Ni-olivine catalysts prepared by thermal impregnation: Structure, steam reforming activity, and stability

Ni-olivine catalysts prepared by thermal impregnation are candidate materials for in-bed catalytic tar removal during fluidized bed biomass gasification. The present work examined the structure and surface properties of the Ni-olivine catalysts prepared by thermal impregnation following preparation, during reduction by in-situ techniques, and following naphthalene-steam reforming in simulated biomass derived syngas. Catalysts were characterized by BET surface area, laser Raman spectroscopy (LRS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). During the preparation, secondary phases containing Mg (i.e., (Mg,Fe)3Si2O5(OH)4 and MgFe2O4) reacted to form an olivine phase enriched in Mg and either MgO or Mg-enriched (Mg,Ni)O. The presence of excess steam in the naphthalene-steam reforming appeared to limit coking and also caused behavior to be different than was observed under reducing conditions. Post-reaction characterization indicated the loss of a metallic phase through a possible alloying process and the exchange of Fe for Mg in the olivine structure. Either can potentially explain the high coke resistance of the Ni-olivine catalysts prepared by thermal impregnation compared to Ni-olivine catalysts prepared by incipient wetness impregnation or the olivine support. Finally, the properties of the olivine catalysts with and without Ni were compared through activity for methanol- and ethylene-steam reforming.

Graphical abstractThe present work examines the structure and surface properties of the Ni-olivine catalysts prepared by thermal impregnation following preparation, during reduction by in-situ techniques, and following naphthalene-steam reforming in simulated biomass derived syngas. The figure shows the Raman spectra of olivine catalysts with and without Ni.Figure optionsDownload full-size imageDownload as PowerPoint slide