Hydrogenation of acetylene has been investigated on Au-iron oxide catalysts containing 4.5, 3.0, 5.6 wt% Au prepared by deposition-precipitation (DP) with urea, adsorption of Au sol (SA) and by co-precipitation (CP) of HAuCl4 and Fe(NO3)(3), respectively. The latter method produced Au particles supported on 2-line ferrihydrite (Fe5HO8 center dot 4H(2)O). Au/iron oxide catalyst precursors (Au/alpha-Fe2O3 and Au/2-line ferrihydrite) were characterized by BET, TGA, TPR and XRD, and the Au particle size by TEM measurements. The TPR measurements confirm the ease of transformation of 2-line ferrihydrite to magnetite (Fe3O4) and that the formation of magnetite from alpha-Fe2O3 depends strongly on the size of the gold and the supporting oxide particles. Particle size effect of gold has been investigated in semi-hydrogenation of acetylene. Temperature of hydrogen treatment has been observed to play a crucial role in the activity and ethylene selectivity. Au/FeOx samples hydrogen treated at 353-473 K prior to introduction of the reactants (H-2:C2H2 = 140, 0.11% C2H2) show very limited over-hydrogenation (ethane formation is less than approximate to 1%) and 2-4% selectivity of oligomer (C4+) formation at 353-473 K. Hydrogen treatment of the samples at T > 573 K but lower than the wustite (FeO) stability point (approximate to 843 K) resulted in partial reduction of Fe3O4 and formation of Fe-0. The shift of Au(1 1 1) XRD line to higher 2 Theta provided evidence for the incorporation of Fe-0 into the Au particles. Modification of the Au/Fe2O3 perimeter and appearance of Fe-0 co-catalyst and Fe-Au ensembles on the surface increased the hydrogenation activity but decreased the selectivity of ethylene formation. (C) 2010 Elsevier B.V. All rights reserved.