Formation, Structure, and HDN Activity of Unsupported Molybdenum Phosphide

A molybdenum phosphide catalyst was prepared from an aqueous solution of (NH4)6Mo7O24·4H2O and (NH4)2HPO4 by precipitation, calcination, and subsequent reduction in H2 at 923 K. Raman spectroscopic measurements revealed that the aqueous solution contained MoO42−, HPO42−, and P2Mo5O6−23 anions. Powder XRD measurements showed that pure molybdenum phosphide had formed after precipitation and reduction with H2. MoP crystallizes in the tungsten carbide structure in which each Mo atom is trigonal-prismatically coordinated by six P atoms. The molybdenum phosphide was tested for catalytic activity in the HDN reaction of o-propylaniline at 643 K and 3.0 MPa. The intrinsic HDN activity of the surface Mo atoms of MoP was about 6 times higher than that of Mo edge atoms in γ-Al2O3-supported MoS2. Their selectivity is comparable to that of an Ni-promoted MoS2 catalyst.