Ammonia synthesis over rhenium supported on mesoporous silica MCM-41

Mesoporous silicon (oxy)nitride (MS(O)N) and mesoporous silica MCM-41 (M41) were examined as supports of catalyst for ammonia synthesis from N2 and H2. Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Rh, Ta, W, Ir, or Pt-loaded MS(O)N and MS(O)N itself were catalytically inert for the synthesis reaction at 673–773 K, while Re, Mo, and Ru-loaded MS(O)N were active. Among the latter metals Re showed the highest activity and thus catalytic activity of Re supported was studied as a function of support, amount of Re supported, Re precursor used in the preparation, and additive. M41 was a good support. The role of Re precursor upon activity was limited. The activity of Re/M41 increased linearly with increasing Re content in the range 0–30 wt.% and was approximately constant between 30–60 wt.% Re. The most active Re/M41 with 30 wt.% Re showed equivalent activity to those of Ru/MgO and doubly-promoted iron catalysts at an atmospheric pressure. Several additives such as Cs, Ba, La, and Ce did not increase the activity of Re/M41. Finally the activation energy and the reaction orders on the respective components on Re/M41 were determined to be 63.0 kJ mol−1 and PN20.95PH20.52PNH3-1.22 at 623–693 K and an atmospheric pressure. The order on hydrogen was positive in sharp contrast to those reported on other Re catalysts and would be very important for the practical application.

Re-MCM-41 showed high catalytic activity for ammonia synthesis, which was comparable to those of Fe and Ru catalysts. Kinetic analyses revealed the positive reaction order on hydrogen on Re-MCM-41 in sharp contrast to negative ones on other Re catalysts.Figure optionsDownload as PowerPoint slideHighlights
► Ammonia synthesis was catalyzed on various Re catalysts.
► Re-supported mesoporous silica showed a high catalytic activity.
► The catalytic activity was comparable with those of well-known Fe and Ru catalysts.
► Positive reaction order on hydrogen in contrast to negative ones on other catalysts.