were beneficial on gasoline yield, gasoline selectivity, and research octane number. A major contribution of the in situ metal traps was an important reduction in coke yield. Consistent with this result a reduced catalyst deactivation was observed with FCCTs.