Reciprocal-space and real-space neutron investigation of nanostructured Mo_2C and WC

摘要

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 Mo_2C and WC prepared by decomposing and carburizing ammonium paramolybdate [(NH_4)_6Mo_7O_(24) centre dot 4H_2O] and ammonium paratungstate [(NH_4)_(10)W_(12)O_(41) cemtre dot 5H_2O] in flowing 50 percent CH_4/50 percent H_2. Surface areas as high as 52 m~2/g for Mo_2C 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.