Steam reforming of hydrocarbons from biomass-derived syngas over MgAl2O4-supported transition metals and bimetallic IrNi catalysts

This study presents an investigation into the steam reforming of hydrocarbons from biomass gasifier derived syngas over MgAl2O4-supported transition metals (Ni, Rh, Ir, Ru, Pt, and Pd) and novel bimetallic IrNi catalysts. Using a model syngas consisting of H-2, CO, CO2, CH4, C2H4, and H2O, Ir and Rh catalysts were found to be the most stable catalysts (at 850 degrees C,1 bar, 114,000 h(-1)). When benzene and naphthalene are added to the feed (as a tar simulant) stability is affected by both tar concentration and type of tar. Catalytic deactivation, caused primarily by coking can be minimized by operating at a high reaction temperature (e.g., 850 degrees C). In addition, promoting Ni catalyst with Ir significantly enhances stability. By using bimetallic formulations of it and Ni (0.5-5.0% Ir, 15%Ni), nickel sintering during the reaction is reduced. Surprisingly, IrNi catalysts also offer more stability than catalysts with Ir particles alone. In agreement with theoretical calculations, small Ir degrees clusters (similar to 2-3 atoms) supported on large Ni degrees particles (>= 5 nm) present more resistance to coking than either small Ir degrees clusters or Ni degrees particles alone. Hence, superior stability of the bimetallic catalysts results from both resistance to coking and a decrease in nickel sintering. Minimal loss of activity of 12% for TOS = 80 h is demonstrated for a bimetallic catalyst with optimal concentrations of 2.5% Ir and 15% Ni. Both monometallic Ir and Ni catalysts suffer substantial loss of activity (i.e., >= 40% loss, TOS = 80 h) under comparable conditions. Published by Elsevier B.V.