HYDROGENATION OF TETRALIN OVER SULFIDED NICKEL-TUNGSTATE ALUMINA AND NICKEL-MOLYBDATE/ALUMINA CATALYSTS/

Nickel-tungstate/alumina (NiW/Al2O3) and nickel-molybdate/alumina (NiM o/Al2O3) catalysts were prepared using an incipient wetness impregnati on method with citric acid as a complexing agent. The hydrogenation ac tivity of both sulfided catalysts was measured in a continuous-flow re actor as well as in a batch tube-bomb reactor with tetralin as an arom atic compound. Activity and stability of both sulfided catalysts were then compared in detail. The hydrogenation activity of the two catalys ts depended on the partial pressure of the hydrogen sulfide (H2S) in t he reaction atmosphere, where dimethyl disulfide (DMDS) was added to c ontrol its pressure. The sulfided NiW/Al2O3 catalyst was advantageous in hydrogenating tetralin under low H2S partial pressure, and the stru cture of the sulfide phases was quite stable in the reducing atmospher e which was measured by XPS and EXAFS methods. On the other hand, the sulfided NiMo/Al2O3 catalyst was advantageous in hydrogenating tetrali n under high BS partial pressure, where the hydrogenation activity of both catalysts were inhibited by H2S. The sulfided NiMo/Al2O3 catalyst under low H2S partial pressure was less stable than the sulfided NiW/ Al2O3 catalyst due to structural changes of the active phases, such as migration of the Ni species into gamma-Al2O3 to form the NiAl2O4 phas e and sintering of the MoS2-like phase as confirmed by an XPS and an E XAFS. The superiority of the sulfided NiW/Al2O3 catalyst over the sulf ided NiMo/Al2O3 catalyst was indicated in deep hydrogenation of low-su lfur feedstocks. (C) 1997 Elsevier Science B.V.