Optimization of thermally impregnated Ni–olivine catalysts for tar removal

Abstract

Thermally impregnated Ni–olivines are potential catalysts for hot cleanup of tars generated in fluidized bed biomass gasifiers. The present study examined the influence of synthesis parameters, namely Ni precursor, preparation temperature, and olivine support upon the physiochemical and catalytic properties of Ni–olivine catalysts prepared by thermal impregnation. Catalytic activity and stability was monitored by reforming naphthalene, a model tar compound in simulated biomass-derived syngas and by reforming methane. Physiochemical properties, which include both structural (XRD, TPR, and Raman spectroscopy) and surface measurements (BET surface area and XPS), were evaluated for both fresh and spent catalysts. Choice of Ni precursor (NiO or Ni) demonstrated minimal influence upon physiochemical properties and catalytic activity and stability for naphthalene- and methane-steam reforming. The synthesis temperature (1100 and 1400 °C) and olivine support, however, did have an impact. Large structural changes and deactivation were observed when lower synthesis temperatures were used, which indicated that this formulation was not desirable. The use of the Washington olivine as the support demonstrated improved catalytic performance and stability compared to two other olivine supports and further characterization showed that treatments are important in determining the final structural features.