Preferential oxidation of carbon monoxide with iron-promoted platinum catalysts supported on metal foams

Abstract

A series of 5 wt% Pt/0.5 wt% Fe/γ-Al 2O 3 catalysts supported on metal foams of different geometries were synthesized and tested for preferential oxidation of a low CO concentration in the presence of a high H 2 concentration. The catalysts were tested in a fixed bed adiabatic reactor at a total pressure of 0.2 MPa (absolute) to simulate fuel processor operating pressure. The inlet temperature was varied from 80 °C to 170 °C, and the gas hourly space velocity ranged from 5000 h −1 to 45,000 h −1. The inlet gas composition to the reactor reproduced that of the effluent stream from the water-gas-shift reactor in a typical fuel processor: H 2 42%, CO 2 9%, H 2O 12%, CO 1.0%, O 2 0.5–1.0%, and N 2 35–35.5%. The geometry of a foam is characterized by the volume fraction of solid material (cell density) and by the number of pores per inch. The catalysts with lower cell densities generally exhibited higher CO conversions and selectivities. Under most operating conditions, the CO conversion and selectivity of the best metal foam catalysts were comparable to those of a 400 cells per square inch, ceramic straight-channel monolith with the same nominal catalyst loading. Both the reverse water-gas-shift (r-WGS) reaction and transport resistances affected the performance of these catalysts. Under adiabatic conditions, the r-WGS reaction made it impossible to achieve low outlet CO concentrations. The effects of space velocity and linear velocity were studied independently using various catalyst lengths and volumetric gas flow rates. At a constant space velocity, the CO conversion increased with higher linear velocities, suggesting a significant mass transfer resistance between the bulk gas and the catalyst surface.