Reciprocal-space and real-space neutron investigation of nanostructured Mo2C and WC

As possible substitute materials for platinum group metal heterogeneous catalysts, high surface area carbides of the early transition metals Mo and W are of great interest. Here we report nanostructured, high surface area Mo2C and WC prepared by decomposing and carburizing ammonium paramolybdate [(NH4)(6)Mo7O24 center dot 4H(2)O] and ammonium paratungstate [(NH4)(10)W12O41 center dot 5H(2)O] in flowing 50%CH4/50%H-2. Surface areas as high as 52 m(2)/g for Mo2C and 24 m(2)/g for WC were obtained, with both structures crystallizing in structures appropriate for catalytic activity. We have studied these materials using a combination of neutron diffraction Rietveld refinement, X-ray photoelectron spectroscopy, surface area measurements, and scanning transmission electron microscopy. In addition, we have used pair-distribution function (PDF) analysis of the neutron total scattering data as a means of establishing the presence of graphitic carbon in the as-prepared materials. (c) 2008 Elsevier Masson SAS. All rights reserved.