Preferential oxidation of carbon monoxide with Pt/Fe monolithic catalysts: interactions between external transport and the reverse water-gas-shift reaction

A series of Pt/Al2O3 catalysts, promoted with Fe and supported on 400 cpsi (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 0.20 mPa inlet temperatures of 80-170 degreesC, and a space velocity of 30,000 h(-1). The inlet gas composition was-H-2: 42%, CO2: 9%, H2O: 12%. CO: 0-1.0%, O-2 : 0-1.0%, with N-2 as the balance. For a catalyst containing 5 wt.% Pt in the washcoat, the carbon monoxide and oxygen conversions increased as the iron concentration in the washcoat was increased up to about 0.5 wt.% Fe. The reverse water-gas-shift (r-WGS) reaction played an important role in determining the outlet CO concentration. A catalyst with 1.6 g/in.(3) (0.098 g/cm(3)) of an alumina washcoat containing 5 wt.% Pt/Al2O3 promoted with 0.5 wt.% 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. (C) 2003 Elsevier B.V. All rights reserved.