Synthesis and characterization of group V metal carbide and nitride catalysts

Group V transition metal carbides and nitrides were prepared via the temperature programmed reaction (TPR) of corresponding oxides with NH{dollar}sb3{dollar} or a CH{dollar}rmsb4/Hsb2{dollar} mixture. Except for the tantalum compounds, phase-pure carbides and nitrides were prepared. The vanadium carbides and nitrides were the most active and selective catalysts. Therefore the principal focus of the research was the preparation, characterization, and evaluation of high surface area vanadium nitride catalysts.; A series of vanadium nitrides with surface areas up to 60 m{dollar}sp2{dollar}/g was prepared. Thermal gravimetric analysis coupled with x-ray diffraction and scanning electron microscopy indicated that the solid-state reaction proceeded by the sequential reduction of {dollar}rm Vsb2Osb5{dollar} to VO{dollar}sb{lcub}0.9{rcub}{dollar} and concluded with the topotactic substitution of nitrogen for oxygen in VO{dollar}sb{lcub}0.9{rcub}{dollar}. The transformation of {dollar}rm Vsb2Osb5{dollar} to VN was pseudomorphic. An experimental design was executed to determine effects of the heating rates and space velocities on the VN microstructures. The heating rates had minor effects on the surface areas and pore size distributions; however, increasing the space velocity significantly increased the surface area. The materials were mostly mesoporous. Oxygen chemisorption on the vanadium nitrides scaled linearly with the surface area. The corresponding O/V{dollar}sb{lcub}rm surface{rcub}{dollar} ratio was {dollar}approx{dollar}0.6.; The vanadium nitrides were active for butane activation and pyridine hydrodenitrogenation. During butane activation, their selectivities towards dehydrogenation products were as high as 98%. The major product in pyridine hydrodenitrogenation was pentane. The reaction rates increased almost linearly with the surface area suggesting that these reactions were structure insensitive. The vanadium nitrides were not active for crotonaldehyde hydrogenation; however, they catalyzed an interesting ring formation reaction that produced methylbenzaldehyde and xylene from crotonaldehyde.; A new method was demonstrated for the production of very high surface area vanadium nitrides. Vanadium nitrides with surface areas up to {dollar}approx{dollar}150 m{dollar}sp2{dollar}/g were prepared via the TPR of vanadium oxide aerogels with NH{dollar}sb3{dollar}. The oxide aerogels were prepared using vanadium tri-n-propoxy oxide followed by the supercritical extraction of ethanol. The vanadium oxide aerogels and resulting nitrides were mesoporous and fibrous. Gravimetric butane conversion rates for these nitrides increased almost linearly with the surface area. Butane activation rates for these high surface area vanadium nitrides were comparable to that of a commercial Pt-Sn/Al{dollar}rmsb2Osb3{dollar} catalyst.