Design of water gas shift catalysts for hydrogen production in fuel processors

Low sulfur hydrocarbon fuels can be converted to fuel cell grade H-2 using a compact fuel processor architecture. The necessary high volumetric activity water gas shift (WGS) Pt on ceria-zirconia catalysts reacts CO-rich reformate with steam to yield H-2 and CO2. Such highly selective, non-pyrophoric noble metal/Ce([1-(x+y)])Zr(x)Dp(y)O(2) catalysts were developed through coordinated atomic modeling, syntheses, structural characterization, kinetic performance tests, and micro-kinetic analyses. Density functional simulations made with the VASP code suggested that the undoped catalyst WGS activity would be limited by the strong binding of CO intermediates, blocking the reoxidation of the reduced oxide by water. These predictions were confirmed by in situ cylindrical internal reflection-Fourier transform infrared spectroscopy and by micro-kinetic analyses of the micro-reactor results. Atomic simulations were used to evaluate the impact transition metal dopants had on the surface chemistry of cubic ceria-zirconia. VASP predicted that acidic transition metal dopants such as Nb, Mo, Ta, and W would increase the oxide surface affinity for water and thus increase the turnover rate of the catalyst. The efficacy of Mo-doped ceria-zirconia compositions was confirmed at lower temperatures in replicated catalyst synthesis-reactor studies.