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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.

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Samples of barium‐promoted carbon‐supported cobalt catalysts for ammonia synthesis were prepared; the cobalt content was constant (27.4 wt %) and the amount of barium introduced differed within the range of 0–0.88 mmol gC+Co−1. Turbostratic carbon was used as the support. Several techniques, including X‐ray powder diffraction, TEM, Thermogravimetric analysis–mass spectrometry (methanation studies) and H2 temperature‐programmed desorption were used to examine the properties of the carbon support or catalytic materials. The reaction rate measurements were performed under the following conditions: T=400 °C, p=9.0 MPa, x NH 3=8.5 mol %, H2/N2=3:1. It was found that barium is an important component of the cobalt catalysts supported on activated carbon for ammonia synthesis. Barium inhibits the process of carbon support methanation, which also results in a decrease in the sintering of the active phase (cobalt). Moreover, even a small amount of barium significantly activates the cobalt surface in ammonia synthesis, suggesting that barium locates primarily on the surface of cobalt.

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interest recently because of its potential as a simple technique for CO removal from H 2 -rich feed gases for fuel cells [1,[3][4][5][6][7]. Due to the poor reserves of natural gas in some regions of the world, conversion of syngas from coal or biomass to synthetic natural gas (SNG) via the methanation reaction is also attracting great attention [8][9][10][11]. That is the reason why many groups are still working to obtain highly active and selective catalysts for that reaction.Supported Ni-based catalysts have been applied commercially on methanation due to their high activity, selectivity to CH 4 and low costs [1,8,11]. However, hydrogenation of CO x to methane can be catalyzed by several metals [12][13][14]. Some experimental works and density functional theory (DFT) calculations also indicate that ruthenium exhibits excellent activity in CO methanation [1,4,15,16]. Ruthenium dispersed on high-surface area oxide supports has been found to exhibit high activity in the methanation of CO and CO 2 [3,5,13,14]. Many literature reports give information about the influence of different factors on the activity of oxide-supported Ru systems [1,6,7,12,13,16,17]. However, there are few papers dealing with the activity of ruthenium deposited on thermally modified carbons [18,19]. There is also lack of information concerning the effect of Ru crystallite sizes on the activity of Ru/C systems. In the present work we made an effort to examine the influence of the ruthenium particle size in the wide range of its dispersion on the catalytic activity of Ru/graphitized carbon systems in CO methanation. The activity tests were conducted in H 2 -rich streams with very low CO concentrations (0.5 vol% CO) to simulate industrial conditions of hydrogen cleaning for NH 3 synthesis or fuel cells application. AbstractThe influence of the ruthenium crystallite size on the catalytic activity of Ru/graphitized carbon systems in carbon monoxide methanation was evaluated. Four graphitized carbon materials differing in their surface area were used as supports for Ru. The average size of Ru crystallites in Ru/C materials was estimated by X-ray powder diffraction, transmission electron microscopy and CO chemisorption. Dispersion of the active phase clearly depends on the carbon texture. The activity tests conducted in H 2 -rich streams with very low CO concentrations (0.5 vol% CO) have shown that the activity of Ru/carbon catalysts changes with the ruthenium particles size (d). The highest activities were obtained for ruthenium particles in the range 4-8 nm in size.

In modern research on catalysts for NH 3 synthesis a lot of attention is paid to cobalt. In this work the new catalytic systems based on cobalt are presented. Unsupported cobalt catalysts singly promoted (La or Ba) and doubly promoted (La and Ba) were prepared and tested in NH 3 synthesis reaction under commercial synthesis conditions. Characterization studies revealed that lanthanum plays a role of a structural promoter, which improves the surface of catalyst precursors and prevents from sintering during calcination. However, lanthanum has a negative effect on the reduction of cobalt oxide, but the addition of barium promoter (Co/La/Ba catalyst) diminishes the negative impact of La. The co-promotion of cobalt with lanthanum and barium results in the increasing of the active phase surface and improvement of its activity in NH 3 synthesis.