Some features of acetylene hydrogenation on Au-iron oxide catalyst

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 (Fe5HO8·4H2O). Au/iron oxide catalyst precursors (Au/α-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 α-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 (H2:C2H2 = 140, 0.11% C2H2) show very limited over-hydrogenation (ethane formation is less than ≈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 wüstite (FeO) stability point (≈843 K) resulted in partial reduction of Fe3O4 and formation of Fe0. The shift of Au(1 1 1) XRD line to higher 2Θ provided evidence for the incorporation of Fe0 into the Au particles. Modification of the Au/Fe2O3 perimeter and appearance of Fe0 co-catalyst and Fe–Au ensembles on the surface increased the hydrogenation activity but decreased the selectivity of ethylene formation.

Au/FeOx catalysts supporting Au particles of 2.5, 3.3, 3.5 and 7.5 nm in average is highly selective in semi-hydrogenation of acetylene (H2/C2H2 = 140, 1100 ppm C2H2) in the 323–473 K temperature range and the ethane formation selectivity is less than 1% at 100% C2H2 conversion. The hydrogenation is accompanied with oligomer formation, the C4+ selectivity is typically 2–4%. Hydrogen treatment at T > 573 K brings about modification of the Au–FeOx interface. Appearance of Fe0 and AuFe particles significantly increased the hydrogenation activity but decreased the semi-hydrogenation selectivity.Figure optionsDownload high-quality image (90 K)Download as PowerPoint slide