Carbon deposited on Ni/Ce-Zr-O isooctane autothermal reforming catalysts

On-board reforming of liquid fuels is attractive for fuel-cell-powered auxiliary power unit (APU) applications in heavy-duty vehicles. However, a technology barrier is catalyst deactivation due to carbon deposition. In this work, we studied carbon identification and the effect of nickel loading on carbon growth during isooctane autothermal reforming (iC(8)-ATR) over Ni-supported Ce-Zr-O (Ni/CZO) catalysts. The crystallographic phase, type, deposition amount, and morphologies of deposited carbon were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Two types of carbon, coating and filamentous, were identified by SEM, with binding energies of 281.6 and 284.5 eV in Cls XPS spectra and oxidation temperatures of 392 and 572 degrees C in TGA curves, respectively. Both coating and filamentous carbon were X-ray amorphous for nickel loadings <= 5%, even though deposited carbon reached up to 60.2%. Over the entire nickel loading range of 1-15%, with corresponding nickel crystal sizes of 30-103 nm, the coating carbon formation rates were low (0.04 g/m(Ni) (2)h) and independent of nickel particle size. The growth rates of filamentous carbon increased with increasing nickel particle size. Filamentous carbon growth may require not only a critical nickel particle size, but also a certain minimum number of nickel particles per unit support area. The results suggest a strategy for inhibiting the growth of filamentous carbon on Ni/CZO catalysts during autothermal reforming of liquid fuels. (C) 2007 Elsevier Inc. All rights reserved.