Formation, structure, and HDN activity of unsupported molybdenum phosphide

A molybdenum phosphide catalyst was prepared from an aqueous solution of (NH4)(6)Mo7O24. 4H(2)O and (NH4)(2)HPO4 by precipitation, calcination, and subsequent reduction in H-2 at 923 K. Raman spectroscopic measurements revealed that the aqueous solution contained MoO42-, HPO42-, and P2Mo5O236- anions. Powder XRD measurements showed that pure molybdenum phosphide had formed after precipitation and reduction with H-2. 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 gamma-Al2O3-supported MoS2. Their selectivity is comparable to that of an Ni-promoted MoS2 catalyst. (C) 2000 Academic Press.