Hydrogenation of tetralin over sulfided nickel-tungstate/alumina and nickel-molybdate/alumina catalysts

Nickel-tungstate/alumina (NiW/Al2O3) and nickel-molybdate/alumina (NiMo/Al2O3) catalysts were prepared using an incipient wetness impregnation method with citric acid as a complexing agent. The hydrogenation activity of both sulfided catalysts was measured in a continuous-flow reactor as well as in a batch tube-bomb reactor with tetralin as an aromatic compound. Activity and stability of both sulfided catalysts were then compared in detail. The hydrogenation activity of the two catalysts depended on the partial pressure of the hydrogen sulfide (H2S) in the reaction atmosphere, where dimethyl disulfide (DMDS) was added to control its pressure. The sulfided NiW/Al2O3 catalyst was advantageous in hydrogenating tetralin under low H2S partial pressure, and the structure of the sulfide phases was quite stable in the reducing atmosphere which was measured by XPS and EXAFS methods. On the other hand, the sulfided NiMo/Al2O3 catalyst was advantageous in hydrogenating tetralin 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 phase and sintering of the MoS2-like phase as confirmed by an XPS and an EXAFS. The superiority of the sulfided NiW/Al2O3 catalyst over the sulfided NiMo/Al2O3 catalyst was indicated in deep hydrogenation of low-sulfur feedstocks. (C) 1997 Elsevier Science B.V.