Cobalt Catalyst Doped with Cerium and Barium Obtained by Co-Precipitation Method for Ammonia Synthesis Process

Abstract

Unsupported cobalt catalysts promoted with barium (symbol Co/Ba), cerium (Co/Ce) or both (Co/Ce/ Ba) were synthesized and tested in ammonia synthesis at 6.3 MPa. The Ba-free Co and Co/Ce oxide forms of the catalysts were prepared by precipitation/co-precipitation and a subsequent calcination at 500°C. The Co and Co/Ce powders were impregnated with an aqueous solution of barium nitrite. Nitrogen physisorption and H 2 chemisorption measurements revealed that cerium and barium play the role of structural promoters, which hinder the sintering of cobalt oxide during calcination and stabilize the surface of cobalt under reduction conditions. It seems that barium also modifies the surface of the active phase, i.e., cobalt. The kinetic studies of NH 3 synthesis have shown that the co-promoted material (Co/Ce/Ba) is about 2-3 times more active than the system doped with barium (Co/Ba) and more than ten times as active as that with Ce. At 400°C and at low conversion (1% NH 3 ), the ammonia synthesis rate (TOF) over Co/Ce/Ba proved to be almost 60% as high as that obtained for the commercial iron catalyst (KMI, H. Topsøe) commonly used in ammonia plants all over the world. Moreover, at the same temperature and a high ammonia concentration (8%) the co-promoted cobalt catalyst is over two times more active than the fused iron catalyst. Another asset of the cobalt catalyst is its high thermal stability.

Development and Recent Progress on Ammonia Synthesis Catalysts for Haber–Bosch Process

“…The preparation method of the doubly promoted cobalt catalyst was again investigated by Rarog‐Pilecka et al in 2011 with barium‐ and cerium‐promoted cobalt catalysts prepared through the coprecipitation method. [ 126 ] To prepare the catalysts, they added potassium carbonate to an aqueous solution of either cobalt nitrate or cobalt nitrate and cerium nitrate to obtain the cobalt and cerium carbonates. After drying, these carbonates were then treated at 500 °C in air overnight to obtain the oxide catalyst.…”

“…Again barium nitrate was added as a promoter using the standard impregnation method. [ 126 ] When evaluating the activity, they used a pressure of 6.2 MPa with a gas mole ratio of H 2 /N 2 of 3/1. Again, the highest activity was for the doubly promoted catalyst, with the highest turnover frequency being 0.370 s −1 at a temperature of 430 °C.…”

“…Again, the highest activity was for the doubly promoted catalyst, with the highest turnover frequency being 0.370 s −1 at a temperature of 430 °C. [ 126 ]…”

Chlorine‐Tolerant Ruthenium Catalyst Derived Using the Unique Anion‐Exchange Properties of 12 CaO⋅7 Al2O3 for Ammonia Synthesis

“…The optimum Ru particles ize for ammonia synthesis hasb een reported to be 1.8-3.5 nm because the relative number of active sites (B5type step sites) increases with ad ecrease in the Ru particle size. [18][19][20] The optimal Ru particle size of the present catalyst is thus considered to be ak ey reason for the highc atalytic performance.…”

“…[5,17] However, such high-temperature treatment leads to the grain growth of the Ru nanoparticles by sintering (the optimal Ru particles ize for ammonia synthesis is in the range of 1.8-3.5 nm). [18][19][20] As aresult, Cl-free Ru precursors provide catalysts with ah ighera ctivity than those prepared with the RuCl 3 precursor. [13] Therefore, the development of highly efficients upport materials that are not subject to Cl poisoning is important for both fundamentalresearch and the industrial application of RuCl 3 .…”