Effects of H2S and phenanthrene on the activity of Ni and Rh-based catalysts for the reforming of a simulated biomass-derived producer gas

A series of Rh and Ni-based catalysts were tested for the reforming of methane and phenanthrene using a feed composition similar in terms of main components to that of the producer gas obtained from wood gasification. The objective was to identify formulations that would enable reforming methane and tars without the need to purify the producer gas. Phenanthrene was chosen as a representative tar because this compound is produced in significant concentrations during low-temperature gasification of woody biomasses and its three-ring structure favors coke formation. The concentration of H2S used was set at the higher range of typical values, i.e. 200 ppm, to make these tests more challenging. At 900 degrees C, 200 ppm of H2S induced a significantly higher activity loss for methane reforming than that induced by 200 ppm of phenanthrene. The rate of methane consumption in the presence of both poisons varied linearly with the Rh metal surface area. The slight deviation observed at higher loading was in part due to heat and mass transport limitations. The rate of methane consumption per unit of metal surface area was about 5-fold higher on Rh than that on Ni. No information could be derived from the measure of apparent activation energies, due to changes in adsorption coverages of reactants and poisons with temperature. Incomplete conversion of polycyclic aromatic hydrocarbons, well-known coke precursors, was obtained at 875 degrees C and 850 degrees C.