A series of Pt/Al 2 O 3 catalysts, promoted with Fe and supported on 400cpsi (cells per square inch) (62 cells/cm 2 ) ceramic straight-channel monoliths, was synthesized and evaluated for preferential oxidation (PROX) of a low concentration of CO in the presence of a high concentration of H 2 . These catalysts were evaluated in an adiabatic reactor at a total pressure of 0.20mPa inlet temperatures of 80-170 o C, and a space velocity of 30,000h - 1 . The inlet gas composition was-H 2 : 42%, CO 2 : 9%, H 2 O: 12%, CO: 0-1.0%, O 2 : 0-1.0%, with N 2 as the balance. For a catalyst containing 5wt.% Pt in the washcoat, the carbon monoxide and oxygen conversions increased as the iron concentration in the washcoat was increased up to about 0.5wt.% Fe. The reverse water-gas-shift (r-WGS) reaction played an important role in determining the outlet CO concentration.A catalyst with 1.6g/in. 3 (0.098g/cm 3 ) of an alumina washcoat containing 5wt.% Pt/Al 2 O 3 promoted with 0.5wt.% Fe was selected for detailed investigation. The effects of both space velocity and linear velocity were studied. External transport was a significant resistance with this catalyst, at the above experimental conditions. The external resistances to heat and mass transfer, coupled with the effect of the r-WGS reaction, reduced the observed CO conversion and selectivity.