Vanadium Hydride as an Ammonia Synthesis Catalyst

Early 3d transition metals, such as Ti, V, or Nb are known to be inactive for the Haber-Bosch process, due to their strong M-N bonds. However, recently some hydride compounds have been found to effectively counteract this effect, imparting catalytic activity on a wide range of elements. With these hydride catalysts, hydride (and nitride) bulk diffusion mechanisms have been proposed; if so, more open structures should enhance their activity. Here, we expand the study to hydrides of other early transition metals, V and Nb. These metals benefit from body-centered cubic (bcc) related structures which enhance hydride diffusion, in addition to having relatively lower M-N bond strengths. The activity of vanadium hydride, most likely with an active composition of VH0.44N0.16, is superior to the previously reported BaTiO2.5H0.5, and comparable to TiH2 and Cs-Ru/MgO at 400 degrees C under 5 MPa. These results show that there is more potential for developing new single-phase hydride catalysts of previously overlooked elements without sacrificing activity.

Automated summary

Early transition metals V and Nb show enhanced catalytic activity through hydride diffusion due to their body-centered cubic (bcc) related structures and relatively lower M-N bond strengths. The activity of vanadium hydride surpasses previously reported hydrogenated titanium and is comparable to TiH2 and Cs-Ru/MgO at 400°C under 5 MPa. These findings suggest potential for developing new single-phase hydride catalysts for previously overlooked elements without compromising activity levels.