Effect of gallium as an additive in hydrodesulfurization WS2/γ-Al2O3 catalysts

The effect of gallium in W/Ga(x)–γ-Al2O3 catalysts was investigated in the hydrodesulfurization of dibenzothiophene. The γ-Al2O3 carrier was modified by the gallium addition prior to W impregnation and further calcination at 723 K. An electrophoretic study was carried out on the calcined Ga samples at 0, 0.29, 0.55, 0.84, 1.09, 1.43, 1.71 and 2.22 wt.% of Ga and it indicated that Ga addition affected significantly the surface of alumina. The presence of at least two gallium species was proposed, at low gallium content GaAl2O4 species decreased the isoelectric point (IEP) and probably the formation of Ga2O3 at higher contents increased again the IEP. Raman spectroscopy showed that the gallium incorporation had a strong effect in the formation of WOx species at the surface of catalysts. The highest amount of irregular WOx particles calculated by the Raman (OWO + WO)/W–O–W band intensities ratio was found on the W/Ga(1.09)–γ-Al2O3 catalyst. The presence of gallium induced higher activity on the dibenzothiophene hydrodesulfurization reaction in all catalysts tested. The highest Raman ratio and the highest activity were found for the W/Ga(1.09)–γ-Al2O3 catalyst, suggesting that better dispersed W species could be responsible for the highest HDS activities.

Raman spectroscopy showed that gallium incorporation had a strong effect in the formation of WOx species at the surface of catalysts. Our results confirm clearly a positive effect of Ga on the HDS activity for WS2 catalysts.Figure optionsDownload high-quality image (97 K)Download as PowerPoint slide