Kinetic Model for Steam Reforming of Hexadecane in Microchannels

An experimental and numerical investigation on diesel surrogate reforming in microchannels with a rhodium ceria coating is presented. The reforming experiments were performed with hexadecane as well as methane and propane for elucidating heterogeneous reforming chemistry of saturated hydrocarbons. The reforming results showed that linear alkanes exhibit a linear dependency of the turnover frequency on the reciprocal number of carbon atoms per fuel molecule. Based on this observation, a kinetic was set up which combines a global reaction equation for the dissociative adsorption of long-chain hydrocarbons with an elementary surface reaction mechanism for C1 species. This kinetic description is coupled with models for convective and diffusive transport in the gas phase of a microchannel. The model adequately describes the observed conversion and the correlation between the turnover frequency and the number of carbon atoms in the fuel. The model still needs improvement concerning the water gas shift reaction, which is identified as a consecutive reaction in hydrocarbon reforming. Therefore, a reaction scheme is proposed (see Figure 1), in which the hydrocarbon molecules are split on the rhodium metallic sites, whereas the water gas shift equilibrium is established on the ceria sites.