Effects of small MoO_3 additions on the properties of nickel catalysts for the steam reforming of hydrocarbons III.Reduction of Ni-Mo/Al_2O_3 catalysts

摘要

Ni/Al_2O_3 catalyst modified by small amounts of Mo show unusual properties in the steam reforming of hydrocarbons.There are no data about the effect of small amounts of molybdenum on reduction of the Ni-Mo supported catalysts.The properties of these very complex systems depend on the conditions of successive preparation stages (calcination,reduction) or the process conditions.A series of Ni/Al_2O_3 catalysts modified by Mo were prepared in order to investigate the influence of promoter amounts and preparation sequence on their properties.Temperature programmed reduction (TPR) has been employed to study the reducibility of Ni-Mo/Al_2O_3 catalysts.Catalysts were further characterized by BET area,H_2 chemisorption and X-ray diffraction measurements.The TPR curves of Ni-Mo/Al_2O_3 catalysts are very complex.Mo addition leads to the decrease of catalysts reducibility.However,complete reduction of NiO and MoO_3 can be achieved at 800 deg C.The reduction course depends on the sequence of nickel and molybdenum addition into the support.Precise measurements of Ni peaks positions in the XRD pattern of Ni/Al_2O_3 and Ni-Mo/Al_2O_3 samples show the possibility of Ni-Mo solid solution formation.