Preparation and characterization of MCM-41 and silica supported nickel boride catalysts

Ni-B/MCM-41 and Ni-B/SiO₂ catalysts were prepared by low-temperature reduction of surface-adsorbed nickel chloride with ethanolic sodium borohydride solution. XRD analysis showed that the MCM-41 framework of Ni-B/MCM-41 catalyst remained intact, while nitrogen adsorption-desorption study revealed uniform pore size distribution of the channel system. Thermal treatment of this catalyst under nitrogen at 450°C indicated the presence of a segregated nickel phase on the surface of MCM-41. On amorphous silica, however, amorphous nickel boride alloy may have formed. As-synthesized Ni-B/MCM-41 is more susceptible to oxidation than Ni-B/SiO₂ probably due to the smaller size of its alloy particles. This suggestion is also supported by the EXAFS results. The lower activity of Ni-B/MCM-41 catalyst than Ni-B/SiO₂ in benzene hydrogenation reaction probably reflects the lower reducibility of nickel oxide phase than nickel boride alloy phase.