This dissertation investigates the use of heterogeneous molybdenum catalysts for use in water-gas shift (WGS) and methane dehydroaromatization (MDA) chemistry. The WGS reaction, CO + H₂O [special characters omitted] H₂ + CO₂, is catalyzed by unsupported molybdenum carbide (Mo₂C). The MDA reaction, 6 CH₄ [special characters omitted] C₆H₆ + 9 H₂, is catalyzed by a zeolite-supported molybdenum catalyst, Mo/HZSM-5. Both reactions involve Mo₂C, hydrogen production, and are industrially relevant.

The composition of the near-surface carbide phase in a variety of unsupported Mo₂C powders was investigated using high-resolution XPS. Mo ₂C powders with elevated carbon contents were prepared via temperature programmed carburization of a molybdate, and were handled with or without air exposure. Binding energies, peak widths and line shapes were investigated for six carbon environments. The XPS of some catalysts suggest that non-Mo ₂C carbide phases are present near the surface, e.g., α-MoC _1-x and MoO_xC_y. The catalytic performance of Mo ₂C for water-gas shift catalysts were evaluated in a flow reactor by FTIR, GC, and MS. Catalyst activities were enhanced by reduction in hydrogen gas at temperatures between 450 and 850°C. High CO conversion and low lightoff temperature (< 250°C) were achieved when the catalysts were activated at 600°C. Catalysts activated at 825°C had higher lightoff temperatures (>300°C). The activity of catalysts with high graphite content were unaffected by H₂-TPR at 600°C. The activity of these catalysts increased after H₂-TPR at 825°C. Catalysts with higher concentrations of MoO_xC_y did not perform better than those with low levels. The MoO_xC_y phase diminished upon activation at 600°C.

The local structure of molybdate ions in the crystalline materials MgMoO ₄ and MgMo₂O₇ and in Mo/HZSM-5 (Mo wt% = 2, 4, and 6) and (Si/Al = 15, 25, and 39) was explored by EXAFS at the Mo K-edge, using both Fourier and Wavelet Transforms. Curvefitting analysis of the FT-EXAFS of MgMoO₄ and MgMo₂O₇ reveals the need to include several single- and multiple-scattering paths in order to locate the Mo-Mo paths. Curvefitting of the FT-EXAFS of in Mo/HZSM-5 is unable to distinguish between possible mono-molybdate and di-molybdate structures. The coordinates of the WT-EXAFS maxima provide strong evidence for the presence of dimolybdates, especially at low Mo loading and high Si/Al ratios.