Preparation And Aromatic Hydrogenation Performance Of Unsupported NiAl(Si)Mo Catalyst

As environmental regulations on the aromatic content of oil become more stringent,looking for high activity and cost-effective hydrodearomatization?HDA?catalyst is of great significance.In this paper,effects of nickel source material and Al,Si promoters on the physicochemical and aromatics hydrogenation performance of unsupported NiMo catalysts were investigated.Four NiMo catalysts were synthesized by a chemical precipitation method using different nickel source materials such as insoluble flower-like,spherical nickel hydroxide and soluble nickel nitrate,nickel acetate.Their structure and morphology were characterized and their differences on the catalytic activity were compared using the HDA of naphthalene as a probe.Results reveal that nickel source had great effect on the crystalline structure and surface area.The NiMo precursors prepared from nickel nitrate and nickel acetate have a phase of ammonium nickel molybdate?ANM?and a phase transformation from ANM to MoS₂ and Ni₃S₂after sulphidation.However the NiMo precursors prepared from nickel hydroxide did not find ANM and only Ni₃S₂ nanoparticles were detected on the sufided unsupported catalysts.The selectivity of decalin was increased with the increasing of reaction temperature and the catalysts prepared from soluble nickel sources had a higher hydrogenation activity.The NiMo catalysts prepared by using flower-like and spherical nickel hydroxide showed good pore structure and morphology,which can increase the specific surface area of unsupported catalysts and promote better dispersion of active components.A series of NiAlMo precursors with various Ni/Al molar ratios were synthesized by incorporation of aluminum promoter into the NiMo component.It was found that aluminum contents had a profound effect on the active structure and hydroprocessing behavior of the catalysts.Increasing contents of aluminum in the precursors led to phase transformations from ANM to amorphous,and the reduction of molybdate shifted to lower temperatures.And at the same time the specific surface area and pore volume of NiMo precursor were also increased.The Ni9.5Al0.5Mo10 catalyst showed higher HDA activity compared with the other NiAlMo catalysts,due to its short length and highly stacked MoS₂ nanoparticles.The Al10Mo10 catalyst had poor activity but can be used for the selective hydrogenation of naphthalene to tetralin.A series of NiSiMo precursors with various Ni/Si molar ratios were synthesized by incorporation of silicon promoter into the NiMo component.Results reveal that the introduction of Si had little effect on the phase structure of NiMo precursor,but it improved the pore structure properties,and the reductions of molybdate shifted to lower temperatures.All the prepared NiSiMo catalysts presented much higher low-temperature?220-260 ^oC?activity than NiMo catalyst,but lower selectivity to decalin.The Si10Mo10 catalyst exhibited the highest selectivity to tetralin?about 100%?,but lower HDA conversion.