The desire for increased fuel economy and decreased carbon dioxide emissions are two important driving forces in the development of more efficient vehicles that emit less greenhouse gases. Since fuel cell vehicles have not yet been commercialized, a hybrid system consisting of a conventional internal combustion engine (ICE) for propulsion and a fuel cell-powered auxiliary power unit (APU), which replaces the ICE under heavy NOx and CO emissions conditions (low speed and idling operations), 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 using gasoline or diesel fuel. Catalytic autothermal reforming (ATR) is an attractive option for hydrogen generation due to its low cost, simplicity, and better energy efficiency compared with 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 (e.g., structure, formulation, preparation), but can be controlled to some extent by reaction conditions (e.g., type of fuel, steam to carbon ratio, oxygen to carbon ratio, temperature). In this work, we are going to address the morphological study of deposited carbon derived from dodecane reforming over Ni-based monolith catalysts. Two types of Ni-based monolithic catalysts, Ni/Monolith and Ni/Ceria-Zirconia (CZO)/Monolith, were used to compare the accumulated amount of carbon which is formed from steam reforming (SR), partial oxidation (POX), and ATR, respectively. Carbon morphologies and axial distribution along monolith channels and inside the pores of the ceramic were characterized by scanning electron microscopy (SEM) coupled with energy-dispersive x-ray spectroscopy (EDX). These results were discussed in light of dodecane reforming mechanisms and the role of reactants over Ni catalysts.