The desire for increased fuel economy and lowered CO₂ emissions are two important driving factors in the development of more efficient vehicles that emit less greenhouse gases. Fuel cell vehicles could potentially address these problems, but have not yet been commercialized. A hybrid system consisting of a conventional internal combustion engine (ICE) and a fuel cell powered auxiliary power unit (APU) could be a promising choice due to higher energy efficiency and lower emissions. The APU is a combination of a fuel cell and an on-board hydrogen generation system utilizing gasoline or diesel fuel. Catalytic autothermal reforming (ATR) is expected to be the best option for hydrogen generation due to its low cost, simplicity, and better energy efficiency compared to steam reforming or partial oxidation. Nickel-based catalysts have been the catalyst of choice for steam reforming to produce hydrogen due to their good activity and long-term stability. The formation of carbon deposits during reaction, however, is one of the main causes of catalyst deactivation during hydrocarbon reforming. Unlike sulfur, carbon deposition is a problem caused by intrinsic properties of the catalyst (structure, formulation, preparation), but to some extent can be controlled by reaction conditions (type of fuel, steam to carbon ratio, oxygen to carbon ratio, temperature).

This work deals with a combined study of carbon identification and the effect of nickel loading on carbon growth during isooctane autothermal reforming (iC₈-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 C1s XPS spectra and oxidation temperatures of 392 and 572 °C in TGA curves, respectively. Over the entire nickel loading range of 1-15 wt%, with corresponding nickel crystal sizes of 30-103 nm, the coating carbon formation rate on all Ni/CZO catalysts was low (0.04 g/m²_Ni•hr) and independent of nickel crystal size. The growth rate of filaments (carbon nanotubes) increased with the increase of nickel particle size whereas the formation of carbon nanotubes depended on surface nickel particle density on CZO. XRD patterns showed that both coating carbon and carbon nanotubes were amorphous for nickel loadings ≤ 5%, even though deposited carbon reached up to 60.2 wt%. The results suggest a strategy for inhibiting the growth of filamentous carbon on Ni/CZO catalysts during H2 production from liquid fuels by using low surface nickel particle density (< 1.0×10¹² particles /m²) and keeping the nickel particle size small (≤ 30 nm).