Unsupported molybdenum nitride (Mo{sub 2}N) and molybdenum carbide supported on alumina (Mo{sub 2}C/Al{sub 2}O{sub 3}) were compared against commercial sulfided MoS{sub 2}/Al{sub 2}O{sub 3} and Ni-Mo-S/Al{sub 2}O{sub 3} for hydrotreating coal-derived gas oil at 633 K (360 {degrees}C) and 13.7 MPa (2000 psig). When the catalytic rates were compared on the basis of active sites measured by chemisorption, the nitrides and carbides were estimated to have activities as much as five times that of Ni-Mo-S/Al{sub 2}O{sub 3} and MoS{sub 2}/Al{sub 2}O{sub 3}. The comparison was based on sites titrated by CO on the carbide and nitride and by O{sub 2} on the sulfided catalysts. The gas oil product quality from the carbide and nitride catalysts was significantly better than the thermal blank, indicating that the materials were active under practical hydrotreating conditions. X-ray photoelectron spectroscopy analysis after reaction of the Mo{sub 2}N and Mo{sub 2}C/Al{sub 2}O{sub 3} catalysts indicated that surface sulfiding was not extensive.

This paper applies plane parallel radiance transport techniques to scattering from vegetation. The leaves, stems, and branches are represented as a volume density of scattering surfaces, depending only on height and the vertical component of the surface normal. Ordinary differential equations are written for the multiply scattered radiance as a function of the height above the ground, with the sky radiance and ground reflectance as boundary conditions. They are solved using a two-pass integration scheme to unify the two-point boundary conditions, and Fourier series for the dependence on the azimuthal angle. The resulting radiance distribution is used to precompute diffuse and specular `ambient` shading tables, as a function of height and surface normal, to be used in rendering, together with a z-buffer shadow algorithm for direct solar illumination.