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.

Graphical abstractRe-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 full-size imageDownload 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.